xref: /openbmc/linux/kernel/ptrace.c (revision e868d61272caa648214046a096e5a6bfc068dc8c)
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/capability.h>
11 #include <linux/module.h>
12 #include <linux/sched.h>
13 #include <linux/errno.h>
14 #include <linux/mm.h>
15 #include <linux/highmem.h>
16 #include <linux/pagemap.h>
17 #include <linux/smp_lock.h>
18 #include <linux/ptrace.h>
19 #include <linux/security.h>
20 #include <linux/signal.h>
21 #include <linux/audit.h>
22 
23 #include <asm/pgtable.h>
24 #include <asm/uaccess.h>
25 
26 /*
27  * ptrace a task: make the debugger its new parent and
28  * move it to the ptrace list.
29  *
30  * Must be called with the tasklist lock write-held.
31  */
32 void __ptrace_link(struct task_struct *child, struct task_struct *new_parent)
33 {
34 	BUG_ON(!list_empty(&child->ptrace_list));
35 	if (child->parent == new_parent)
36 		return;
37 	list_add(&child->ptrace_list, &child->parent->ptrace_children);
38 	remove_parent(child);
39 	child->parent = new_parent;
40 	add_parent(child);
41 }
42 
43 /*
44  * Turn a tracing stop into a normal stop now, since with no tracer there
45  * would be no way to wake it up with SIGCONT or SIGKILL.  If there was a
46  * signal sent that would resume the child, but didn't because it was in
47  * TASK_TRACED, resume it now.
48  * Requires that irqs be disabled.
49  */
50 void ptrace_untrace(struct task_struct *child)
51 {
52 	spin_lock(&child->sighand->siglock);
53 	if (child->state == TASK_TRACED) {
54 		if (child->signal->flags & SIGNAL_STOP_STOPPED) {
55 			child->state = TASK_STOPPED;
56 		} else {
57 			signal_wake_up(child, 1);
58 		}
59 	}
60 	spin_unlock(&child->sighand->siglock);
61 }
62 
63 /*
64  * unptrace a task: move it back to its original parent and
65  * remove it from the ptrace list.
66  *
67  * Must be called with the tasklist lock write-held.
68  */
69 void __ptrace_unlink(struct task_struct *child)
70 {
71 	BUG_ON(!child->ptrace);
72 
73 	child->ptrace = 0;
74 	if (!list_empty(&child->ptrace_list)) {
75 		list_del_init(&child->ptrace_list);
76 		remove_parent(child);
77 		child->parent = child->real_parent;
78 		add_parent(child);
79 	}
80 
81 	if (child->state == TASK_TRACED)
82 		ptrace_untrace(child);
83 }
84 
85 /*
86  * Check that we have indeed attached to the thing..
87  */
88 int ptrace_check_attach(struct task_struct *child, int kill)
89 {
90 	int ret = -ESRCH;
91 
92 	/*
93 	 * We take the read lock around doing both checks to close a
94 	 * possible race where someone else was tracing our child and
95 	 * detached between these two checks.  After this locked check,
96 	 * we are sure that this is our traced child and that can only
97 	 * be changed by us so it's not changing right after this.
98 	 */
99 	read_lock(&tasklist_lock);
100 	if ((child->ptrace & PT_PTRACED) && child->parent == current &&
101 	    (!(child->ptrace & PT_ATTACHED) || child->real_parent != current)
102 	    && child->signal != NULL) {
103 		ret = 0;
104 		spin_lock_irq(&child->sighand->siglock);
105 		if (child->state == TASK_STOPPED) {
106 			child->state = TASK_TRACED;
107 		} else if (child->state != TASK_TRACED && !kill) {
108 			ret = -ESRCH;
109 		}
110 		spin_unlock_irq(&child->sighand->siglock);
111 	}
112 	read_unlock(&tasklist_lock);
113 
114 	if (!ret && !kill) {
115 		wait_task_inactive(child);
116 	}
117 
118 	/* All systems go.. */
119 	return ret;
120 }
121 
122 static int may_attach(struct task_struct *task)
123 {
124 	/* May we inspect the given task?
125 	 * This check is used both for attaching with ptrace
126 	 * and for allowing access to sensitive information in /proc.
127 	 *
128 	 * ptrace_attach denies several cases that /proc allows
129 	 * because setting up the necessary parent/child relationship
130 	 * or halting the specified task is impossible.
131 	 */
132 	int dumpable = 0;
133 	/* Don't let security modules deny introspection */
134 	if (task == current)
135 		return 0;
136 	if (((current->uid != task->euid) ||
137 	     (current->uid != task->suid) ||
138 	     (current->uid != task->uid) ||
139 	     (current->gid != task->egid) ||
140 	     (current->gid != task->sgid) ||
141 	     (current->gid != task->gid)) && !capable(CAP_SYS_PTRACE))
142 		return -EPERM;
143 	smp_rmb();
144 	if (task->mm)
145 		dumpable = task->mm->dumpable;
146 	if (!dumpable && !capable(CAP_SYS_PTRACE))
147 		return -EPERM;
148 
149 	return security_ptrace(current, task);
150 }
151 
152 int ptrace_may_attach(struct task_struct *task)
153 {
154 	int err;
155 	task_lock(task);
156 	err = may_attach(task);
157 	task_unlock(task);
158 	return !err;
159 }
160 
161 int ptrace_attach(struct task_struct *task)
162 {
163 	int retval;
164 
165 	audit_ptrace(task);
166 
167 	retval = -EPERM;
168 	if (task->pid <= 1)
169 		goto out;
170 	if (task->tgid == current->tgid)
171 		goto out;
172 
173 repeat:
174 	/*
175 	 * Nasty, nasty.
176 	 *
177 	 * We want to hold both the task-lock and the
178 	 * tasklist_lock for writing at the same time.
179 	 * But that's against the rules (tasklist_lock
180 	 * is taken for reading by interrupts on other
181 	 * cpu's that may have task_lock).
182 	 */
183 	task_lock(task);
184 	local_irq_disable();
185 	if (!write_trylock(&tasklist_lock)) {
186 		local_irq_enable();
187 		task_unlock(task);
188 		do {
189 			cpu_relax();
190 		} while (!write_can_lock(&tasklist_lock));
191 		goto repeat;
192 	}
193 
194 	if (!task->mm)
195 		goto bad;
196 	/* the same process cannot be attached many times */
197 	if (task->ptrace & PT_PTRACED)
198 		goto bad;
199 	retval = may_attach(task);
200 	if (retval)
201 		goto bad;
202 
203 	/* Go */
204 	task->ptrace |= PT_PTRACED | ((task->real_parent != current)
205 				      ? PT_ATTACHED : 0);
206 	if (capable(CAP_SYS_PTRACE))
207 		task->ptrace |= PT_PTRACE_CAP;
208 
209 	__ptrace_link(task, current);
210 
211 	force_sig_specific(SIGSTOP, task);
212 
213 bad:
214 	write_unlock_irq(&tasklist_lock);
215 	task_unlock(task);
216 out:
217 	return retval;
218 }
219 
220 static inline void __ptrace_detach(struct task_struct *child, unsigned int data)
221 {
222 	child->exit_code = data;
223 	/* .. re-parent .. */
224 	__ptrace_unlink(child);
225 	/* .. and wake it up. */
226 	if (child->exit_state != EXIT_ZOMBIE)
227 		wake_up_process(child);
228 }
229 
230 int ptrace_detach(struct task_struct *child, unsigned int data)
231 {
232 	if (!valid_signal(data))
233 		return -EIO;
234 
235 	/* Architecture-specific hardware disable .. */
236 	ptrace_disable(child);
237 
238 	write_lock_irq(&tasklist_lock);
239 	/* protect against de_thread()->release_task() */
240 	if (child->ptrace)
241 		__ptrace_detach(child, data);
242 	write_unlock_irq(&tasklist_lock);
243 
244 	return 0;
245 }
246 
247 int ptrace_readdata(struct task_struct *tsk, unsigned long src, char __user *dst, int len)
248 {
249 	int copied = 0;
250 
251 	while (len > 0) {
252 		char buf[128];
253 		int this_len, retval;
254 
255 		this_len = (len > sizeof(buf)) ? sizeof(buf) : len;
256 		retval = access_process_vm(tsk, src, buf, this_len, 0);
257 		if (!retval) {
258 			if (copied)
259 				break;
260 			return -EIO;
261 		}
262 		if (copy_to_user(dst, buf, retval))
263 			return -EFAULT;
264 		copied += retval;
265 		src += retval;
266 		dst += retval;
267 		len -= retval;
268 	}
269 	return copied;
270 }
271 
272 int ptrace_writedata(struct task_struct *tsk, char __user *src, unsigned long dst, int len)
273 {
274 	int copied = 0;
275 
276 	while (len > 0) {
277 		char buf[128];
278 		int this_len, retval;
279 
280 		this_len = (len > sizeof(buf)) ? sizeof(buf) : len;
281 		if (copy_from_user(buf, src, this_len))
282 			return -EFAULT;
283 		retval = access_process_vm(tsk, dst, buf, this_len, 1);
284 		if (!retval) {
285 			if (copied)
286 				break;
287 			return -EIO;
288 		}
289 		copied += retval;
290 		src += retval;
291 		dst += retval;
292 		len -= retval;
293 	}
294 	return copied;
295 }
296 
297 static int ptrace_setoptions(struct task_struct *child, long data)
298 {
299 	child->ptrace &= ~PT_TRACE_MASK;
300 
301 	if (data & PTRACE_O_TRACESYSGOOD)
302 		child->ptrace |= PT_TRACESYSGOOD;
303 
304 	if (data & PTRACE_O_TRACEFORK)
305 		child->ptrace |= PT_TRACE_FORK;
306 
307 	if (data & PTRACE_O_TRACEVFORK)
308 		child->ptrace |= PT_TRACE_VFORK;
309 
310 	if (data & PTRACE_O_TRACECLONE)
311 		child->ptrace |= PT_TRACE_CLONE;
312 
313 	if (data & PTRACE_O_TRACEEXEC)
314 		child->ptrace |= PT_TRACE_EXEC;
315 
316 	if (data & PTRACE_O_TRACEVFORKDONE)
317 		child->ptrace |= PT_TRACE_VFORK_DONE;
318 
319 	if (data & PTRACE_O_TRACEEXIT)
320 		child->ptrace |= PT_TRACE_EXIT;
321 
322 	return (data & ~PTRACE_O_MASK) ? -EINVAL : 0;
323 }
324 
325 static int ptrace_getsiginfo(struct task_struct *child, siginfo_t __user * data)
326 {
327 	siginfo_t lastinfo;
328 	int error = -ESRCH;
329 
330 	read_lock(&tasklist_lock);
331 	if (likely(child->sighand != NULL)) {
332 		error = -EINVAL;
333 		spin_lock_irq(&child->sighand->siglock);
334 		if (likely(child->last_siginfo != NULL)) {
335 			lastinfo = *child->last_siginfo;
336 			error = 0;
337 		}
338 		spin_unlock_irq(&child->sighand->siglock);
339 	}
340 	read_unlock(&tasklist_lock);
341 	if (!error)
342 		return copy_siginfo_to_user(data, &lastinfo);
343 	return error;
344 }
345 
346 static int ptrace_setsiginfo(struct task_struct *child, siginfo_t __user * data)
347 {
348 	siginfo_t newinfo;
349 	int error = -ESRCH;
350 
351 	if (copy_from_user(&newinfo, data, sizeof (siginfo_t)))
352 		return -EFAULT;
353 
354 	read_lock(&tasklist_lock);
355 	if (likely(child->sighand != NULL)) {
356 		error = -EINVAL;
357 		spin_lock_irq(&child->sighand->siglock);
358 		if (likely(child->last_siginfo != NULL)) {
359 			*child->last_siginfo = newinfo;
360 			error = 0;
361 		}
362 		spin_unlock_irq(&child->sighand->siglock);
363 	}
364 	read_unlock(&tasklist_lock);
365 	return error;
366 }
367 
368 int ptrace_request(struct task_struct *child, long request,
369 		   long addr, long data)
370 {
371 	int ret = -EIO;
372 
373 	switch (request) {
374 #ifdef PTRACE_OLDSETOPTIONS
375 	case PTRACE_OLDSETOPTIONS:
376 #endif
377 	case PTRACE_SETOPTIONS:
378 		ret = ptrace_setoptions(child, data);
379 		break;
380 	case PTRACE_GETEVENTMSG:
381 		ret = put_user(child->ptrace_message, (unsigned long __user *) data);
382 		break;
383 	case PTRACE_GETSIGINFO:
384 		ret = ptrace_getsiginfo(child, (siginfo_t __user *) data);
385 		break;
386 	case PTRACE_SETSIGINFO:
387 		ret = ptrace_setsiginfo(child, (siginfo_t __user *) data);
388 		break;
389 	default:
390 		break;
391 	}
392 
393 	return ret;
394 }
395 
396 /**
397  * ptrace_traceme  --  helper for PTRACE_TRACEME
398  *
399  * Performs checks and sets PT_PTRACED.
400  * Should be used by all ptrace implementations for PTRACE_TRACEME.
401  */
402 int ptrace_traceme(void)
403 {
404 	int ret = -EPERM;
405 
406 	/*
407 	 * Are we already being traced?
408 	 */
409 	task_lock(current);
410 	if (!(current->ptrace & PT_PTRACED)) {
411 		ret = security_ptrace(current->parent, current);
412 		/*
413 		 * Set the ptrace bit in the process ptrace flags.
414 		 */
415 		if (!ret)
416 			current->ptrace |= PT_PTRACED;
417 	}
418 	task_unlock(current);
419 	return ret;
420 }
421 
422 /**
423  * ptrace_get_task_struct  --  grab a task struct reference for ptrace
424  * @pid:       process id to grab a task_struct reference of
425  *
426  * This function is a helper for ptrace implementations.  It checks
427  * permissions and then grabs a task struct for use of the actual
428  * ptrace implementation.
429  *
430  * Returns the task_struct for @pid or an ERR_PTR() on failure.
431  */
432 struct task_struct *ptrace_get_task_struct(pid_t pid)
433 {
434 	struct task_struct *child;
435 
436 	/*
437 	 * Tracing init is not allowed.
438 	 */
439 	if (pid == 1)
440 		return ERR_PTR(-EPERM);
441 
442 	read_lock(&tasklist_lock);
443 	child = find_task_by_pid(pid);
444 	if (child)
445 		get_task_struct(child);
446 
447 	read_unlock(&tasklist_lock);
448 	if (!child)
449 		return ERR_PTR(-ESRCH);
450 	return child;
451 }
452 
453 #ifndef __ARCH_SYS_PTRACE
454 asmlinkage long sys_ptrace(long request, long pid, long addr, long data)
455 {
456 	struct task_struct *child;
457 	long ret;
458 
459 	/*
460 	 * This lock_kernel fixes a subtle race with suid exec
461 	 */
462 	lock_kernel();
463 	if (request == PTRACE_TRACEME) {
464 		ret = ptrace_traceme();
465 		goto out;
466 	}
467 
468 	child = ptrace_get_task_struct(pid);
469 	if (IS_ERR(child)) {
470 		ret = PTR_ERR(child);
471 		goto out;
472 	}
473 
474 	if (request == PTRACE_ATTACH) {
475 		ret = ptrace_attach(child);
476 		goto out_put_task_struct;
477 	}
478 
479 	ret = ptrace_check_attach(child, request == PTRACE_KILL);
480 	if (ret < 0)
481 		goto out_put_task_struct;
482 
483 	ret = arch_ptrace(child, request, addr, data);
484 	if (ret < 0)
485 		goto out_put_task_struct;
486 
487  out_put_task_struct:
488 	put_task_struct(child);
489  out:
490 	unlock_kernel();
491 	return ret;
492 }
493 #endif /* __ARCH_SYS_PTRACE */
494