fs/coredump.c

   1 #include <linux/slab.h>
   2 #include <linux/file.h>
   3 #include <linux/fdtable.h>
   4 #include <linux/mm.h>
   5 #include <linux/stat.h>
   6 #include <linux/fcntl.h>
   7 #include <linux/swap.h>
   8 #include <linux/string.h>
   9 #include <linux/init.h>
  10 #include <linux/pagemap.h>
  11 #include <linux/perf_event.h>
  12 #include <linux/highmem.h>
  13 #include <linux/spinlock.h>
  14 #include <linux/key.h>
  15 #include <linux/personality.h>
  16 #include <linux/binfmts.h>
  17 #include <linux/coredump.h>
  18 #include <linux/utsname.h>
  19 #include <linux/pid_namespace.h>
  20 #include <linux/module.h>
  21 #include <linux/namei.h>
  22 #include <linux/mount.h>
  23 #include <linux/security.h>
  24 #include <linux/syscalls.h>
  25 #include <linux/tsacct_kern.h>
  26 #include <linux/cn_proc.h>
  27 #include <linux/audit.h>
  28 #include <linux/tracehook.h>
  29 #include <linux/kmod.h>
  30 #include <linux/fsnotify.h>
  31 #include <linux/fs_struct.h>
  32 #include <linux/pipe_fs_i.h>
  33 #include <linux/oom.h>
  34 #include <linux/compat.h>
  35
  36 #include <asm/uaccess.h>
  37 #include <asm/mmu_context.h>
  38 #include <asm/tlb.h>
  39 #include <asm/exec.h>
  40
  41 #include <trace/events/task.h>
  42 #include "internal.h"
  43 #include "coredump.h"
  44
  45 #include <trace/events/sched.h>
  46
  47 int core_uses_pid;
  48 unsigned int core_pipe_limit;
  49 char core_pattern[CORENAME_MAX_SIZE] = "core";
  50 static int core_name_size = CORENAME_MAX_SIZE;
  51
  52 struct core_name {
  53         char *corename;
  54         int used, size;
  55 };
  56
  57 /* The maximal length of core_pattern is also specified in sysctl.c */
  58
  59 static int expand_corename(struct core_name *cn, int size)
  60 {
  61         char *corename = krealloc(cn->corename, size, GFP_KERNEL);
  62
  63         if (!corename)
  64                 return -ENOMEM;
  65
  66         if (size > core_name_size) /* racy but harmless */
  67                 core_name_size = size;
  68
  69         cn->size = ksize(corename);
  70         cn->corename = corename;
  71         return 0;
  72 }
  73
  74 static int cn_vprintf(struct core_name *cn, const char *fmt, va_list arg)
  75 {
  76         int free, need;
  77
  78 again:
  79         free = cn->size - cn->used;
  80         need = vsnprintf(cn->corename + cn->used, free, fmt, arg);
  81         if (need < free) {
  82                 cn->used += need;
  83                 return 0;
  84         }
  85
  86         if (!expand_corename(cn, cn->size + need - free + 1))
  87                 goto again;
  88
  89         return -ENOMEM;
  90 }
  91
  92 static int cn_printf(struct core_name *cn, const char *fmt, ...)
  93 {
  94         va_list arg;
  95         int ret;
  96
  97         va_start(arg, fmt);
  98         ret = cn_vprintf(cn, fmt, arg);
  99         va_end(arg);
 100
 101         return ret;
 102 }
 103
 104 static int cn_esc_printf(struct core_name *cn, const char *fmt, ...)
 105 {
 106         int cur = cn->used;
 107         va_list arg;
 108         int ret;
 109
 110         va_start(arg, fmt);
 111         ret = cn_vprintf(cn, fmt, arg);
 112         va_end(arg);
 113
 114         for (; cur < cn->used; ++cur) {
 115                 if (cn->corename[cur] == '/')
 116                         cn->corename[cur] = '!';
 117         }
 118         return ret;
 119 }
 120
 121 static int cn_print_exe_file(struct core_name *cn)
 122 {
 123         struct file *exe_file;
 124         char *pathbuf, *path;
 125         int ret;
 126
 127         exe_file = get_mm_exe_file(current->mm);
 128         if (!exe_file)
 129                 return cn_esc_printf(cn, "%s (path unknown)", current->comm);
 130
 131         pathbuf = kmalloc(PATH_MAX, GFP_TEMPORARY);
 132         if (!pathbuf) {
 133                 ret = -ENOMEM;
 134                 goto put_exe_file;
 135         }
 136
 137         path = d_path(&exe_file->f_path, pathbuf, PATH_MAX);
 138         if (IS_ERR(path)) {
 139                 ret = PTR_ERR(path);
 140                 goto free_buf;
 141         }
 142
 143         ret = cn_esc_printf(cn, "%s", path);
 144
 145 free_buf:
 146         kfree(pathbuf);
 147 put_exe_file:
 148         fput(exe_file);
 149         return ret;
 150 }
 151
 152 /* format_corename will inspect the pattern parameter, and output a
 153  * name into corename, which must have space for at least
 154  * CORENAME_MAX_SIZE bytes plus one byte for the zero terminator.
 155  */
 156 static int format_corename(struct core_name *cn, struct coredump_params *cprm)
 157 {
 158         const struct cred *cred = current_cred();
 159         const char *pat_ptr = core_pattern;
 160         int ispipe = (*pat_ptr == '|');
 161         int pid_in_pattern = 0;
 162         int err = 0;
 163
 164         cn->used = 0;
 165         cn->corename = NULL;
 166         if (expand_corename(cn, core_name_size))
 167                 return -ENOMEM;
 168         cn->corename[0] = '\0';
 169
 170         if (ispipe)
 171                 ++pat_ptr;
 172
 173         /* Repeat as long as we have more pattern to process and more output
 174            space */
 175         while (*pat_ptr) {
 176                 if (*pat_ptr != '%') {
 177                         err = cn_printf(cn, "%c", *pat_ptr++);
 178                 } else {
 179                         switch (*++pat_ptr) {
 180                         /* single % at the end, drop that */
 181                         case 0:
 182                                 goto out;
 183                         /* Double percent, output one percent */
 184                         case '%':
 185                                 err = cn_printf(cn, "%c", '%');
 186                                 break;
 187                         /* pid */
 188                         case 'p':
 189                                 pid_in_pattern = 1;
 190                                 err = cn_printf(cn, "%d",
 191                                               task_tgid_vnr(current));
 192                                 break;
 193                         /* uid */
 194                         case 'u':
 195                                 err = cn_printf(cn, "%d", cred->uid);
 196                                 break;
 197                         /* gid */
 198                         case 'g':
 199                                 err = cn_printf(cn, "%d", cred->gid);
 200                                 break;
 201                         case 'd':
 202                                 err = cn_printf(cn, "%d",
 203                                         __get_dumpable(cprm->mm_flags));
 204                                 break;
 205                         /* signal that caused the coredump */
 206                         case 's':
 207                                 err = cn_printf(cn, "%ld", cprm->siginfo->si_signo);
 208                                 break;
 209                         /* UNIX time of coredump */
 210                         case 't': {
 211                                 struct timeval tv;
 212                                 do_gettimeofday(&tv);
 213                                 err = cn_printf(cn, "%lu", tv.tv_sec);
 214                                 break;
 215                         }
 216                         /* hostname */
 217                         case 'h':
 218                                 down_read(&uts_sem);
 219                                 err = cn_esc_printf(cn, "%s",
 220                                               utsname()->nodename);
 221                                 up_read(&uts_sem);
 222                                 break;
 223                         /* executable */
 224                         case 'e':
 225                                 err = cn_esc_printf(cn, "%s", current->comm);
 226                                 break;
 227                         case 'E':
 228                                 err = cn_print_exe_file(cn);
 229                                 break;
 230                         /* core limit size */
 231                         case 'c':
 232                                 err = cn_printf(cn, "%lu",
 233                                               rlimit(RLIMIT_CORE));
 234                                 break;
 235                         default:
 236                                 break;
 237                         }
 238                         ++pat_ptr;
 239                 }
 240
 241                 if (err)
 242                         return err;
 243         }
 244
 245 out:
 246         /* Backward compatibility with core_uses_pid:
 247          *
 248          * If core_pattern does not include a %p (as is the default)
 249          * and core_uses_pid is set, then .%pid will be appended to
 250          * the filename. Do not do this for piped commands. */
 251         if (!ispipe && !pid_in_pattern && core_uses_pid) {
 252                 err = cn_printf(cn, ".%d", task_tgid_vnr(current));
 253                 if (err)
 254                         return err;
 255         }
 256         return ispipe;
 257 }
 258
 259 static int zap_process(struct task_struct *start, int exit_code)
 260 {
 261         struct task_struct *t;
 262         int nr = 0;
 263
 264         start->signal->group_exit_code = exit_code;
 265         start->signal->group_stop_count = 0;
 266
 267         t = start;
 268         do {
 269                 task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);
 270                 if (t != current && t->mm) {
 271                         sigaddset(&t->pending.signal, SIGKILL);
 272                         signal_wake_up(t, 1);
 273                         nr++;
 274                 }
 275         } while_each_thread(start, t);
 276
 277         return nr;
 278 }
 279
 280 static int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
 281                         struct core_state *core_state, int exit_code)
 282 {
 283         struct task_struct *g, *p;
 284         unsigned long flags;
 285         int nr = -EAGAIN;
 286
 287         spin_lock_irq(&tsk->sighand->siglock);
 288         if (!signal_group_exit(tsk->signal)) {
 289                 mm->core_state = core_state;
 290                 nr = zap_process(tsk, exit_code);
 291                 tsk->signal->group_exit_task = tsk;
 292                 /* ignore all signals except SIGKILL, see prepare_signal() */
 293                 tsk->signal->flags = SIGNAL_GROUP_COREDUMP;
 294                 clear_tsk_thread_flag(tsk, TIF_SIGPENDING);
 295         }
 296         spin_unlock_irq(&tsk->sighand->siglock);
 297         if (unlikely(nr < 0))
 298                 return nr;
 299
 300         tsk->flags = PF_DUMPCORE;
 301         if (atomic_read(&mm->mm_users) == nr + 1)
 302                 goto done;
 303         /*
 304          * We should find and kill all tasks which use this mm, and we should
 305          * count them correctly into ->nr_threads. We don't take tasklist
 306          * lock, but this is safe wrt:
 307          *
 308          * fork:
 309          *      None of sub-threads can fork after zap_process(leader). All
 310          *      processes which were created before this point should be
 311          *      visible to zap_threads() because copy_process() adds the new
 312          *      process to the tail of init_task.tasks list, and lock/unlock
 313          *      of ->siglock provides a memory barrier.
 314          *
 315          * do_exit:
 316          *      The caller holds mm->mmap_sem. This means that the task which
 317          *      uses this mm can't pass exit_mm(), so it can't exit or clear
 318          *      its ->mm.
 319          *
 320          * de_thread:
 321          *      It does list_replace_rcu(&leader->tasks, &current->tasks),
 322          *      we must see either old or new leader, this does not matter.
 323          *      However, it can change p->sighand, so lock_task_sighand(p)
 324          *      must be used. Since p->mm != NULL and we hold ->mmap_sem
 325          *      it can't fail.
 326          *
 327          *      Note also that "g" can be the old leader with ->mm == NULL
 328          *      and already unhashed and thus removed from ->thread_group.
 329          *      This is OK, __unhash_process()->list_del_rcu() does not
 330          *      clear the ->next pointer, we will find the new leader via
 331          *      next_thread().
 332          */
 333         rcu_read_lock();
 334         for_each_process(g) {
 335                 if (g == tsk->group_leader)
 336                         continue;
 337                 if (g->flags & PF_KTHREAD)
 338                         continue;
 339                 p = g;
 340                 do {
 341                         if (p->mm) {
 342                                 if (unlikely(p->mm == mm)) {
 343                                         lock_task_sighand(p, &flags);
 344                                         nr += zap_process(p, exit_code);
 345                                         p->signal->flags = SIGNAL_GROUP_EXIT;
 346                                         unlock_task_sighand(p, &flags);
 347                                 }
 348                                 break;
 349                         }
 350                 } while_each_thread(g, p);
 351         }
 352         rcu_read_unlock();
 353 done:
 354         atomic_set(&core_state->nr_threads, nr);
 355         return nr;
 356 }
 357
 358 static int coredump_wait(int exit_code, struct core_state *core_state)
 359 {
 360         struct task_struct *tsk = current;
 361         struct mm_struct *mm = tsk->mm;
 362         int core_waiters = -EBUSY;
 363
 364         init_completion(&core_state->startup);
 365         core_state->dumper.task = tsk;
 366         core_state->dumper.next = NULL;
 367
 368         down_write(&mm->mmap_sem);
 369         if (!mm->core_state)
 370                 core_waiters = zap_threads(tsk, mm, core_state, exit_code);
 371         up_write(&mm->mmap_sem);
 372
 373         if (core_waiters > 0) {
 374                 struct core_thread *ptr;
 375
 376                 wait_for_completion(&core_state->startup);
 377                 /*
 378                  * Wait for all the threads to become inactive, so that
 379                  * all the thread context (extended register state, like
 380                  * fpu etc) gets copied to the memory.
 381                  */
 382                 ptr = core_state->dumper.next;
 383                 while (ptr != NULL) {
 384                         wait_task_inactive(ptr->task, 0);
 385                         ptr = ptr->next;
 386                 }
 387         }
 388
 389         return core_waiters;
 390 }
 391
 392 static void coredump_finish(struct mm_struct *mm, bool core_dumped)
 393 {
 394         struct core_thread *curr, *next;
 395         struct task_struct *task;
 396
 397         spin_lock_irq(&current->sighand->siglock);
 398         if (core_dumped && !__fatal_signal_pending(current))
 399                 current->signal->group_exit_code |= 0x80;
 400         current->signal->group_exit_task = NULL;
 401         current->signal->flags = SIGNAL_GROUP_EXIT;
 402         spin_unlock_irq(&current->sighand->siglock);
 403
 404         next = mm->core_state->dumper.next;
 405         while ((curr = next) != NULL) {
 406                 next = curr->next;
 407                 task = curr->task;
 408                 /*
 409                  * see exit_mm(), curr->task must not see
 410                  * ->task == NULL before we read ->next.
 411                  */
 412                 smp_mb();
 413                 curr->task = NULL;
 414                 wake_up_process(task);
 415         }
 416
 417         mm->core_state = NULL;
 418 }
 419
 420 static bool dump_interrupted(void)
 421 {
 422         /*
 423          * SIGKILL or freezing() interrupt the coredumping. Perhaps we
 424          * can do try_to_freeze() and check __fatal_signal_pending(),
 425          * but then we need to teach dump_write() to restart and clear
 426          * TIF_SIGPENDING.
 427          */
 428         return signal_pending(current);
 429 }
 430
 431 static void wait_for_dump_helpers(struct file *file)
 432 {
 433         struct pipe_inode_info *pipe = file->private_data;
 434
 435         pipe_lock(pipe);
 436         pipe->readers++;
 437         pipe->writers--;
 438         wake_up_interruptible_sync(&pipe->wait);
 439         kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
 440         pipe_unlock(pipe);
 441
 442         /*
 443          * We actually want wait_event_freezable() but then we need
 444          * to clear TIF_SIGPENDING and improve dump_interrupted().
 445          */
 446         wait_event_interruptible(pipe->wait, pipe->readers == 1);
 447
 448         pipe_lock(pipe);
 449         pipe->readers--;
 450         pipe->writers++;
 451         pipe_unlock(pipe);
 452 }
 453
 454 /*
 455  * umh_pipe_setup
 456  * helper function to customize the process used
 457  * to collect the core in userspace.  Specifically
 458  * it sets up a pipe and installs it as fd 0 (stdin)
 459  * for the process.  Returns 0 on success, or
 460  * PTR_ERR on failure.
 461  * Note that it also sets the core limit to 1.  This
 462  * is a special value that we use to trap recursive
 463  * core dumps
 464  */
 465 static int umh_pipe_setup(struct subprocess_info *info, struct cred *new)
 466 {
 467         struct file *files[2];
 468         struct coredump_params *cp = (struct coredump_params *)info->data;
 469         int err = create_pipe_files(files, 0);
 470         if (err)
 471                 return err;
 472
 473         cp->file = files[1];
 474
 475         err = replace_fd(0, files[0], 0);
 476         fput(files[0]);
 477         /* and disallow core files too */
 478         current->signal->rlim[RLIMIT_CORE] = (struct rlimit){1, 1};
 479
 480         return err;
 481 }
 482
 483 void do_coredump(siginfo_t *siginfo)
 484 {
 485         struct core_state core_state;
 486         struct core_name cn;
 487         struct mm_struct *mm = current->mm;
 488         struct linux_binfmt * binfmt;
 489         const struct cred *old_cred;
 490         struct cred *cred;
 491         int retval = 0;
 492         int flag = 0;
 493         int ispipe;
 494         struct files_struct *displaced;
 495         bool need_nonrelative = false;
 496         bool core_dumped = false;
 497         static atomic_t core_dump_count = ATOMIC_INIT(0);
 498         struct coredump_params cprm = {
 499                 .siginfo = siginfo,
 500                 .regs = signal_pt_regs(),
 501                 .limit = rlimit(RLIMIT_CORE),
 502                 /*
 503                  * We must use the same mm->flags while dumping core to avoid
 504                  * inconsistency of bit flags, since this flag is not protected
 505                  * by any locks.
 506                  */
 507                 .mm_flags = mm->flags,
 508         };
 509
 510         audit_core_dumps(siginfo->si_signo);
 511
 512         binfmt = mm->binfmt;
 513         if (!binfmt || !binfmt->core_dump)
 514                 goto fail;
 515         if (!__get_dumpable(cprm.mm_flags))
 516                 goto fail;
 517
 518         cred = prepare_creds();
 519         if (!cred)
 520                 goto fail;
 521         /*
 522          * We cannot trust fsuid as being the "true" uid of the process
 523          * nor do we know its entire history. We only know it was tainted
 524          * so we dump it as root in mode 2, and only into a controlled
 525          * environment (pipe handler or fully qualified path).
 526          */
 527         if (__get_dumpable(cprm.mm_flags) == SUID_DUMP_ROOT) {
 528                 /* Setuid core dump mode */
 529                 flag = O_EXCL;          /* Stop rewrite attacks */
 530                 cred->fsuid = GLOBAL_ROOT_UID;  /* Dump root private */
 531                 need_nonrelative = true;
 532         }
 533
 534         retval = coredump_wait(siginfo->si_signo, &core_state);
 535         if (retval < 0)
 536                 goto fail_creds;
 537
 538         old_cred = override_creds(cred);
 539
 540         ispipe = format_corename(&cn, &cprm);
 541
 542         if (ispipe) {
 543                 int dump_count;
 544                 char **helper_argv;
 545                 struct subprocess_info *sub_info;
 546
 547                 if (ispipe < 0) {
 548                         printk(KERN_WARNING "format_corename failed\n");
 549                         printk(KERN_WARNING "Aborting core\n");
 550                         goto fail_unlock;
 551                 }
 552
 553                 if (cprm.limit == 1) {
 554                         /* See umh_pipe_setup() which sets RLIMIT_CORE = 1.
 555                          *
 556                          * Normally core limits are irrelevant to pipes, since
 557                          * we're not writing to the file system, but we use
 558                          * cprm.limit of 1 here as a speacial value, this is a
 559                          * consistent way to catch recursive crashes.
 560                          * We can still crash if the core_pattern binary sets
 561                          * RLIM_CORE = !1, but it runs as root, and can do
 562                          * lots of stupid things.
 563                          *
 564                          * Note that we use task_tgid_vnr here to grab the pid
 565                          * of the process group leader.  That way we get the
 566                          * right pid if a thread in a multi-threaded
 567                          * core_pattern process dies.
 568                          */
 569                         printk(KERN_WARNING
 570                                 "Process %d(%s) has RLIMIT_CORE set to 1\n",
 571                                 task_tgid_vnr(current), current->comm);
 572                         printk(KERN_WARNING "Aborting core\n");
 573                         goto fail_unlock;
 574                 }
 575                 cprm.limit = RLIM_INFINITY;
 576
 577                 dump_count = atomic_inc_return(&core_dump_count);
 578                 if (core_pipe_limit && (core_pipe_limit < dump_count)) {
 579                         printk(KERN_WARNING "Pid %d(%s) over core_pipe_limit\n",
 580                                task_tgid_vnr(current), current->comm);
 581                         printk(KERN_WARNING "Skipping core dump\n");
 582                         goto fail_dropcount;
 583                 }
 584
 585                 helper_argv = argv_split(GFP_KERNEL, cn.corename, NULL);
 586                 if (!helper_argv) {
 587                         printk(KERN_WARNING "%s failed to allocate memory\n",
 588                                __func__);
 589                         goto fail_dropcount;
 590                 }
 591
 592                 retval = -ENOMEM;
 593                 sub_info = call_usermodehelper_setup(helper_argv[0],
 594                                                 helper_argv, NULL, GFP_KERNEL,
 595                                                 umh_pipe_setup, NULL, &cprm);
 596                 if (sub_info)
 597                         retval = call_usermodehelper_exec(sub_info,
 598                                                           UMH_WAIT_EXEC);
 599
 600                 argv_free(helper_argv);
 601                 if (retval) {
 602                         printk(KERN_INFO "Core dump to |%s pipe failed\n",
 603                                cn.corename);
 604                         goto close_fail;
 605                 }
 606         } else {
 607                 struct inode *inode;
 608
 609                 if (cprm.limit < binfmt->min_coredump)
 610                         goto fail_unlock;
 611
 612                 if (need_nonrelative && cn.corename[0] != '/') {
 613                         printk(KERN_WARNING "Pid %d(%s) can only dump core "\
 614                                 "to fully qualified path!\n",
 615                                 task_tgid_vnr(current), current->comm);
 616                         printk(KERN_WARNING "Skipping core dump\n");
 617                         goto fail_unlock;
 618                 }
 619
 620                 cprm.file = filp_open(cn.corename,
 621                                  O_CREAT | 2 | O_NOFOLLOW | O_LARGEFILE | flag,
 622                                  0600);
 623                 if (IS_ERR(cprm.file))
 624                         goto fail_unlock;
 625
 626                 inode = file_inode(cprm.file);
 627                 if (inode->i_nlink > 1)
 628                         goto close_fail;
 629                 if (d_unhashed(cprm.file->f_path.dentry))
 630                         goto close_fail;
 631                 /*
 632                  * AK: actually i see no reason to not allow this for named
 633                  * pipes etc, but keep the previous behaviour for now.
 634                  */
 635                 if (!S_ISREG(inode->i_mode))
 636                         goto close_fail;
 637                 /*
 638                  * Dont allow local users get cute and trick others to coredump
 639                  * into their pre-created files.
 640                  */
 641                 if (!uid_eq(inode->i_uid, current_fsuid()))
 642                         goto close_fail;
 643                 if (!cprm.file->f_op || !cprm.file->f_op->write)
 644                         goto close_fail;
 645                 if (do_truncate(cprm.file->f_path.dentry, 0, 0, cprm.file))
 646                         goto close_fail;
 647         }
 648
 649         /* get us an unshared descriptor table; almost always a no-op */
 650         retval = unshare_files(&displaced);
 651         if (retval)
 652                 goto close_fail;
 653         if (displaced)
 654                 put_files_struct(displaced);
 655         if (!dump_interrupted()) {
 656                 file_start_write(cprm.file);
 657                 core_dumped = binfmt->core_dump(&cprm);
 658                 file_end_write(cprm.file);
 659         }
 660         if (ispipe && core_pipe_limit)
 661                 wait_for_dump_helpers(cprm.file);
 662 close_fail:
 663         if (cprm.file)
 664                 filp_close(cprm.file, NULL);
 665 fail_dropcount:
 666         if (ispipe)
 667                 atomic_dec(&core_dump_count);
 668 fail_unlock:
 669         kfree(cn.corename);
 670         coredump_finish(mm, core_dumped);
 671         revert_creds(old_cred);
 672 fail_creds:
 673         put_cred(cred);
 674 fail:
 675         return;
 676 }
 677
 678 /*
 679  * Core dumping helper functions.  These are the only things you should
 680  * do on a core-file: use only these functions to write out all the
 681  * necessary info.
 682  */
 683 int dump_write(struct file *file, const void *addr, int nr)
 684 {
 685         return !dump_interrupted() &&
 686                 access_ok(VERIFY_READ, addr, nr) &&
 687                 file->f_op->write(file, addr, nr, &file->f_pos) == nr;
 688 }
 689 EXPORT_SYMBOL(dump_write);
 690
 691 int dump_seek(struct file *file, loff_t off)
 692 {
 693         int ret = 1;
 694
 695         if (file->f_op->llseek && file->f_op->llseek != no_llseek) {
 696                 if (dump_interrupted() ||
 697                     file->f_op->llseek(file, off, SEEK_CUR) < 0)
 698                         return 0;
 699         } else {
 700                 char *buf = (char *)get_zeroed_page(GFP_KERNEL);
 701
 702                 if (!buf)
 703                         return 0;
 704                 while (off > 0) {
 705                         unsigned long n = off;
 706
 707                         if (n > PAGE_SIZE)
 708                                 n = PAGE_SIZE;
 709                         if (!dump_write(file, buf, n)) {
 710                                 ret = 0;
 711                                 break;
 712                         }
 713                         off -= n;
 714                 }
 715                 free_page((unsigned long)buf);
 716         }
 717         return ret;
 718 }
 719 EXPORT_SYMBOL(dump_seek);