linux/kernel/ptrace.c
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   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