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(&current->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(&current->cred_exec_mutex);
 234 out:
 235         return retval;
 236 }
 237
 238 static inline void __ptrace_detach(struct task_struct *child, unsigned int data)
 239 {
 240         child->exit_code = data;
 241         /* .. re-parent .. */
 242         __ptrace_unlink(child);
 243         /* .. and wake it up. */
 244         if (child->exit_state != EXIT_ZOMBIE)
 245                 wake_up_process(child);
 246 }
 247
 248 int ptrace_detach(struct task_struct *child, unsigned int data)
 249 {
 250         if (!valid_signal(data))
 251                 return -EIO;
 252
 253         /* Architecture-specific hardware disable .. */
 254         ptrace_disable(child);
 255         clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
 256
 257         write_lock_irq(&tasklist_lock);
 258         /* protect against de_thread()->release_task() */
 259         if (child->ptrace)
 260                 __ptrace_detach(child, data);
 261         write_unlock_irq(&tasklist_lock);
 262
 263         return 0;
 264 }
 265
 266 int ptrace_readdata(struct task_struct *tsk, unsigned long src, char __user *dst, int len)
 267 {
 268         int copied = 0;
 269
 270         while (len > 0) {
 271                 char buf[128];
 272                 int this_len, retval;
 273
 274                 this_len = (len > sizeof(buf)) ? sizeof(buf) : len;
 275                 retval = access_process_vm(tsk, src, buf, this_len, 0);
 276                 if (!retval) {
 277                         if (copied)
 278                                 break;
 279                         return -EIO;
 280                 }
 281                 if (copy_to_user(dst, buf, retval))
 282                         return -EFAULT;
 283                 copied += retval;
 284                 src += retval;
 285                 dst += retval;
 286                 len -= retval;
 287         }
 288         return copied;
 289 }
 290
 291 int ptrace_writedata(struct task_struct *tsk, char __user *src, unsigned long dst, int len)
 292 {
 293         int copied = 0;
 294
 295         while (len > 0) {
 296                 char buf[128];
 297                 int this_len, retval;
 298
 299                 this_len = (len > sizeof(buf)) ? sizeof(buf) : len;
 300                 if (copy_from_user(buf, src, this_len))
 301                         return -EFAULT;
 302                 retval = access_process_vm(tsk, dst, buf, this_len, 1);
 303                 if (!retval) {
 304                         if (copied)
 305                                 break;
 306                         return -EIO;
 307                 }
 308                 copied += retval;
 309                 src += retval;
 310                 dst += retval;
 311                 len -= retval;
 312         }
 313         return copied;
 314 }
 315
 316 static int ptrace_setoptions(struct task_struct *child, long data)
 317 {
 318         child->ptrace &= ~PT_TRACE_MASK;
 319
 320         if (data & PTRACE_O_TRACESYSGOOD)
 321                 child->ptrace |= PT_TRACESYSGOOD;
 322
 323         if (data & PTRACE_O_TRACEFORK)
 324                 child->ptrace |= PT_TRACE_FORK;
 325
 326         if (data & PTRACE_O_TRACEVFORK)
 327                 child->ptrace |= PT_TRACE_VFORK;
 328
 329         if (data & PTRACE_O_TRACECLONE)
 330                 child->ptrace |= PT_TRACE_CLONE;
 331
 332         if (data & PTRACE_O_TRACEEXEC)
 333                 child->ptrace |= PT_TRACE_EXEC;
 334
 335         if (data & PTRACE_O_TRACEVFORKDONE)
 336                 child->ptrace |= PT_TRACE_VFORK_DONE;
 337
 338         if (data & PTRACE_O_TRACEEXIT)
 339                 child->ptrace |= PT_TRACE_EXIT;
 340
 341         return (data & ~PTRACE_O_MASK) ? -EINVAL : 0;
 342 }
 343
 344 static int ptrace_getsiginfo(struct task_struct *child, siginfo_t *info)
 345 {
 346         int error = -ESRCH;
 347
 348         read_lock(&tasklist_lock);
 349         if (likely(child->sighand != NULL)) {
 350                 error = -EINVAL;
 351                 spin_lock_irq(&child->sighand->siglock);
 352                 if (likely(child->last_siginfo != NULL)) {
 353                         *info = *child->last_siginfo;
 354                         error = 0;
 355                 }
 356                 spin_unlock_irq(&child->sighand->siglock);
 357         }
 358         read_unlock(&tasklist_lock);
 359         return error;
 360 }
 361
 362 static int ptrace_setsiginfo(struct task_struct *child, const siginfo_t *info)
 363 {
 364         int error = -ESRCH;
 365
 366         read_lock(&tasklist_lock);
 367         if (likely(child->sighand != NULL)) {
 368                 error = -EINVAL;
 369                 spin_lock_irq(&child->sighand->siglock);
 370                 if (likely(child->last_siginfo != NULL)) {
 371                         *child->last_siginfo = *info;
 372                         error = 0;
 373                 }
 374                 spin_unlock_irq(&child->sighand->siglock);
 375         }
 376         read_unlock(&tasklist_lock);
 377         return error;
 378 }
 379
 380
 381 #ifdef PTRACE_SINGLESTEP
 382 #define is_singlestep(request)          ((request) == PTRACE_SINGLESTEP)
 383 #else
 384 #define is_singlestep(request)          0
 385 #endif
 386
 387 #ifdef PTRACE_SINGLEBLOCK
 388 #define is_singleblock(request)         ((request) == PTRACE_SINGLEBLOCK)
 389 #else
 390 #define is_singleblock(request)         0
 391 #endif
 392
 393 #ifdef PTRACE_SYSEMU
 394 #define is_sysemu_singlestep(request)   ((request) == PTRACE_SYSEMU_SINGLESTEP)
 395 #else
 396 #define is_sysemu_singlestep(request)   0
 397 #endif
 398
 399 static int ptrace_resume(struct task_struct *child, long request, long data)
 400 {
 401         if (!valid_signal(data))
 402                 return -EIO;
 403
 404         if (request == PTRACE_SYSCALL)
 405                 set_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
 406         else
 407                 clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
 408
 409 #ifdef TIF_SYSCALL_EMU
 410         if (request == PTRACE_SYSEMU || request == PTRACE_SYSEMU_SINGLESTEP)
 411                 set_tsk_thread_flag(child, TIF_SYSCALL_EMU);
 412         else
 413                 clear_tsk_thread_flag(child, TIF_SYSCALL_EMU);
 414 #endif
 415
 416         if (is_singleblock(request)) {
 417                 if (unlikely(!arch_has_block_step()))
 418                         return -EIO;
 419                 user_enable_block_step(child);
 420         } else if (is_singlestep(request) || is_sysemu_singlestep(request)) {
 421                 if (unlikely(!arch_has_single_step()))
 422                         return -EIO;
 423                 user_enable_single_step(child);
 424         }
 425         else
 426                 user_disable_single_step(child);
 427
 428         child->exit_code = data;
 429         wake_up_process(child);
 430
 431         return 0;
 432 }
 433
 434 int ptrace_request(struct task_struct *child, long request,
 435                    long addr, long data)
 436 {
 437         int ret = -EIO;
 438         siginfo_t siginfo;
 439
 440         switch (request) {
 441         case PTRACE_PEEKTEXT:
 442         case PTRACE_PEEKDATA:
 443                 return generic_ptrace_peekdata(child, addr, data);
 444         case PTRACE_POKETEXT:
 445         case PTRACE_POKEDATA:
 446                 return generic_ptrace_pokedata(child, addr, data);
 447
 448 #ifdef PTRACE_OLDSETOPTIONS
 449         case PTRACE_OLDSETOPTIONS:
 450 #endif
 451         case PTRACE_SETOPTIONS:
 452                 ret = ptrace_setoptions(child, data);
 453                 break;
 454         case PTRACE_GETEVENTMSG:
 455                 ret = put_user(child->ptrace_message, (unsigned long __user *) data);
 456                 break;
 457
 458         case PTRACE_GETSIGINFO:
 459                 ret = ptrace_getsiginfo(child, &siginfo);
 460                 if (!ret)
 461                         ret = copy_siginfo_to_user((siginfo_t __user *) data,
 462                                                    &siginfo);
 463                 break;
 464
 465         case PTRACE_SETSIGINFO:
 466                 if (copy_from_user(&siginfo, (siginfo_t __user *) data,
 467                                    sizeof siginfo))
 468                         ret = -EFAULT;
 469                 else
 470                         ret = ptrace_setsiginfo(child, &siginfo);
 471                 break;
 472
 473         case PTRACE_DETACH:      /* detach a process that was attached. */
 474                 ret = ptrace_detach(child, data);
 475                 break;
 476
 477 #ifdef PTRACE_SINGLESTEP
 478         case PTRACE_SINGLESTEP:
 479 #endif
 480 #ifdef PTRACE_SINGLEBLOCK
 481         case PTRACE_SINGLEBLOCK:
 482 #endif
 483 #ifdef PTRACE_SYSEMU
 484         case PTRACE_SYSEMU:
 485         case PTRACE_SYSEMU_SINGLESTEP:
 486 #endif
 487         case PTRACE_SYSCALL:
 488         case PTRACE_CONT:
 489                 return ptrace_resume(child, request, data);
 490
 491         case PTRACE_KILL:
 492                 if (child->exit_state)  /* already dead */
 493                         return 0;
 494                 return ptrace_resume(child, request, SIGKILL);
 495
 496         default:
 497                 break;
 498         }
 499
 500         return ret;
 501 }
 502
 503 /**
 504  * ptrace_traceme  --  helper for PTRACE_TRACEME
 505  *
 506  * Performs checks and sets PT_PTRACED.
 507  * Should be used by all ptrace implementations for PTRACE_TRACEME.
 508  */
 509 int ptrace_traceme(void)
 510 {
 511         int ret = -EPERM;
 512
 513         /*
 514          * Are we already being traced?
 515          */
 516 repeat:
 517         task_lock(current);
 518         if (!(current->ptrace & PT_PTRACED)) {
 519                 /*
 520                  * See ptrace_attach() comments about the locking here.
 521                  */
 522                 unsigned long flags;
 523                 if (!write_trylock_irqsave(&tasklist_lock, flags)) {
 524                         task_unlock(current);
 525                         do {
 526                                 cpu_relax();
 527                         } while (!write_can_lock(&tasklist_lock));
 528                         goto repeat;
 529                 }
 530
 531                 ret = security_ptrace_traceme(current->parent);
 532
 533                 /*
 534                  * Set the ptrace bit in the process ptrace flags.
 535                  * Then link us on our parent's ptraced list.
 536                  */
 537                 if (!ret) {
 538                         current->ptrace |= PT_PTRACED;
 539                         __ptrace_link(current, current->real_parent);
 540                 }
 541
 542                 write_unlock_irqrestore(&tasklist_lock, flags);
 543         }
 544         task_unlock(current);
 545         return ret;
 546 }
 547
 548 /**
 549  * ptrace_get_task_struct  --  grab a task struct reference for ptrace
 550  * @pid:       process id to grab a task_struct reference of
 551  *
 552  * This function is a helper for ptrace implementations.  It checks
 553  * permissions and then grabs a task struct for use of the actual
 554  * ptrace implementation.
 555  *
 556  * Returns the task_struct for @pid or an ERR_PTR() on failure.
 557  */
 558 struct task_struct *ptrace_get_task_struct(pid_t pid)
 559 {
 560         struct task_struct *child;
 561
 562         read_lock(&tasklist_lock);
 563         child = find_task_by_vpid(pid);
 564         if (child)
 565                 get_task_struct(child);
 566
 567         read_unlock(&tasklist_lock);
 568         if (!child)
 569                 return ERR_PTR(-ESRCH);
 570         return child;
 571 }
 572
 573 #ifndef arch_ptrace_attach
 574 #define arch_ptrace_attach(child)       do { } while (0)
 575 #endif
 576
 577 SYSCALL_DEFINE4(ptrace, long, request, long, pid, long, addr, long, data)
 578 {
 579         struct task_struct *child;
 580         long ret;
 581
 582         /*
 583          * This lock_kernel fixes a subtle race with suid exec
 584          */
 585         lock_kernel();
 586         if (request == PTRACE_TRACEME) {
 587                 ret = ptrace_traceme();
 588                 if (!ret)
 589                         arch_ptrace_attach(current);
 590                 goto out;
 591         }
 592
 593         child = ptrace_get_task_struct(pid);
 594         if (IS_ERR(child)) {
 595                 ret = PTR_ERR(child);
 596                 goto out;
 597         }
 598
 599         if (request == PTRACE_ATTACH) {
 600                 ret = ptrace_attach(child);
 601                 /*
 602                  * Some architectures need to do book-keeping after
 603                  * a ptrace attach.
 604                  */
 605                 if (!ret)
 606                         arch_ptrace_attach(child);
 607                 goto out_put_task_struct;
 608         }
 609
 610         ret = ptrace_check_attach(child, request == PTRACE_KILL);
 611         if (ret < 0)
 612                 goto out_put_task_struct;
 613
 614         ret = arch_ptrace(child, request, addr, data);
 615         if (ret < 0)
 616                 goto out_put_task_struct;
 617
 618  out_put_task_struct:
 619         put_task_struct(child);
 620  out:
 621         unlock_kernel();
 622         return ret;
 623 }
 624
 625 int generic_ptrace_peekdata(struct task_struct *tsk, long addr, long data)
 626 {
 627         unsigned long tmp;
 628         int copied;
 629
 630         copied = access_process_vm(tsk, addr, &tmp, sizeof(tmp), 0);
 631         if (copied != sizeof(tmp))
 632                 return -EIO;
 633         return put_user(tmp, (unsigned long __user *)data);
 634 }
 635
 636 int generic_ptrace_pokedata(struct task_struct *tsk, long addr, long data)
 637 {
 638         int copied;
 639
 640         copied = access_process_vm(tsk, addr, &data, sizeof(data), 1);
 641         return (copied == sizeof(data)) ? 0 : -EIO;
 642 }
 643
 644 #if defined CONFIG_COMPAT
 645 #include <linux/compat.h>
 646
 647 int compat_ptrace_request(struct task_struct *child, compat_long_t request,
 648                           compat_ulong_t addr, compat_ulong_t data)
 649 {
 650         compat_ulong_t __user *datap = compat_ptr(data);
 651         compat_ulong_t word;
 652         siginfo_t siginfo;
 653         int ret;
 654
 655         switch (request) {
 656         case PTRACE_PEEKTEXT:
 657         case PTRACE_PEEKDATA:
 658                 ret = access_process_vm(child, addr, &word, sizeof(word), 0);
 659                 if (ret != sizeof(word))
 660                         ret = -EIO;
 661                 else
 662                         ret = put_user(word, datap);
 663                 break;
 664
 665         case PTRACE_POKETEXT:
 666         case PTRACE_POKEDATA:
 667                 ret = access_process_vm(child, addr, &data, sizeof(data), 1);
 668                 ret = (ret != sizeof(data) ? -EIO : 0);
 669                 break;
 670
 671         case PTRACE_GETEVENTMSG:
 672                 ret = put_user((compat_ulong_t) child->ptrace_message, datap);
 673                 break;
 674
 675         case PTRACE_GETSIGINFO:
 676                 ret = ptrace_getsiginfo(child, &siginfo);
 677                 if (!ret)
 678                         ret = copy_siginfo_to_user32(
 679                                 (struct compat_siginfo __user *) datap,
 680                                 &siginfo);
 681                 break;
 682
 683         case PTRACE_SETSIGINFO:
 684                 memset(&siginfo, 0, sizeof siginfo);
 685                 if (copy_siginfo_from_user32(
 686                             &siginfo, (struct compat_siginfo __user *) datap))
 687                         ret = -EFAULT;
 688                 else
 689                         ret = ptrace_setsiginfo(child, &siginfo);
 690                 break;
 691
 692         default:
 693                 ret = ptrace_request(child, request, addr, data);
 694         }
 695
 696         return ret;
 697 }
 698
 699 asmlinkage long compat_sys_ptrace(compat_long_t request, compat_long_t pid,
 700                                   compat_long_t addr, compat_long_t data)
 701 {
 702         struct task_struct *child;
 703         long ret;
 704
 705         /*
 706          * This lock_kernel fixes a subtle race with suid exec
 707          */
 708         lock_kernel();
 709         if (request == PTRACE_TRACEME) {
 710                 ret = ptrace_traceme();
 711                 goto out;
 712         }
 713
 714         child = ptrace_get_task_struct(pid);
 715         if (IS_ERR(child)) {
 716                 ret = PTR_ERR(child);
 717                 goto out;
 718         }
 719
 720         if (request == PTRACE_ATTACH) {
 721                 ret = ptrace_attach(child);
 722                 /*
 723                  * Some architectures need to do book-keeping after
 724                  * a ptrace attach.
 725                  */
 726                 if (!ret)
 727                         arch_ptrace_attach(child);
 728                 goto out_put_task_struct;
 729         }
 730
 731         ret = ptrace_check_attach(child, request == PTRACE_KILL);
 732         if (!ret)
 733                 ret = compat_arch_ptrace(child, request, addr, data);
 734
 735  out_put_task_struct:
 736         put_task_struct(child);
 737  out:
 738         unlock_kernel();
 739         return ret;
 740 }
 741 #endif  /* CONFIG_COMPAT */