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  * Initialize a new task whose father had been ptraced.
  29  *
  30  * Called from copy_process().
  31  */
  32 void ptrace_fork(struct task_struct *child, unsigned long clone_flags)
  33 {
  34         arch_ptrace_fork(child, clone_flags);
  35 }
  36
  37 /*
  38  * ptrace a task: make the debugger its new parent and
  39  * move it to the ptrace list.
  40  *
  41  * Must be called with the tasklist lock write-held.
  42  */
  43 void __ptrace_link(struct task_struct *child, struct task_struct *new_parent)
  44 {
  45         BUG_ON(!list_empty(&child->ptrace_entry));
  46         list_add(&child->ptrace_entry, &new_parent->ptraced);
  47         child->parent = new_parent;
  48 }
  49
  50 /*
  51  * Turn a tracing stop into a normal stop now, since with no tracer there
  52  * would be no way to wake it up with SIGCONT or SIGKILL.  If there was a
  53  * signal sent that would resume the child, but didn't because it was in
  54  * TASK_TRACED, resume it now.
  55  * Requires that irqs be disabled.
  56  */
  57 static void ptrace_untrace(struct task_struct *child)
  58 {
  59         spin_lock(&child->sighand->siglock);
  60         if (task_is_traced(child)) {
  61                 /*
  62                  * If the group stop is completed or in progress,
  63                  * this thread was already counted as stopped.
  64                  */
  65                 if (child->signal->flags & SIGNAL_STOP_STOPPED ||
  66                     child->signal->group_stop_count)
  67                         __set_task_state(child, TASK_STOPPED);
  68                 else
  69                         signal_wake_up(child, 1);
  70         }
  71         spin_unlock(&child->sighand->siglock);
  72 }
  73
  74 /*
  75  * unptrace a task: move it back to its original parent and
  76  * remove it from the ptrace list.
  77  *
  78  * Must be called with the tasklist lock write-held.
  79  */
  80 void __ptrace_unlink(struct task_struct *child)
  81 {
  82         BUG_ON(!child->ptrace);
  83
  84         child->ptrace = 0;
  85         child->parent = child->real_parent;
  86         list_del_init(&child->ptrace_entry);
  87
  88         arch_ptrace_untrace(child);
  89         if (task_is_traced(child))
  90                 ptrace_untrace(child);
  91 }
  92
  93 /*
  94  * Check that we have indeed attached to the thing..
  95  */
  96 int ptrace_check_attach(struct task_struct *child, int kill)
  97 {
  98         int ret = -ESRCH;
  99
 100         /*
 101          * We take the read lock around doing both checks to close a
 102          * possible race where someone else was tracing our child and
 103          * detached between these two checks.  After this locked check,
 104          * we are sure that this is our traced child and that can only
 105          * be changed by us so it's not changing right after this.
 106          */
 107         read_lock(&tasklist_lock);
 108         if ((child->ptrace & PT_PTRACED) && child->parent == current) {
 109                 ret = 0;
 110                 /*
 111                  * child->sighand can't be NULL, release_task()
 112                  * does ptrace_unlink() before __exit_signal().
 113                  */
 114                 spin_lock_irq(&child->sighand->siglock);
 115                 if (task_is_stopped(child))
 116                         child->state = TASK_TRACED;
 117                 else if (!task_is_traced(child) && !kill)
 118                         ret = -ESRCH;
 119                 spin_unlock_irq(&child->sighand->siglock);
 120         }
 121         read_unlock(&tasklist_lock);
 122
 123         if (!ret && !kill)
 124                 ret = wait_task_inactive(child, TASK_TRACED) ? 0 : -ESRCH;
 125
 126         /* All systems go.. */
 127         return ret;
 128 }
 129
 130 int __ptrace_may_access(struct task_struct *task, unsigned int mode)
 131 {
 132         const struct cred *cred = current_cred(), *tcred;
 133
 134         /* May we inspect the given task?
 135          * This check is used both for attaching with ptrace
 136          * and for allowing access to sensitive information in /proc.
 137          *
 138          * ptrace_attach denies several cases that /proc allows
 139          * because setting up the necessary parent/child relationship
 140          * or halting the specified task is impossible.
 141          */
 142         int dumpable = 0;
 143         /* Don't let security modules deny introspection */
 144         if (task == current)
 145                 return 0;
 146         rcu_read_lock();
 147         tcred = __task_cred(task);
 148         if ((cred->uid != tcred->euid ||
 149              cred->uid != tcred->suid ||
 150              cred->uid != tcred->uid  ||
 151              cred->gid != tcred->egid ||
 152              cred->gid != tcred->sgid ||
 153              cred->gid != tcred->gid) &&
 154             !capable(CAP_SYS_PTRACE)) {
 155                 rcu_read_unlock();
 156                 return -EPERM;
 157         }
 158         rcu_read_unlock();
 159         smp_rmb();
 160         if (task->mm)
 161                 dumpable = get_dumpable(task->mm);
 162         if (!dumpable && !capable(CAP_SYS_PTRACE))
 163                 return -EPERM;
 164
 165         return security_ptrace_may_access(task, mode);
 166 }
 167
 168 bool ptrace_may_access(struct task_struct *task, unsigned int mode)
 169 {
 170         int err;
 171         task_lock(task);
 172         err = __ptrace_may_access(task, mode);
 173         task_unlock(task);
 174         return !err;
 175 }
 176
 177 int ptrace_attach(struct task_struct *task)
 178 {
 179         int retval;
 180         unsigned long flags;
 181
 182         audit_ptrace(task);
 183
 184         retval = -EPERM;
 185         if (same_thread_group(task, current))
 186                 goto out;
 187
 188         /* Protect exec's credential calculations against our interference;
 189          * SUID, SGID and LSM creds get determined differently under ptrace.
 190          */
 191         retval = mutex_lock_interruptible(&current->cred_exec_mutex);
 192         if (retval  < 0)
 193                 goto out;
 194
 195         retval = -EPERM;
 196 repeat:
 197         /*
 198          * Nasty, nasty.
 199          *
 200          * We want to hold both the task-lock and the
 201          * tasklist_lock for writing at the same time.
 202          * But that's against the rules (tasklist_lock
 203          * is taken for reading by interrupts on other
 204          * cpu's that may have task_lock).
 205          */
 206         task_lock(task);
 207         if (!write_trylock_irqsave(&tasklist_lock, flags)) {
 208                 task_unlock(task);
 209                 do {
 210                         cpu_relax();
 211                 } while (!write_can_lock(&tasklist_lock));
 212                 goto repeat;
 213         }
 214
 215         if (!task->mm)
 216                 goto bad;
 217         /* the same process cannot be attached many times */
 218         if (task->ptrace & PT_PTRACED)
 219                 goto bad;
 220         retval = __ptrace_may_access(task, PTRACE_MODE_ATTACH);
 221         if (retval)
 222                 goto bad;
 223
 224         /* Go */
 225         task->ptrace |= PT_PTRACED;
 226         if (capable(CAP_SYS_PTRACE))
 227                 task->ptrace |= PT_PTRACE_CAP;
 228
 229         __ptrace_link(task, current);
 230
 231         send_sig_info(SIGSTOP, SEND_SIG_FORCED, task);
 232 bad:
 233         write_unlock_irqrestore(&tasklist_lock, flags);
 234         task_unlock(task);
 235         mutex_unlock(&current->cred_exec_mutex);
 236 out:
 237         return retval;
 238 }
 239
 240 /*
 241  * Called with irqs disabled, returns true if childs should reap themselves.
 242  */
 243 static int ignoring_children(struct sighand_struct *sigh)
 244 {
 245         int ret;
 246         spin_lock(&sigh->siglock);
 247         ret = (sigh->action[SIGCHLD-1].sa.sa_handler == SIG_IGN) ||
 248               (sigh->action[SIGCHLD-1].sa.sa_flags & SA_NOCLDWAIT);
 249         spin_unlock(&sigh->siglock);
 250         return ret;
 251 }
 252
 253 /*
 254  * Called with tasklist_lock held for writing.
 255  * Unlink a traced task, and clean it up if it was a traced zombie.
 256  * Return true if it needs to be reaped with release_task().
 257  * (We can't call release_task() here because we already hold tasklist_lock.)
 258  *
 259  * If it's a zombie, our attachedness prevented normal parent notification
 260  * or self-reaping.  Do notification now if it would have happened earlier.
 261  * If it should reap itself, return true.
 262  *
 263  * If it's our own child, there is no notification to do.
 264  * But if our normal children self-reap, then this child
 265  * was prevented by ptrace and we must reap it now.
 266  */
 267 static bool __ptrace_detach(struct task_struct *tracer, struct task_struct *p)
 268 {
 269         __ptrace_unlink(p);
 270
 271         if (p->exit_state == EXIT_ZOMBIE) {
 272                 if (!task_detached(p) && thread_group_empty(p)) {
 273                         if (!same_thread_group(p->real_parent, tracer))
 274                                 do_notify_parent(p, p->exit_signal);
 275                         else if (ignoring_children(tracer->sighand))
 276                                 p->exit_signal = -1;
 277                 }
 278                 if (task_detached(p)) {
 279                         /* Mark it as in the process of being reaped. */
 280                         p->exit_state = EXIT_DEAD;
 281                         return true;
 282                 }
 283         }
 284
 285         return false;
 286 }
 287
 288 int ptrace_detach(struct task_struct *child, unsigned int data)
 289 {
 290         bool dead = false;
 291
 292         if (!valid_signal(data))
 293                 return -EIO;
 294
 295         /* Architecture-specific hardware disable .. */
 296         ptrace_disable(child);
 297         clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
 298
 299         write_lock_irq(&tasklist_lock);
 300         /*
 301          * This child can be already killed. Make sure de_thread() or
 302          * our sub-thread doing do_wait() didn't do release_task() yet.
 303          */
 304         if (child->ptrace) {
 305                 child->exit_code = data;
 306                 dead = __ptrace_detach(current, child);
 307         }
 308         write_unlock_irq(&tasklist_lock);
 309
 310         if (unlikely(dead))
 311                 release_task(child);
 312
 313         return 0;
 314 }
 315
 316 /*
 317  * Detach all tasks we were using ptrace on.
 318  */
 319 void exit_ptrace(struct task_struct *tracer)
 320 {
 321         struct task_struct *p, *n;
 322         LIST_HEAD(ptrace_dead);
 323
 324         write_lock_irq(&tasklist_lock);
 325         list_for_each_entry_safe(p, n, &tracer->ptraced, ptrace_entry) {
 326                 if (__ptrace_detach(tracer, p))
 327                         list_add(&p->ptrace_entry, &ptrace_dead);
 328         }
 329         write_unlock_irq(&tasklist_lock);
 330
 331         BUG_ON(!list_empty(&tracer->ptraced));
 332
 333         list_for_each_entry_safe(p, n, &ptrace_dead, ptrace_entry) {
 334                 list_del_init(&p->ptrace_entry);
 335                 release_task(p);
 336         }
 337 }
 338
 339 int ptrace_readdata(struct task_struct *tsk, unsigned long src, char __user *dst, int len)
 340 {
 341         int copied = 0;
 342
 343         while (len > 0) {
 344                 char buf[128];
 345                 int this_len, retval;
 346
 347                 this_len = (len > sizeof(buf)) ? sizeof(buf) : len;
 348                 retval = access_process_vm(tsk, src, buf, this_len, 0);
 349                 if (!retval) {
 350                         if (copied)
 351                                 break;
 352                         return -EIO;
 353                 }
 354                 if (copy_to_user(dst, buf, retval))
 355                         return -EFAULT;
 356                 copied += retval;
 357                 src += retval;
 358                 dst += retval;
 359                 len -= retval;
 360         }
 361         return copied;
 362 }
 363
 364 int ptrace_writedata(struct task_struct *tsk, char __user *src, unsigned long dst, int len)
 365 {
 366         int copied = 0;
 367
 368         while (len > 0) {
 369                 char buf[128];
 370                 int this_len, retval;
 371
 372                 this_len = (len > sizeof(buf)) ? sizeof(buf) : len;
 373                 if (copy_from_user(buf, src, this_len))
 374                         return -EFAULT;
 375                 retval = access_process_vm(tsk, dst, buf, this_len, 1);
 376                 if (!retval) {
 377                         if (copied)
 378                                 break;
 379                         return -EIO;
 380                 }
 381                 copied += retval;
 382                 src += retval;
 383                 dst += retval;
 384                 len -= retval;
 385         }
 386         return copied;
 387 }
 388
 389 static int ptrace_setoptions(struct task_struct *child, long data)
 390 {
 391         child->ptrace &= ~PT_TRACE_MASK;
 392
 393         if (data & PTRACE_O_TRACESYSGOOD)
 394                 child->ptrace |= PT_TRACESYSGOOD;
 395
 396         if (data & PTRACE_O_TRACEFORK)
 397                 child->ptrace |= PT_TRACE_FORK;
 398
 399         if (data & PTRACE_O_TRACEVFORK)
 400                 child->ptrace |= PT_TRACE_VFORK;
 401
 402         if (data & PTRACE_O_TRACECLONE)
 403                 child->ptrace |= PT_TRACE_CLONE;
 404
 405         if (data & PTRACE_O_TRACEEXEC)
 406                 child->ptrace |= PT_TRACE_EXEC;
 407
 408         if (data & PTRACE_O_TRACEVFORKDONE)
 409                 child->ptrace |= PT_TRACE_VFORK_DONE;
 410
 411         if (data & PTRACE_O_TRACEEXIT)
 412                 child->ptrace |= PT_TRACE_EXIT;
 413
 414         return (data & ~PTRACE_O_MASK) ? -EINVAL : 0;
 415 }
 416
 417 static int ptrace_getsiginfo(struct task_struct *child, siginfo_t *info)
 418 {
 419         int error = -ESRCH;
 420
 421         read_lock(&tasklist_lock);
 422         if (likely(child->sighand != NULL)) {
 423                 error = -EINVAL;
 424                 spin_lock_irq(&child->sighand->siglock);
 425                 if (likely(child->last_siginfo != NULL)) {
 426                         *info = *child->last_siginfo;
 427                         error = 0;
 428                 }
 429                 spin_unlock_irq(&child->sighand->siglock);
 430         }
 431         read_unlock(&tasklist_lock);
 432         return error;
 433 }
 434
 435 static int ptrace_setsiginfo(struct task_struct *child, const siginfo_t *info)
 436 {
 437         int error = -ESRCH;
 438
 439         read_lock(&tasklist_lock);
 440         if (likely(child->sighand != NULL)) {
 441                 error = -EINVAL;
 442                 spin_lock_irq(&child->sighand->siglock);
 443                 if (likely(child->last_siginfo != NULL)) {
 444                         *child->last_siginfo = *info;
 445                         error = 0;
 446                 }
 447                 spin_unlock_irq(&child->sighand->siglock);
 448         }
 449         read_unlock(&tasklist_lock);
 450         return error;
 451 }
 452
 453
 454 #ifdef PTRACE_SINGLESTEP
 455 #define is_singlestep(request)          ((request) == PTRACE_SINGLESTEP)
 456 #else
 457 #define is_singlestep(request)          0
 458 #endif
 459
 460 #ifdef PTRACE_SINGLEBLOCK
 461 #define is_singleblock(request)         ((request) == PTRACE_SINGLEBLOCK)
 462 #else
 463 #define is_singleblock(request)         0
 464 #endif
 465
 466 #ifdef PTRACE_SYSEMU
 467 #define is_sysemu_singlestep(request)   ((request) == PTRACE_SYSEMU_SINGLESTEP)
 468 #else
 469 #define is_sysemu_singlestep(request)   0
 470 #endif
 471
 472 static int ptrace_resume(struct task_struct *child, long request, long data)
 473 {
 474         if (!valid_signal(data))
 475                 return -EIO;
 476
 477         if (request == PTRACE_SYSCALL)
 478                 set_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
 479         else
 480                 clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
 481
 482 #ifdef TIF_SYSCALL_EMU
 483         if (request == PTRACE_SYSEMU || request == PTRACE_SYSEMU_SINGLESTEP)
 484                 set_tsk_thread_flag(child, TIF_SYSCALL_EMU);
 485         else
 486                 clear_tsk_thread_flag(child, TIF_SYSCALL_EMU);
 487 #endif
 488
 489         if (is_singleblock(request)) {
 490                 if (unlikely(!arch_has_block_step()))
 491                         return -EIO;
 492                 user_enable_block_step(child);
 493         } else if (is_singlestep(request) || is_sysemu_singlestep(request)) {
 494                 if (unlikely(!arch_has_single_step()))
 495                         return -EIO;
 496                 user_enable_single_step(child);
 497         } else {
 498                 user_disable_single_step(child);
 499         }
 500
 501         child->exit_code = data;
 502         wake_up_process(child);
 503
 504         return 0;
 505 }
 506
 507 int ptrace_request(struct task_struct *child, long request,
 508                    long addr, long data)
 509 {
 510         int ret = -EIO;
 511         siginfo_t siginfo;
 512
 513         switch (request) {
 514         case PTRACE_PEEKTEXT:
 515         case PTRACE_PEEKDATA:
 516                 return generic_ptrace_peekdata(child, addr, data);
 517         case PTRACE_POKETEXT:
 518         case PTRACE_POKEDATA:
 519                 return generic_ptrace_pokedata(child, addr, data);
 520
 521 #ifdef PTRACE_OLDSETOPTIONS
 522         case PTRACE_OLDSETOPTIONS:
 523 #endif
 524         case PTRACE_SETOPTIONS:
 525                 ret = ptrace_setoptions(child, data);
 526                 break;
 527         case PTRACE_GETEVENTMSG:
 528                 ret = put_user(child->ptrace_message, (unsigned long __user *) data);
 529                 break;
 530
 531         case PTRACE_GETSIGINFO:
 532                 ret = ptrace_getsiginfo(child, &siginfo);
 533                 if (!ret)
 534                         ret = copy_siginfo_to_user((siginfo_t __user *) data,
 535                                                    &siginfo);
 536                 break;
 537
 538         case PTRACE_SETSIGINFO:
 539                 if (copy_from_user(&siginfo, (siginfo_t __user *) data,
 540                                    sizeof siginfo))
 541                         ret = -EFAULT;
 542                 else
 543                         ret = ptrace_setsiginfo(child, &siginfo);
 544                 break;
 545
 546         case PTRACE_DETACH:      /* detach a process that was attached. */
 547                 ret = ptrace_detach(child, data);
 548                 break;
 549
 550 #ifdef PTRACE_SINGLESTEP
 551         case PTRACE_SINGLESTEP:
 552 #endif
 553 #ifdef PTRACE_SINGLEBLOCK
 554         case PTRACE_SINGLEBLOCK:
 555 #endif
 556 #ifdef PTRACE_SYSEMU
 557         case PTRACE_SYSEMU:
 558         case PTRACE_SYSEMU_SINGLESTEP:
 559 #endif
 560         case PTRACE_SYSCALL:
 561         case PTRACE_CONT:
 562                 return ptrace_resume(child, request, data);
 563
 564         case PTRACE_KILL:
 565                 if (child->exit_state)  /* already dead */
 566                         return 0;
 567                 return ptrace_resume(child, request, SIGKILL);
 568
 569         default:
 570                 break;
 571         }
 572
 573         return ret;
 574 }
 575
 576 /**
 577  * ptrace_traceme  --  helper for PTRACE_TRACEME
 578  *
 579  * Performs checks and sets PT_PTRACED.
 580  * Should be used by all ptrace implementations for PTRACE_TRACEME.
 581  */
 582 int ptrace_traceme(void)
 583 {
 584         int ret = -EPERM;
 585
 586         /*
 587          * Are we already being traced?
 588          */
 589 repeat:
 590         task_lock(current);
 591         if (!(current->ptrace & PT_PTRACED)) {
 592                 /*
 593                  * See ptrace_attach() comments about the locking here.
 594                  */
 595                 unsigned long flags;
 596                 if (!write_trylock_irqsave(&tasklist_lock, flags)) {
 597                         task_unlock(current);
 598                         do {
 599                                 cpu_relax();
 600                         } while (!write_can_lock(&tasklist_lock));
 601                         goto repeat;
 602                 }
 603
 604                 ret = security_ptrace_traceme(current->parent);
 605
 606                 /*
 607                  * Set the ptrace bit in the process ptrace flags.
 608                  * Then link us on our parent's ptraced list.
 609                  */
 610                 if (!ret) {
 611                         current->ptrace |= PT_PTRACED;
 612                         __ptrace_link(current, current->real_parent);
 613                 }
 614
 615                 write_unlock_irqrestore(&tasklist_lock, flags);
 616         }
 617         task_unlock(current);
 618         return ret;
 619 }
 620
 621 /**
 622  * ptrace_get_task_struct  --  grab a task struct reference for ptrace
 623  * @pid:       process id to grab a task_struct reference of
 624  *
 625  * This function is a helper for ptrace implementations.  It checks
 626  * permissions and then grabs a task struct for use of the actual
 627  * ptrace implementation.
 628  *
 629  * Returns the task_struct for @pid or an ERR_PTR() on failure.
 630  */
 631 struct task_struct *ptrace_get_task_struct(pid_t pid)
 632 {
 633         struct task_struct *child;
 634
 635         read_lock(&tasklist_lock);
 636         child = find_task_by_vpid(pid);
 637         if (child)
 638                 get_task_struct(child);
 639
 640         read_unlock(&tasklist_lock);
 641         if (!child)
 642                 return ERR_PTR(-ESRCH);
 643         return child;
 644 }
 645
 646 #ifndef arch_ptrace_attach
 647 #define arch_ptrace_attach(child)       do { } while (0)
 648 #endif
 649
 650 SYSCALL_DEFINE4(ptrace, long, request, long, pid, long, addr, long, data)
 651 {
 652         struct task_struct *child;
 653         long ret;
 654
 655         /*
 656          * This lock_kernel fixes a subtle race with suid exec
 657          */
 658         lock_kernel();
 659         if (request == PTRACE_TRACEME) {
 660                 ret = ptrace_traceme();
 661                 if (!ret)
 662                         arch_ptrace_attach(current);
 663                 goto out;
 664         }
 665
 666         child = ptrace_get_task_struct(pid);
 667         if (IS_ERR(child)) {
 668                 ret = PTR_ERR(child);
 669                 goto out;
 670         }
 671
 672         if (request == PTRACE_ATTACH) {
 673                 ret = ptrace_attach(child);
 674                 /*
 675                  * Some architectures need to do book-keeping after
 676                  * a ptrace attach.
 677                  */
 678                 if (!ret)
 679                         arch_ptrace_attach(child);
 680                 goto out_put_task_struct;
 681         }
 682
 683         ret = ptrace_check_attach(child, request == PTRACE_KILL);
 684         if (ret < 0)
 685                 goto out_put_task_struct;
 686
 687         ret = arch_ptrace(child, request, addr, data);
 688
 689  out_put_task_struct:
 690         put_task_struct(child);
 691  out:
 692         unlock_kernel();
 693         return ret;
 694 }
 695
 696 int generic_ptrace_peekdata(struct task_struct *tsk, long addr, long data)
 697 {
 698         unsigned long tmp;
 699         int copied;
 700
 701         copied = access_process_vm(tsk, addr, &tmp, sizeof(tmp), 0);
 702         if (copied != sizeof(tmp))
 703                 return -EIO;
 704         return put_user(tmp, (unsigned long __user *)data);
 705 }
 706
 707 int generic_ptrace_pokedata(struct task_struct *tsk, long addr, long data)
 708 {
 709         int copied;
 710
 711         copied = access_process_vm(tsk, addr, &data, sizeof(data), 1);
 712         return (copied == sizeof(data)) ? 0 : -EIO;
 713 }
 714
 715 #if defined CONFIG_COMPAT
 716 #include <linux/compat.h>
 717
 718 int compat_ptrace_request(struct task_struct *child, compat_long_t request,
 719                           compat_ulong_t addr, compat_ulong_t data)
 720 {
 721         compat_ulong_t __user *datap = compat_ptr(data);
 722         compat_ulong_t word;
 723         siginfo_t siginfo;
 724         int ret;
 725
 726         switch (request) {
 727         case PTRACE_PEEKTEXT:
 728         case PTRACE_PEEKDATA:
 729                 ret = access_process_vm(child, addr, &word, sizeof(word), 0);
 730                 if (ret != sizeof(word))
 731                         ret = -EIO;
 732                 else
 733                         ret = put_user(word, datap);
 734                 break;
 735
 736         case PTRACE_POKETEXT:
 737         case PTRACE_POKEDATA:
 738                 ret = access_process_vm(child, addr, &data, sizeof(data), 1);
 739                 ret = (ret != sizeof(data) ? -EIO : 0);
 740                 break;
 741
 742         case PTRACE_GETEVENTMSG:
 743                 ret = put_user((compat_ulong_t) child->ptrace_message, datap);
 744                 break;
 745
 746         case PTRACE_GETSIGINFO:
 747                 ret = ptrace_getsiginfo(child, &siginfo);
 748                 if (!ret)
 749                         ret = copy_siginfo_to_user32(
 750                                 (struct compat_siginfo __user *) datap,
 751                                 &siginfo);
 752                 break;
 753
 754         case PTRACE_SETSIGINFO:
 755                 memset(&siginfo, 0, sizeof siginfo);
 756                 if (copy_siginfo_from_user32(
 757                             &siginfo, (struct compat_siginfo __user *) datap))
 758                         ret = -EFAULT;
 759                 else
 760                         ret = ptrace_setsiginfo(child, &siginfo);
 761                 break;
 762
 763         default:
 764                 ret = ptrace_request(child, request, addr, data);
 765         }
 766
 767         return ret;
 768 }
 769
 770 asmlinkage long compat_sys_ptrace(compat_long_t request, compat_long_t pid,
 771                                   compat_long_t addr, compat_long_t data)
 772 {
 773         struct task_struct *child;
 774         long ret;
 775
 776         /*
 777          * This lock_kernel fixes a subtle race with suid exec
 778          */
 779         lock_kernel();
 780         if (request == PTRACE_TRACEME) {
 781                 ret = ptrace_traceme();
 782                 goto out;
 783         }
 784
 785         child = ptrace_get_task_struct(pid);
 786         if (IS_ERR(child)) {
 787                 ret = PTR_ERR(child);
 788                 goto out;
 789         }
 790
 791         if (request == PTRACE_ATTACH) {
 792                 ret = ptrace_attach(child);
 793                 /*
 794                  * Some architectures need to do book-keeping after
 795                  * a ptrace attach.
 796                  */
 797                 if (!ret)
 798                         arch_ptrace_attach(child);
 799                 goto out_put_task_struct;
 800         }
 801
 802         ret = ptrace_check_attach(child, request == PTRACE_KILL);
 803         if (!ret)
 804                 ret = compat_arch_ptrace(child, request, addr, data);
 805
 806  out_put_task_struct:
 807         put_task_struct(child);
 808  out:
 809         unlock_kernel();
 810         return ret;
 811 }
 812 #endif  /* CONFIG_COMPAT */