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