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
  25 #include <asm/pgtable.h>
  26 #include <asm/uaccess.h>
  27
  28
  29 /*
  30  * Initialize a new task whose father had been ptraced.
  31  *
  32  * Called from copy_process().
  33  */
  34 void ptrace_fork(struct task_struct *child, unsigned long clone_flags)
  35 {
  36         arch_ptrace_fork(child, clone_flags);
  37 }
  38
  39 /*
  40  * ptrace a task: make the debugger its new parent and
  41  * move it to the ptrace list.
  42  *
  43  * Must be called with the tasklist lock write-held.
  44  */
  45 void __ptrace_link(struct task_struct *child, struct task_struct *new_parent)
  46 {
  47         BUG_ON(!list_empty(&child->ptrace_entry));
  48         list_add(&child->ptrace_entry, &new_parent->ptraced);
  49         child->parent = new_parent;
  50 }
  51
  52 /*
  53  * Turn a tracing stop into a normal stop now, since with no tracer there
  54  * would be no way to wake it up with SIGCONT or SIGKILL.  If there was a
  55  * signal sent that would resume the child, but didn't because it was in
  56  * TASK_TRACED, resume it now.
  57  * Requires that irqs be disabled.
  58  */
  59 static void ptrace_untrace(struct task_struct *child)
  60 {
  61         spin_lock(&child->sighand->siglock);
  62         if (task_is_traced(child)) {
  63                 if (child->signal->flags & SIGNAL_STOP_STOPPED) {
  64                         __set_task_state(child, TASK_STOPPED);
  65                 } else {
  66                         signal_wake_up(child, 1);
  67                 }
  68         }
  69         spin_unlock(&child->sighand->siglock);
  70 }
  71
  72 /*
  73  * unptrace a task: move it back to its original parent and
  74  * remove it from the ptrace list.
  75  *
  76  * Must be called with the tasklist lock write-held.
  77  */
  78 void __ptrace_unlink(struct task_struct *child)
  79 {
  80         BUG_ON(!child->ptrace);
  81
  82         child->ptrace = 0;
  83         child->parent = child->real_parent;
  84         list_del_init(&child->ptrace_entry);
  85
  86         arch_ptrace_untrace(child);
  87         if (task_is_traced(child))
  88                 ptrace_untrace(child);
  89 }
  90
  91 /*
  92  * Check that we have indeed attached to the thing..
  93  */
  94 int ptrace_check_attach(struct task_struct *child, int kill)
  95 {
  96         int ret = -ESRCH;
  97
  98         /*
  99          * We take the read lock around doing both checks to close a
 100          * possible race where someone else was tracing our child and
 101          * detached between these two checks.  After this locked check,
 102          * we are sure that this is our traced child and that can only
 103          * be changed by us so it's not changing right after this.
 104          */
 105         read_lock(&tasklist_lock);
 106         if ((child->ptrace & PT_PTRACED) && child->parent == current) {
 107                 ret = 0;
 108                 /*
 109                  * child->sighand can't be NULL, release_task()
 110                  * does ptrace_unlink() before __exit_signal().
 111                  */
 112                 spin_lock_irq(&child->sighand->siglock);
 113                 if (task_is_stopped(child))
 114                         child->state = TASK_TRACED;
 115                 else if (!task_is_traced(child) && !kill)
 116                         ret = -ESRCH;
 117                 spin_unlock_irq(&child->sighand->siglock);
 118         }
 119         read_unlock(&tasklist_lock);
 120
 121         if (!ret && !kill)
 122                 ret = wait_task_inactive(child, TASK_TRACED) ? 0 : -ESRCH;
 123
 124         /* All systems go.. */
 125         return ret;
 126 }
 127
 128 int __ptrace_may_access(struct task_struct *task, unsigned int mode)
 129 {
 130         const struct cred *cred = current_cred(), *tcred;
 131
 132         /* May we inspect the given task?
 133          * This check is used both for attaching with ptrace
 134          * and for allowing access to sensitive information in /proc.
 135          *
 136          * ptrace_attach denies several cases that /proc allows
 137          * because setting up the necessary parent/child relationship
 138          * or halting the specified task is impossible.
 139          */
 140         int dumpable = 0;
 141         /* Don't let security modules deny introspection */
 142         if (task == current)
 143                 return 0;
 144         rcu_read_lock();
 145         tcred = __task_cred(task);
 146         if ((cred->uid != tcred->euid ||
 147              cred->uid != tcred->suid ||
 148              cred->uid != tcred->uid  ||
 149              cred->gid != tcred->egid ||
 150              cred->gid != tcred->sgid ||
 151              cred->gid != tcred->gid) &&
 152             !capable(CAP_SYS_PTRACE)) {
 153                 rcu_read_unlock();
 154                 return -EPERM;
 155         }
 156         rcu_read_unlock();
 157         smp_rmb();
 158         if (task->mm)
 159                 dumpable = get_dumpable(task->mm);
 160         if (!dumpable && !capable(CAP_SYS_PTRACE))
 161                 return -EPERM;
 162
 163         return security_ptrace_may_access(task, mode);
 164 }
 165
 166 bool ptrace_may_access(struct task_struct *task, unsigned int mode)
 167 {
 168         int err;
 169         task_lock(task);
 170         err = __ptrace_may_access(task, mode);
 171         task_unlock(task);
 172         return (!err ? true : false);
 173 }
 174
 175 int ptrace_attach(struct task_struct *task)
 176 {
 177         int retval;
 178         unsigned long flags;
 179
 180         audit_ptrace(task);
 181
 182         retval = -EPERM;
 183         if (same_thread_group(task, current))
 184                 goto out;
 185
 186         /* Protect exec's credential calculations against our interference;
 187          * SUID, SGID and LSM creds get determined differently under ptrace.
 188          */
 189         retval = mutex_lock_interruptible(&task->cred_exec_mutex);
 190         if (retval  < 0)
 191                 goto out;
 192
 193         retval = -EPERM;
 194 repeat:
 195         /*
 196          * Nasty, nasty.
 197          *
 198          * We want to hold both the task-lock and the
 199          * tasklist_lock for writing at the same time.
 200          * But that's against the rules (tasklist_lock
 201          * is taken for reading by interrupts on other
 202          * cpu's that may have task_lock).
 203          */
 204         task_lock(task);
 205         if (!write_trylock_irqsave(&tasklist_lock, flags)) {
 206                 task_unlock(task);
 207                 do {
 208                         cpu_relax();
 209                 } while (!write_can_lock(&tasklist_lock));
 210                 goto repeat;
 211         }
 212
 213         if (!task->mm)
 214                 goto bad;
 215         /* the same process cannot be attached many times */
 216         if (task->ptrace & PT_PTRACED)
 217                 goto bad;
 218         retval = __ptrace_may_access(task, PTRACE_MODE_ATTACH);
 219         if (retval)
 220                 goto bad;
 221
 222         /* Go */
 223         task->ptrace |= PT_PTRACED;
 224         if (capable(CAP_SYS_PTRACE))
 225                 task->ptrace |= PT_PTRACE_CAP;
 226
 227         __ptrace_link(task, current);
 228
 229         send_sig_info(SIGSTOP, SEND_SIG_FORCED, task);
 230 bad:
 231         write_unlock_irqrestore(&tasklist_lock, flags);
 232         task_unlock(task);
 233         mutex_unlock(&task->cred_exec_mutex);
 234 out:
 235         return retval;
 236 }
 237
 238 int ptrace_detach(struct task_struct *child, unsigned int data)
 239 {
 240         int dead = 0;
 241
 242         if (!valid_signal(data))
 243                 return -EIO;
 244
 245         /* Architecture-specific hardware disable .. */
 246         ptrace_disable(child);
 247         clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
 248
 249         write_lock_irq(&tasklist_lock);
 250         /* protect against de_thread()->release_task() */
 251         if (child->ptrace) {
 252                 child->exit_code = data;
 253
 254                 dead = __ptrace_detach(current, child);
 255
 256                 if (!child->exit_state)
 257                         wake_up_process(child);
 258         }
 259         write_unlock_irq(&tasklist_lock);
 260
 261         if (unlikely(dead))
 262                 release_task(child);
 263
 264         return 0;
 265 }
 266
 267 int ptrace_readdata(struct task_struct *tsk, unsigned long src, char __user *dst, int len)
 268 {
 269         int copied = 0;
 270
 271         while (len > 0) {
 272                 char buf[128];
 273                 int this_len, retval;
 274
 275                 this_len = (len > sizeof(buf)) ? sizeof(buf) : len;
 276                 retval = access_process_vm(tsk, src, buf, this_len, 0);
 277                 if (!retval) {
 278                         if (copied)
 279                                 break;
 280                         return -EIO;
 281                 }
 282                 if (copy_to_user(dst, buf, retval))
 283                         return -EFAULT;
 284                 copied += retval;
 285                 src += retval;
 286                 dst += retval;
 287                 len -= retval;
 288         }
 289         return copied;
 290 }
 291
 292 int ptrace_writedata(struct task_struct *tsk, char __user *src, unsigned long dst, int len)
 293 {
 294         int copied = 0;
 295
 296         while (len > 0) {
 297                 char buf[128];
 298                 int this_len, retval;
 299
 300                 this_len = (len > sizeof(buf)) ? sizeof(buf) : len;
 301                 if (copy_from_user(buf, src, this_len))
 302                         return -EFAULT;
 303                 retval = access_process_vm(tsk, dst, buf, this_len, 1);
 304                 if (!retval) {
 305                         if (copied)
 306                                 break;
 307                         return -EIO;
 308                 }
 309                 copied += retval;
 310                 src += retval;
 311                 dst += retval;
 312                 len -= retval;
 313         }
 314         return copied;
 315 }
 316
 317 static int ptrace_setoptions(struct task_struct *child, long data)
 318 {
 319         child->ptrace &= ~PT_TRACE_MASK;
 320
 321         if (data & PTRACE_O_TRACESYSGOOD)
 322                 child->ptrace |= PT_TRACESYSGOOD;
 323
 324         if (data & PTRACE_O_TRACEFORK)
 325                 child->ptrace |= PT_TRACE_FORK;
 326
 327         if (data & PTRACE_O_TRACEVFORK)
 328                 child->ptrace |= PT_TRACE_VFORK;
 329
 330         if (data & PTRACE_O_TRACECLONE)
 331                 child->ptrace |= PT_TRACE_CLONE;
 332
 333         if (data & PTRACE_O_TRACEEXEC)
 334                 child->ptrace |= PT_TRACE_EXEC;
 335
 336         if (data & PTRACE_O_TRACEVFORKDONE)
 337                 child->ptrace |= PT_TRACE_VFORK_DONE;
 338
 339         if (data & PTRACE_O_TRACEEXIT)
 340                 child->ptrace |= PT_TRACE_EXIT;
 341
 342         return (data & ~PTRACE_O_MASK) ? -EINVAL : 0;
 343 }
 344
 345 static int ptrace_getsiginfo(struct task_struct *child, siginfo_t *info)
 346 {
 347         int error = -ESRCH;
 348
 349         read_lock(&tasklist_lock);
 350         if (likely(child->sighand != NULL)) {
 351                 error = -EINVAL;
 352                 spin_lock_irq(&child->sighand->siglock);
 353                 if (likely(child->last_siginfo != NULL)) {
 354                         *info = *child->last_siginfo;
 355                         error = 0;
 356                 }
 357                 spin_unlock_irq(&child->sighand->siglock);
 358         }
 359         read_unlock(&tasklist_lock);
 360         return error;
 361 }
 362
 363 static int ptrace_setsiginfo(struct task_struct *child, const siginfo_t *info)
 364 {
 365         int error = -ESRCH;
 366
 367         read_lock(&tasklist_lock);
 368         if (likely(child->sighand != NULL)) {
 369                 error = -EINVAL;
 370                 spin_lock_irq(&child->sighand->siglock);
 371                 if (likely(child->last_siginfo != NULL)) {
 372                         *child->last_siginfo = *info;
 373                         error = 0;
 374                 }
 375                 spin_unlock_irq(&child->sighand->siglock);
 376         }
 377         read_unlock(&tasklist_lock);
 378         return error;
 379 }
 380
 381
 382 #ifdef PTRACE_SINGLESTEP
 383 #define is_singlestep(request)          ((request) == PTRACE_SINGLESTEP)
 384 #else
 385 #define is_singlestep(request)          0
 386 #endif
 387
 388 #ifdef PTRACE_SINGLEBLOCK
 389 #define is_singleblock(request)         ((request) == PTRACE_SINGLEBLOCK)
 390 #else
 391 #define is_singleblock(request)         0
 392 #endif
 393
 394 #ifdef PTRACE_SYSEMU
 395 #define is_sysemu_singlestep(request)   ((request) == PTRACE_SYSEMU_SINGLESTEP)
 396 #else
 397 #define is_sysemu_singlestep(request)   0
 398 #endif
 399
 400 static int ptrace_resume(struct task_struct *child, long request, long data)
 401 {
 402         if (!valid_signal(data))
 403                 return -EIO;
 404
 405         if (request == PTRACE_SYSCALL)
 406                 set_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
 407         else
 408                 clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
 409
 410 #ifdef TIF_SYSCALL_EMU
 411         if (request == PTRACE_SYSEMU || request == PTRACE_SYSEMU_SINGLESTEP)
 412                 set_tsk_thread_flag(child, TIF_SYSCALL_EMU);
 413         else
 414                 clear_tsk_thread_flag(child, TIF_SYSCALL_EMU);
 415 #endif
 416
 417         if (is_singleblock(request)) {
 418                 if (unlikely(!arch_has_block_step()))
 419                         return -EIO;
 420                 user_enable_block_step(child);
 421         } else if (is_singlestep(request) || is_sysemu_singlestep(request)) {
 422                 if (unlikely(!arch_has_single_step()))
 423                         return -EIO;
 424                 user_enable_single_step(child);
 425         }
 426         else
 427                 user_disable_single_step(child);
 428
 429         child->exit_code = data;
 430         wake_up_process(child);
 431
 432         return 0;
 433 }
 434
 435 int ptrace_request(struct task_struct *child, long request,
 436                    long addr, long data)
 437 {
 438         int ret = -EIO;
 439         siginfo_t siginfo;
 440
 441         switch (request) {
 442         case PTRACE_PEEKTEXT:
 443         case PTRACE_PEEKDATA:
 444                 return generic_ptrace_peekdata(child, addr, data);
 445         case PTRACE_POKETEXT:
 446         case PTRACE_POKEDATA:
 447                 return generic_ptrace_pokedata(child, addr, data);
 448
 449 #ifdef PTRACE_OLDSETOPTIONS
 450         case PTRACE_OLDSETOPTIONS:
 451 #endif
 452         case PTRACE_SETOPTIONS:
 453                 ret = ptrace_setoptions(child, data);
 454                 break;
 455         case PTRACE_GETEVENTMSG:
 456                 ret = put_user(child->ptrace_message, (unsigned long __user *) data);
 457                 break;
 458
 459         case PTRACE_GETSIGINFO:
 460                 ret = ptrace_getsiginfo(child, &siginfo);
 461                 if (!ret)
 462                         ret = copy_siginfo_to_user((siginfo_t __user *) data,
 463                                                    &siginfo);
 464                 break;
 465
 466         case PTRACE_SETSIGINFO:
 467                 if (copy_from_user(&siginfo, (siginfo_t __user *) data,
 468                                    sizeof siginfo))
 469                         ret = -EFAULT;
 470                 else
 471                         ret = ptrace_setsiginfo(child, &siginfo);
 472                 break;
 473
 474         case PTRACE_DETACH:      /* detach a process that was attached. */
 475                 ret = ptrace_detach(child, data);
 476                 break;
 477
 478 #ifdef PTRACE_SINGLESTEP
 479         case PTRACE_SINGLESTEP:
 480 #endif
 481 #ifdef PTRACE_SINGLEBLOCK
 482         case PTRACE_SINGLEBLOCK:
 483 #endif
 484 #ifdef PTRACE_SYSEMU
 485         case PTRACE_SYSEMU:
 486         case PTRACE_SYSEMU_SINGLESTEP:
 487 #endif
 488         case PTRACE_SYSCALL:
 489         case PTRACE_CONT:
 490                 return ptrace_resume(child, request, data);
 491
 492         case PTRACE_KILL:
 493                 if (child->exit_state)  /* already dead */
 494                         return 0;
 495                 return ptrace_resume(child, request, SIGKILL);
 496
 497         default:
 498                 break;
 499         }
 500
 501         return ret;
 502 }
 503
 504 /**
 505  * ptrace_traceme  --  helper for PTRACE_TRACEME
 506  *
 507  * Performs checks and sets PT_PTRACED.
 508  * Should be used by all ptrace implementations for PTRACE_TRACEME.
 509  */
 510 int ptrace_traceme(void)
 511 {
 512         int ret = -EPERM;
 513
 514         /*
 515          * Are we already being traced?
 516          */
 517 repeat:
 518         task_lock(current);
 519         if (!(current->ptrace & PT_PTRACED)) {
 520                 /*
 521                  * See ptrace_attach() comments about the locking here.
 522                  */
 523                 unsigned long flags;
 524                 if (!write_trylock_irqsave(&tasklist_lock, flags)) {
 525                         task_unlock(current);
 526                         do {
 527                                 cpu_relax();
 528                         } while (!write_can_lock(&tasklist_lock));
 529                         goto repeat;
 530                 }
 531
 532                 ret = security_ptrace_traceme(current->parent);
 533
 534                 /*
 535                  * Set the ptrace bit in the process ptrace flags.
 536                  * Then link us on our parent's ptraced list.
 537                  */
 538                 if (!ret) {
 539                         current->ptrace |= PT_PTRACED;
 540                         __ptrace_link(current, current->real_parent);
 541                 }
 542
 543                 write_unlock_irqrestore(&tasklist_lock, flags);
 544         }
 545         task_unlock(current);
 546         return ret;
 547 }
 548
 549 /**
 550  * ptrace_get_task_struct  --  grab a task struct reference for ptrace
 551  * @pid:       process id to grab a task_struct reference of
 552  *
 553  * This function is a helper for ptrace implementations.  It checks
 554  * permissions and then grabs a task struct for use of the actual
 555  * ptrace implementation.
 556  *
 557  * Returns the task_struct for @pid or an ERR_PTR() on failure.
 558  */
 559 struct task_struct *ptrace_get_task_struct(pid_t pid)
 560 {
 561         struct task_struct *child;
 562
 563         read_lock(&tasklist_lock);
 564         child = find_task_by_vpid(pid);
 565         if (child)
 566                 get_task_struct(child);
 567
 568         read_unlock(&tasklist_lock);
 569         if (!child)
 570                 return ERR_PTR(-ESRCH);
 571         return child;
 572 }
 573
 574 #ifndef arch_ptrace_attach
 575 #define arch_ptrace_attach(child)       do { } while (0)
 576 #endif
 577
 578 SYSCALL_DEFINE4(ptrace, long, request, long, pid, long, addr, long, data)
 579 {
 580         struct task_struct *child;
 581         long ret;
 582
 583         /*
 584          * This lock_kernel fixes a subtle race with suid exec
 585          */
 586         lock_kernel();
 587         if (request == PTRACE_TRACEME) {
 588                 ret = ptrace_traceme();
 589                 if (!ret)
 590                         arch_ptrace_attach(current);
 591                 goto out;
 592         }
 593
 594         child = ptrace_get_task_struct(pid);
 595         if (IS_ERR(child)) {
 596                 ret = PTR_ERR(child);
 597                 goto out;
 598         }
 599
 600         if (request == PTRACE_ATTACH) {
 601                 ret = ptrace_attach(child);
 602                 /*
 603                  * Some architectures need to do book-keeping after
 604                  * a ptrace attach.
 605                  */
 606                 if (!ret)
 607                         arch_ptrace_attach(child);
 608                 goto out_put_task_struct;
 609         }
 610
 611         ret = ptrace_check_attach(child, request == PTRACE_KILL);
 612         if (ret < 0)
 613                 goto out_put_task_struct;
 614
 615         ret = arch_ptrace(child, request, addr, data);
 616         if (ret < 0)
 617                 goto out_put_task_struct;
 618
 619  out_put_task_struct:
 620         put_task_struct(child);
 621  out:
 622         unlock_kernel();
 623         return ret;
 624 }
 625
 626 int generic_ptrace_peekdata(struct task_struct *tsk, long addr, long data)
 627 {
 628         unsigned long tmp;
 629         int copied;
 630
 631         copied = access_process_vm(tsk, addr, &tmp, sizeof(tmp), 0);
 632         if (copied != sizeof(tmp))
 633                 return -EIO;
 634         return put_user(tmp, (unsigned long __user *)data);
 635 }
 636
 637 int generic_ptrace_pokedata(struct task_struct *tsk, long addr, long data)
 638 {
 639         int copied;
 640
 641         copied = access_process_vm(tsk, addr, &data, sizeof(data), 1);
 642         return (copied == sizeof(data)) ? 0 : -EIO;
 643 }
 644
 645 #if defined CONFIG_COMPAT
 646 #include <linux/compat.h>
 647
 648 int compat_ptrace_request(struct task_struct *child, compat_long_t request,
 649                           compat_ulong_t addr, compat_ulong_t data)
 650 {
 651         compat_ulong_t __user *datap = compat_ptr(data);
 652         compat_ulong_t word;
 653         siginfo_t siginfo;
 654         int ret;
 655
 656         switch (request) {
 657         case PTRACE_PEEKTEXT:
 658         case PTRACE_PEEKDATA:
 659                 ret = access_process_vm(child, addr, &word, sizeof(word), 0);
 660                 if (ret != sizeof(word))
 661                         ret = -EIO;
 662                 else
 663                         ret = put_user(word, datap);
 664                 break;
 665
 666         case PTRACE_POKETEXT:
 667         case PTRACE_POKEDATA:
 668                 ret = access_process_vm(child, addr, &data, sizeof(data), 1);
 669                 ret = (ret != sizeof(data) ? -EIO : 0);
 670                 break;
 671
 672         case PTRACE_GETEVENTMSG:
 673                 ret = put_user((compat_ulong_t) child->ptrace_message, datap);
 674                 break;
 675
 676         case PTRACE_GETSIGINFO:
 677                 ret = ptrace_getsiginfo(child, &siginfo);
 678                 if (!ret)
 679                         ret = copy_siginfo_to_user32(
 680                                 (struct compat_siginfo __user *) datap,
 681                                 &siginfo);
 682                 break;
 683
 684         case PTRACE_SETSIGINFO:
 685                 memset(&siginfo, 0, sizeof siginfo);
 686                 if (copy_siginfo_from_user32(
 687                             &siginfo, (struct compat_siginfo __user *) datap))
 688                         ret = -EFAULT;
 689                 else
 690                         ret = ptrace_setsiginfo(child, &siginfo);
 691                 break;
 692
 693         default:
 694                 ret = ptrace_request(child, request, addr, data);
 695         }
 696
 697         return ret;
 698 }
 699
 700 asmlinkage long compat_sys_ptrace(compat_long_t request, compat_long_t pid,
 701                                   compat_long_t addr, compat_long_t data)
 702 {
 703         struct task_struct *child;
 704         long ret;
 705
 706         /*
 707          * This lock_kernel fixes a subtle race with suid exec
 708          */
 709         lock_kernel();
 710         if (request == PTRACE_TRACEME) {
 711                 ret = ptrace_traceme();
 712                 goto out;
 713         }
 714
 715         child = ptrace_get_task_struct(pid);
 716         if (IS_ERR(child)) {
 717                 ret = PTR_ERR(child);
 718                 goto out;
 719         }
 720
 721         if (request == PTRACE_ATTACH) {
 722                 ret = ptrace_attach(child);
 723                 /*
 724                  * Some architectures need to do book-keeping after
 725                  * a ptrace attach.
 726                  */
 727                 if (!ret)
 728                         arch_ptrace_attach(child);
 729                 goto out_put_task_struct;
 730         }
 731
 732         ret = ptrace_check_attach(child, request == PTRACE_KILL);
 733         if (!ret)
 734                 ret = compat_arch_ptrace(child, request, addr, data);
 735
 736  out_put_task_struct:
 737         put_task_struct(child);
 738  out:
 739         unlock_kernel();
 740         return ret;
 741 }
 742 #endif  /* CONFIG_COMPAT */