Merge commit 'v2.6.30-rc3' into tracing/hw-branch-tracing
[linux-2.6.git] / kernel / ptrace.c
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 #include <linux/pid_namespace.h>
23 #include <linux/syscalls.h>
24 #include <linux/uaccess.h>
25
26
27 /*
28  * ptrace a task: make the debugger its new parent and
29  * move it to the ptrace list.
30  *
31  * Must be called with the tasklist lock write-held.
32  */
33 void __ptrace_link(struct task_struct *child, struct task_struct *new_parent)
34 {
35         BUG_ON(!list_empty(&child->ptrace_entry));
36         list_add(&child->ptrace_entry, &new_parent->ptraced);
37         child->parent = new_parent;
38 }
39
40 /*
41  * Turn a tracing stop into a normal stop now, since with no tracer there
42  * would be no way to wake it up with SIGCONT or SIGKILL.  If there was a
43  * signal sent that would resume the child, but didn't because it was in
44  * TASK_TRACED, resume it now.
45  * Requires that irqs be disabled.
46  */
47 static void ptrace_untrace(struct task_struct *child)
48 {
49         spin_lock(&child->sighand->siglock);
50         if (task_is_traced(child)) {
51                 /*
52                  * If the group stop is completed or in progress,
53                  * this thread was already counted as stopped.
54                  */
55                 if (child->signal->flags & SIGNAL_STOP_STOPPED ||
56                     child->signal->group_stop_count)
57                         __set_task_state(child, TASK_STOPPED);
58                 else
59                         signal_wake_up(child, 1);
60         }
61         spin_unlock(&child->sighand->siglock);
62 }
63
64 /*
65  * unptrace a task: move it back to its original parent and
66  * remove it from the ptrace list.
67  *
68  * Must be called with the tasklist lock write-held.
69  */
70 void __ptrace_unlink(struct task_struct *child)
71 {
72         BUG_ON(!child->ptrace);
73
74         child->ptrace = 0;
75         child->parent = child->real_parent;
76         list_del_init(&child->ptrace_entry);
77
78         arch_ptrace_untrace(child);
79         if (task_is_traced(child))
80                 ptrace_untrace(child);
81 }
82
83 /*
84  * Check that we have indeed attached to the thing..
85  */
86 int ptrace_check_attach(struct task_struct *child, int kill)
87 {
88         int ret = -ESRCH;
89
90         /*
91          * We take the read lock around doing both checks to close a
92          * possible race where someone else was tracing our child and
93          * detached between these two checks.  After this locked check,
94          * we are sure that this is our traced child and that can only
95          * be changed by us so it's not changing right after this.
96          */
97         read_lock(&tasklist_lock);
98         if ((child->ptrace & PT_PTRACED) && child->parent == current) {
99                 ret = 0;
100                 /*
101                  * child->sighand can't be NULL, release_task()
102                  * does ptrace_unlink() before __exit_signal().
103                  */
104                 spin_lock_irq(&child->sighand->siglock);
105                 if (task_is_stopped(child))
106                         child->state = TASK_TRACED;
107                 else if (!task_is_traced(child) && !kill)
108                         ret = -ESRCH;
109                 spin_unlock_irq(&child->sighand->siglock);
110         }
111         read_unlock(&tasklist_lock);
112
113         if (!ret && !kill)
114                 ret = wait_task_inactive(child, TASK_TRACED) ? 0 : -ESRCH;
115
116         /* All systems go.. */
117         return ret;
118 }
119
120 int __ptrace_may_access(struct task_struct *task, unsigned int mode)
121 {
122         const struct cred *cred = current_cred(), *tcred;
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         rcu_read_lock();
137         tcred = __task_cred(task);
138         if ((cred->uid != tcred->euid ||
139              cred->uid != tcred->suid ||
140              cred->uid != tcred->uid  ||
141              cred->gid != tcred->egid ||
142              cred->gid != tcred->sgid ||
143              cred->gid != tcred->gid) &&
144             !capable(CAP_SYS_PTRACE)) {
145                 rcu_read_unlock();
146                 return -EPERM;
147         }
148         rcu_read_unlock();
149         smp_rmb();
150         if (task->mm)
151                 dumpable = get_dumpable(task->mm);
152         if (!dumpable && !capable(CAP_SYS_PTRACE))
153                 return -EPERM;
154
155         return security_ptrace_may_access(task, mode);
156 }
157
158 bool ptrace_may_access(struct task_struct *task, unsigned int mode)
159 {
160         int err;
161         task_lock(task);
162         err = __ptrace_may_access(task, mode);
163         task_unlock(task);
164         return !err;
165 }
166
167 int ptrace_attach(struct task_struct *task)
168 {
169         int retval;
170         unsigned long flags;
171
172         audit_ptrace(task);
173
174         retval = -EPERM;
175         if (same_thread_group(task, current))
176                 goto out;
177
178         /* Protect exec's credential calculations against our interference;
179          * SUID, SGID and LSM creds get determined differently under ptrace.
180          */
181         retval = mutex_lock_interruptible(&current->cred_exec_mutex);
182         if (retval  < 0)
183                 goto out;
184
185         retval = -EPERM;
186 repeat:
187         /*
188          * Nasty, nasty.
189          *
190          * We want to hold both the task-lock and the
191          * tasklist_lock for writing at the same time.
192          * But that's against the rules (tasklist_lock
193          * is taken for reading by interrupts on other
194          * cpu's that may have task_lock).
195          */
196         task_lock(task);
197         if (!write_trylock_irqsave(&tasklist_lock, flags)) {
198                 task_unlock(task);
199                 do {
200                         cpu_relax();
201                 } while (!write_can_lock(&tasklist_lock));
202                 goto repeat;
203         }
204
205         if (!task->mm)
206                 goto bad;
207         /* the same process cannot be attached many times */
208         if (task->ptrace & PT_PTRACED)
209                 goto bad;
210         retval = __ptrace_may_access(task, PTRACE_MODE_ATTACH);
211         if (retval)
212                 goto bad;
213
214         /* Go */
215         task->ptrace |= PT_PTRACED;
216         if (capable(CAP_SYS_PTRACE))
217                 task->ptrace |= PT_PTRACE_CAP;
218
219         __ptrace_link(task, current);
220
221         send_sig_info(SIGSTOP, SEND_SIG_FORCED, task);
222 bad:
223         write_unlock_irqrestore(&tasklist_lock, flags);
224         task_unlock(task);
225         mutex_unlock(&current->cred_exec_mutex);
226 out:
227         return retval;
228 }
229
230 /*
231  * Called with irqs disabled, returns true if childs should reap themselves.
232  */
233 static int ignoring_children(struct sighand_struct *sigh)
234 {
235         int ret;
236         spin_lock(&sigh->siglock);
237         ret = (sigh->action[SIGCHLD-1].sa.sa_handler == SIG_IGN) ||
238               (sigh->action[SIGCHLD-1].sa.sa_flags & SA_NOCLDWAIT);
239         spin_unlock(&sigh->siglock);
240         return ret;
241 }
242
243 /*
244  * Called with tasklist_lock held for writing.
245  * Unlink a traced task, and clean it up if it was a traced zombie.
246  * Return true if it needs to be reaped with release_task().
247  * (We can't call release_task() here because we already hold tasklist_lock.)
248  *
249  * If it's a zombie, our attachedness prevented normal parent notification
250  * or self-reaping.  Do notification now if it would have happened earlier.
251  * If it should reap itself, return true.
252  *
253  * If it's our own child, there is no notification to do.
254  * But if our normal children self-reap, then this child
255  * was prevented by ptrace and we must reap it now.
256  */
257 static bool __ptrace_detach(struct task_struct *tracer, struct task_struct *p)
258 {
259         __ptrace_unlink(p);
260
261         if (p->exit_state == EXIT_ZOMBIE) {
262                 if (!task_detached(p) && thread_group_empty(p)) {
263                         if (!same_thread_group(p->real_parent, tracer))
264                                 do_notify_parent(p, p->exit_signal);
265                         else if (ignoring_children(tracer->sighand))
266                                 p->exit_signal = -1;
267                 }
268                 if (task_detached(p)) {
269                         /* Mark it as in the process of being reaped. */
270                         p->exit_state = EXIT_DEAD;
271                         return true;
272                 }
273         }
274
275         return false;
276 }
277
278 int ptrace_detach(struct task_struct *child, unsigned int data)
279 {
280         bool dead = false;
281
282         if (!valid_signal(data))
283                 return -EIO;
284
285         /* Architecture-specific hardware disable .. */
286         ptrace_disable(child);
287         clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
288
289         write_lock_irq(&tasklist_lock);
290         /*
291          * This child can be already killed. Make sure de_thread() or
292          * our sub-thread doing do_wait() didn't do release_task() yet.
293          */
294         if (child->ptrace) {
295                 child->exit_code = data;
296                 dead = __ptrace_detach(current, child);
297         }
298         write_unlock_irq(&tasklist_lock);
299
300         if (unlikely(dead))
301                 release_task(child);
302
303         return 0;
304 }
305
306 /*
307  * Detach all tasks we were using ptrace on.
308  */
309 void exit_ptrace(struct task_struct *tracer)
310 {
311         struct task_struct *p, *n;
312         LIST_HEAD(ptrace_dead);
313
314         write_lock_irq(&tasklist_lock);
315         list_for_each_entry_safe(p, n, &tracer->ptraced, ptrace_entry) {
316                 if (__ptrace_detach(tracer, p))
317                         list_add(&p->ptrace_entry, &ptrace_dead);
318         }
319         write_unlock_irq(&tasklist_lock);
320
321         BUG_ON(!list_empty(&tracer->ptraced));
322
323         list_for_each_entry_safe(p, n, &ptrace_dead, ptrace_entry) {
324                 list_del_init(&p->ptrace_entry);
325                 release_task(p);
326         }
327 }
328
329 int ptrace_readdata(struct task_struct *tsk, unsigned long src, char __user *dst, int len)
330 {
331         int copied = 0;
332
333         while (len > 0) {
334                 char buf[128];
335                 int this_len, retval;
336
337                 this_len = (len > sizeof(buf)) ? sizeof(buf) : len;
338                 retval = access_process_vm(tsk, src, buf, this_len, 0);
339                 if (!retval) {
340                         if (copied)
341                                 break;
342                         return -EIO;
343                 }
344                 if (copy_to_user(dst, buf, retval))
345                         return -EFAULT;
346                 copied += retval;
347                 src += retval;
348                 dst += retval;
349                 len -= retval;
350         }
351         return copied;
352 }
353
354 int ptrace_writedata(struct task_struct *tsk, char __user *src, unsigned long dst, int len)
355 {
356         int copied = 0;
357
358         while (len > 0) {
359                 char buf[128];
360                 int this_len, retval;
361
362                 this_len = (len > sizeof(buf)) ? sizeof(buf) : len;
363                 if (copy_from_user(buf, src, this_len))
364                         return -EFAULT;
365                 retval = access_process_vm(tsk, dst, buf, this_len, 1);
366                 if (!retval) {
367                         if (copied)
368                                 break;
369                         return -EIO;
370                 }
371                 copied += retval;
372                 src += retval;
373                 dst += retval;
374                 len -= retval;
375         }
376         return copied;
377 }
378
379 static int ptrace_setoptions(struct task_struct *child, long data)
380 {
381         child->ptrace &= ~PT_TRACE_MASK;
382
383         if (data & PTRACE_O_TRACESYSGOOD)
384                 child->ptrace |= PT_TRACESYSGOOD;
385
386         if (data & PTRACE_O_TRACEFORK)
387                 child->ptrace |= PT_TRACE_FORK;
388
389         if (data & PTRACE_O_TRACEVFORK)
390                 child->ptrace |= PT_TRACE_VFORK;
391
392         if (data & PTRACE_O_TRACECLONE)
393                 child->ptrace |= PT_TRACE_CLONE;
394
395         if (data & PTRACE_O_TRACEEXEC)
396                 child->ptrace |= PT_TRACE_EXEC;
397
398         if (data & PTRACE_O_TRACEVFORKDONE)
399                 child->ptrace |= PT_TRACE_VFORK_DONE;
400
401         if (data & PTRACE_O_TRACEEXIT)
402                 child->ptrace |= PT_TRACE_EXIT;
403
404         return (data & ~PTRACE_O_MASK) ? -EINVAL : 0;
405 }
406
407 static int ptrace_getsiginfo(struct task_struct *child, siginfo_t *info)
408 {
409         int error = -ESRCH;
410
411         read_lock(&tasklist_lock);
412         if (likely(child->sighand != NULL)) {
413                 error = -EINVAL;
414                 spin_lock_irq(&child->sighand->siglock);
415                 if (likely(child->last_siginfo != NULL)) {
416                         *info = *child->last_siginfo;
417                         error = 0;
418                 }
419                 spin_unlock_irq(&child->sighand->siglock);
420         }
421         read_unlock(&tasklist_lock);
422         return error;
423 }
424
425 static int ptrace_setsiginfo(struct task_struct *child, const siginfo_t *info)
426 {
427         int error = -ESRCH;
428
429         read_lock(&tasklist_lock);
430         if (likely(child->sighand != NULL)) {
431                 error = -EINVAL;
432                 spin_lock_irq(&child->sighand->siglock);
433                 if (likely(child->last_siginfo != NULL)) {
434                         *child->last_siginfo = *info;
435                         error = 0;
436                 }
437                 spin_unlock_irq(&child->sighand->siglock);
438         }
439         read_unlock(&tasklist_lock);
440         return error;
441 }
442
443
444 #ifdef PTRACE_SINGLESTEP
445 #define is_singlestep(request)          ((request) == PTRACE_SINGLESTEP)
446 #else
447 #define is_singlestep(request)          0
448 #endif
449
450 #ifdef PTRACE_SINGLEBLOCK
451 #define is_singleblock(request)         ((request) == PTRACE_SINGLEBLOCK)
452 #else
453 #define is_singleblock(request)         0
454 #endif
455
456 #ifdef PTRACE_SYSEMU
457 #define is_sysemu_singlestep(request)   ((request) == PTRACE_SYSEMU_SINGLESTEP)
458 #else
459 #define is_sysemu_singlestep(request)   0
460 #endif
461
462 static int ptrace_resume(struct task_struct *child, long request, long data)
463 {
464         if (!valid_signal(data))
465                 return -EIO;
466
467         if (request == PTRACE_SYSCALL)
468                 set_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
469         else
470                 clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
471
472 #ifdef TIF_SYSCALL_EMU
473         if (request == PTRACE_SYSEMU || request == PTRACE_SYSEMU_SINGLESTEP)
474                 set_tsk_thread_flag(child, TIF_SYSCALL_EMU);
475         else
476                 clear_tsk_thread_flag(child, TIF_SYSCALL_EMU);
477 #endif
478
479         if (is_singleblock(request)) {
480                 if (unlikely(!arch_has_block_step()))
481                         return -EIO;
482                 user_enable_block_step(child);
483         } else if (is_singlestep(request) || is_sysemu_singlestep(request)) {
484                 if (unlikely(!arch_has_single_step()))
485                         return -EIO;
486                 user_enable_single_step(child);
487         } else {
488                 user_disable_single_step(child);
489         }
490
491         child->exit_code = data;
492         wake_up_process(child);
493
494         return 0;
495 }
496
497 int ptrace_request(struct task_struct *child, long request,
498                    long addr, long data)
499 {
500         int ret = -EIO;
501         siginfo_t siginfo;
502
503         switch (request) {
504         case PTRACE_PEEKTEXT:
505         case PTRACE_PEEKDATA:
506                 return generic_ptrace_peekdata(child, addr, data);
507         case PTRACE_POKETEXT:
508         case PTRACE_POKEDATA:
509                 return generic_ptrace_pokedata(child, addr, data);
510
511 #ifdef PTRACE_OLDSETOPTIONS
512         case PTRACE_OLDSETOPTIONS:
513 #endif
514         case PTRACE_SETOPTIONS:
515                 ret = ptrace_setoptions(child, data);
516                 break;
517         case PTRACE_GETEVENTMSG:
518                 ret = put_user(child->ptrace_message, (unsigned long __user *) data);
519                 break;
520
521         case PTRACE_GETSIGINFO:
522                 ret = ptrace_getsiginfo(child, &siginfo);
523                 if (!ret)
524                         ret = copy_siginfo_to_user((siginfo_t __user *) data,
525                                                    &siginfo);
526                 break;
527
528         case PTRACE_SETSIGINFO:
529                 if (copy_from_user(&siginfo, (siginfo_t __user *) data,
530                                    sizeof siginfo))
531                         ret = -EFAULT;
532                 else
533                         ret = ptrace_setsiginfo(child, &siginfo);
534                 break;
535
536         case PTRACE_DETACH:      /* detach a process that was attached. */
537                 ret = ptrace_detach(child, data);
538                 break;
539
540 #ifdef PTRACE_SINGLESTEP
541         case PTRACE_SINGLESTEP:
542 #endif
543 #ifdef PTRACE_SINGLEBLOCK
544         case PTRACE_SINGLEBLOCK:
545 #endif
546 #ifdef PTRACE_SYSEMU
547         case PTRACE_SYSEMU:
548         case PTRACE_SYSEMU_SINGLESTEP:
549 #endif
550         case PTRACE_SYSCALL:
551         case PTRACE_CONT:
552                 return ptrace_resume(child, request, data);
553
554         case PTRACE_KILL:
555                 if (child->exit_state)  /* already dead */
556                         return 0;
557                 return ptrace_resume(child, request, SIGKILL);
558
559         default:
560                 break;
561         }
562
563         return ret;
564 }
565
566 /**
567  * ptrace_traceme  --  helper for PTRACE_TRACEME
568  *
569  * Performs checks and sets PT_PTRACED.
570  * Should be used by all ptrace implementations for PTRACE_TRACEME.
571  */
572 int ptrace_traceme(void)
573 {
574         int ret = -EPERM;
575
576         /*
577          * Are we already being traced?
578          */
579 repeat:
580         task_lock(current);
581         if (!(current->ptrace & PT_PTRACED)) {
582                 /*
583                  * See ptrace_attach() comments about the locking here.
584                  */
585                 unsigned long flags;
586                 if (!write_trylock_irqsave(&tasklist_lock, flags)) {
587                         task_unlock(current);
588                         do {
589                                 cpu_relax();
590                         } while (!write_can_lock(&tasklist_lock));
591                         goto repeat;
592                 }
593
594                 ret = security_ptrace_traceme(current->parent);
595
596                 /*
597                  * Check PF_EXITING to ensure ->real_parent has not passed
598                  * exit_ptrace(). Otherwise we don't report the error but
599                  * pretend ->real_parent untraces us right after return.
600                  */
601                 if (!ret && !(current->real_parent->flags & PF_EXITING)) {
602                         current->ptrace |= PT_PTRACED;
603                         __ptrace_link(current, current->real_parent);
604                 }
605
606                 write_unlock_irqrestore(&tasklist_lock, flags);
607         }
608         task_unlock(current);
609         return ret;
610 }
611
612 /**
613  * ptrace_get_task_struct  --  grab a task struct reference for ptrace
614  * @pid:       process id to grab a task_struct reference of
615  *
616  * This function is a helper for ptrace implementations.  It checks
617  * permissions and then grabs a task struct for use of the actual
618  * ptrace implementation.
619  *
620  * Returns the task_struct for @pid or an ERR_PTR() on failure.
621  */
622 struct task_struct *ptrace_get_task_struct(pid_t pid)
623 {
624         struct task_struct *child;
625
626         read_lock(&tasklist_lock);
627         child = find_task_by_vpid(pid);
628         if (child)
629                 get_task_struct(child);
630
631         read_unlock(&tasklist_lock);
632         if (!child)
633                 return ERR_PTR(-ESRCH);
634         return child;
635 }
636
637 #ifndef arch_ptrace_attach
638 #define arch_ptrace_attach(child)       do { } while (0)
639 #endif
640
641 SYSCALL_DEFINE4(ptrace, long, request, long, pid, long, addr, long, data)
642 {
643         struct task_struct *child;
644         long ret;
645
646         /*
647          * This lock_kernel fixes a subtle race with suid exec
648          */
649         lock_kernel();
650         if (request == PTRACE_TRACEME) {
651                 ret = ptrace_traceme();
652                 if (!ret)
653                         arch_ptrace_attach(current);
654                 goto out;
655         }
656
657         child = ptrace_get_task_struct(pid);
658         if (IS_ERR(child)) {
659                 ret = PTR_ERR(child);
660                 goto out;
661         }
662
663         if (request == PTRACE_ATTACH) {
664                 ret = ptrace_attach(child);
665                 /*
666                  * Some architectures need to do book-keeping after
667                  * a ptrace attach.
668                  */
669                 if (!ret)
670                         arch_ptrace_attach(child);
671                 goto out_put_task_struct;
672         }
673
674         ret = ptrace_check_attach(child, request == PTRACE_KILL);
675         if (ret < 0)
676                 goto out_put_task_struct;
677
678         ret = arch_ptrace(child, request, addr, data);
679
680  out_put_task_struct:
681         put_task_struct(child);
682  out:
683         unlock_kernel();
684         return ret;
685 }
686
687 int generic_ptrace_peekdata(struct task_struct *tsk, long addr, long data)
688 {
689         unsigned long tmp;
690         int copied;
691
692         copied = access_process_vm(tsk, addr, &tmp, sizeof(tmp), 0);
693         if (copied != sizeof(tmp))
694                 return -EIO;
695         return put_user(tmp, (unsigned long __user *)data);
696 }
697
698 int generic_ptrace_pokedata(struct task_struct *tsk, long addr, long data)
699 {
700         int copied;
701
702         copied = access_process_vm(tsk, addr, &data, sizeof(data), 1);
703         return (copied == sizeof(data)) ? 0 : -EIO;
704 }
705
706 #if defined CONFIG_COMPAT
707 #include <linux/compat.h>
708
709 int compat_ptrace_request(struct task_struct *child, compat_long_t request,
710                           compat_ulong_t addr, compat_ulong_t data)
711 {
712         compat_ulong_t __user *datap = compat_ptr(data);
713         compat_ulong_t word;
714         siginfo_t siginfo;
715         int ret;
716
717         switch (request) {
718         case PTRACE_PEEKTEXT:
719         case PTRACE_PEEKDATA:
720                 ret = access_process_vm(child, addr, &word, sizeof(word), 0);
721                 if (ret != sizeof(word))
722                         ret = -EIO;
723                 else
724                         ret = put_user(word, datap);
725                 break;
726
727         case PTRACE_POKETEXT:
728         case PTRACE_POKEDATA:
729                 ret = access_process_vm(child, addr, &data, sizeof(data), 1);
730                 ret = (ret != sizeof(data) ? -EIO : 0);
731                 break;
732
733         case PTRACE_GETEVENTMSG:
734                 ret = put_user((compat_ulong_t) child->ptrace_message, datap);
735                 break;
736
737         case PTRACE_GETSIGINFO:
738                 ret = ptrace_getsiginfo(child, &siginfo);
739                 if (!ret)
740                         ret = copy_siginfo_to_user32(
741                                 (struct compat_siginfo __user *) datap,
742                                 &siginfo);
743                 break;
744
745         case PTRACE_SETSIGINFO:
746                 memset(&siginfo, 0, sizeof siginfo);
747                 if (copy_siginfo_from_user32(
748                             &siginfo, (struct compat_siginfo __user *) datap))
749                         ret = -EFAULT;
750                 else
751                         ret = ptrace_setsiginfo(child, &siginfo);
752                 break;
753
754         default:
755                 ret = ptrace_request(child, request, addr, data);
756         }
757
758         return ret;
759 }
760
761 asmlinkage long compat_sys_ptrace(compat_long_t request, compat_long_t pid,
762                                   compat_long_t addr, compat_long_t data)
763 {
764         struct task_struct *child;
765         long ret;
766
767         /*
768          * This lock_kernel fixes a subtle race with suid exec
769          */
770         lock_kernel();
771         if (request == PTRACE_TRACEME) {
772                 ret = ptrace_traceme();
773                 goto out;
774         }
775
776         child = ptrace_get_task_struct(pid);
777         if (IS_ERR(child)) {
778                 ret = PTR_ERR(child);
779                 goto out;
780         }
781
782         if (request == PTRACE_ATTACH) {
783                 ret = ptrace_attach(child);
784                 /*
785                  * Some architectures need to do book-keeping after
786                  * a ptrace attach.
787                  */
788                 if (!ret)
789                         arch_ptrace_attach(child);
790                 goto out_put_task_struct;
791         }
792
793         ret = ptrace_check_attach(child, request == PTRACE_KILL);
794         if (!ret)
795                 ret = compat_arch_ptrace(child, request, addr, data);
796
797  out_put_task_struct:
798         put_task_struct(child);
799  out:
800         unlock_kernel();
801         return ret;
802 }
803 #endif  /* CONFIG_COMPAT */