xref: /openbmc/linux/kernel/ptrace.c (revision 87c2ce3b) 
1 /*
2  * linux/kernel/ptrace.c
3  *
4  * (C) Copyright 1999 Linus Torvalds
5  *
6  * Common interfaces for "ptrace()" which we do not want
7  * to continually duplicate across every architecture.
8  */
9 
10 #include <linux/module.h>
11 #include <linux/sched.h>
12 #include <linux/errno.h>
13 #include <linux/mm.h>
14 #include <linux/highmem.h>
15 #include <linux/pagemap.h>
16 #include <linux/smp_lock.h>
17 #include <linux/ptrace.h>
18 #include <linux/security.h>
19 #include <linux/signal.h>
20 
21 #include <asm/pgtable.h>
22 #include <asm/uaccess.h>
23 
24 /*
25  * ptrace a task: make the debugger its new parent and
26  * move it to the ptrace list.
27  *
28  * Must be called with the tasklist lock write-held.
29  */
30 void __ptrace_link(task_t *child, task_t *new_parent)
31 {
32 	if (!list_empty(&child->ptrace_list))
33 		BUG();
34 	if (child->parent == new_parent)
35 		return;
36 	list_add(&child->ptrace_list, &child->parent->ptrace_children);
37 	REMOVE_LINKS(child);
38 	child->parent = new_parent;
39 	SET_LINKS(child);
40 }
41 
42 /*
43  * Turn a tracing stop into a normal stop now, since with no tracer there
44  * would be no way to wake it up with SIGCONT or SIGKILL.  If there was a
45  * signal sent that would resume the child, but didn't because it was in
46  * TASK_TRACED, resume it now.
47  * Requires that irqs be disabled.
48  */
49 void ptrace_untrace(task_t *child)
50 {
51 	spin_lock(&child->sighand->siglock);
52 	if (child->state == TASK_TRACED) {
53 		if (child->signal->flags & SIGNAL_STOP_STOPPED) {
54 			child->state = TASK_STOPPED;
55 		} else {
56 			signal_wake_up(child, 1);
57 		}
58 	}
59 	if (child->signal->flags & SIGNAL_GROUP_EXIT) {
60 		sigaddset(&child->pending.signal, SIGKILL);
61 		signal_wake_up(child, 1);
62 	}
63 	spin_unlock(&child->sighand->siglock);
64 }
65 
66 /*
67  * unptrace a task: move it back to its original parent and
68  * remove it from the ptrace list.
69  *
70  * Must be called with the tasklist lock write-held.
71  */
72 void __ptrace_unlink(task_t *child)
73 {
74 	if (!child->ptrace)
75 		BUG();
76 	child->ptrace = 0;
77 	if (!list_empty(&child->ptrace_list)) {
78 		list_del_init(&child->ptrace_list);
79 		REMOVE_LINKS(child);
80 		child->parent = child->real_parent;
81 		SET_LINKS(child);
82 	}
83 
84 	ptrace_untrace(child);
85 }
86 
87 /*
88  * Check that we have indeed attached to the thing..
89  */
90 int ptrace_check_attach(struct task_struct *child, int kill)
91 {
92 	int ret = -ESRCH;
93 
94 	/*
95 	 * We take the read lock around doing both checks to close a
96 	 * possible race where someone else was tracing our child and
97 	 * detached between these two checks.  After this locked check,
98 	 * we are sure that this is our traced child and that can only
99 	 * be changed by us so it's not changing right after this.
100 	 */
101 	read_lock(&tasklist_lock);
102 	if ((child->ptrace & PT_PTRACED) && child->parent == current &&
103 	    (!(child->ptrace & PT_ATTACHED) || child->real_parent != current)
104 	    && child->signal != NULL) {
105 		ret = 0;
106 		spin_lock_irq(&child->sighand->siglock);
107 		if (child->state == TASK_STOPPED) {
108 			child->state = TASK_TRACED;
109 		} else if (child->state != TASK_TRACED && !kill) {
110 			ret = -ESRCH;
111 		}
112 		spin_unlock_irq(&child->sighand->siglock);
113 	}
114 	read_unlock(&tasklist_lock);
115 
116 	if (!ret && !kill) {
117 		wait_task_inactive(child);
118 	}
119 
120 	/* All systems go.. */
121 	return ret;
122 }
123 
124 static int may_attach(struct task_struct *task)
125 {
126 	if (!task->mm)
127 		return -EPERM;
128 	if (((current->uid != task->euid) ||
129 	     (current->uid != task->suid) ||
130 	     (current->uid != task->uid) ||
131 	     (current->gid != task->egid) ||
132 	     (current->gid != task->sgid) ||
133 	     (current->gid != task->gid)) && !capable(CAP_SYS_PTRACE))
134 		return -EPERM;
135 	smp_rmb();
136 	if (!task->mm->dumpable && !capable(CAP_SYS_PTRACE))
137 		return -EPERM;
138 
139 	return security_ptrace(current, task);
140 }
141 
142 int ptrace_may_attach(struct task_struct *task)
143 {
144 	int err;
145 	task_lock(task);
146 	err = may_attach(task);
147 	task_unlock(task);
148 	return !err;
149 }
150 
151 int ptrace_attach(struct task_struct *task)
152 {
153 	int retval;
154 	task_lock(task);
155 	retval = -EPERM;
156 	if (task->pid <= 1)
157 		goto bad;
158 	if (task->tgid == current->tgid)
159 		goto bad;
160 	/* the same process cannot be attached many times */
161 	if (task->ptrace & PT_PTRACED)
162 		goto bad;
163 	retval = may_attach(task);
164 	if (retval)
165 		goto bad;
166 
167 	/* Go */
168 	task->ptrace |= PT_PTRACED | ((task->real_parent != current)
169 				      ? PT_ATTACHED : 0);
170 	if (capable(CAP_SYS_PTRACE))
171 		task->ptrace |= PT_PTRACE_CAP;
172 	task_unlock(task);
173 
174 	write_lock_irq(&tasklist_lock);
175 	__ptrace_link(task, current);
176 	write_unlock_irq(&tasklist_lock);
177 
178 	force_sig_specific(SIGSTOP, task);
179 	return 0;
180 
181 bad:
182 	task_unlock(task);
183 	return retval;
184 }
185 
186 int ptrace_detach(struct task_struct *child, unsigned int data)
187 {
188 	if (!valid_signal(data))
189 		return	-EIO;
190 
191 	/* Architecture-specific hardware disable .. */
192 	ptrace_disable(child);
193 
194 	/* .. re-parent .. */
195 	child->exit_code = data;
196 
197 	write_lock_irq(&tasklist_lock);
198 	__ptrace_unlink(child);
199 	/* .. and wake it up. */
200 	if (child->exit_state != EXIT_ZOMBIE)
201 		wake_up_process(child);
202 	write_unlock_irq(&tasklist_lock);
203 
204 	return 0;
205 }
206 
207 /*
208  * Access another process' address space.
209  * Source/target buffer must be kernel space,
210  * Do not walk the page table directly, use get_user_pages
211  */
212 
213 int access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, int len, int write)
214 {
215 	struct mm_struct *mm;
216 	struct vm_area_struct *vma;
217 	struct page *page;
218 	void *old_buf = buf;
219 
220 	mm = get_task_mm(tsk);
221 	if (!mm)
222 		return 0;
223 
224 	down_read(&mm->mmap_sem);
225 	/* ignore errors, just check how much was sucessfully transfered */
226 	while (len) {
227 		int bytes, ret, offset;
228 		void *maddr;
229 
230 		ret = get_user_pages(tsk, mm, addr, 1,
231 				write, 1, &page, &vma);
232 		if (ret <= 0)
233 			break;
234 
235 		bytes = len;
236 		offset = addr & (PAGE_SIZE-1);
237 		if (bytes > PAGE_SIZE-offset)
238 			bytes = PAGE_SIZE-offset;
239 
240 		maddr = kmap(page);
241 		if (write) {
242 			copy_to_user_page(vma, page, addr,
243 					  maddr + offset, buf, bytes);
244 			if (!PageCompound(page))
245 				set_page_dirty_lock(page);
246 		} else {
247 			copy_from_user_page(vma, page, addr,
248 					    buf, maddr + offset, bytes);
249 		}
250 		kunmap(page);
251 		page_cache_release(page);
252 		len -= bytes;
253 		buf += bytes;
254 		addr += bytes;
255 	}
256 	up_read(&mm->mmap_sem);
257 	mmput(mm);
258 
259 	return buf - old_buf;
260 }
261 
262 int ptrace_readdata(struct task_struct *tsk, unsigned long src, char __user *dst, int len)
263 {
264 	int copied = 0;
265 
266 	while (len > 0) {
267 		char buf[128];
268 		int this_len, retval;
269 
270 		this_len = (len > sizeof(buf)) ? sizeof(buf) : len;
271 		retval = access_process_vm(tsk, src, buf, this_len, 0);
272 		if (!retval) {
273 			if (copied)
274 				break;
275 			return -EIO;
276 		}
277 		if (copy_to_user(dst, buf, retval))
278 			return -EFAULT;
279 		copied += retval;
280 		src += retval;
281 		dst += retval;
282 		len -= retval;
283 	}
284 	return copied;
285 }
286 
287 int ptrace_writedata(struct task_struct *tsk, char __user *src, unsigned long dst, int len)
288 {
289 	int copied = 0;
290 
291 	while (len > 0) {
292 		char buf[128];
293 		int this_len, retval;
294 
295 		this_len = (len > sizeof(buf)) ? sizeof(buf) : len;
296 		if (copy_from_user(buf, src, this_len))
297 			return -EFAULT;
298 		retval = access_process_vm(tsk, dst, buf, this_len, 1);
299 		if (!retval) {
300 			if (copied)
301 				break;
302 			return -EIO;
303 		}
304 		copied += retval;
305 		src += retval;
306 		dst += retval;
307 		len -= retval;
308 	}
309 	return copied;
310 }
311 
312 static int ptrace_setoptions(struct task_struct *child, long data)
313 {
314 	child->ptrace &= ~PT_TRACE_MASK;
315 
316 	if (data & PTRACE_O_TRACESYSGOOD)
317 		child->ptrace |= PT_TRACESYSGOOD;
318 
319 	if (data & PTRACE_O_TRACEFORK)
320 		child->ptrace |= PT_TRACE_FORK;
321 
322 	if (data & PTRACE_O_TRACEVFORK)
323 		child->ptrace |= PT_TRACE_VFORK;
324 
325 	if (data & PTRACE_O_TRACECLONE)
326 		child->ptrace |= PT_TRACE_CLONE;
327 
328 	if (data & PTRACE_O_TRACEEXEC)
329 		child->ptrace |= PT_TRACE_EXEC;
330 
331 	if (data & PTRACE_O_TRACEVFORKDONE)
332 		child->ptrace |= PT_TRACE_VFORK_DONE;
333 
334 	if (data & PTRACE_O_TRACEEXIT)
335 		child->ptrace |= PT_TRACE_EXIT;
336 
337 	return (data & ~PTRACE_O_MASK) ? -EINVAL : 0;
338 }
339 
340 static int ptrace_getsiginfo(struct task_struct *child, siginfo_t __user * data)
341 {
342 	siginfo_t lastinfo;
343 	int error = -ESRCH;
344 
345 	read_lock(&tasklist_lock);
346 	if (likely(child->sighand != NULL)) {
347 		error = -EINVAL;
348 		spin_lock_irq(&child->sighand->siglock);
349 		if (likely(child->last_siginfo != NULL)) {
350 			lastinfo = *child->last_siginfo;
351 			error = 0;
352 		}
353 		spin_unlock_irq(&child->sighand->siglock);
354 	}
355 	read_unlock(&tasklist_lock);
356 	if (!error)
357 		return copy_siginfo_to_user(data, &lastinfo);
358 	return error;
359 }
360 
361 static int ptrace_setsiginfo(struct task_struct *child, siginfo_t __user * data)
362 {
363 	siginfo_t newinfo;
364 	int error = -ESRCH;
365 
366 	if (copy_from_user(&newinfo, data, sizeof (siginfo_t)))
367 		return -EFAULT;
368 
369 	read_lock(&tasklist_lock);
370 	if (likely(child->sighand != NULL)) {
371 		error = -EINVAL;
372 		spin_lock_irq(&child->sighand->siglock);
373 		if (likely(child->last_siginfo != NULL)) {
374 			*child->last_siginfo = newinfo;
375 			error = 0;
376 		}
377 		spin_unlock_irq(&child->sighand->siglock);
378 	}
379 	read_unlock(&tasklist_lock);
380 	return error;
381 }
382 
383 int ptrace_request(struct task_struct *child, long request,
384 		   long addr, long data)
385 {
386 	int ret = -EIO;
387 
388 	switch (request) {
389 #ifdef PTRACE_OLDSETOPTIONS
390 	case PTRACE_OLDSETOPTIONS:
391 #endif
392 	case PTRACE_SETOPTIONS:
393 		ret = ptrace_setoptions(child, data);
394 		break;
395 	case PTRACE_GETEVENTMSG:
396 		ret = put_user(child->ptrace_message, (unsigned long __user *) data);
397 		break;
398 	case PTRACE_GETSIGINFO:
399 		ret = ptrace_getsiginfo(child, (siginfo_t __user *) data);
400 		break;
401 	case PTRACE_SETSIGINFO:
402 		ret = ptrace_setsiginfo(child, (siginfo_t __user *) data);
403 		break;
404 	default:
405 		break;
406 	}
407 
408 	return ret;
409 }
410 
411 /**
412  * ptrace_traceme  --  helper for PTRACE_TRACEME
413  *
414  * Performs checks and sets PT_PTRACED.
415  * Should be used by all ptrace implementations for PTRACE_TRACEME.
416  */
417 int ptrace_traceme(void)
418 {
419 	int ret;
420 
421 	/*
422 	 * Are we already being traced?
423 	 */
424 	if (current->ptrace & PT_PTRACED)
425 		return -EPERM;
426 	ret = security_ptrace(current->parent, current);
427 	if (ret)
428 		return -EPERM;
429 	/*
430 	 * Set the ptrace bit in the process ptrace flags.
431 	 */
432 	current->ptrace |= PT_PTRACED;
433 	return 0;
434 }
435 
436 /**
437  * ptrace_get_task_struct  --  grab a task struct reference for ptrace
438  * @pid:       process id to grab a task_struct reference of
439  *
440  * This function is a helper for ptrace implementations.  It checks
441  * permissions and then grabs a task struct for use of the actual
442  * ptrace implementation.
443  *
444  * Returns the task_struct for @pid or an ERR_PTR() on failure.
445  */
446 struct task_struct *ptrace_get_task_struct(pid_t pid)
447 {
448 	struct task_struct *child;
449 
450 	/*
451 	 * Tracing init is not allowed.
452 	 */
453 	if (pid == 1)
454 		return ERR_PTR(-EPERM);
455 
456 	read_lock(&tasklist_lock);
457 	child = find_task_by_pid(pid);
458 	if (child)
459 		get_task_struct(child);
460 	read_unlock(&tasklist_lock);
461 	if (!child)
462 		return ERR_PTR(-ESRCH);
463 	return child;
464 }
465 
466 #ifndef __ARCH_SYS_PTRACE
467 asmlinkage long sys_ptrace(long request, long pid, long addr, long data)
468 {
469 	struct task_struct *child;
470 	long ret;
471 
472 	/*
473 	 * This lock_kernel fixes a subtle race with suid exec
474 	 */
475 	lock_kernel();
476 	if (request == PTRACE_TRACEME) {
477 		ret = ptrace_traceme();
478 		goto out;
479 	}
480 
481 	child = ptrace_get_task_struct(pid);
482 	if (IS_ERR(child)) {
483 		ret = PTR_ERR(child);
484 		goto out;
485 	}
486 
487 	if (request == PTRACE_ATTACH) {
488 		ret = ptrace_attach(child);
489 		goto out_put_task_struct;
490 	}
491 
492 	ret = ptrace_check_attach(child, request == PTRACE_KILL);
493 	if (ret < 0)
494 		goto out_put_task_struct;
495 
496 	ret = arch_ptrace(child, request, addr, data);
497 	if (ret < 0)
498 		goto out_put_task_struct;
499 
500  out_put_task_struct:
501 	put_task_struct(child);
502  out:
503 	unlock_kernel();
504 	return ret;
505 }
506 #endif /* __ARCH_SYS_PTRACE */
507