xref: /openbmc/linux/kernel/fork.c (revision f5ad1c74)
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  *  linux/kernel/fork.c
4  *
5  *  Copyright (C) 1991, 1992  Linus Torvalds
6  */
7 
8 /*
9  *  'fork.c' contains the help-routines for the 'fork' system call
10  * (see also entry.S and others).
11  * Fork is rather simple, once you get the hang of it, but the memory
12  * management can be a bitch. See 'mm/memory.c': 'copy_page_range()'
13  */
14 
15 #include <linux/anon_inodes.h>
16 #include <linux/slab.h>
17 #include <linux/sched/autogroup.h>
18 #include <linux/sched/mm.h>
19 #include <linux/sched/coredump.h>
20 #include <linux/sched/user.h>
21 #include <linux/sched/numa_balancing.h>
22 #include <linux/sched/stat.h>
23 #include <linux/sched/task.h>
24 #include <linux/sched/task_stack.h>
25 #include <linux/sched/cputime.h>
26 #include <linux/seq_file.h>
27 #include <linux/rtmutex.h>
28 #include <linux/init.h>
29 #include <linux/unistd.h>
30 #include <linux/module.h>
31 #include <linux/vmalloc.h>
32 #include <linux/completion.h>
33 #include <linux/personality.h>
34 #include <linux/mempolicy.h>
35 #include <linux/sem.h>
36 #include <linux/file.h>
37 #include <linux/fdtable.h>
38 #include <linux/iocontext.h>
39 #include <linux/key.h>
40 #include <linux/binfmts.h>
41 #include <linux/mman.h>
42 #include <linux/mmu_notifier.h>
43 #include <linux/fs.h>
44 #include <linux/mm.h>
45 #include <linux/vmacache.h>
46 #include <linux/nsproxy.h>
47 #include <linux/capability.h>
48 #include <linux/cpu.h>
49 #include <linux/cgroup.h>
50 #include <linux/security.h>
51 #include <linux/hugetlb.h>
52 #include <linux/seccomp.h>
53 #include <linux/swap.h>
54 #include <linux/syscalls.h>
55 #include <linux/jiffies.h>
56 #include <linux/futex.h>
57 #include <linux/compat.h>
58 #include <linux/kthread.h>
59 #include <linux/task_io_accounting_ops.h>
60 #include <linux/rcupdate.h>
61 #include <linux/ptrace.h>
62 #include <linux/mount.h>
63 #include <linux/audit.h>
64 #include <linux/memcontrol.h>
65 #include <linux/ftrace.h>
66 #include <linux/proc_fs.h>
67 #include <linux/profile.h>
68 #include <linux/rmap.h>
69 #include <linux/ksm.h>
70 #include <linux/acct.h>
71 #include <linux/userfaultfd_k.h>
72 #include <linux/tsacct_kern.h>
73 #include <linux/cn_proc.h>
74 #include <linux/freezer.h>
75 #include <linux/delayacct.h>
76 #include <linux/taskstats_kern.h>
77 #include <linux/random.h>
78 #include <linux/tty.h>
79 #include <linux/blkdev.h>
80 #include <linux/fs_struct.h>
81 #include <linux/magic.h>
82 #include <linux/perf_event.h>
83 #include <linux/posix-timers.h>
84 #include <linux/user-return-notifier.h>
85 #include <linux/oom.h>
86 #include <linux/khugepaged.h>
87 #include <linux/signalfd.h>
88 #include <linux/uprobes.h>
89 #include <linux/aio.h>
90 #include <linux/compiler.h>
91 #include <linux/sysctl.h>
92 #include <linux/kcov.h>
93 #include <linux/livepatch.h>
94 #include <linux/thread_info.h>
95 #include <linux/stackleak.h>
96 #include <linux/kasan.h>
97 #include <linux/scs.h>
98 #include <linux/io_uring.h>
99 
100 #include <asm/pgalloc.h>
101 #include <linux/uaccess.h>
102 #include <asm/mmu_context.h>
103 #include <asm/cacheflush.h>
104 #include <asm/tlbflush.h>
105 
106 #include <trace/events/sched.h>
107 
108 #define CREATE_TRACE_POINTS
109 #include <trace/events/task.h>
110 
111 /*
112  * Minimum number of threads to boot the kernel
113  */
114 #define MIN_THREADS 20
115 
116 /*
117  * Maximum number of threads
118  */
119 #define MAX_THREADS FUTEX_TID_MASK
120 
121 /*
122  * Protected counters by write_lock_irq(&tasklist_lock)
123  */
124 unsigned long total_forks;	/* Handle normal Linux uptimes. */
125 int nr_threads;			/* The idle threads do not count.. */
126 
127 static int max_threads;		/* tunable limit on nr_threads */
128 
129 #define NAMED_ARRAY_INDEX(x)	[x] = __stringify(x)
130 
131 static const char * const resident_page_types[] = {
132 	NAMED_ARRAY_INDEX(MM_FILEPAGES),
133 	NAMED_ARRAY_INDEX(MM_ANONPAGES),
134 	NAMED_ARRAY_INDEX(MM_SWAPENTS),
135 	NAMED_ARRAY_INDEX(MM_SHMEMPAGES),
136 };
137 
138 DEFINE_PER_CPU(unsigned long, process_counts) = 0;
139 
140 __cacheline_aligned DEFINE_RWLOCK(tasklist_lock);  /* outer */
141 
142 #ifdef CONFIG_PROVE_RCU
143 int lockdep_tasklist_lock_is_held(void)
144 {
145 	return lockdep_is_held(&tasklist_lock);
146 }
147 EXPORT_SYMBOL_GPL(lockdep_tasklist_lock_is_held);
148 #endif /* #ifdef CONFIG_PROVE_RCU */
149 
150 int nr_processes(void)
151 {
152 	int cpu;
153 	int total = 0;
154 
155 	for_each_possible_cpu(cpu)
156 		total += per_cpu(process_counts, cpu);
157 
158 	return total;
159 }
160 
161 void __weak arch_release_task_struct(struct task_struct *tsk)
162 {
163 }
164 
165 #ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
166 static struct kmem_cache *task_struct_cachep;
167 
168 static inline struct task_struct *alloc_task_struct_node(int node)
169 {
170 	return kmem_cache_alloc_node(task_struct_cachep, GFP_KERNEL, node);
171 }
172 
173 static inline void free_task_struct(struct task_struct *tsk)
174 {
175 	kmem_cache_free(task_struct_cachep, tsk);
176 }
177 #endif
178 
179 #ifndef CONFIG_ARCH_THREAD_STACK_ALLOCATOR
180 
181 /*
182  * Allocate pages if THREAD_SIZE is >= PAGE_SIZE, otherwise use a
183  * kmemcache based allocator.
184  */
185 # if THREAD_SIZE >= PAGE_SIZE || defined(CONFIG_VMAP_STACK)
186 
187 #ifdef CONFIG_VMAP_STACK
188 /*
189  * vmalloc() is a bit slow, and calling vfree() enough times will force a TLB
190  * flush.  Try to minimize the number of calls by caching stacks.
191  */
192 #define NR_CACHED_STACKS 2
193 static DEFINE_PER_CPU(struct vm_struct *, cached_stacks[NR_CACHED_STACKS]);
194 
195 static int free_vm_stack_cache(unsigned int cpu)
196 {
197 	struct vm_struct **cached_vm_stacks = per_cpu_ptr(cached_stacks, cpu);
198 	int i;
199 
200 	for (i = 0; i < NR_CACHED_STACKS; i++) {
201 		struct vm_struct *vm_stack = cached_vm_stacks[i];
202 
203 		if (!vm_stack)
204 			continue;
205 
206 		vfree(vm_stack->addr);
207 		cached_vm_stacks[i] = NULL;
208 	}
209 
210 	return 0;
211 }
212 #endif
213 
214 static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
215 {
216 #ifdef CONFIG_VMAP_STACK
217 	void *stack;
218 	int i;
219 
220 	for (i = 0; i < NR_CACHED_STACKS; i++) {
221 		struct vm_struct *s;
222 
223 		s = this_cpu_xchg(cached_stacks[i], NULL);
224 
225 		if (!s)
226 			continue;
227 
228 		/* Clear the KASAN shadow of the stack. */
229 		kasan_unpoison_shadow(s->addr, THREAD_SIZE);
230 
231 		/* Clear stale pointers from reused stack. */
232 		memset(s->addr, 0, THREAD_SIZE);
233 
234 		tsk->stack_vm_area = s;
235 		tsk->stack = s->addr;
236 		return s->addr;
237 	}
238 
239 	/*
240 	 * Allocated stacks are cached and later reused by new threads,
241 	 * so memcg accounting is performed manually on assigning/releasing
242 	 * stacks to tasks. Drop __GFP_ACCOUNT.
243 	 */
244 	stack = __vmalloc_node_range(THREAD_SIZE, THREAD_ALIGN,
245 				     VMALLOC_START, VMALLOC_END,
246 				     THREADINFO_GFP & ~__GFP_ACCOUNT,
247 				     PAGE_KERNEL,
248 				     0, node, __builtin_return_address(0));
249 
250 	/*
251 	 * We can't call find_vm_area() in interrupt context, and
252 	 * free_thread_stack() can be called in interrupt context,
253 	 * so cache the vm_struct.
254 	 */
255 	if (stack) {
256 		tsk->stack_vm_area = find_vm_area(stack);
257 		tsk->stack = stack;
258 	}
259 	return stack;
260 #else
261 	struct page *page = alloc_pages_node(node, THREADINFO_GFP,
262 					     THREAD_SIZE_ORDER);
263 
264 	if (likely(page)) {
265 		tsk->stack = kasan_reset_tag(page_address(page));
266 		return tsk->stack;
267 	}
268 	return NULL;
269 #endif
270 }
271 
272 static inline void free_thread_stack(struct task_struct *tsk)
273 {
274 #ifdef CONFIG_VMAP_STACK
275 	struct vm_struct *vm = task_stack_vm_area(tsk);
276 
277 	if (vm) {
278 		int i;
279 
280 		for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++)
281 			memcg_kmem_uncharge_page(vm->pages[i], 0);
282 
283 		for (i = 0; i < NR_CACHED_STACKS; i++) {
284 			if (this_cpu_cmpxchg(cached_stacks[i],
285 					NULL, tsk->stack_vm_area) != NULL)
286 				continue;
287 
288 			return;
289 		}
290 
291 		vfree_atomic(tsk->stack);
292 		return;
293 	}
294 #endif
295 
296 	__free_pages(virt_to_page(tsk->stack), THREAD_SIZE_ORDER);
297 }
298 # else
299 static struct kmem_cache *thread_stack_cache;
300 
301 static unsigned long *alloc_thread_stack_node(struct task_struct *tsk,
302 						  int node)
303 {
304 	unsigned long *stack;
305 	stack = kmem_cache_alloc_node(thread_stack_cache, THREADINFO_GFP, node);
306 	stack = kasan_reset_tag(stack);
307 	tsk->stack = stack;
308 	return stack;
309 }
310 
311 static void free_thread_stack(struct task_struct *tsk)
312 {
313 	kmem_cache_free(thread_stack_cache, tsk->stack);
314 }
315 
316 void thread_stack_cache_init(void)
317 {
318 	thread_stack_cache = kmem_cache_create_usercopy("thread_stack",
319 					THREAD_SIZE, THREAD_SIZE, 0, 0,
320 					THREAD_SIZE, NULL);
321 	BUG_ON(thread_stack_cache == NULL);
322 }
323 # endif
324 #endif
325 
326 /* SLAB cache for signal_struct structures (tsk->signal) */
327 static struct kmem_cache *signal_cachep;
328 
329 /* SLAB cache for sighand_struct structures (tsk->sighand) */
330 struct kmem_cache *sighand_cachep;
331 
332 /* SLAB cache for files_struct structures (tsk->files) */
333 struct kmem_cache *files_cachep;
334 
335 /* SLAB cache for fs_struct structures (tsk->fs) */
336 struct kmem_cache *fs_cachep;
337 
338 /* SLAB cache for vm_area_struct structures */
339 static struct kmem_cache *vm_area_cachep;
340 
341 /* SLAB cache for mm_struct structures (tsk->mm) */
342 static struct kmem_cache *mm_cachep;
343 
344 struct vm_area_struct *vm_area_alloc(struct mm_struct *mm)
345 {
346 	struct vm_area_struct *vma;
347 
348 	vma = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
349 	if (vma)
350 		vma_init(vma, mm);
351 	return vma;
352 }
353 
354 struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig)
355 {
356 	struct vm_area_struct *new = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
357 
358 	if (new) {
359 		ASSERT_EXCLUSIVE_WRITER(orig->vm_flags);
360 		ASSERT_EXCLUSIVE_WRITER(orig->vm_file);
361 		/*
362 		 * orig->shared.rb may be modified concurrently, but the clone
363 		 * will be reinitialized.
364 		 */
365 		*new = data_race(*orig);
366 		INIT_LIST_HEAD(&new->anon_vma_chain);
367 		new->vm_next = new->vm_prev = NULL;
368 	}
369 	return new;
370 }
371 
372 void vm_area_free(struct vm_area_struct *vma)
373 {
374 	kmem_cache_free(vm_area_cachep, vma);
375 }
376 
377 static void account_kernel_stack(struct task_struct *tsk, int account)
378 {
379 	void *stack = task_stack_page(tsk);
380 	struct vm_struct *vm = task_stack_vm_area(tsk);
381 
382 
383 	/* All stack pages are in the same node. */
384 	if (vm)
385 		mod_lruvec_page_state(vm->pages[0], NR_KERNEL_STACK_KB,
386 				      account * (THREAD_SIZE / 1024));
387 	else
388 		mod_lruvec_kmem_state(stack, NR_KERNEL_STACK_KB,
389 				      account * (THREAD_SIZE / 1024));
390 }
391 
392 static int memcg_charge_kernel_stack(struct task_struct *tsk)
393 {
394 #ifdef CONFIG_VMAP_STACK
395 	struct vm_struct *vm = task_stack_vm_area(tsk);
396 	int ret;
397 
398 	BUILD_BUG_ON(IS_ENABLED(CONFIG_VMAP_STACK) && PAGE_SIZE % 1024 != 0);
399 
400 	if (vm) {
401 		int i;
402 
403 		BUG_ON(vm->nr_pages != THREAD_SIZE / PAGE_SIZE);
404 
405 		for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++) {
406 			/*
407 			 * If memcg_kmem_charge_page() fails, page's
408 			 * memory cgroup pointer is NULL, and
409 			 * memcg_kmem_uncharge_page() in free_thread_stack()
410 			 * will ignore this page.
411 			 */
412 			ret = memcg_kmem_charge_page(vm->pages[i], GFP_KERNEL,
413 						     0);
414 			if (ret)
415 				return ret;
416 		}
417 	}
418 #endif
419 	return 0;
420 }
421 
422 static void release_task_stack(struct task_struct *tsk)
423 {
424 	if (WARN_ON(tsk->state != TASK_DEAD))
425 		return;  /* Better to leak the stack than to free prematurely */
426 
427 	account_kernel_stack(tsk, -1);
428 	free_thread_stack(tsk);
429 	tsk->stack = NULL;
430 #ifdef CONFIG_VMAP_STACK
431 	tsk->stack_vm_area = NULL;
432 #endif
433 }
434 
435 #ifdef CONFIG_THREAD_INFO_IN_TASK
436 void put_task_stack(struct task_struct *tsk)
437 {
438 	if (refcount_dec_and_test(&tsk->stack_refcount))
439 		release_task_stack(tsk);
440 }
441 #endif
442 
443 void free_task(struct task_struct *tsk)
444 {
445 	scs_release(tsk);
446 
447 #ifndef CONFIG_THREAD_INFO_IN_TASK
448 	/*
449 	 * The task is finally done with both the stack and thread_info,
450 	 * so free both.
451 	 */
452 	release_task_stack(tsk);
453 #else
454 	/*
455 	 * If the task had a separate stack allocation, it should be gone
456 	 * by now.
457 	 */
458 	WARN_ON_ONCE(refcount_read(&tsk->stack_refcount) != 0);
459 #endif
460 	rt_mutex_debug_task_free(tsk);
461 	ftrace_graph_exit_task(tsk);
462 	arch_release_task_struct(tsk);
463 	if (tsk->flags & PF_KTHREAD)
464 		free_kthread_struct(tsk);
465 	free_task_struct(tsk);
466 }
467 EXPORT_SYMBOL(free_task);
468 
469 #ifdef CONFIG_MMU
470 static __latent_entropy int dup_mmap(struct mm_struct *mm,
471 					struct mm_struct *oldmm)
472 {
473 	struct vm_area_struct *mpnt, *tmp, *prev, **pprev;
474 	struct rb_node **rb_link, *rb_parent;
475 	int retval;
476 	unsigned long charge;
477 	LIST_HEAD(uf);
478 
479 	uprobe_start_dup_mmap();
480 	if (mmap_write_lock_killable(oldmm)) {
481 		retval = -EINTR;
482 		goto fail_uprobe_end;
483 	}
484 	flush_cache_dup_mm(oldmm);
485 	uprobe_dup_mmap(oldmm, mm);
486 	/*
487 	 * Not linked in yet - no deadlock potential:
488 	 */
489 	mmap_write_lock_nested(mm, SINGLE_DEPTH_NESTING);
490 
491 	/* No ordering required: file already has been exposed. */
492 	RCU_INIT_POINTER(mm->exe_file, get_mm_exe_file(oldmm));
493 
494 	mm->total_vm = oldmm->total_vm;
495 	mm->data_vm = oldmm->data_vm;
496 	mm->exec_vm = oldmm->exec_vm;
497 	mm->stack_vm = oldmm->stack_vm;
498 
499 	rb_link = &mm->mm_rb.rb_node;
500 	rb_parent = NULL;
501 	pprev = &mm->mmap;
502 	retval = ksm_fork(mm, oldmm);
503 	if (retval)
504 		goto out;
505 	retval = khugepaged_fork(mm, oldmm);
506 	if (retval)
507 		goto out;
508 
509 	prev = NULL;
510 	for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
511 		struct file *file;
512 
513 		if (mpnt->vm_flags & VM_DONTCOPY) {
514 			vm_stat_account(mm, mpnt->vm_flags, -vma_pages(mpnt));
515 			continue;
516 		}
517 		charge = 0;
518 		/*
519 		 * Don't duplicate many vmas if we've been oom-killed (for
520 		 * example)
521 		 */
522 		if (fatal_signal_pending(current)) {
523 			retval = -EINTR;
524 			goto out;
525 		}
526 		if (mpnt->vm_flags & VM_ACCOUNT) {
527 			unsigned long len = vma_pages(mpnt);
528 
529 			if (security_vm_enough_memory_mm(oldmm, len)) /* sic */
530 				goto fail_nomem;
531 			charge = len;
532 		}
533 		tmp = vm_area_dup(mpnt);
534 		if (!tmp)
535 			goto fail_nomem;
536 		retval = vma_dup_policy(mpnt, tmp);
537 		if (retval)
538 			goto fail_nomem_policy;
539 		tmp->vm_mm = mm;
540 		retval = dup_userfaultfd(tmp, &uf);
541 		if (retval)
542 			goto fail_nomem_anon_vma_fork;
543 		if (tmp->vm_flags & VM_WIPEONFORK) {
544 			/*
545 			 * VM_WIPEONFORK gets a clean slate in the child.
546 			 * Don't prepare anon_vma until fault since we don't
547 			 * copy page for current vma.
548 			 */
549 			tmp->anon_vma = NULL;
550 		} else if (anon_vma_fork(tmp, mpnt))
551 			goto fail_nomem_anon_vma_fork;
552 		tmp->vm_flags &= ~(VM_LOCKED | VM_LOCKONFAULT);
553 		file = tmp->vm_file;
554 		if (file) {
555 			struct inode *inode = file_inode(file);
556 			struct address_space *mapping = file->f_mapping;
557 
558 			get_file(file);
559 			if (tmp->vm_flags & VM_DENYWRITE)
560 				put_write_access(inode);
561 			i_mmap_lock_write(mapping);
562 			if (tmp->vm_flags & VM_SHARED)
563 				mapping_allow_writable(mapping);
564 			flush_dcache_mmap_lock(mapping);
565 			/* insert tmp into the share list, just after mpnt */
566 			vma_interval_tree_insert_after(tmp, mpnt,
567 					&mapping->i_mmap);
568 			flush_dcache_mmap_unlock(mapping);
569 			i_mmap_unlock_write(mapping);
570 		}
571 
572 		/*
573 		 * Clear hugetlb-related page reserves for children. This only
574 		 * affects MAP_PRIVATE mappings. Faults generated by the child
575 		 * are not guaranteed to succeed, even if read-only
576 		 */
577 		if (is_vm_hugetlb_page(tmp))
578 			reset_vma_resv_huge_pages(tmp);
579 
580 		/*
581 		 * Link in the new vma and copy the page table entries.
582 		 */
583 		*pprev = tmp;
584 		pprev = &tmp->vm_next;
585 		tmp->vm_prev = prev;
586 		prev = tmp;
587 
588 		__vma_link_rb(mm, tmp, rb_link, rb_parent);
589 		rb_link = &tmp->vm_rb.rb_right;
590 		rb_parent = &tmp->vm_rb;
591 
592 		mm->map_count++;
593 		if (!(tmp->vm_flags & VM_WIPEONFORK))
594 			retval = copy_page_range(tmp, mpnt);
595 
596 		if (tmp->vm_ops && tmp->vm_ops->open)
597 			tmp->vm_ops->open(tmp);
598 
599 		if (retval)
600 			goto out;
601 	}
602 	/* a new mm has just been created */
603 	retval = arch_dup_mmap(oldmm, mm);
604 out:
605 	mmap_write_unlock(mm);
606 	flush_tlb_mm(oldmm);
607 	mmap_write_unlock(oldmm);
608 	dup_userfaultfd_complete(&uf);
609 fail_uprobe_end:
610 	uprobe_end_dup_mmap();
611 	return retval;
612 fail_nomem_anon_vma_fork:
613 	mpol_put(vma_policy(tmp));
614 fail_nomem_policy:
615 	vm_area_free(tmp);
616 fail_nomem:
617 	retval = -ENOMEM;
618 	vm_unacct_memory(charge);
619 	goto out;
620 }
621 
622 static inline int mm_alloc_pgd(struct mm_struct *mm)
623 {
624 	mm->pgd = pgd_alloc(mm);
625 	if (unlikely(!mm->pgd))
626 		return -ENOMEM;
627 	return 0;
628 }
629 
630 static inline void mm_free_pgd(struct mm_struct *mm)
631 {
632 	pgd_free(mm, mm->pgd);
633 }
634 #else
635 static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
636 {
637 	mmap_write_lock(oldmm);
638 	RCU_INIT_POINTER(mm->exe_file, get_mm_exe_file(oldmm));
639 	mmap_write_unlock(oldmm);
640 	return 0;
641 }
642 #define mm_alloc_pgd(mm)	(0)
643 #define mm_free_pgd(mm)
644 #endif /* CONFIG_MMU */
645 
646 static void check_mm(struct mm_struct *mm)
647 {
648 	int i;
649 
650 	BUILD_BUG_ON_MSG(ARRAY_SIZE(resident_page_types) != NR_MM_COUNTERS,
651 			 "Please make sure 'struct resident_page_types[]' is updated as well");
652 
653 	for (i = 0; i < NR_MM_COUNTERS; i++) {
654 		long x = atomic_long_read(&mm->rss_stat.count[i]);
655 
656 		if (unlikely(x))
657 			pr_alert("BUG: Bad rss-counter state mm:%p type:%s val:%ld\n",
658 				 mm, resident_page_types[i], x);
659 	}
660 
661 	if (mm_pgtables_bytes(mm))
662 		pr_alert("BUG: non-zero pgtables_bytes on freeing mm: %ld\n",
663 				mm_pgtables_bytes(mm));
664 
665 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
666 	VM_BUG_ON_MM(mm->pmd_huge_pte, mm);
667 #endif
668 }
669 
670 #define allocate_mm()	(kmem_cache_alloc(mm_cachep, GFP_KERNEL))
671 #define free_mm(mm)	(kmem_cache_free(mm_cachep, (mm)))
672 
673 /*
674  * Called when the last reference to the mm
675  * is dropped: either by a lazy thread or by
676  * mmput. Free the page directory and the mm.
677  */
678 void __mmdrop(struct mm_struct *mm)
679 {
680 	BUG_ON(mm == &init_mm);
681 	WARN_ON_ONCE(mm == current->mm);
682 	WARN_ON_ONCE(mm == current->active_mm);
683 	mm_free_pgd(mm);
684 	destroy_context(mm);
685 	mmu_notifier_subscriptions_destroy(mm);
686 	check_mm(mm);
687 	put_user_ns(mm->user_ns);
688 	free_mm(mm);
689 }
690 EXPORT_SYMBOL_GPL(__mmdrop);
691 
692 static void mmdrop_async_fn(struct work_struct *work)
693 {
694 	struct mm_struct *mm;
695 
696 	mm = container_of(work, struct mm_struct, async_put_work);
697 	__mmdrop(mm);
698 }
699 
700 static void mmdrop_async(struct mm_struct *mm)
701 {
702 	if (unlikely(atomic_dec_and_test(&mm->mm_count))) {
703 		INIT_WORK(&mm->async_put_work, mmdrop_async_fn);
704 		schedule_work(&mm->async_put_work);
705 	}
706 }
707 
708 static inline void free_signal_struct(struct signal_struct *sig)
709 {
710 	taskstats_tgid_free(sig);
711 	sched_autogroup_exit(sig);
712 	/*
713 	 * __mmdrop is not safe to call from softirq context on x86 due to
714 	 * pgd_dtor so postpone it to the async context
715 	 */
716 	if (sig->oom_mm)
717 		mmdrop_async(sig->oom_mm);
718 	kmem_cache_free(signal_cachep, sig);
719 }
720 
721 static inline void put_signal_struct(struct signal_struct *sig)
722 {
723 	if (refcount_dec_and_test(&sig->sigcnt))
724 		free_signal_struct(sig);
725 }
726 
727 void __put_task_struct(struct task_struct *tsk)
728 {
729 	WARN_ON(!tsk->exit_state);
730 	WARN_ON(refcount_read(&tsk->usage));
731 	WARN_ON(tsk == current);
732 
733 	io_uring_free(tsk);
734 	cgroup_free(tsk);
735 	task_numa_free(tsk, true);
736 	security_task_free(tsk);
737 	exit_creds(tsk);
738 	delayacct_tsk_free(tsk);
739 	put_signal_struct(tsk->signal);
740 
741 	if (!profile_handoff_task(tsk))
742 		free_task(tsk);
743 }
744 EXPORT_SYMBOL_GPL(__put_task_struct);
745 
746 void __init __weak arch_task_cache_init(void) { }
747 
748 /*
749  * set_max_threads
750  */
751 static void set_max_threads(unsigned int max_threads_suggested)
752 {
753 	u64 threads;
754 	unsigned long nr_pages = totalram_pages();
755 
756 	/*
757 	 * The number of threads shall be limited such that the thread
758 	 * structures may only consume a small part of the available memory.
759 	 */
760 	if (fls64(nr_pages) + fls64(PAGE_SIZE) > 64)
761 		threads = MAX_THREADS;
762 	else
763 		threads = div64_u64((u64) nr_pages * (u64) PAGE_SIZE,
764 				    (u64) THREAD_SIZE * 8UL);
765 
766 	if (threads > max_threads_suggested)
767 		threads = max_threads_suggested;
768 
769 	max_threads = clamp_t(u64, threads, MIN_THREADS, MAX_THREADS);
770 }
771 
772 #ifdef CONFIG_ARCH_WANTS_DYNAMIC_TASK_STRUCT
773 /* Initialized by the architecture: */
774 int arch_task_struct_size __read_mostly;
775 #endif
776 
777 #ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
778 static void task_struct_whitelist(unsigned long *offset, unsigned long *size)
779 {
780 	/* Fetch thread_struct whitelist for the architecture. */
781 	arch_thread_struct_whitelist(offset, size);
782 
783 	/*
784 	 * Handle zero-sized whitelist or empty thread_struct, otherwise
785 	 * adjust offset to position of thread_struct in task_struct.
786 	 */
787 	if (unlikely(*size == 0))
788 		*offset = 0;
789 	else
790 		*offset += offsetof(struct task_struct, thread);
791 }
792 #endif /* CONFIG_ARCH_TASK_STRUCT_ALLOCATOR */
793 
794 void __init fork_init(void)
795 {
796 	int i;
797 #ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
798 #ifndef ARCH_MIN_TASKALIGN
799 #define ARCH_MIN_TASKALIGN	0
800 #endif
801 	int align = max_t(int, L1_CACHE_BYTES, ARCH_MIN_TASKALIGN);
802 	unsigned long useroffset, usersize;
803 
804 	/* create a slab on which task_structs can be allocated */
805 	task_struct_whitelist(&useroffset, &usersize);
806 	task_struct_cachep = kmem_cache_create_usercopy("task_struct",
807 			arch_task_struct_size, align,
808 			SLAB_PANIC|SLAB_ACCOUNT,
809 			useroffset, usersize, NULL);
810 #endif
811 
812 	/* do the arch specific task caches init */
813 	arch_task_cache_init();
814 
815 	set_max_threads(MAX_THREADS);
816 
817 	init_task.signal->rlim[RLIMIT_NPROC].rlim_cur = max_threads/2;
818 	init_task.signal->rlim[RLIMIT_NPROC].rlim_max = max_threads/2;
819 	init_task.signal->rlim[RLIMIT_SIGPENDING] =
820 		init_task.signal->rlim[RLIMIT_NPROC];
821 
822 	for (i = 0; i < UCOUNT_COUNTS; i++) {
823 		init_user_ns.ucount_max[i] = max_threads/2;
824 	}
825 
826 #ifdef CONFIG_VMAP_STACK
827 	cpuhp_setup_state(CPUHP_BP_PREPARE_DYN, "fork:vm_stack_cache",
828 			  NULL, free_vm_stack_cache);
829 #endif
830 
831 	scs_init();
832 
833 	lockdep_init_task(&init_task);
834 	uprobes_init();
835 }
836 
837 int __weak arch_dup_task_struct(struct task_struct *dst,
838 					       struct task_struct *src)
839 {
840 	*dst = *src;
841 	return 0;
842 }
843 
844 void set_task_stack_end_magic(struct task_struct *tsk)
845 {
846 	unsigned long *stackend;
847 
848 	stackend = end_of_stack(tsk);
849 	*stackend = STACK_END_MAGIC;	/* for overflow detection */
850 }
851 
852 static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
853 {
854 	struct task_struct *tsk;
855 	unsigned long *stack;
856 	struct vm_struct *stack_vm_area __maybe_unused;
857 	int err;
858 
859 	if (node == NUMA_NO_NODE)
860 		node = tsk_fork_get_node(orig);
861 	tsk = alloc_task_struct_node(node);
862 	if (!tsk)
863 		return NULL;
864 
865 	stack = alloc_thread_stack_node(tsk, node);
866 	if (!stack)
867 		goto free_tsk;
868 
869 	if (memcg_charge_kernel_stack(tsk))
870 		goto free_stack;
871 
872 	stack_vm_area = task_stack_vm_area(tsk);
873 
874 	err = arch_dup_task_struct(tsk, orig);
875 
876 	/*
877 	 * arch_dup_task_struct() clobbers the stack-related fields.  Make
878 	 * sure they're properly initialized before using any stack-related
879 	 * functions again.
880 	 */
881 	tsk->stack = stack;
882 #ifdef CONFIG_VMAP_STACK
883 	tsk->stack_vm_area = stack_vm_area;
884 #endif
885 #ifdef CONFIG_THREAD_INFO_IN_TASK
886 	refcount_set(&tsk->stack_refcount, 1);
887 #endif
888 
889 	if (err)
890 		goto free_stack;
891 
892 	err = scs_prepare(tsk, node);
893 	if (err)
894 		goto free_stack;
895 
896 #ifdef CONFIG_SECCOMP
897 	/*
898 	 * We must handle setting up seccomp filters once we're under
899 	 * the sighand lock in case orig has changed between now and
900 	 * then. Until then, filter must be NULL to avoid messing up
901 	 * the usage counts on the error path calling free_task.
902 	 */
903 	tsk->seccomp.filter = NULL;
904 #endif
905 
906 	setup_thread_stack(tsk, orig);
907 	clear_user_return_notifier(tsk);
908 	clear_tsk_need_resched(tsk);
909 	set_task_stack_end_magic(tsk);
910 	clear_syscall_work_syscall_user_dispatch(tsk);
911 
912 #ifdef CONFIG_STACKPROTECTOR
913 	tsk->stack_canary = get_random_canary();
914 #endif
915 	if (orig->cpus_ptr == &orig->cpus_mask)
916 		tsk->cpus_ptr = &tsk->cpus_mask;
917 
918 	/*
919 	 * One for the user space visible state that goes away when reaped.
920 	 * One for the scheduler.
921 	 */
922 	refcount_set(&tsk->rcu_users, 2);
923 	/* One for the rcu users */
924 	refcount_set(&tsk->usage, 1);
925 #ifdef CONFIG_BLK_DEV_IO_TRACE
926 	tsk->btrace_seq = 0;
927 #endif
928 	tsk->splice_pipe = NULL;
929 	tsk->task_frag.page = NULL;
930 	tsk->wake_q.next = NULL;
931 
932 	account_kernel_stack(tsk, 1);
933 
934 	kcov_task_init(tsk);
935 	kmap_local_fork(tsk);
936 
937 #ifdef CONFIG_FAULT_INJECTION
938 	tsk->fail_nth = 0;
939 #endif
940 
941 #ifdef CONFIG_BLK_CGROUP
942 	tsk->throttle_queue = NULL;
943 	tsk->use_memdelay = 0;
944 #endif
945 
946 #ifdef CONFIG_MEMCG
947 	tsk->active_memcg = NULL;
948 #endif
949 	return tsk;
950 
951 free_stack:
952 	free_thread_stack(tsk);
953 free_tsk:
954 	free_task_struct(tsk);
955 	return NULL;
956 }
957 
958 __cacheline_aligned_in_smp DEFINE_SPINLOCK(mmlist_lock);
959 
960 static unsigned long default_dump_filter = MMF_DUMP_FILTER_DEFAULT;
961 
962 static int __init coredump_filter_setup(char *s)
963 {
964 	default_dump_filter =
965 		(simple_strtoul(s, NULL, 0) << MMF_DUMP_FILTER_SHIFT) &
966 		MMF_DUMP_FILTER_MASK;
967 	return 1;
968 }
969 
970 __setup("coredump_filter=", coredump_filter_setup);
971 
972 #include <linux/init_task.h>
973 
974 static void mm_init_aio(struct mm_struct *mm)
975 {
976 #ifdef CONFIG_AIO
977 	spin_lock_init(&mm->ioctx_lock);
978 	mm->ioctx_table = NULL;
979 #endif
980 }
981 
982 static __always_inline void mm_clear_owner(struct mm_struct *mm,
983 					   struct task_struct *p)
984 {
985 #ifdef CONFIG_MEMCG
986 	if (mm->owner == p)
987 		WRITE_ONCE(mm->owner, NULL);
988 #endif
989 }
990 
991 static void mm_init_owner(struct mm_struct *mm, struct task_struct *p)
992 {
993 #ifdef CONFIG_MEMCG
994 	mm->owner = p;
995 #endif
996 }
997 
998 static void mm_init_uprobes_state(struct mm_struct *mm)
999 {
1000 #ifdef CONFIG_UPROBES
1001 	mm->uprobes_state.xol_area = NULL;
1002 #endif
1003 }
1004 
1005 static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p,
1006 	struct user_namespace *user_ns)
1007 {
1008 	mm->mmap = NULL;
1009 	mm->mm_rb = RB_ROOT;
1010 	mm->vmacache_seqnum = 0;
1011 	atomic_set(&mm->mm_users, 1);
1012 	atomic_set(&mm->mm_count, 1);
1013 	seqcount_init(&mm->write_protect_seq);
1014 	mmap_init_lock(mm);
1015 	INIT_LIST_HEAD(&mm->mmlist);
1016 	mm->core_state = NULL;
1017 	mm_pgtables_bytes_init(mm);
1018 	mm->map_count = 0;
1019 	mm->locked_vm = 0;
1020 	atomic_set(&mm->has_pinned, 0);
1021 	atomic64_set(&mm->pinned_vm, 0);
1022 	memset(&mm->rss_stat, 0, sizeof(mm->rss_stat));
1023 	spin_lock_init(&mm->page_table_lock);
1024 	spin_lock_init(&mm->arg_lock);
1025 	mm_init_cpumask(mm);
1026 	mm_init_aio(mm);
1027 	mm_init_owner(mm, p);
1028 	RCU_INIT_POINTER(mm->exe_file, NULL);
1029 	mmu_notifier_subscriptions_init(mm);
1030 	init_tlb_flush_pending(mm);
1031 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
1032 	mm->pmd_huge_pte = NULL;
1033 #endif
1034 	mm_init_uprobes_state(mm);
1035 
1036 	if (current->mm) {
1037 		mm->flags = current->mm->flags & MMF_INIT_MASK;
1038 		mm->def_flags = current->mm->def_flags & VM_INIT_DEF_MASK;
1039 	} else {
1040 		mm->flags = default_dump_filter;
1041 		mm->def_flags = 0;
1042 	}
1043 
1044 	if (mm_alloc_pgd(mm))
1045 		goto fail_nopgd;
1046 
1047 	if (init_new_context(p, mm))
1048 		goto fail_nocontext;
1049 
1050 	mm->user_ns = get_user_ns(user_ns);
1051 	return mm;
1052 
1053 fail_nocontext:
1054 	mm_free_pgd(mm);
1055 fail_nopgd:
1056 	free_mm(mm);
1057 	return NULL;
1058 }
1059 
1060 /*
1061  * Allocate and initialize an mm_struct.
1062  */
1063 struct mm_struct *mm_alloc(void)
1064 {
1065 	struct mm_struct *mm;
1066 
1067 	mm = allocate_mm();
1068 	if (!mm)
1069 		return NULL;
1070 
1071 	memset(mm, 0, sizeof(*mm));
1072 	return mm_init(mm, current, current_user_ns());
1073 }
1074 
1075 static inline void __mmput(struct mm_struct *mm)
1076 {
1077 	VM_BUG_ON(atomic_read(&mm->mm_users));
1078 
1079 	uprobe_clear_state(mm);
1080 	exit_aio(mm);
1081 	ksm_exit(mm);
1082 	khugepaged_exit(mm); /* must run before exit_mmap */
1083 	exit_mmap(mm);
1084 	mm_put_huge_zero_page(mm);
1085 	set_mm_exe_file(mm, NULL);
1086 	if (!list_empty(&mm->mmlist)) {
1087 		spin_lock(&mmlist_lock);
1088 		list_del(&mm->mmlist);
1089 		spin_unlock(&mmlist_lock);
1090 	}
1091 	if (mm->binfmt)
1092 		module_put(mm->binfmt->module);
1093 	mmdrop(mm);
1094 }
1095 
1096 /*
1097  * Decrement the use count and release all resources for an mm.
1098  */
1099 void mmput(struct mm_struct *mm)
1100 {
1101 	might_sleep();
1102 
1103 	if (atomic_dec_and_test(&mm->mm_users))
1104 		__mmput(mm);
1105 }
1106 EXPORT_SYMBOL_GPL(mmput);
1107 
1108 #ifdef CONFIG_MMU
1109 static void mmput_async_fn(struct work_struct *work)
1110 {
1111 	struct mm_struct *mm = container_of(work, struct mm_struct,
1112 					    async_put_work);
1113 
1114 	__mmput(mm);
1115 }
1116 
1117 void mmput_async(struct mm_struct *mm)
1118 {
1119 	if (atomic_dec_and_test(&mm->mm_users)) {
1120 		INIT_WORK(&mm->async_put_work, mmput_async_fn);
1121 		schedule_work(&mm->async_put_work);
1122 	}
1123 }
1124 #endif
1125 
1126 /**
1127  * set_mm_exe_file - change a reference to the mm's executable file
1128  *
1129  * This changes mm's executable file (shown as symlink /proc/[pid]/exe).
1130  *
1131  * Main users are mmput() and sys_execve(). Callers prevent concurrent
1132  * invocations: in mmput() nobody alive left, in execve task is single
1133  * threaded. sys_prctl(PR_SET_MM_MAP/EXE_FILE) also needs to set the
1134  * mm->exe_file, but does so without using set_mm_exe_file() in order
1135  * to do avoid the need for any locks.
1136  */
1137 void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
1138 {
1139 	struct file *old_exe_file;
1140 
1141 	/*
1142 	 * It is safe to dereference the exe_file without RCU as
1143 	 * this function is only called if nobody else can access
1144 	 * this mm -- see comment above for justification.
1145 	 */
1146 	old_exe_file = rcu_dereference_raw(mm->exe_file);
1147 
1148 	if (new_exe_file)
1149 		get_file(new_exe_file);
1150 	rcu_assign_pointer(mm->exe_file, new_exe_file);
1151 	if (old_exe_file)
1152 		fput(old_exe_file);
1153 }
1154 
1155 /**
1156  * get_mm_exe_file - acquire a reference to the mm's executable file
1157  *
1158  * Returns %NULL if mm has no associated executable file.
1159  * User must release file via fput().
1160  */
1161 struct file *get_mm_exe_file(struct mm_struct *mm)
1162 {
1163 	struct file *exe_file;
1164 
1165 	rcu_read_lock();
1166 	exe_file = rcu_dereference(mm->exe_file);
1167 	if (exe_file && !get_file_rcu(exe_file))
1168 		exe_file = NULL;
1169 	rcu_read_unlock();
1170 	return exe_file;
1171 }
1172 EXPORT_SYMBOL(get_mm_exe_file);
1173 
1174 /**
1175  * get_task_exe_file - acquire a reference to the task's executable file
1176  *
1177  * Returns %NULL if task's mm (if any) has no associated executable file or
1178  * this is a kernel thread with borrowed mm (see the comment above get_task_mm).
1179  * User must release file via fput().
1180  */
1181 struct file *get_task_exe_file(struct task_struct *task)
1182 {
1183 	struct file *exe_file = NULL;
1184 	struct mm_struct *mm;
1185 
1186 	task_lock(task);
1187 	mm = task->mm;
1188 	if (mm) {
1189 		if (!(task->flags & PF_KTHREAD))
1190 			exe_file = get_mm_exe_file(mm);
1191 	}
1192 	task_unlock(task);
1193 	return exe_file;
1194 }
1195 EXPORT_SYMBOL(get_task_exe_file);
1196 
1197 /**
1198  * get_task_mm - acquire a reference to the task's mm
1199  *
1200  * Returns %NULL if the task has no mm.  Checks PF_KTHREAD (meaning
1201  * this kernel workthread has transiently adopted a user mm with use_mm,
1202  * to do its AIO) is not set and if so returns a reference to it, after
1203  * bumping up the use count.  User must release the mm via mmput()
1204  * after use.  Typically used by /proc and ptrace.
1205  */
1206 struct mm_struct *get_task_mm(struct task_struct *task)
1207 {
1208 	struct mm_struct *mm;
1209 
1210 	task_lock(task);
1211 	mm = task->mm;
1212 	if (mm) {
1213 		if (task->flags & PF_KTHREAD)
1214 			mm = NULL;
1215 		else
1216 			mmget(mm);
1217 	}
1218 	task_unlock(task);
1219 	return mm;
1220 }
1221 EXPORT_SYMBOL_GPL(get_task_mm);
1222 
1223 struct mm_struct *mm_access(struct task_struct *task, unsigned int mode)
1224 {
1225 	struct mm_struct *mm;
1226 	int err;
1227 
1228 	err =  mutex_lock_killable(&task->signal->exec_update_mutex);
1229 	if (err)
1230 		return ERR_PTR(err);
1231 
1232 	mm = get_task_mm(task);
1233 	if (mm && mm != current->mm &&
1234 			!ptrace_may_access(task, mode)) {
1235 		mmput(mm);
1236 		mm = ERR_PTR(-EACCES);
1237 	}
1238 	mutex_unlock(&task->signal->exec_update_mutex);
1239 
1240 	return mm;
1241 }
1242 
1243 static void complete_vfork_done(struct task_struct *tsk)
1244 {
1245 	struct completion *vfork;
1246 
1247 	task_lock(tsk);
1248 	vfork = tsk->vfork_done;
1249 	if (likely(vfork)) {
1250 		tsk->vfork_done = NULL;
1251 		complete(vfork);
1252 	}
1253 	task_unlock(tsk);
1254 }
1255 
1256 static int wait_for_vfork_done(struct task_struct *child,
1257 				struct completion *vfork)
1258 {
1259 	int killed;
1260 
1261 	freezer_do_not_count();
1262 	cgroup_enter_frozen();
1263 	killed = wait_for_completion_killable(vfork);
1264 	cgroup_leave_frozen(false);
1265 	freezer_count();
1266 
1267 	if (killed) {
1268 		task_lock(child);
1269 		child->vfork_done = NULL;
1270 		task_unlock(child);
1271 	}
1272 
1273 	put_task_struct(child);
1274 	return killed;
1275 }
1276 
1277 /* Please note the differences between mmput and mm_release.
1278  * mmput is called whenever we stop holding onto a mm_struct,
1279  * error success whatever.
1280  *
1281  * mm_release is called after a mm_struct has been removed
1282  * from the current process.
1283  *
1284  * This difference is important for error handling, when we
1285  * only half set up a mm_struct for a new process and need to restore
1286  * the old one.  Because we mmput the new mm_struct before
1287  * restoring the old one. . .
1288  * Eric Biederman 10 January 1998
1289  */
1290 static void mm_release(struct task_struct *tsk, struct mm_struct *mm)
1291 {
1292 	uprobe_free_utask(tsk);
1293 
1294 	/* Get rid of any cached register state */
1295 	deactivate_mm(tsk, mm);
1296 
1297 	/*
1298 	 * Signal userspace if we're not exiting with a core dump
1299 	 * because we want to leave the value intact for debugging
1300 	 * purposes.
1301 	 */
1302 	if (tsk->clear_child_tid) {
1303 		if (!(tsk->signal->flags & SIGNAL_GROUP_COREDUMP) &&
1304 		    atomic_read(&mm->mm_users) > 1) {
1305 			/*
1306 			 * We don't check the error code - if userspace has
1307 			 * not set up a proper pointer then tough luck.
1308 			 */
1309 			put_user(0, tsk->clear_child_tid);
1310 			do_futex(tsk->clear_child_tid, FUTEX_WAKE,
1311 					1, NULL, NULL, 0, 0);
1312 		}
1313 		tsk->clear_child_tid = NULL;
1314 	}
1315 
1316 	/*
1317 	 * All done, finally we can wake up parent and return this mm to him.
1318 	 * Also kthread_stop() uses this completion for synchronization.
1319 	 */
1320 	if (tsk->vfork_done)
1321 		complete_vfork_done(tsk);
1322 }
1323 
1324 void exit_mm_release(struct task_struct *tsk, struct mm_struct *mm)
1325 {
1326 	futex_exit_release(tsk);
1327 	mm_release(tsk, mm);
1328 }
1329 
1330 void exec_mm_release(struct task_struct *tsk, struct mm_struct *mm)
1331 {
1332 	futex_exec_release(tsk);
1333 	mm_release(tsk, mm);
1334 }
1335 
1336 /**
1337  * dup_mm() - duplicates an existing mm structure
1338  * @tsk: the task_struct with which the new mm will be associated.
1339  * @oldmm: the mm to duplicate.
1340  *
1341  * Allocates a new mm structure and duplicates the provided @oldmm structure
1342  * content into it.
1343  *
1344  * Return: the duplicated mm or NULL on failure.
1345  */
1346 static struct mm_struct *dup_mm(struct task_struct *tsk,
1347 				struct mm_struct *oldmm)
1348 {
1349 	struct mm_struct *mm;
1350 	int err;
1351 
1352 	mm = allocate_mm();
1353 	if (!mm)
1354 		goto fail_nomem;
1355 
1356 	memcpy(mm, oldmm, sizeof(*mm));
1357 
1358 	if (!mm_init(mm, tsk, mm->user_ns))
1359 		goto fail_nomem;
1360 
1361 	err = dup_mmap(mm, oldmm);
1362 	if (err)
1363 		goto free_pt;
1364 
1365 	mm->hiwater_rss = get_mm_rss(mm);
1366 	mm->hiwater_vm = mm->total_vm;
1367 
1368 	if (mm->binfmt && !try_module_get(mm->binfmt->module))
1369 		goto free_pt;
1370 
1371 	return mm;
1372 
1373 free_pt:
1374 	/* don't put binfmt in mmput, we haven't got module yet */
1375 	mm->binfmt = NULL;
1376 	mm_init_owner(mm, NULL);
1377 	mmput(mm);
1378 
1379 fail_nomem:
1380 	return NULL;
1381 }
1382 
1383 static int copy_mm(unsigned long clone_flags, struct task_struct *tsk)
1384 {
1385 	struct mm_struct *mm, *oldmm;
1386 	int retval;
1387 
1388 	tsk->min_flt = tsk->maj_flt = 0;
1389 	tsk->nvcsw = tsk->nivcsw = 0;
1390 #ifdef CONFIG_DETECT_HUNG_TASK
1391 	tsk->last_switch_count = tsk->nvcsw + tsk->nivcsw;
1392 	tsk->last_switch_time = 0;
1393 #endif
1394 
1395 	tsk->mm = NULL;
1396 	tsk->active_mm = NULL;
1397 
1398 	/*
1399 	 * Are we cloning a kernel thread?
1400 	 *
1401 	 * We need to steal a active VM for that..
1402 	 */
1403 	oldmm = current->mm;
1404 	if (!oldmm)
1405 		return 0;
1406 
1407 	/* initialize the new vmacache entries */
1408 	vmacache_flush(tsk);
1409 
1410 	if (clone_flags & CLONE_VM) {
1411 		mmget(oldmm);
1412 		mm = oldmm;
1413 		goto good_mm;
1414 	}
1415 
1416 	retval = -ENOMEM;
1417 	mm = dup_mm(tsk, current->mm);
1418 	if (!mm)
1419 		goto fail_nomem;
1420 
1421 good_mm:
1422 	tsk->mm = mm;
1423 	tsk->active_mm = mm;
1424 	return 0;
1425 
1426 fail_nomem:
1427 	return retval;
1428 }
1429 
1430 static int copy_fs(unsigned long clone_flags, struct task_struct *tsk)
1431 {
1432 	struct fs_struct *fs = current->fs;
1433 	if (clone_flags & CLONE_FS) {
1434 		/* tsk->fs is already what we want */
1435 		spin_lock(&fs->lock);
1436 		if (fs->in_exec) {
1437 			spin_unlock(&fs->lock);
1438 			return -EAGAIN;
1439 		}
1440 		fs->users++;
1441 		spin_unlock(&fs->lock);
1442 		return 0;
1443 	}
1444 	tsk->fs = copy_fs_struct(fs);
1445 	if (!tsk->fs)
1446 		return -ENOMEM;
1447 	return 0;
1448 }
1449 
1450 static int copy_files(unsigned long clone_flags, struct task_struct *tsk)
1451 {
1452 	struct files_struct *oldf, *newf;
1453 	int error = 0;
1454 
1455 	/*
1456 	 * A background process may not have any files ...
1457 	 */
1458 	oldf = current->files;
1459 	if (!oldf)
1460 		goto out;
1461 
1462 	if (clone_flags & CLONE_FILES) {
1463 		atomic_inc(&oldf->count);
1464 		goto out;
1465 	}
1466 
1467 	newf = dup_fd(oldf, NR_OPEN_MAX, &error);
1468 	if (!newf)
1469 		goto out;
1470 
1471 	tsk->files = newf;
1472 	error = 0;
1473 out:
1474 	return error;
1475 }
1476 
1477 static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
1478 {
1479 #ifdef CONFIG_BLOCK
1480 	struct io_context *ioc = current->io_context;
1481 	struct io_context *new_ioc;
1482 
1483 	if (!ioc)
1484 		return 0;
1485 	/*
1486 	 * Share io context with parent, if CLONE_IO is set
1487 	 */
1488 	if (clone_flags & CLONE_IO) {
1489 		ioc_task_link(ioc);
1490 		tsk->io_context = ioc;
1491 	} else if (ioprio_valid(ioc->ioprio)) {
1492 		new_ioc = get_task_io_context(tsk, GFP_KERNEL, NUMA_NO_NODE);
1493 		if (unlikely(!new_ioc))
1494 			return -ENOMEM;
1495 
1496 		new_ioc->ioprio = ioc->ioprio;
1497 		put_io_context(new_ioc);
1498 	}
1499 #endif
1500 	return 0;
1501 }
1502 
1503 static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
1504 {
1505 	struct sighand_struct *sig;
1506 
1507 	if (clone_flags & CLONE_SIGHAND) {
1508 		refcount_inc(&current->sighand->count);
1509 		return 0;
1510 	}
1511 	sig = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
1512 	RCU_INIT_POINTER(tsk->sighand, sig);
1513 	if (!sig)
1514 		return -ENOMEM;
1515 
1516 	refcount_set(&sig->count, 1);
1517 	spin_lock_irq(&current->sighand->siglock);
1518 	memcpy(sig->action, current->sighand->action, sizeof(sig->action));
1519 	spin_unlock_irq(&current->sighand->siglock);
1520 
1521 	/* Reset all signal handler not set to SIG_IGN to SIG_DFL. */
1522 	if (clone_flags & CLONE_CLEAR_SIGHAND)
1523 		flush_signal_handlers(tsk, 0);
1524 
1525 	return 0;
1526 }
1527 
1528 void __cleanup_sighand(struct sighand_struct *sighand)
1529 {
1530 	if (refcount_dec_and_test(&sighand->count)) {
1531 		signalfd_cleanup(sighand);
1532 		/*
1533 		 * sighand_cachep is SLAB_TYPESAFE_BY_RCU so we can free it
1534 		 * without an RCU grace period, see __lock_task_sighand().
1535 		 */
1536 		kmem_cache_free(sighand_cachep, sighand);
1537 	}
1538 }
1539 
1540 /*
1541  * Initialize POSIX timer handling for a thread group.
1542  */
1543 static void posix_cpu_timers_init_group(struct signal_struct *sig)
1544 {
1545 	struct posix_cputimers *pct = &sig->posix_cputimers;
1546 	unsigned long cpu_limit;
1547 
1548 	cpu_limit = READ_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
1549 	posix_cputimers_group_init(pct, cpu_limit);
1550 }
1551 
1552 static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
1553 {
1554 	struct signal_struct *sig;
1555 
1556 	if (clone_flags & CLONE_THREAD)
1557 		return 0;
1558 
1559 	sig = kmem_cache_zalloc(signal_cachep, GFP_KERNEL);
1560 	tsk->signal = sig;
1561 	if (!sig)
1562 		return -ENOMEM;
1563 
1564 	sig->nr_threads = 1;
1565 	atomic_set(&sig->live, 1);
1566 	refcount_set(&sig->sigcnt, 1);
1567 
1568 	/* list_add(thread_node, thread_head) without INIT_LIST_HEAD() */
1569 	sig->thread_head = (struct list_head)LIST_HEAD_INIT(tsk->thread_node);
1570 	tsk->thread_node = (struct list_head)LIST_HEAD_INIT(sig->thread_head);
1571 
1572 	init_waitqueue_head(&sig->wait_chldexit);
1573 	sig->curr_target = tsk;
1574 	init_sigpending(&sig->shared_pending);
1575 	INIT_HLIST_HEAD(&sig->multiprocess);
1576 	seqlock_init(&sig->stats_lock);
1577 	prev_cputime_init(&sig->prev_cputime);
1578 
1579 #ifdef CONFIG_POSIX_TIMERS
1580 	INIT_LIST_HEAD(&sig->posix_timers);
1581 	hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
1582 	sig->real_timer.function = it_real_fn;
1583 #endif
1584 
1585 	task_lock(current->group_leader);
1586 	memcpy(sig->rlim, current->signal->rlim, sizeof sig->rlim);
1587 	task_unlock(current->group_leader);
1588 
1589 	posix_cpu_timers_init_group(sig);
1590 
1591 	tty_audit_fork(sig);
1592 	sched_autogroup_fork(sig);
1593 
1594 	sig->oom_score_adj = current->signal->oom_score_adj;
1595 	sig->oom_score_adj_min = current->signal->oom_score_adj_min;
1596 
1597 	mutex_init(&sig->cred_guard_mutex);
1598 	mutex_init(&sig->exec_update_mutex);
1599 
1600 	return 0;
1601 }
1602 
1603 static void copy_seccomp(struct task_struct *p)
1604 {
1605 #ifdef CONFIG_SECCOMP
1606 	/*
1607 	 * Must be called with sighand->lock held, which is common to
1608 	 * all threads in the group. Holding cred_guard_mutex is not
1609 	 * needed because this new task is not yet running and cannot
1610 	 * be racing exec.
1611 	 */
1612 	assert_spin_locked(&current->sighand->siglock);
1613 
1614 	/* Ref-count the new filter user, and assign it. */
1615 	get_seccomp_filter(current);
1616 	p->seccomp = current->seccomp;
1617 
1618 	/*
1619 	 * Explicitly enable no_new_privs here in case it got set
1620 	 * between the task_struct being duplicated and holding the
1621 	 * sighand lock. The seccomp state and nnp must be in sync.
1622 	 */
1623 	if (task_no_new_privs(current))
1624 		task_set_no_new_privs(p);
1625 
1626 	/*
1627 	 * If the parent gained a seccomp mode after copying thread
1628 	 * flags and between before we held the sighand lock, we have
1629 	 * to manually enable the seccomp thread flag here.
1630 	 */
1631 	if (p->seccomp.mode != SECCOMP_MODE_DISABLED)
1632 		set_task_syscall_work(p, SECCOMP);
1633 #endif
1634 }
1635 
1636 SYSCALL_DEFINE1(set_tid_address, int __user *, tidptr)
1637 {
1638 	current->clear_child_tid = tidptr;
1639 
1640 	return task_pid_vnr(current);
1641 }
1642 
1643 static void rt_mutex_init_task(struct task_struct *p)
1644 {
1645 	raw_spin_lock_init(&p->pi_lock);
1646 #ifdef CONFIG_RT_MUTEXES
1647 	p->pi_waiters = RB_ROOT_CACHED;
1648 	p->pi_top_task = NULL;
1649 	p->pi_blocked_on = NULL;
1650 #endif
1651 }
1652 
1653 static inline void init_task_pid_links(struct task_struct *task)
1654 {
1655 	enum pid_type type;
1656 
1657 	for (type = PIDTYPE_PID; type < PIDTYPE_MAX; ++type) {
1658 		INIT_HLIST_NODE(&task->pid_links[type]);
1659 	}
1660 }
1661 
1662 static inline void
1663 init_task_pid(struct task_struct *task, enum pid_type type, struct pid *pid)
1664 {
1665 	if (type == PIDTYPE_PID)
1666 		task->thread_pid = pid;
1667 	else
1668 		task->signal->pids[type] = pid;
1669 }
1670 
1671 static inline void rcu_copy_process(struct task_struct *p)
1672 {
1673 #ifdef CONFIG_PREEMPT_RCU
1674 	p->rcu_read_lock_nesting = 0;
1675 	p->rcu_read_unlock_special.s = 0;
1676 	p->rcu_blocked_node = NULL;
1677 	INIT_LIST_HEAD(&p->rcu_node_entry);
1678 #endif /* #ifdef CONFIG_PREEMPT_RCU */
1679 #ifdef CONFIG_TASKS_RCU
1680 	p->rcu_tasks_holdout = false;
1681 	INIT_LIST_HEAD(&p->rcu_tasks_holdout_list);
1682 	p->rcu_tasks_idle_cpu = -1;
1683 #endif /* #ifdef CONFIG_TASKS_RCU */
1684 #ifdef CONFIG_TASKS_TRACE_RCU
1685 	p->trc_reader_nesting = 0;
1686 	p->trc_reader_special.s = 0;
1687 	INIT_LIST_HEAD(&p->trc_holdout_list);
1688 #endif /* #ifdef CONFIG_TASKS_TRACE_RCU */
1689 }
1690 
1691 struct pid *pidfd_pid(const struct file *file)
1692 {
1693 	if (file->f_op == &pidfd_fops)
1694 		return file->private_data;
1695 
1696 	return ERR_PTR(-EBADF);
1697 }
1698 
1699 static int pidfd_release(struct inode *inode, struct file *file)
1700 {
1701 	struct pid *pid = file->private_data;
1702 
1703 	file->private_data = NULL;
1704 	put_pid(pid);
1705 	return 0;
1706 }
1707 
1708 #ifdef CONFIG_PROC_FS
1709 /**
1710  * pidfd_show_fdinfo - print information about a pidfd
1711  * @m: proc fdinfo file
1712  * @f: file referencing a pidfd
1713  *
1714  * Pid:
1715  * This function will print the pid that a given pidfd refers to in the
1716  * pid namespace of the procfs instance.
1717  * If the pid namespace of the process is not a descendant of the pid
1718  * namespace of the procfs instance 0 will be shown as its pid. This is
1719  * similar to calling getppid() on a process whose parent is outside of
1720  * its pid namespace.
1721  *
1722  * NSpid:
1723  * If pid namespaces are supported then this function will also print
1724  * the pid of a given pidfd refers to for all descendant pid namespaces
1725  * starting from the current pid namespace of the instance, i.e. the
1726  * Pid field and the first entry in the NSpid field will be identical.
1727  * If the pid namespace of the process is not a descendant of the pid
1728  * namespace of the procfs instance 0 will be shown as its first NSpid
1729  * entry and no others will be shown.
1730  * Note that this differs from the Pid and NSpid fields in
1731  * /proc/<pid>/status where Pid and NSpid are always shown relative to
1732  * the  pid namespace of the procfs instance. The difference becomes
1733  * obvious when sending around a pidfd between pid namespaces from a
1734  * different branch of the tree, i.e. where no ancestoral relation is
1735  * present between the pid namespaces:
1736  * - create two new pid namespaces ns1 and ns2 in the initial pid
1737  *   namespace (also take care to create new mount namespaces in the
1738  *   new pid namespace and mount procfs)
1739  * - create a process with a pidfd in ns1
1740  * - send pidfd from ns1 to ns2
1741  * - read /proc/self/fdinfo/<pidfd> and observe that both Pid and NSpid
1742  *   have exactly one entry, which is 0
1743  */
1744 static void pidfd_show_fdinfo(struct seq_file *m, struct file *f)
1745 {
1746 	struct pid *pid = f->private_data;
1747 	struct pid_namespace *ns;
1748 	pid_t nr = -1;
1749 
1750 	if (likely(pid_has_task(pid, PIDTYPE_PID))) {
1751 		ns = proc_pid_ns(file_inode(m->file)->i_sb);
1752 		nr = pid_nr_ns(pid, ns);
1753 	}
1754 
1755 	seq_put_decimal_ll(m, "Pid:\t", nr);
1756 
1757 #ifdef CONFIG_PID_NS
1758 	seq_put_decimal_ll(m, "\nNSpid:\t", nr);
1759 	if (nr > 0) {
1760 		int i;
1761 
1762 		/* If nr is non-zero it means that 'pid' is valid and that
1763 		 * ns, i.e. the pid namespace associated with the procfs
1764 		 * instance, is in the pid namespace hierarchy of pid.
1765 		 * Start at one below the already printed level.
1766 		 */
1767 		for (i = ns->level + 1; i <= pid->level; i++)
1768 			seq_put_decimal_ll(m, "\t", pid->numbers[i].nr);
1769 	}
1770 #endif
1771 	seq_putc(m, '\n');
1772 }
1773 #endif
1774 
1775 /*
1776  * Poll support for process exit notification.
1777  */
1778 static __poll_t pidfd_poll(struct file *file, struct poll_table_struct *pts)
1779 {
1780 	struct pid *pid = file->private_data;
1781 	__poll_t poll_flags = 0;
1782 
1783 	poll_wait(file, &pid->wait_pidfd, pts);
1784 
1785 	/*
1786 	 * Inform pollers only when the whole thread group exits.
1787 	 * If the thread group leader exits before all other threads in the
1788 	 * group, then poll(2) should block, similar to the wait(2) family.
1789 	 */
1790 	if (thread_group_exited(pid))
1791 		poll_flags = EPOLLIN | EPOLLRDNORM;
1792 
1793 	return poll_flags;
1794 }
1795 
1796 const struct file_operations pidfd_fops = {
1797 	.release = pidfd_release,
1798 	.poll = pidfd_poll,
1799 #ifdef CONFIG_PROC_FS
1800 	.show_fdinfo = pidfd_show_fdinfo,
1801 #endif
1802 };
1803 
1804 static void __delayed_free_task(struct rcu_head *rhp)
1805 {
1806 	struct task_struct *tsk = container_of(rhp, struct task_struct, rcu);
1807 
1808 	free_task(tsk);
1809 }
1810 
1811 static __always_inline void delayed_free_task(struct task_struct *tsk)
1812 {
1813 	if (IS_ENABLED(CONFIG_MEMCG))
1814 		call_rcu(&tsk->rcu, __delayed_free_task);
1815 	else
1816 		free_task(tsk);
1817 }
1818 
1819 static void copy_oom_score_adj(u64 clone_flags, struct task_struct *tsk)
1820 {
1821 	/* Skip if kernel thread */
1822 	if (!tsk->mm)
1823 		return;
1824 
1825 	/* Skip if spawning a thread or using vfork */
1826 	if ((clone_flags & (CLONE_VM | CLONE_THREAD | CLONE_VFORK)) != CLONE_VM)
1827 		return;
1828 
1829 	/* We need to synchronize with __set_oom_adj */
1830 	mutex_lock(&oom_adj_mutex);
1831 	set_bit(MMF_MULTIPROCESS, &tsk->mm->flags);
1832 	/* Update the values in case they were changed after copy_signal */
1833 	tsk->signal->oom_score_adj = current->signal->oom_score_adj;
1834 	tsk->signal->oom_score_adj_min = current->signal->oom_score_adj_min;
1835 	mutex_unlock(&oom_adj_mutex);
1836 }
1837 
1838 /*
1839  * This creates a new process as a copy of the old one,
1840  * but does not actually start it yet.
1841  *
1842  * It copies the registers, and all the appropriate
1843  * parts of the process environment (as per the clone
1844  * flags). The actual kick-off is left to the caller.
1845  */
1846 static __latent_entropy struct task_struct *copy_process(
1847 					struct pid *pid,
1848 					int trace,
1849 					int node,
1850 					struct kernel_clone_args *args)
1851 {
1852 	int pidfd = -1, retval;
1853 	struct task_struct *p;
1854 	struct multiprocess_signals delayed;
1855 	struct file *pidfile = NULL;
1856 	u64 clone_flags = args->flags;
1857 	struct nsproxy *nsp = current->nsproxy;
1858 
1859 	/*
1860 	 * Don't allow sharing the root directory with processes in a different
1861 	 * namespace
1862 	 */
1863 	if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
1864 		return ERR_PTR(-EINVAL);
1865 
1866 	if ((clone_flags & (CLONE_NEWUSER|CLONE_FS)) == (CLONE_NEWUSER|CLONE_FS))
1867 		return ERR_PTR(-EINVAL);
1868 
1869 	/*
1870 	 * Thread groups must share signals as well, and detached threads
1871 	 * can only be started up within the thread group.
1872 	 */
1873 	if ((clone_flags & CLONE_THREAD) && !(clone_flags & CLONE_SIGHAND))
1874 		return ERR_PTR(-EINVAL);
1875 
1876 	/*
1877 	 * Shared signal handlers imply shared VM. By way of the above,
1878 	 * thread groups also imply shared VM. Blocking this case allows
1879 	 * for various simplifications in other code.
1880 	 */
1881 	if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))
1882 		return ERR_PTR(-EINVAL);
1883 
1884 	/*
1885 	 * Siblings of global init remain as zombies on exit since they are
1886 	 * not reaped by their parent (swapper). To solve this and to avoid
1887 	 * multi-rooted process trees, prevent global and container-inits
1888 	 * from creating siblings.
1889 	 */
1890 	if ((clone_flags & CLONE_PARENT) &&
1891 				current->signal->flags & SIGNAL_UNKILLABLE)
1892 		return ERR_PTR(-EINVAL);
1893 
1894 	/*
1895 	 * If the new process will be in a different pid or user namespace
1896 	 * do not allow it to share a thread group with the forking task.
1897 	 */
1898 	if (clone_flags & CLONE_THREAD) {
1899 		if ((clone_flags & (CLONE_NEWUSER | CLONE_NEWPID)) ||
1900 		    (task_active_pid_ns(current) != nsp->pid_ns_for_children))
1901 			return ERR_PTR(-EINVAL);
1902 	}
1903 
1904 	/*
1905 	 * If the new process will be in a different time namespace
1906 	 * do not allow it to share VM or a thread group with the forking task.
1907 	 */
1908 	if (clone_flags & (CLONE_THREAD | CLONE_VM)) {
1909 		if (nsp->time_ns != nsp->time_ns_for_children)
1910 			return ERR_PTR(-EINVAL);
1911 	}
1912 
1913 	if (clone_flags & CLONE_PIDFD) {
1914 		/*
1915 		 * - CLONE_DETACHED is blocked so that we can potentially
1916 		 *   reuse it later for CLONE_PIDFD.
1917 		 * - CLONE_THREAD is blocked until someone really needs it.
1918 		 */
1919 		if (clone_flags & (CLONE_DETACHED | CLONE_THREAD))
1920 			return ERR_PTR(-EINVAL);
1921 	}
1922 
1923 	/*
1924 	 * Force any signals received before this point to be delivered
1925 	 * before the fork happens.  Collect up signals sent to multiple
1926 	 * processes that happen during the fork and delay them so that
1927 	 * they appear to happen after the fork.
1928 	 */
1929 	sigemptyset(&delayed.signal);
1930 	INIT_HLIST_NODE(&delayed.node);
1931 
1932 	spin_lock_irq(&current->sighand->siglock);
1933 	if (!(clone_flags & CLONE_THREAD))
1934 		hlist_add_head(&delayed.node, &current->signal->multiprocess);
1935 	recalc_sigpending();
1936 	spin_unlock_irq(&current->sighand->siglock);
1937 	retval = -ERESTARTNOINTR;
1938 	if (signal_pending(current))
1939 		goto fork_out;
1940 
1941 	retval = -ENOMEM;
1942 	p = dup_task_struct(current, node);
1943 	if (!p)
1944 		goto fork_out;
1945 
1946 	/*
1947 	 * This _must_ happen before we call free_task(), i.e. before we jump
1948 	 * to any of the bad_fork_* labels. This is to avoid freeing
1949 	 * p->set_child_tid which is (ab)used as a kthread's data pointer for
1950 	 * kernel threads (PF_KTHREAD).
1951 	 */
1952 	p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? args->child_tid : NULL;
1953 	/*
1954 	 * Clear TID on mm_release()?
1955 	 */
1956 	p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? args->child_tid : NULL;
1957 
1958 	ftrace_graph_init_task(p);
1959 
1960 	rt_mutex_init_task(p);
1961 
1962 	lockdep_assert_irqs_enabled();
1963 #ifdef CONFIG_PROVE_LOCKING
1964 	DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
1965 #endif
1966 	retval = -EAGAIN;
1967 	if (atomic_read(&p->real_cred->user->processes) >=
1968 			task_rlimit(p, RLIMIT_NPROC)) {
1969 		if (p->real_cred->user != INIT_USER &&
1970 		    !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN))
1971 			goto bad_fork_free;
1972 	}
1973 	current->flags &= ~PF_NPROC_EXCEEDED;
1974 
1975 	retval = copy_creds(p, clone_flags);
1976 	if (retval < 0)
1977 		goto bad_fork_free;
1978 
1979 	/*
1980 	 * If multiple threads are within copy_process(), then this check
1981 	 * triggers too late. This doesn't hurt, the check is only there
1982 	 * to stop root fork bombs.
1983 	 */
1984 	retval = -EAGAIN;
1985 	if (data_race(nr_threads >= max_threads))
1986 		goto bad_fork_cleanup_count;
1987 
1988 	delayacct_tsk_init(p);	/* Must remain after dup_task_struct() */
1989 	p->flags &= ~(PF_SUPERPRIV | PF_WQ_WORKER | PF_IDLE);
1990 	p->flags |= PF_FORKNOEXEC;
1991 	INIT_LIST_HEAD(&p->children);
1992 	INIT_LIST_HEAD(&p->sibling);
1993 	rcu_copy_process(p);
1994 	p->vfork_done = NULL;
1995 	spin_lock_init(&p->alloc_lock);
1996 
1997 	init_sigpending(&p->pending);
1998 
1999 	p->utime = p->stime = p->gtime = 0;
2000 #ifdef CONFIG_ARCH_HAS_SCALED_CPUTIME
2001 	p->utimescaled = p->stimescaled = 0;
2002 #endif
2003 	prev_cputime_init(&p->prev_cputime);
2004 
2005 #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
2006 	seqcount_init(&p->vtime.seqcount);
2007 	p->vtime.starttime = 0;
2008 	p->vtime.state = VTIME_INACTIVE;
2009 #endif
2010 
2011 #ifdef CONFIG_IO_URING
2012 	p->io_uring = NULL;
2013 #endif
2014 
2015 #if defined(SPLIT_RSS_COUNTING)
2016 	memset(&p->rss_stat, 0, sizeof(p->rss_stat));
2017 #endif
2018 
2019 	p->default_timer_slack_ns = current->timer_slack_ns;
2020 
2021 #ifdef CONFIG_PSI
2022 	p->psi_flags = 0;
2023 #endif
2024 
2025 	task_io_accounting_init(&p->ioac);
2026 	acct_clear_integrals(p);
2027 
2028 	posix_cputimers_init(&p->posix_cputimers);
2029 
2030 	p->io_context = NULL;
2031 	audit_set_context(p, NULL);
2032 	cgroup_fork(p);
2033 #ifdef CONFIG_NUMA
2034 	p->mempolicy = mpol_dup(p->mempolicy);
2035 	if (IS_ERR(p->mempolicy)) {
2036 		retval = PTR_ERR(p->mempolicy);
2037 		p->mempolicy = NULL;
2038 		goto bad_fork_cleanup_threadgroup_lock;
2039 	}
2040 #endif
2041 #ifdef CONFIG_CPUSETS
2042 	p->cpuset_mem_spread_rotor = NUMA_NO_NODE;
2043 	p->cpuset_slab_spread_rotor = NUMA_NO_NODE;
2044 	seqcount_spinlock_init(&p->mems_allowed_seq, &p->alloc_lock);
2045 #endif
2046 #ifdef CONFIG_TRACE_IRQFLAGS
2047 	memset(&p->irqtrace, 0, sizeof(p->irqtrace));
2048 	p->irqtrace.hardirq_disable_ip	= _THIS_IP_;
2049 	p->irqtrace.softirq_enable_ip	= _THIS_IP_;
2050 	p->softirqs_enabled		= 1;
2051 	p->softirq_context		= 0;
2052 #endif
2053 
2054 	p->pagefault_disabled = 0;
2055 
2056 #ifdef CONFIG_LOCKDEP
2057 	lockdep_init_task(p);
2058 #endif
2059 
2060 #ifdef CONFIG_DEBUG_MUTEXES
2061 	p->blocked_on = NULL; /* not blocked yet */
2062 #endif
2063 #ifdef CONFIG_BCACHE
2064 	p->sequential_io	= 0;
2065 	p->sequential_io_avg	= 0;
2066 #endif
2067 
2068 	/* Perform scheduler related setup. Assign this task to a CPU. */
2069 	retval = sched_fork(clone_flags, p);
2070 	if (retval)
2071 		goto bad_fork_cleanup_policy;
2072 
2073 	retval = perf_event_init_task(p);
2074 	if (retval)
2075 		goto bad_fork_cleanup_policy;
2076 	retval = audit_alloc(p);
2077 	if (retval)
2078 		goto bad_fork_cleanup_perf;
2079 	/* copy all the process information */
2080 	shm_init_task(p);
2081 	retval = security_task_alloc(p, clone_flags);
2082 	if (retval)
2083 		goto bad_fork_cleanup_audit;
2084 	retval = copy_semundo(clone_flags, p);
2085 	if (retval)
2086 		goto bad_fork_cleanup_security;
2087 	retval = copy_files(clone_flags, p);
2088 	if (retval)
2089 		goto bad_fork_cleanup_semundo;
2090 	retval = copy_fs(clone_flags, p);
2091 	if (retval)
2092 		goto bad_fork_cleanup_files;
2093 	retval = copy_sighand(clone_flags, p);
2094 	if (retval)
2095 		goto bad_fork_cleanup_fs;
2096 	retval = copy_signal(clone_flags, p);
2097 	if (retval)
2098 		goto bad_fork_cleanup_sighand;
2099 	retval = copy_mm(clone_flags, p);
2100 	if (retval)
2101 		goto bad_fork_cleanup_signal;
2102 	retval = copy_namespaces(clone_flags, p);
2103 	if (retval)
2104 		goto bad_fork_cleanup_mm;
2105 	retval = copy_io(clone_flags, p);
2106 	if (retval)
2107 		goto bad_fork_cleanup_namespaces;
2108 	retval = copy_thread(clone_flags, args->stack, args->stack_size, p, args->tls);
2109 	if (retval)
2110 		goto bad_fork_cleanup_io;
2111 
2112 	stackleak_task_init(p);
2113 
2114 	if (pid != &init_struct_pid) {
2115 		pid = alloc_pid(p->nsproxy->pid_ns_for_children, args->set_tid,
2116 				args->set_tid_size);
2117 		if (IS_ERR(pid)) {
2118 			retval = PTR_ERR(pid);
2119 			goto bad_fork_cleanup_thread;
2120 		}
2121 	}
2122 
2123 	/*
2124 	 * This has to happen after we've potentially unshared the file
2125 	 * descriptor table (so that the pidfd doesn't leak into the child
2126 	 * if the fd table isn't shared).
2127 	 */
2128 	if (clone_flags & CLONE_PIDFD) {
2129 		retval = get_unused_fd_flags(O_RDWR | O_CLOEXEC);
2130 		if (retval < 0)
2131 			goto bad_fork_free_pid;
2132 
2133 		pidfd = retval;
2134 
2135 		pidfile = anon_inode_getfile("[pidfd]", &pidfd_fops, pid,
2136 					      O_RDWR | O_CLOEXEC);
2137 		if (IS_ERR(pidfile)) {
2138 			put_unused_fd(pidfd);
2139 			retval = PTR_ERR(pidfile);
2140 			goto bad_fork_free_pid;
2141 		}
2142 		get_pid(pid);	/* held by pidfile now */
2143 
2144 		retval = put_user(pidfd, args->pidfd);
2145 		if (retval)
2146 			goto bad_fork_put_pidfd;
2147 	}
2148 
2149 #ifdef CONFIG_BLOCK
2150 	p->plug = NULL;
2151 #endif
2152 	futex_init_task(p);
2153 
2154 	/*
2155 	 * sigaltstack should be cleared when sharing the same VM
2156 	 */
2157 	if ((clone_flags & (CLONE_VM|CLONE_VFORK)) == CLONE_VM)
2158 		sas_ss_reset(p);
2159 
2160 	/*
2161 	 * Syscall tracing and stepping should be turned off in the
2162 	 * child regardless of CLONE_PTRACE.
2163 	 */
2164 	user_disable_single_step(p);
2165 	clear_task_syscall_work(p, SYSCALL_TRACE);
2166 #if defined(CONFIG_GENERIC_ENTRY) || defined(TIF_SYSCALL_EMU)
2167 	clear_task_syscall_work(p, SYSCALL_EMU);
2168 #endif
2169 	clear_tsk_latency_tracing(p);
2170 
2171 	/* ok, now we should be set up.. */
2172 	p->pid = pid_nr(pid);
2173 	if (clone_flags & CLONE_THREAD) {
2174 		p->group_leader = current->group_leader;
2175 		p->tgid = current->tgid;
2176 	} else {
2177 		p->group_leader = p;
2178 		p->tgid = p->pid;
2179 	}
2180 
2181 	p->nr_dirtied = 0;
2182 	p->nr_dirtied_pause = 128 >> (PAGE_SHIFT - 10);
2183 	p->dirty_paused_when = 0;
2184 
2185 	p->pdeath_signal = 0;
2186 	INIT_LIST_HEAD(&p->thread_group);
2187 	p->task_works = NULL;
2188 
2189 #ifdef CONFIG_KRETPROBES
2190 	p->kretprobe_instances.first = NULL;
2191 #endif
2192 
2193 	/*
2194 	 * Ensure that the cgroup subsystem policies allow the new process to be
2195 	 * forked. It should be noted that the new process's css_set can be changed
2196 	 * between here and cgroup_post_fork() if an organisation operation is in
2197 	 * progress.
2198 	 */
2199 	retval = cgroup_can_fork(p, args);
2200 	if (retval)
2201 		goto bad_fork_put_pidfd;
2202 
2203 	/*
2204 	 * From this point on we must avoid any synchronous user-space
2205 	 * communication until we take the tasklist-lock. In particular, we do
2206 	 * not want user-space to be able to predict the process start-time by
2207 	 * stalling fork(2) after we recorded the start_time but before it is
2208 	 * visible to the system.
2209 	 */
2210 
2211 	p->start_time = ktime_get_ns();
2212 	p->start_boottime = ktime_get_boottime_ns();
2213 
2214 	/*
2215 	 * Make it visible to the rest of the system, but dont wake it up yet.
2216 	 * Need tasklist lock for parent etc handling!
2217 	 */
2218 	write_lock_irq(&tasklist_lock);
2219 
2220 	/* CLONE_PARENT re-uses the old parent */
2221 	if (clone_flags & (CLONE_PARENT|CLONE_THREAD)) {
2222 		p->real_parent = current->real_parent;
2223 		p->parent_exec_id = current->parent_exec_id;
2224 		if (clone_flags & CLONE_THREAD)
2225 			p->exit_signal = -1;
2226 		else
2227 			p->exit_signal = current->group_leader->exit_signal;
2228 	} else {
2229 		p->real_parent = current;
2230 		p->parent_exec_id = current->self_exec_id;
2231 		p->exit_signal = args->exit_signal;
2232 	}
2233 
2234 	klp_copy_process(p);
2235 
2236 	spin_lock(&current->sighand->siglock);
2237 
2238 	/*
2239 	 * Copy seccomp details explicitly here, in case they were changed
2240 	 * before holding sighand lock.
2241 	 */
2242 	copy_seccomp(p);
2243 
2244 	rseq_fork(p, clone_flags);
2245 
2246 	/* Don't start children in a dying pid namespace */
2247 	if (unlikely(!(ns_of_pid(pid)->pid_allocated & PIDNS_ADDING))) {
2248 		retval = -ENOMEM;
2249 		goto bad_fork_cancel_cgroup;
2250 	}
2251 
2252 	/* Let kill terminate clone/fork in the middle */
2253 	if (fatal_signal_pending(current)) {
2254 		retval = -EINTR;
2255 		goto bad_fork_cancel_cgroup;
2256 	}
2257 
2258 	/* past the last point of failure */
2259 	if (pidfile)
2260 		fd_install(pidfd, pidfile);
2261 
2262 	init_task_pid_links(p);
2263 	if (likely(p->pid)) {
2264 		ptrace_init_task(p, (clone_flags & CLONE_PTRACE) || trace);
2265 
2266 		init_task_pid(p, PIDTYPE_PID, pid);
2267 		if (thread_group_leader(p)) {
2268 			init_task_pid(p, PIDTYPE_TGID, pid);
2269 			init_task_pid(p, PIDTYPE_PGID, task_pgrp(current));
2270 			init_task_pid(p, PIDTYPE_SID, task_session(current));
2271 
2272 			if (is_child_reaper(pid)) {
2273 				ns_of_pid(pid)->child_reaper = p;
2274 				p->signal->flags |= SIGNAL_UNKILLABLE;
2275 			}
2276 			p->signal->shared_pending.signal = delayed.signal;
2277 			p->signal->tty = tty_kref_get(current->signal->tty);
2278 			/*
2279 			 * Inherit has_child_subreaper flag under the same
2280 			 * tasklist_lock with adding child to the process tree
2281 			 * for propagate_has_child_subreaper optimization.
2282 			 */
2283 			p->signal->has_child_subreaper = p->real_parent->signal->has_child_subreaper ||
2284 							 p->real_parent->signal->is_child_subreaper;
2285 			list_add_tail(&p->sibling, &p->real_parent->children);
2286 			list_add_tail_rcu(&p->tasks, &init_task.tasks);
2287 			attach_pid(p, PIDTYPE_TGID);
2288 			attach_pid(p, PIDTYPE_PGID);
2289 			attach_pid(p, PIDTYPE_SID);
2290 			__this_cpu_inc(process_counts);
2291 		} else {
2292 			current->signal->nr_threads++;
2293 			atomic_inc(&current->signal->live);
2294 			refcount_inc(&current->signal->sigcnt);
2295 			task_join_group_stop(p);
2296 			list_add_tail_rcu(&p->thread_group,
2297 					  &p->group_leader->thread_group);
2298 			list_add_tail_rcu(&p->thread_node,
2299 					  &p->signal->thread_head);
2300 		}
2301 		attach_pid(p, PIDTYPE_PID);
2302 		nr_threads++;
2303 	}
2304 	total_forks++;
2305 	hlist_del_init(&delayed.node);
2306 	spin_unlock(&current->sighand->siglock);
2307 	syscall_tracepoint_update(p);
2308 	write_unlock_irq(&tasklist_lock);
2309 
2310 	proc_fork_connector(p);
2311 	sched_post_fork(p);
2312 	cgroup_post_fork(p, args);
2313 	perf_event_fork(p);
2314 
2315 	trace_task_newtask(p, clone_flags);
2316 	uprobe_copy_process(p, clone_flags);
2317 
2318 	copy_oom_score_adj(clone_flags, p);
2319 
2320 	return p;
2321 
2322 bad_fork_cancel_cgroup:
2323 	spin_unlock(&current->sighand->siglock);
2324 	write_unlock_irq(&tasklist_lock);
2325 	cgroup_cancel_fork(p, args);
2326 bad_fork_put_pidfd:
2327 	if (clone_flags & CLONE_PIDFD) {
2328 		fput(pidfile);
2329 		put_unused_fd(pidfd);
2330 	}
2331 bad_fork_free_pid:
2332 	if (pid != &init_struct_pid)
2333 		free_pid(pid);
2334 bad_fork_cleanup_thread:
2335 	exit_thread(p);
2336 bad_fork_cleanup_io:
2337 	if (p->io_context)
2338 		exit_io_context(p);
2339 bad_fork_cleanup_namespaces:
2340 	exit_task_namespaces(p);
2341 bad_fork_cleanup_mm:
2342 	if (p->mm) {
2343 		mm_clear_owner(p->mm, p);
2344 		mmput(p->mm);
2345 	}
2346 bad_fork_cleanup_signal:
2347 	if (!(clone_flags & CLONE_THREAD))
2348 		free_signal_struct(p->signal);
2349 bad_fork_cleanup_sighand:
2350 	__cleanup_sighand(p->sighand);
2351 bad_fork_cleanup_fs:
2352 	exit_fs(p); /* blocking */
2353 bad_fork_cleanup_files:
2354 	exit_files(p); /* blocking */
2355 bad_fork_cleanup_semundo:
2356 	exit_sem(p);
2357 bad_fork_cleanup_security:
2358 	security_task_free(p);
2359 bad_fork_cleanup_audit:
2360 	audit_free(p);
2361 bad_fork_cleanup_perf:
2362 	perf_event_free_task(p);
2363 bad_fork_cleanup_policy:
2364 	lockdep_free_task(p);
2365 #ifdef CONFIG_NUMA
2366 	mpol_put(p->mempolicy);
2367 bad_fork_cleanup_threadgroup_lock:
2368 #endif
2369 	delayacct_tsk_free(p);
2370 bad_fork_cleanup_count:
2371 	atomic_dec(&p->cred->user->processes);
2372 	exit_creds(p);
2373 bad_fork_free:
2374 	p->state = TASK_DEAD;
2375 	put_task_stack(p);
2376 	delayed_free_task(p);
2377 fork_out:
2378 	spin_lock_irq(&current->sighand->siglock);
2379 	hlist_del_init(&delayed.node);
2380 	spin_unlock_irq(&current->sighand->siglock);
2381 	return ERR_PTR(retval);
2382 }
2383 
2384 static inline void init_idle_pids(struct task_struct *idle)
2385 {
2386 	enum pid_type type;
2387 
2388 	for (type = PIDTYPE_PID; type < PIDTYPE_MAX; ++type) {
2389 		INIT_HLIST_NODE(&idle->pid_links[type]); /* not really needed */
2390 		init_task_pid(idle, type, &init_struct_pid);
2391 	}
2392 }
2393 
2394 struct task_struct *fork_idle(int cpu)
2395 {
2396 	struct task_struct *task;
2397 	struct kernel_clone_args args = {
2398 		.flags = CLONE_VM,
2399 	};
2400 
2401 	task = copy_process(&init_struct_pid, 0, cpu_to_node(cpu), &args);
2402 	if (!IS_ERR(task)) {
2403 		init_idle_pids(task);
2404 		init_idle(task, cpu);
2405 	}
2406 
2407 	return task;
2408 }
2409 
2410 struct mm_struct *copy_init_mm(void)
2411 {
2412 	return dup_mm(NULL, &init_mm);
2413 }
2414 
2415 /*
2416  *  Ok, this is the main fork-routine.
2417  *
2418  * It copies the process, and if successful kick-starts
2419  * it and waits for it to finish using the VM if required.
2420  *
2421  * args->exit_signal is expected to be checked for sanity by the caller.
2422  */
2423 pid_t kernel_clone(struct kernel_clone_args *args)
2424 {
2425 	u64 clone_flags = args->flags;
2426 	struct completion vfork;
2427 	struct pid *pid;
2428 	struct task_struct *p;
2429 	int trace = 0;
2430 	pid_t nr;
2431 
2432 	/*
2433 	 * For legacy clone() calls, CLONE_PIDFD uses the parent_tid argument
2434 	 * to return the pidfd. Hence, CLONE_PIDFD and CLONE_PARENT_SETTID are
2435 	 * mutually exclusive. With clone3() CLONE_PIDFD has grown a separate
2436 	 * field in struct clone_args and it still doesn't make sense to have
2437 	 * them both point at the same memory location. Performing this check
2438 	 * here has the advantage that we don't need to have a separate helper
2439 	 * to check for legacy clone().
2440 	 */
2441 	if ((args->flags & CLONE_PIDFD) &&
2442 	    (args->flags & CLONE_PARENT_SETTID) &&
2443 	    (args->pidfd == args->parent_tid))
2444 		return -EINVAL;
2445 
2446 	/*
2447 	 * Determine whether and which event to report to ptracer.  When
2448 	 * called from kernel_thread or CLONE_UNTRACED is explicitly
2449 	 * requested, no event is reported; otherwise, report if the event
2450 	 * for the type of forking is enabled.
2451 	 */
2452 	if (!(clone_flags & CLONE_UNTRACED)) {
2453 		if (clone_flags & CLONE_VFORK)
2454 			trace = PTRACE_EVENT_VFORK;
2455 		else if (args->exit_signal != SIGCHLD)
2456 			trace = PTRACE_EVENT_CLONE;
2457 		else
2458 			trace = PTRACE_EVENT_FORK;
2459 
2460 		if (likely(!ptrace_event_enabled(current, trace)))
2461 			trace = 0;
2462 	}
2463 
2464 	p = copy_process(NULL, trace, NUMA_NO_NODE, args);
2465 	add_latent_entropy();
2466 
2467 	if (IS_ERR(p))
2468 		return PTR_ERR(p);
2469 
2470 	/*
2471 	 * Do this prior waking up the new thread - the thread pointer
2472 	 * might get invalid after that point, if the thread exits quickly.
2473 	 */
2474 	trace_sched_process_fork(current, p);
2475 
2476 	pid = get_task_pid(p, PIDTYPE_PID);
2477 	nr = pid_vnr(pid);
2478 
2479 	if (clone_flags & CLONE_PARENT_SETTID)
2480 		put_user(nr, args->parent_tid);
2481 
2482 	if (clone_flags & CLONE_VFORK) {
2483 		p->vfork_done = &vfork;
2484 		init_completion(&vfork);
2485 		get_task_struct(p);
2486 	}
2487 
2488 	wake_up_new_task(p);
2489 
2490 	/* forking complete and child started to run, tell ptracer */
2491 	if (unlikely(trace))
2492 		ptrace_event_pid(trace, pid);
2493 
2494 	if (clone_flags & CLONE_VFORK) {
2495 		if (!wait_for_vfork_done(p, &vfork))
2496 			ptrace_event_pid(PTRACE_EVENT_VFORK_DONE, pid);
2497 	}
2498 
2499 	put_pid(pid);
2500 	return nr;
2501 }
2502 
2503 /*
2504  * Create a kernel thread.
2505  */
2506 pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
2507 {
2508 	struct kernel_clone_args args = {
2509 		.flags		= ((lower_32_bits(flags) | CLONE_VM |
2510 				    CLONE_UNTRACED) & ~CSIGNAL),
2511 		.exit_signal	= (lower_32_bits(flags) & CSIGNAL),
2512 		.stack		= (unsigned long)fn,
2513 		.stack_size	= (unsigned long)arg,
2514 	};
2515 
2516 	return kernel_clone(&args);
2517 }
2518 
2519 #ifdef __ARCH_WANT_SYS_FORK
2520 SYSCALL_DEFINE0(fork)
2521 {
2522 #ifdef CONFIG_MMU
2523 	struct kernel_clone_args args = {
2524 		.exit_signal = SIGCHLD,
2525 	};
2526 
2527 	return kernel_clone(&args);
2528 #else
2529 	/* can not support in nommu mode */
2530 	return -EINVAL;
2531 #endif
2532 }
2533 #endif
2534 
2535 #ifdef __ARCH_WANT_SYS_VFORK
2536 SYSCALL_DEFINE0(vfork)
2537 {
2538 	struct kernel_clone_args args = {
2539 		.flags		= CLONE_VFORK | CLONE_VM,
2540 		.exit_signal	= SIGCHLD,
2541 	};
2542 
2543 	return kernel_clone(&args);
2544 }
2545 #endif
2546 
2547 #ifdef __ARCH_WANT_SYS_CLONE
2548 #ifdef CONFIG_CLONE_BACKWARDS
2549 SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
2550 		 int __user *, parent_tidptr,
2551 		 unsigned long, tls,
2552 		 int __user *, child_tidptr)
2553 #elif defined(CONFIG_CLONE_BACKWARDS2)
2554 SYSCALL_DEFINE5(clone, unsigned long, newsp, unsigned long, clone_flags,
2555 		 int __user *, parent_tidptr,
2556 		 int __user *, child_tidptr,
2557 		 unsigned long, tls)
2558 #elif defined(CONFIG_CLONE_BACKWARDS3)
2559 SYSCALL_DEFINE6(clone, unsigned long, clone_flags, unsigned long, newsp,
2560 		int, stack_size,
2561 		int __user *, parent_tidptr,
2562 		int __user *, child_tidptr,
2563 		unsigned long, tls)
2564 #else
2565 SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
2566 		 int __user *, parent_tidptr,
2567 		 int __user *, child_tidptr,
2568 		 unsigned long, tls)
2569 #endif
2570 {
2571 	struct kernel_clone_args args = {
2572 		.flags		= (lower_32_bits(clone_flags) & ~CSIGNAL),
2573 		.pidfd		= parent_tidptr,
2574 		.child_tid	= child_tidptr,
2575 		.parent_tid	= parent_tidptr,
2576 		.exit_signal	= (lower_32_bits(clone_flags) & CSIGNAL),
2577 		.stack		= newsp,
2578 		.tls		= tls,
2579 	};
2580 
2581 	return kernel_clone(&args);
2582 }
2583 #endif
2584 
2585 #ifdef __ARCH_WANT_SYS_CLONE3
2586 
2587 noinline static int copy_clone_args_from_user(struct kernel_clone_args *kargs,
2588 					      struct clone_args __user *uargs,
2589 					      size_t usize)
2590 {
2591 	int err;
2592 	struct clone_args args;
2593 	pid_t *kset_tid = kargs->set_tid;
2594 
2595 	BUILD_BUG_ON(offsetofend(struct clone_args, tls) !=
2596 		     CLONE_ARGS_SIZE_VER0);
2597 	BUILD_BUG_ON(offsetofend(struct clone_args, set_tid_size) !=
2598 		     CLONE_ARGS_SIZE_VER1);
2599 	BUILD_BUG_ON(offsetofend(struct clone_args, cgroup) !=
2600 		     CLONE_ARGS_SIZE_VER2);
2601 	BUILD_BUG_ON(sizeof(struct clone_args) != CLONE_ARGS_SIZE_VER2);
2602 
2603 	if (unlikely(usize > PAGE_SIZE))
2604 		return -E2BIG;
2605 	if (unlikely(usize < CLONE_ARGS_SIZE_VER0))
2606 		return -EINVAL;
2607 
2608 	err = copy_struct_from_user(&args, sizeof(args), uargs, usize);
2609 	if (err)
2610 		return err;
2611 
2612 	if (unlikely(args.set_tid_size > MAX_PID_NS_LEVEL))
2613 		return -EINVAL;
2614 
2615 	if (unlikely(!args.set_tid && args.set_tid_size > 0))
2616 		return -EINVAL;
2617 
2618 	if (unlikely(args.set_tid && args.set_tid_size == 0))
2619 		return -EINVAL;
2620 
2621 	/*
2622 	 * Verify that higher 32bits of exit_signal are unset and that
2623 	 * it is a valid signal
2624 	 */
2625 	if (unlikely((args.exit_signal & ~((u64)CSIGNAL)) ||
2626 		     !valid_signal(args.exit_signal)))
2627 		return -EINVAL;
2628 
2629 	if ((args.flags & CLONE_INTO_CGROUP) &&
2630 	    (args.cgroup > INT_MAX || usize < CLONE_ARGS_SIZE_VER2))
2631 		return -EINVAL;
2632 
2633 	*kargs = (struct kernel_clone_args){
2634 		.flags		= args.flags,
2635 		.pidfd		= u64_to_user_ptr(args.pidfd),
2636 		.child_tid	= u64_to_user_ptr(args.child_tid),
2637 		.parent_tid	= u64_to_user_ptr(args.parent_tid),
2638 		.exit_signal	= args.exit_signal,
2639 		.stack		= args.stack,
2640 		.stack_size	= args.stack_size,
2641 		.tls		= args.tls,
2642 		.set_tid_size	= args.set_tid_size,
2643 		.cgroup		= args.cgroup,
2644 	};
2645 
2646 	if (args.set_tid &&
2647 		copy_from_user(kset_tid, u64_to_user_ptr(args.set_tid),
2648 			(kargs->set_tid_size * sizeof(pid_t))))
2649 		return -EFAULT;
2650 
2651 	kargs->set_tid = kset_tid;
2652 
2653 	return 0;
2654 }
2655 
2656 /**
2657  * clone3_stack_valid - check and prepare stack
2658  * @kargs: kernel clone args
2659  *
2660  * Verify that the stack arguments userspace gave us are sane.
2661  * In addition, set the stack direction for userspace since it's easy for us to
2662  * determine.
2663  */
2664 static inline bool clone3_stack_valid(struct kernel_clone_args *kargs)
2665 {
2666 	if (kargs->stack == 0) {
2667 		if (kargs->stack_size > 0)
2668 			return false;
2669 	} else {
2670 		if (kargs->stack_size == 0)
2671 			return false;
2672 
2673 		if (!access_ok((void __user *)kargs->stack, kargs->stack_size))
2674 			return false;
2675 
2676 #if !defined(CONFIG_STACK_GROWSUP) && !defined(CONFIG_IA64)
2677 		kargs->stack += kargs->stack_size;
2678 #endif
2679 	}
2680 
2681 	return true;
2682 }
2683 
2684 static bool clone3_args_valid(struct kernel_clone_args *kargs)
2685 {
2686 	/* Verify that no unknown flags are passed along. */
2687 	if (kargs->flags &
2688 	    ~(CLONE_LEGACY_FLAGS | CLONE_CLEAR_SIGHAND | CLONE_INTO_CGROUP))
2689 		return false;
2690 
2691 	/*
2692 	 * - make the CLONE_DETACHED bit reuseable for clone3
2693 	 * - make the CSIGNAL bits reuseable for clone3
2694 	 */
2695 	if (kargs->flags & (CLONE_DETACHED | CSIGNAL))
2696 		return false;
2697 
2698 	if ((kargs->flags & (CLONE_SIGHAND | CLONE_CLEAR_SIGHAND)) ==
2699 	    (CLONE_SIGHAND | CLONE_CLEAR_SIGHAND))
2700 		return false;
2701 
2702 	if ((kargs->flags & (CLONE_THREAD | CLONE_PARENT)) &&
2703 	    kargs->exit_signal)
2704 		return false;
2705 
2706 	if (!clone3_stack_valid(kargs))
2707 		return false;
2708 
2709 	return true;
2710 }
2711 
2712 /**
2713  * clone3 - create a new process with specific properties
2714  * @uargs: argument structure
2715  * @size:  size of @uargs
2716  *
2717  * clone3() is the extensible successor to clone()/clone2().
2718  * It takes a struct as argument that is versioned by its size.
2719  *
2720  * Return: On success, a positive PID for the child process.
2721  *         On error, a negative errno number.
2722  */
2723 SYSCALL_DEFINE2(clone3, struct clone_args __user *, uargs, size_t, size)
2724 {
2725 	int err;
2726 
2727 	struct kernel_clone_args kargs;
2728 	pid_t set_tid[MAX_PID_NS_LEVEL];
2729 
2730 	kargs.set_tid = set_tid;
2731 
2732 	err = copy_clone_args_from_user(&kargs, uargs, size);
2733 	if (err)
2734 		return err;
2735 
2736 	if (!clone3_args_valid(&kargs))
2737 		return -EINVAL;
2738 
2739 	return kernel_clone(&kargs);
2740 }
2741 #endif
2742 
2743 void walk_process_tree(struct task_struct *top, proc_visitor visitor, void *data)
2744 {
2745 	struct task_struct *leader, *parent, *child;
2746 	int res;
2747 
2748 	read_lock(&tasklist_lock);
2749 	leader = top = top->group_leader;
2750 down:
2751 	for_each_thread(leader, parent) {
2752 		list_for_each_entry(child, &parent->children, sibling) {
2753 			res = visitor(child, data);
2754 			if (res) {
2755 				if (res < 0)
2756 					goto out;
2757 				leader = child;
2758 				goto down;
2759 			}
2760 up:
2761 			;
2762 		}
2763 	}
2764 
2765 	if (leader != top) {
2766 		child = leader;
2767 		parent = child->real_parent;
2768 		leader = parent->group_leader;
2769 		goto up;
2770 	}
2771 out:
2772 	read_unlock(&tasklist_lock);
2773 }
2774 
2775 #ifndef ARCH_MIN_MMSTRUCT_ALIGN
2776 #define ARCH_MIN_MMSTRUCT_ALIGN 0
2777 #endif
2778 
2779 static void sighand_ctor(void *data)
2780 {
2781 	struct sighand_struct *sighand = data;
2782 
2783 	spin_lock_init(&sighand->siglock);
2784 	init_waitqueue_head(&sighand->signalfd_wqh);
2785 }
2786 
2787 void __init proc_caches_init(void)
2788 {
2789 	unsigned int mm_size;
2790 
2791 	sighand_cachep = kmem_cache_create("sighand_cache",
2792 			sizeof(struct sighand_struct), 0,
2793 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_TYPESAFE_BY_RCU|
2794 			SLAB_ACCOUNT, sighand_ctor);
2795 	signal_cachep = kmem_cache_create("signal_cache",
2796 			sizeof(struct signal_struct), 0,
2797 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
2798 			NULL);
2799 	files_cachep = kmem_cache_create("files_cache",
2800 			sizeof(struct files_struct), 0,
2801 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
2802 			NULL);
2803 	fs_cachep = kmem_cache_create("fs_cache",
2804 			sizeof(struct fs_struct), 0,
2805 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
2806 			NULL);
2807 
2808 	/*
2809 	 * The mm_cpumask is located at the end of mm_struct, and is
2810 	 * dynamically sized based on the maximum CPU number this system
2811 	 * can have, taking hotplug into account (nr_cpu_ids).
2812 	 */
2813 	mm_size = sizeof(struct mm_struct) + cpumask_size();
2814 
2815 	mm_cachep = kmem_cache_create_usercopy("mm_struct",
2816 			mm_size, ARCH_MIN_MMSTRUCT_ALIGN,
2817 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
2818 			offsetof(struct mm_struct, saved_auxv),
2819 			sizeof_field(struct mm_struct, saved_auxv),
2820 			NULL);
2821 	vm_area_cachep = KMEM_CACHE(vm_area_struct, SLAB_PANIC|SLAB_ACCOUNT);
2822 	mmap_init();
2823 	nsproxy_cache_init();
2824 }
2825 
2826 /*
2827  * Check constraints on flags passed to the unshare system call.
2828  */
2829 static int check_unshare_flags(unsigned long unshare_flags)
2830 {
2831 	if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
2832 				CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
2833 				CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWNET|
2834 				CLONE_NEWUSER|CLONE_NEWPID|CLONE_NEWCGROUP|
2835 				CLONE_NEWTIME))
2836 		return -EINVAL;
2837 	/*
2838 	 * Not implemented, but pretend it works if there is nothing
2839 	 * to unshare.  Note that unsharing the address space or the
2840 	 * signal handlers also need to unshare the signal queues (aka
2841 	 * CLONE_THREAD).
2842 	 */
2843 	if (unshare_flags & (CLONE_THREAD | CLONE_SIGHAND | CLONE_VM)) {
2844 		if (!thread_group_empty(current))
2845 			return -EINVAL;
2846 	}
2847 	if (unshare_flags & (CLONE_SIGHAND | CLONE_VM)) {
2848 		if (refcount_read(&current->sighand->count) > 1)
2849 			return -EINVAL;
2850 	}
2851 	if (unshare_flags & CLONE_VM) {
2852 		if (!current_is_single_threaded())
2853 			return -EINVAL;
2854 	}
2855 
2856 	return 0;
2857 }
2858 
2859 /*
2860  * Unshare the filesystem structure if it is being shared
2861  */
2862 static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp)
2863 {
2864 	struct fs_struct *fs = current->fs;
2865 
2866 	if (!(unshare_flags & CLONE_FS) || !fs)
2867 		return 0;
2868 
2869 	/* don't need lock here; in the worst case we'll do useless copy */
2870 	if (fs->users == 1)
2871 		return 0;
2872 
2873 	*new_fsp = copy_fs_struct(fs);
2874 	if (!*new_fsp)
2875 		return -ENOMEM;
2876 
2877 	return 0;
2878 }
2879 
2880 /*
2881  * Unshare file descriptor table if it is being shared
2882  */
2883 int unshare_fd(unsigned long unshare_flags, unsigned int max_fds,
2884 	       struct files_struct **new_fdp)
2885 {
2886 	struct files_struct *fd = current->files;
2887 	int error = 0;
2888 
2889 	if ((unshare_flags & CLONE_FILES) &&
2890 	    (fd && atomic_read(&fd->count) > 1)) {
2891 		*new_fdp = dup_fd(fd, max_fds, &error);
2892 		if (!*new_fdp)
2893 			return error;
2894 	}
2895 
2896 	return 0;
2897 }
2898 
2899 /*
2900  * unshare allows a process to 'unshare' part of the process
2901  * context which was originally shared using clone.  copy_*
2902  * functions used by kernel_clone() cannot be used here directly
2903  * because they modify an inactive task_struct that is being
2904  * constructed. Here we are modifying the current, active,
2905  * task_struct.
2906  */
2907 int ksys_unshare(unsigned long unshare_flags)
2908 {
2909 	struct fs_struct *fs, *new_fs = NULL;
2910 	struct files_struct *fd, *new_fd = NULL;
2911 	struct cred *new_cred = NULL;
2912 	struct nsproxy *new_nsproxy = NULL;
2913 	int do_sysvsem = 0;
2914 	int err;
2915 
2916 	/*
2917 	 * If unsharing a user namespace must also unshare the thread group
2918 	 * and unshare the filesystem root and working directories.
2919 	 */
2920 	if (unshare_flags & CLONE_NEWUSER)
2921 		unshare_flags |= CLONE_THREAD | CLONE_FS;
2922 	/*
2923 	 * If unsharing vm, must also unshare signal handlers.
2924 	 */
2925 	if (unshare_flags & CLONE_VM)
2926 		unshare_flags |= CLONE_SIGHAND;
2927 	/*
2928 	 * If unsharing a signal handlers, must also unshare the signal queues.
2929 	 */
2930 	if (unshare_flags & CLONE_SIGHAND)
2931 		unshare_flags |= CLONE_THREAD;
2932 	/*
2933 	 * If unsharing namespace, must also unshare filesystem information.
2934 	 */
2935 	if (unshare_flags & CLONE_NEWNS)
2936 		unshare_flags |= CLONE_FS;
2937 
2938 	err = check_unshare_flags(unshare_flags);
2939 	if (err)
2940 		goto bad_unshare_out;
2941 	/*
2942 	 * CLONE_NEWIPC must also detach from the undolist: after switching
2943 	 * to a new ipc namespace, the semaphore arrays from the old
2944 	 * namespace are unreachable.
2945 	 */
2946 	if (unshare_flags & (CLONE_NEWIPC|CLONE_SYSVSEM))
2947 		do_sysvsem = 1;
2948 	err = unshare_fs(unshare_flags, &new_fs);
2949 	if (err)
2950 		goto bad_unshare_out;
2951 	err = unshare_fd(unshare_flags, NR_OPEN_MAX, &new_fd);
2952 	if (err)
2953 		goto bad_unshare_cleanup_fs;
2954 	err = unshare_userns(unshare_flags, &new_cred);
2955 	if (err)
2956 		goto bad_unshare_cleanup_fd;
2957 	err = unshare_nsproxy_namespaces(unshare_flags, &new_nsproxy,
2958 					 new_cred, new_fs);
2959 	if (err)
2960 		goto bad_unshare_cleanup_cred;
2961 
2962 	if (new_fs || new_fd || do_sysvsem || new_cred || new_nsproxy) {
2963 		if (do_sysvsem) {
2964 			/*
2965 			 * CLONE_SYSVSEM is equivalent to sys_exit().
2966 			 */
2967 			exit_sem(current);
2968 		}
2969 		if (unshare_flags & CLONE_NEWIPC) {
2970 			/* Orphan segments in old ns (see sem above). */
2971 			exit_shm(current);
2972 			shm_init_task(current);
2973 		}
2974 
2975 		if (new_nsproxy)
2976 			switch_task_namespaces(current, new_nsproxy);
2977 
2978 		task_lock(current);
2979 
2980 		if (new_fs) {
2981 			fs = current->fs;
2982 			spin_lock(&fs->lock);
2983 			current->fs = new_fs;
2984 			if (--fs->users)
2985 				new_fs = NULL;
2986 			else
2987 				new_fs = fs;
2988 			spin_unlock(&fs->lock);
2989 		}
2990 
2991 		if (new_fd) {
2992 			fd = current->files;
2993 			current->files = new_fd;
2994 			new_fd = fd;
2995 		}
2996 
2997 		task_unlock(current);
2998 
2999 		if (new_cred) {
3000 			/* Install the new user namespace */
3001 			commit_creds(new_cred);
3002 			new_cred = NULL;
3003 		}
3004 	}
3005 
3006 	perf_event_namespaces(current);
3007 
3008 bad_unshare_cleanup_cred:
3009 	if (new_cred)
3010 		put_cred(new_cred);
3011 bad_unshare_cleanup_fd:
3012 	if (new_fd)
3013 		put_files_struct(new_fd);
3014 
3015 bad_unshare_cleanup_fs:
3016 	if (new_fs)
3017 		free_fs_struct(new_fs);
3018 
3019 bad_unshare_out:
3020 	return err;
3021 }
3022 
3023 SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
3024 {
3025 	return ksys_unshare(unshare_flags);
3026 }
3027 
3028 /*
3029  *	Helper to unshare the files of the current task.
3030  *	We don't want to expose copy_files internals to
3031  *	the exec layer of the kernel.
3032  */
3033 
3034 int unshare_files(struct files_struct **displaced)
3035 {
3036 	struct task_struct *task = current;
3037 	struct files_struct *copy = NULL;
3038 	int error;
3039 
3040 	error = unshare_fd(CLONE_FILES, NR_OPEN_MAX, &copy);
3041 	if (error || !copy) {
3042 		*displaced = NULL;
3043 		return error;
3044 	}
3045 	*displaced = task->files;
3046 	task_lock(task);
3047 	task->files = copy;
3048 	task_unlock(task);
3049 	return 0;
3050 }
3051 
3052 int sysctl_max_threads(struct ctl_table *table, int write,
3053 		       void *buffer, size_t *lenp, loff_t *ppos)
3054 {
3055 	struct ctl_table t;
3056 	int ret;
3057 	int threads = max_threads;
3058 	int min = 1;
3059 	int max = MAX_THREADS;
3060 
3061 	t = *table;
3062 	t.data = &threads;
3063 	t.extra1 = &min;
3064 	t.extra2 = &max;
3065 
3066 	ret = proc_dointvec_minmax(&t, write, buffer, lenp, ppos);
3067 	if (ret || !write)
3068 		return ret;
3069 
3070 	max_threads = threads;
3071 
3072 	return 0;
3073 }
3074