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