Root/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 */
33void __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 */
47static 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 */
70void __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 */
86int 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
120int __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_access_check(task, mode);
156}
157
158bool 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
167int ptrace_attach(struct task_struct *task)
168{
169    int retval;
170
171    audit_ptrace(task);
172
173    retval = -EPERM;
174    if (unlikely(task->flags & PF_KTHREAD))
175        goto out;
176    if (same_thread_group(task, current))
177        goto out;
178
179    /*
180     * Protect exec's credential calculations against our interference;
181     * interference; SUID, SGID and LSM creds get determined differently
182     * under ptrace.
183     */
184    retval = -ERESTARTNOINTR;
185    if (mutex_lock_interruptible(&task->cred_guard_mutex))
186        goto out;
187
188    task_lock(task);
189    retval = __ptrace_may_access(task, PTRACE_MODE_ATTACH);
190    task_unlock(task);
191    if (retval)
192        goto unlock_creds;
193
194    write_lock_irq(&tasklist_lock);
195    retval = -EPERM;
196    if (unlikely(task->exit_state))
197        goto unlock_tasklist;
198    if (task->ptrace)
199        goto unlock_tasklist;
200
201    task->ptrace = PT_PTRACED;
202    if (capable(CAP_SYS_PTRACE))
203        task->ptrace |= PT_PTRACE_CAP;
204
205    __ptrace_link(task, current);
206    send_sig_info(SIGSTOP, SEND_SIG_FORCED, task);
207
208    retval = 0;
209unlock_tasklist:
210    write_unlock_irq(&tasklist_lock);
211unlock_creds:
212    mutex_unlock(&task->cred_guard_mutex);
213out:
214    return retval;
215}
216
217/**
218 * ptrace_traceme -- helper for PTRACE_TRACEME
219 *
220 * Performs checks and sets PT_PTRACED.
221 * Should be used by all ptrace implementations for PTRACE_TRACEME.
222 */
223int ptrace_traceme(void)
224{
225    int ret = -EPERM;
226
227    write_lock_irq(&tasklist_lock);
228    /* Are we already being traced? */
229    if (!current->ptrace) {
230        ret = security_ptrace_traceme(current->parent);
231        /*
232         * Check PF_EXITING to ensure ->real_parent has not passed
233         * exit_ptrace(). Otherwise we don't report the error but
234         * pretend ->real_parent untraces us right after return.
235         */
236        if (!ret && !(current->real_parent->flags & PF_EXITING)) {
237            current->ptrace = PT_PTRACED;
238            __ptrace_link(current, current->real_parent);
239        }
240    }
241    write_unlock_irq(&tasklist_lock);
242
243    return ret;
244}
245
246/*
247 * Called with irqs disabled, returns true if childs should reap themselves.
248 */
249static int ignoring_children(struct sighand_struct *sigh)
250{
251    int ret;
252    spin_lock(&sigh->siglock);
253    ret = (sigh->action[SIGCHLD-1].sa.sa_handler == SIG_IGN) ||
254          (sigh->action[SIGCHLD-1].sa.sa_flags & SA_NOCLDWAIT);
255    spin_unlock(&sigh->siglock);
256    return ret;
257}
258
259/*
260 * Called with tasklist_lock held for writing.
261 * Unlink a traced task, and clean it up if it was a traced zombie.
262 * Return true if it needs to be reaped with release_task().
263 * (We can't call release_task() here because we already hold tasklist_lock.)
264 *
265 * If it's a zombie, our attachedness prevented normal parent notification
266 * or self-reaping. Do notification now if it would have happened earlier.
267 * If it should reap itself, return true.
268 *
269 * If it's our own child, there is no notification to do. But if our normal
270 * children self-reap, then this child was prevented by ptrace and we must
271 * reap it now, in that case we must also wake up sub-threads sleeping in
272 * do_wait().
273 */
274static bool __ptrace_detach(struct task_struct *tracer, struct task_struct *p)
275{
276    __ptrace_unlink(p);
277
278    if (p->exit_state == EXIT_ZOMBIE) {
279        if (!task_detached(p) && thread_group_empty(p)) {
280            if (!same_thread_group(p->real_parent, tracer))
281                do_notify_parent(p, p->exit_signal);
282            else if (ignoring_children(tracer->sighand)) {
283                __wake_up_parent(p, tracer);
284                p->exit_signal = -1;
285            }
286        }
287        if (task_detached(p)) {
288            /* Mark it as in the process of being reaped. */
289            p->exit_state = EXIT_DEAD;
290            return true;
291        }
292    }
293
294    return false;
295}
296
297int ptrace_detach(struct task_struct *child, unsigned int data)
298{
299    bool dead = false;
300
301    if (!valid_signal(data))
302        return -EIO;
303
304    /* Architecture-specific hardware disable .. */
305    ptrace_disable(child);
306    clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
307
308    write_lock_irq(&tasklist_lock);
309    /*
310     * This child can be already killed. Make sure de_thread() or
311     * our sub-thread doing do_wait() didn't do release_task() yet.
312     */
313    if (child->ptrace) {
314        child->exit_code = data;
315        dead = __ptrace_detach(current, child);
316        if (!child->exit_state)
317            wake_up_process(child);
318    }
319    write_unlock_irq(&tasklist_lock);
320
321    if (unlikely(dead))
322        release_task(child);
323
324    return 0;
325}
326
327/*
328 * Detach all tasks we were using ptrace on.
329 */
330void exit_ptrace(struct task_struct *tracer)
331{
332    struct task_struct *p, *n;
333    LIST_HEAD(ptrace_dead);
334
335    write_lock_irq(&tasklist_lock);
336    list_for_each_entry_safe(p, n, &tracer->ptraced, ptrace_entry) {
337        if (__ptrace_detach(tracer, p))
338            list_add(&p->ptrace_entry, &ptrace_dead);
339    }
340    write_unlock_irq(&tasklist_lock);
341
342    BUG_ON(!list_empty(&tracer->ptraced));
343
344    list_for_each_entry_safe(p, n, &ptrace_dead, ptrace_entry) {
345        list_del_init(&p->ptrace_entry);
346        release_task(p);
347    }
348}
349
350int ptrace_readdata(struct task_struct *tsk, unsigned long src, char __user *dst, int len)
351{
352    int copied = 0;
353
354    while (len > 0) {
355        char buf[128];
356        int this_len, retval;
357
358        this_len = (len > sizeof(buf)) ? sizeof(buf) : len;
359        retval = access_process_vm(tsk, src, buf, this_len, 0);
360        if (!retval) {
361            if (copied)
362                break;
363            return -EIO;
364        }
365        if (copy_to_user(dst, buf, retval))
366            return -EFAULT;
367        copied += retval;
368        src += retval;
369        dst += retval;
370        len -= retval;
371    }
372    return copied;
373}
374
375int ptrace_writedata(struct task_struct *tsk, char __user *src, unsigned long dst, int len)
376{
377    int copied = 0;
378
379    while (len > 0) {
380        char buf[128];
381        int this_len, retval;
382
383        this_len = (len > sizeof(buf)) ? sizeof(buf) : len;
384        if (copy_from_user(buf, src, this_len))
385            return -EFAULT;
386        retval = access_process_vm(tsk, dst, buf, this_len, 1);
387        if (!retval) {
388            if (copied)
389                break;
390            return -EIO;
391        }
392        copied += retval;
393        src += retval;
394        dst += retval;
395        len -= retval;
396    }
397    return copied;
398}
399
400static int ptrace_setoptions(struct task_struct *child, long data)
401{
402    child->ptrace &= ~PT_TRACE_MASK;
403
404    if (data & PTRACE_O_TRACESYSGOOD)
405        child->ptrace |= PT_TRACESYSGOOD;
406
407    if (data & PTRACE_O_TRACEFORK)
408        child->ptrace |= PT_TRACE_FORK;
409
410    if (data & PTRACE_O_TRACEVFORK)
411        child->ptrace |= PT_TRACE_VFORK;
412
413    if (data & PTRACE_O_TRACECLONE)
414        child->ptrace |= PT_TRACE_CLONE;
415
416    if (data & PTRACE_O_TRACEEXEC)
417        child->ptrace |= PT_TRACE_EXEC;
418
419    if (data & PTRACE_O_TRACEVFORKDONE)
420        child->ptrace |= PT_TRACE_VFORK_DONE;
421
422    if (data & PTRACE_O_TRACEEXIT)
423        child->ptrace |= PT_TRACE_EXIT;
424
425    return (data & ~PTRACE_O_MASK) ? -EINVAL : 0;
426}
427
428static int ptrace_getsiginfo(struct task_struct *child, siginfo_t *info)
429{
430    unsigned long flags;
431    int error = -ESRCH;
432
433    if (lock_task_sighand(child, &flags)) {
434        error = -EINVAL;
435        if (likely(child->last_siginfo != NULL)) {
436            *info = *child->last_siginfo;
437            error = 0;
438        }
439        unlock_task_sighand(child, &flags);
440    }
441    return error;
442}
443
444static int ptrace_setsiginfo(struct task_struct *child, const siginfo_t *info)
445{
446    unsigned long flags;
447    int error = -ESRCH;
448
449    if (lock_task_sighand(child, &flags)) {
450        error = -EINVAL;
451        if (likely(child->last_siginfo != NULL)) {
452            *child->last_siginfo = *info;
453            error = 0;
454        }
455        unlock_task_sighand(child, &flags);
456    }
457    return error;
458}
459
460
461#ifdef PTRACE_SINGLESTEP
462#define is_singlestep(request) ((request) == PTRACE_SINGLESTEP)
463#else
464#define is_singlestep(request) 0
465#endif
466
467#ifdef PTRACE_SINGLEBLOCK
468#define is_singleblock(request) ((request) == PTRACE_SINGLEBLOCK)
469#else
470#define is_singleblock(request) 0
471#endif
472
473#ifdef PTRACE_SYSEMU
474#define is_sysemu_singlestep(request) ((request) == PTRACE_SYSEMU_SINGLESTEP)
475#else
476#define is_sysemu_singlestep(request) 0
477#endif
478
479static int ptrace_resume(struct task_struct *child, long request, long data)
480{
481    if (!valid_signal(data))
482        return -EIO;
483
484    if (request == PTRACE_SYSCALL)
485        set_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
486    else
487        clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
488
489#ifdef TIF_SYSCALL_EMU
490    if (request == PTRACE_SYSEMU || request == PTRACE_SYSEMU_SINGLESTEP)
491        set_tsk_thread_flag(child, TIF_SYSCALL_EMU);
492    else
493        clear_tsk_thread_flag(child, TIF_SYSCALL_EMU);
494#endif
495
496    if (is_singleblock(request)) {
497        if (unlikely(!arch_has_block_step()))
498            return -EIO;
499        user_enable_block_step(child);
500    } else if (is_singlestep(request) || is_sysemu_singlestep(request)) {
501        if (unlikely(!arch_has_single_step()))
502            return -EIO;
503        user_enable_single_step(child);
504    } else {
505        user_disable_single_step(child);
506    }
507
508    child->exit_code = data;
509    wake_up_process(child);
510
511    return 0;
512}
513
514int ptrace_request(struct task_struct *child, long request,
515           long addr, long data)
516{
517    int ret = -EIO;
518    siginfo_t siginfo;
519
520    switch (request) {
521    case PTRACE_PEEKTEXT:
522    case PTRACE_PEEKDATA:
523        return generic_ptrace_peekdata(child, addr, data);
524    case PTRACE_POKETEXT:
525    case PTRACE_POKEDATA:
526        return generic_ptrace_pokedata(child, addr, data);
527
528#ifdef PTRACE_OLDSETOPTIONS
529    case PTRACE_OLDSETOPTIONS:
530#endif
531    case PTRACE_SETOPTIONS:
532        ret = ptrace_setoptions(child, data);
533        break;
534    case PTRACE_GETEVENTMSG:
535        ret = put_user(child->ptrace_message, (unsigned long __user *) data);
536        break;
537
538    case PTRACE_GETSIGINFO:
539        ret = ptrace_getsiginfo(child, &siginfo);
540        if (!ret)
541            ret = copy_siginfo_to_user((siginfo_t __user *) data,
542                           &siginfo);
543        break;
544
545    case PTRACE_SETSIGINFO:
546        if (copy_from_user(&siginfo, (siginfo_t __user *) data,
547                   sizeof siginfo))
548            ret = -EFAULT;
549        else
550            ret = ptrace_setsiginfo(child, &siginfo);
551        break;
552
553    case PTRACE_DETACH: /* detach a process that was attached. */
554        ret = ptrace_detach(child, data);
555        break;
556
557#ifdef PTRACE_SINGLESTEP
558    case PTRACE_SINGLESTEP:
559#endif
560#ifdef PTRACE_SINGLEBLOCK
561    case PTRACE_SINGLEBLOCK:
562#endif
563#ifdef PTRACE_SYSEMU
564    case PTRACE_SYSEMU:
565    case PTRACE_SYSEMU_SINGLESTEP:
566#endif
567    case PTRACE_SYSCALL:
568    case PTRACE_CONT:
569        return ptrace_resume(child, request, data);
570
571    case PTRACE_KILL:
572        if (child->exit_state) /* already dead */
573            return 0;
574        return ptrace_resume(child, request, SIGKILL);
575
576    default:
577        break;
578    }
579
580    return ret;
581}
582
583static struct task_struct *ptrace_get_task_struct(pid_t pid)
584{
585    struct task_struct *child;
586
587    rcu_read_lock();
588    child = find_task_by_vpid(pid);
589    if (child)
590        get_task_struct(child);
591    rcu_read_unlock();
592
593    if (!child)
594        return ERR_PTR(-ESRCH);
595    return child;
596}
597
598#ifndef arch_ptrace_attach
599#define arch_ptrace_attach(child) do { } while (0)
600#endif
601
602SYSCALL_DEFINE4(ptrace, long, request, long, pid, long, addr, long, data)
603{
604    struct task_struct *child;
605    long ret;
606
607    /*
608     * This lock_kernel fixes a subtle race with suid exec
609     */
610    lock_kernel();
611    if (request == PTRACE_TRACEME) {
612        ret = ptrace_traceme();
613        if (!ret)
614            arch_ptrace_attach(current);
615        goto out;
616    }
617
618    child = ptrace_get_task_struct(pid);
619    if (IS_ERR(child)) {
620        ret = PTR_ERR(child);
621        goto out;
622    }
623
624    if (request == PTRACE_ATTACH) {
625        ret = ptrace_attach(child);
626        /*
627         * Some architectures need to do book-keeping after
628         * a ptrace attach.
629         */
630        if (!ret)
631            arch_ptrace_attach(child);
632        goto out_put_task_struct;
633    }
634
635    ret = ptrace_check_attach(child, request == PTRACE_KILL);
636    if (ret < 0)
637        goto out_put_task_struct;
638
639    ret = arch_ptrace(child, request, addr, data);
640
641 out_put_task_struct:
642    put_task_struct(child);
643 out:
644    unlock_kernel();
645    return ret;
646}
647
648int generic_ptrace_peekdata(struct task_struct *tsk, long addr, long data)
649{
650    unsigned long tmp;
651    int copied;
652
653    copied = access_process_vm(tsk, addr, &tmp, sizeof(tmp), 0);
654    if (copied != sizeof(tmp))
655        return -EIO;
656    return put_user(tmp, (unsigned long __user *)data);
657}
658
659int generic_ptrace_pokedata(struct task_struct *tsk, long addr, long data)
660{
661    int copied;
662
663    copied = access_process_vm(tsk, addr, &data, sizeof(data), 1);
664    return (copied == sizeof(data)) ? 0 : -EIO;
665}
666
667#if defined CONFIG_COMPAT
668#include <linux/compat.h>
669
670int compat_ptrace_request(struct task_struct *child, compat_long_t request,
671              compat_ulong_t addr, compat_ulong_t data)
672{
673    compat_ulong_t __user *datap = compat_ptr(data);
674    compat_ulong_t word;
675    siginfo_t siginfo;
676    int ret;
677
678    switch (request) {
679    case PTRACE_PEEKTEXT:
680    case PTRACE_PEEKDATA:
681        ret = access_process_vm(child, addr, &word, sizeof(word), 0);
682        if (ret != sizeof(word))
683            ret = -EIO;
684        else
685            ret = put_user(word, datap);
686        break;
687
688    case PTRACE_POKETEXT:
689    case PTRACE_POKEDATA:
690        ret = access_process_vm(child, addr, &data, sizeof(data), 1);
691        ret = (ret != sizeof(data) ? -EIO : 0);
692        break;
693
694    case PTRACE_GETEVENTMSG:
695        ret = put_user((compat_ulong_t) child->ptrace_message, datap);
696        break;
697
698    case PTRACE_GETSIGINFO:
699        ret = ptrace_getsiginfo(child, &siginfo);
700        if (!ret)
701            ret = copy_siginfo_to_user32(
702                (struct compat_siginfo __user *) datap,
703                &siginfo);
704        break;
705
706    case PTRACE_SETSIGINFO:
707        memset(&siginfo, 0, sizeof siginfo);
708        if (copy_siginfo_from_user32(
709                &siginfo, (struct compat_siginfo __user *) datap))
710            ret = -EFAULT;
711        else
712            ret = ptrace_setsiginfo(child, &siginfo);
713        break;
714
715    default:
716        ret = ptrace_request(child, request, addr, data);
717    }
718
719    return ret;
720}
721
722asmlinkage long compat_sys_ptrace(compat_long_t request, compat_long_t pid,
723                  compat_long_t addr, compat_long_t data)
724{
725    struct task_struct *child;
726    long ret;
727
728    /*
729     * This lock_kernel fixes a subtle race with suid exec
730     */
731    lock_kernel();
732    if (request == PTRACE_TRACEME) {
733        ret = ptrace_traceme();
734        goto out;
735    }
736
737    child = ptrace_get_task_struct(pid);
738    if (IS_ERR(child)) {
739        ret = PTR_ERR(child);
740        goto out;
741    }
742
743    if (request == PTRACE_ATTACH) {
744        ret = ptrace_attach(child);
745        /*
746         * Some architectures need to do book-keeping after
747         * a ptrace attach.
748         */
749        if (!ret)
750            arch_ptrace_attach(child);
751        goto out_put_task_struct;
752    }
753
754    ret = ptrace_check_attach(child, request == PTRACE_KILL);
755    if (!ret)
756        ret = compat_arch_ptrace(child, request, addr, data);
757
758 out_put_task_struct:
759    put_task_struct(child);
760 out:
761    unlock_kernel();
762    return ret;
763}
764#endif /* CONFIG_COMPAT */
765

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