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         char *old_corename = cn->corename;
  62
  63         cn->size = CORENAME_MAX_SIZE * atomic_inc_return(&call_count);
  64         cn->corename = krealloc(old_corename, cn->size, GFP_KERNEL);
  65
  66         if (!cn->corename) {
  67                 kfree(old_corename);
  68                 return -ENOMEM;
  69         }
  70
  71         return 0;
  72 }
  73
  74 static int cn_printf(struct core_name *cn, const char *fmt, ...)
  75 {
  76         char *cur;
  77         int need;
  78         int ret;
  79         va_list arg;
  80
  81         va_start(arg, fmt);
  82         need = vsnprintf(NULL, 0, fmt, arg);
  83         va_end(arg);
  84
  85         if (likely(need < cn->size - cn->used - 1))
  86                 goto out_printf;
  87
  88         ret = expand_corename(cn);
  89         if (ret)
  90                 goto expand_fail;
  91
  92 out_printf:
  93         cur = cn->corename + cn->used;
  94         va_start(arg, fmt);
  95         vsnprintf(cur, need + 1, fmt, arg);
  96         va_end(arg);
  97         cn->used += need;
  98         return 0;
  99
 100 expand_fail:
 101         return ret;
 102 }
 103
 104 static void cn_escape(char *str)
 105 {
 106         for (; *str; str++)
 107                 if (*str == '/')
 108                         *str = '!';
 109 }
 110
 111 static int cn_print_exe_file(struct core_name *cn)
 112 {
 113         struct file *exe_file;
 114         char *pathbuf, *path;
 115         int ret;
 116
 117         exe_file = get_mm_exe_file(current->mm);
 118         if (!exe_file) {
 119                 char *commstart = cn->corename + cn->used;
 120                 ret = cn_printf(cn, "%s (path unknown)", current->comm);
 121                 cn_escape(commstart);
 122                 return ret;
 123         }
 124
 125         pathbuf = kmalloc(PATH_MAX, GFP_TEMPORARY);
 126         if (!pathbuf) {
 127                 ret = -ENOMEM;
 128                 goto put_exe_file;
 129         }
 130
 131         path = d_path(&exe_file->f_path, pathbuf, PATH_MAX);
 132         if (IS_ERR(path)) {
 133                 ret = PTR_ERR(path);
 134                 goto free_buf;
 135         }
 136
 137         cn_escape(path);
 138
 139         ret = cn_printf(cn, "%s", path);
 140
 141 free_buf:
 142         kfree(pathbuf);
 143 put_exe_file:
 144         fput(exe_file);
 145         return ret;
 146 }
 147
 148 /* format_corename will inspect the pattern parameter, and output a
 149  * name into corename, which must have space for at least
 150  * CORENAME_MAX_SIZE bytes plus one byte for the zero terminator.
 151  */
 152 static int format_corename(struct core_name *cn, struct coredump_params *cprm)
 153 {
 154         const struct cred *cred = current_cred();
 155         const char *pat_ptr = core_pattern;
 156         int ispipe = (*pat_ptr == '|');
 157         int pid_in_pattern = 0;
 158         int err = 0;
 159
 160         cn->size = CORENAME_MAX_SIZE * atomic_read(&call_count);
 161         cn->corename = kmalloc(cn->size, GFP_KERNEL);
 162         cn->used = 0;
 163
 164         if (!cn->corename)
 165                 return -ENOMEM;
 166
 167         /* Repeat as long as we have more pattern to process and more output
 168            space */
 169         while (*pat_ptr) {
 170                 if (*pat_ptr != '%') {
 171                         if (*pat_ptr == 0)
 172                                 goto out;
 173                         err = cn_printf(cn, "%c", *pat_ptr++);
 174                 } else {
 175                         switch (*++pat_ptr) {
 176                         /* single % at the end, drop that */
 177                         case 0:
 178                                 goto out;
 179                         /* Double percent, output one percent */
 180                         case '%':
 181                                 err = cn_printf(cn, "%c", '%');
 182                                 break;
 183                         /* pid */
 184                         case 'p':
 185                                 pid_in_pattern = 1;
 186                                 err = cn_printf(cn, "%d",
 187                                               task_tgid_vnr(current));
 188                                 break;
 189                         /* uid */
 190                         case 'u':
 191                                 err = cn_printf(cn, "%d", cred->uid);
 192                                 break;
 193                         /* gid */
 194                         case 'g':
 195                                 err = cn_printf(cn, "%d", cred->gid);
 196                                 break;
 197                         case 'd':
 198                                 err = cn_printf(cn, "%d",
 199                                         __get_dumpable(cprm->mm_flags));
 200                                 break;
 201                         /* signal that caused the coredump */
 202                         case 's':
 203                                 err = cn_printf(cn, "%ld", cprm->siginfo->si_signo);
 204                                 break;
 205                         /* UNIX time of coredump */
 206                         case 't': {
 207                                 struct timeval tv;
 208                                 do_gettimeofday(&tv);
 209                                 err = cn_printf(cn, "%lu", tv.tv_sec);
 210                                 break;
 211                         }
 212                         /* hostname */
 213                         case 'h': {
 214                                 char *namestart = cn->corename + cn->used;
 215                                 down_read(&uts_sem);
 216                                 err = cn_printf(cn, "%s",
 217                                               utsname()->nodename);
 218                                 up_read(&uts_sem);
 219                                 cn_escape(namestart);
 220                                 break;
 221                         }
 222                         /* executable */
 223                         case 'e': {
 224                                 char *commstart = cn->corename + cn->used;
 225                                 err = cn_printf(cn, "%s", current->comm);
 226                                 cn_escape(commstart);
 227                                 break;
 228                         }
 229                         case 'E':
 230                                 err = cn_print_exe_file(cn);
 231                                 break;
 232                         /* core limit size */
 233                         case 'c':
 234                                 err = cn_printf(cn, "%lu",
 235                                               rlimit(RLIMIT_CORE));
 236                                 break;
 237                         default:
 238                                 break;
 239                         }
 240                         ++pat_ptr;
 241                 }
 242
 243                 if (err)
 244                         return err;
 245         }
 246
 247         /* Backward compatibility with core_uses_pid:
 248          *
 249          * If core_pattern does not include a %p (as is the default)
 250          * and core_uses_pid is set, then .%pid will be appended to
 251          * the filename. Do not do this for piped commands. */
 252         if (!ispipe && !pid_in_pattern && core_uses_pid) {
 253                 err = cn_printf(cn, ".%d", task_tgid_vnr(current));
 254                 if (err)
 255                         return err;
 256         }
 257 out:
 258         return ispipe;
 259 }
 260
 261 static int zap_process(struct task_struct *start, int exit_code)
 262 {
 263         struct task_struct *t;
 264         int nr = 0;
 265
 266         start->signal->group_exit_code = exit_code;
 267         start->signal->group_stop_count = 0;
 268
 269         t = start;
 270         do {
 271                 task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);
 272                 if (t != current && t->mm) {
 273                         sigaddset(&t->pending.signal, SIGKILL);
 274                         signal_wake_up(t, 1);
 275                         nr++;
 276                 }
 277         } while_each_thread(start, t);
 278
 279         return nr;
 280 }
 281
 282 static int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
 283                         struct core_state *core_state, int exit_code)
 284 {
 285         struct task_struct *g, *p;
 286         unsigned long flags;
 287         int nr = -EAGAIN;
 288
 289         spin_lock_irq(&tsk->sighand->siglock);
 290         if (!signal_group_exit(tsk->signal)) {
 291                 mm->core_state = core_state;
 292                 nr = zap_process(tsk, exit_code);
 293                 tsk->signal->group_exit_task = tsk;
 294                 /* ignore all signals except SIGKILL, see prepare_signal() */
 295                 tsk->signal->flags = SIGNAL_GROUP_COREDUMP;
 296                 clear_tsk_thread_flag(tsk, TIF_SIGPENDING);
 297         }
 298         spin_unlock_irq(&tsk->sighand->siglock);
 299         if (unlikely(nr < 0))
 300                 return nr;
 301
 302         tsk->flags |= PF_DUMPCORE;
 303         if (atomic_read(&mm->mm_users) == nr + 1)
 304                 goto done;
 305         /*
 306          * We should find and kill all tasks which use this mm, and we should
 307          * count them correctly into ->nr_threads. We don't take tasklist
 308          * lock, but this is safe wrt:
 309          *
 310          * fork:
 311          *      None of sub-threads can fork after zap_process(leader). All
 312          *      processes which were created before this point should be
 313          *      visible to zap_threads() because copy_process() adds the new
 314          *      process to the tail of init_task.tasks list, and lock/unlock
 315          *      of ->siglock provides a memory barrier.
 316          *
 317          * do_exit:
 318          *      The caller holds mm->mmap_sem. This means that the task which
 319          *      uses this mm can't pass exit_mm(), so it can't exit or clear
 320          *      its ->mm.
 321          *
 322          * de_thread:
 323          *      It does list_replace_rcu(&leader->tasks, &current->tasks),
 324          *      we must see either old or new leader, this does not matter.
 325          *      However, it can change p->sighand, so lock_task_sighand(p)
 326          *      must be used. Since p->mm != NULL and we hold ->mmap_sem
 327          *      it can't fail.
 328          *
 329          *      Note also that "g" can be the old leader with ->mm == NULL
 330          *      and already unhashed and thus removed from ->thread_group.
 331          *      This is OK, __unhash_process()->list_del_rcu() does not
 332          *      clear the ->next pointer, we will find the new leader via
 333          *      next_thread().
 334          */
 335         rcu_read_lock();
 336         for_each_process(g) {
 337                 if (g == tsk->group_leader)
 338                         continue;
 339                 if (g->flags & PF_KTHREAD)
 340                         continue;
 341                 p = g;
 342                 do {
 343                         if (p->mm) {
 344                                 if (unlikely(p->mm == mm)) {
 345                                         lock_task_sighand(p, &flags);
 346                                         nr += zap_process(p, exit_code);
 347                                         p->signal->flags = SIGNAL_GROUP_EXIT;
 348                                         unlock_task_sighand(p, &flags);
 349                                 }
 350                                 break;
 351                         }
 352                 } while_each_thread(g, p);
 353         }
 354         rcu_read_unlock();
 355 done:
 356         atomic_set(&core_state->nr_threads, nr);
 357         return nr;
 358 }
 359
 360 static int coredump_wait(int exit_code, struct core_state *core_state)
 361 {
 362         struct task_struct *tsk = current;
 363         struct mm_struct *mm = tsk->mm;
 364         int core_waiters = -EBUSY;
 365
 366         init_completion(&core_state->startup);
 367         core_state->dumper.task = tsk;
 368         core_state->dumper.next = NULL;
 369
 370         down_write(&mm->mmap_sem);
 371         if (!mm->core_state)
 372                 core_waiters = zap_threads(tsk, mm, core_state, exit_code);
 373         up_write(&mm->mmap_sem);
 374
 375         if (core_waiters > 0) {
 376                 struct core_thread *ptr;
 377
 378                 wait_for_completion(&core_state->startup);
 379                 /*
 380                  * Wait for all the threads to become inactive, so that
 381                  * all the thread context (extended register state, like
 382                  * fpu etc) gets copied to the memory.
 383                  */
 384                 ptr = core_state->dumper.next;
 385                 while (ptr != NULL) {
 386                         wait_task_inactive(ptr->task, 0);
 387                         ptr = ptr->next;
 388                 }
 389         }
 390
 391         return core_waiters;
 392 }
 393
 394 static void coredump_finish(struct mm_struct *mm, bool core_dumped)
 395 {
 396         struct core_thread *curr, *next;
 397         struct task_struct *task;
 398
 399         spin_lock_irq(&current->sighand->siglock);
 400         if (core_dumped && !__fatal_signal_pending(current))
 401                 current->signal->group_exit_code |= 0x80;
 402         current->signal->group_exit_task = NULL;
 403         current->signal->flags = SIGNAL_GROUP_EXIT;
 404         spin_unlock_irq(&current->sighand->siglock);
 405
 406         next = mm->core_state->dumper.next;
 407         while ((curr = next) != NULL) {
 408                 next = curr->next;
 409                 task = curr->task;
 410                 /*
 411                  * see exit_mm(), curr->task must not see
 412                  * ->task == NULL before we read ->next.
 413                  */
 414                 smp_mb();
 415                 curr->task = NULL;
 416                 wake_up_process(task);
 417         }
 418
 419         mm->core_state = NULL;
 420 }
 421
 422 static bool dump_interrupted(void)
 423 {
 424         /*
 425          * SIGKILL or freezing() interrupt the coredumping. Perhaps we
 426          * can do try_to_freeze() and check __fatal_signal_pending(),
 427          * but then we need to teach dump_write() to restart and clear
 428          * TIF_SIGPENDING.
 429          */
 430         return signal_pending(current);
 431 }
 432
 433 static void wait_for_dump_helpers(struct file *file)
 434 {
 435         struct pipe_inode_info *pipe = file->private_data;
 436
 437         pipe_lock(pipe);
 438         pipe->readers++;
 439         pipe->writers--;
 440         wake_up_interruptible_sync(&pipe->wait);
 441         kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
 442         pipe_unlock(pipe);
 443
 444         /*
 445          * We actually want wait_event_freezable() but then we need
 446          * to clear TIF_SIGPENDING and improve dump_interrupted().
 447          */
 448         wait_event_interruptible(pipe->wait, pipe->readers == 1);
 449
 450         pipe_lock(pipe);
 451         pipe->readers--;
 452         pipe->writers++;
 453         pipe_unlock(pipe);
 454 }
 455
 456 /*
 457  * umh_pipe_setup
 458  * helper function to customize the process used
 459  * to collect the core in userspace.  Specifically
 460  * it sets up a pipe and installs it as fd 0 (stdin)
 461  * for the process.  Returns 0 on success, or
 462  * PTR_ERR on failure.
 463  * Note that it also sets the core limit to 1.  This
 464  * is a special value that we use to trap recursive
 465  * core dumps
 466  */
 467 static int umh_pipe_setup(struct subprocess_info *info, struct cred *new)
 468 {
 469         struct file *files[2];
 470         struct coredump_params *cp = (struct coredump_params *)info->data;
 471         int err = create_pipe_files(files, 0);
 472         if (err)
 473                 return err;
 474
 475         cp->file = files[1];
 476
 477         err = replace_fd(0, files[0], 0);
 478         fput(files[0]);
 479         /* and disallow core files too */
 480         current->signal->rlim[RLIMIT_CORE] = (struct rlimit){1, 1};
 481
 482         return err;
 483 }
 484
 485 void do_coredump(siginfo_t *siginfo)
 486 {
 487         struct core_state core_state;
 488         struct core_name cn;
 489         struct mm_struct *mm = current->mm;
 490         struct linux_binfmt * binfmt;
 491         const struct cred *old_cred;
 492         struct cred *cred;
 493         int retval = 0;
 494         int flag = 0;
 495         int ispipe;
 496         struct files_struct *displaced;
 497         bool need_nonrelative = false;
 498         bool core_dumped = false;
 499         static atomic_t core_dump_count = ATOMIC_INIT(0);
 500         struct coredump_params cprm = {
 501                 .siginfo = siginfo,
 502                 .regs = signal_pt_regs(),
 503                 .limit = rlimit(RLIMIT_CORE),
 504                 /*
 505                  * We must use the same mm->flags while dumping core to avoid
 506                  * inconsistency of bit flags, since this flag is not protected
 507                  * by any locks.
 508                  */
 509                 .mm_flags = mm->flags,
 510         };
 511
 512         audit_core_dumps(siginfo->si_signo);
 513
 514         binfmt = mm->binfmt;
 515         if (!binfmt || !binfmt->core_dump)
 516                 goto fail;
 517         if (!__get_dumpable(cprm.mm_flags))
 518                 goto fail;
 519
 520         cred = prepare_creds();
 521         if (!cred)
 522                 goto fail;
 523         /*
 524          * We cannot trust fsuid as being the "true" uid of the process
 525          * nor do we know its entire history. We only know it was tainted
 526          * so we dump it as root in mode 2, and only into a controlled
 527          * environment (pipe handler or fully qualified path).
 528          */
 529         if (__get_dumpable(cprm.mm_flags) == SUID_DUMP_ROOT) {
 530                 /* Setuid core dump mode */
 531                 flag = O_EXCL;          /* Stop rewrite attacks */
 532                 cred->fsuid = GLOBAL_ROOT_UID;  /* Dump root private */
 533                 need_nonrelative = true;
 534         }
 535
 536         retval = coredump_wait(siginfo->si_signo, &core_state);
 537         if (retval < 0)
 538                 goto fail_creds;
 539
 540         old_cred = override_creds(cred);
 541
 542         ispipe = format_corename(&cn, &cprm);
 543
 544         if (ispipe) {
 545                 int dump_count;
 546                 char **helper_argv;
 547                 struct subprocess_info *sub_info;
 548
 549                 if (ispipe < 0) {
 550                         printk(KERN_WARNING "format_corename failed\n");
 551                         printk(KERN_WARNING "Aborting core\n");
 552                         goto fail_corename;
 553                 }
 554
 555                 if (cprm.limit == 1) {
 556                         /* See umh_pipe_setup() which sets RLIMIT_CORE = 1.
 557                          *
 558                          * Normally core limits are irrelevant to pipes, since
 559                          * we're not writing to the file system, but we use
 560                          * cprm.limit of 1 here as a speacial value, this is a
 561                          * consistent way to catch recursive crashes.
 562                          * We can still crash if the core_pattern binary sets
 563                          * RLIM_CORE = !1, but it runs as root, and can do
 564                          * lots of stupid things.
 565                          *
 566                          * Note that we use task_tgid_vnr here to grab the pid
 567                          * of the process group leader.  That way we get the
 568                          * right pid if a thread in a multi-threaded
 569                          * core_pattern process dies.
 570                          */
 571                         printk(KERN_WARNING
 572                                 "Process %d(%s) has RLIMIT_CORE set to 1\n",
 573                                 task_tgid_vnr(current), current->comm);
 574                         printk(KERN_WARNING "Aborting core\n");
 575                         goto fail_unlock;
 576                 }
 577                 cprm.limit = RLIM_INFINITY;
 578
 579                 dump_count = atomic_inc_return(&core_dump_count);
 580                 if (core_pipe_limit && (core_pipe_limit < dump_count)) {
 581                         printk(KERN_WARNING "Pid %d(%s) over core_pipe_limit\n",
 582                                task_tgid_vnr(current), current->comm);
 583                         printk(KERN_WARNING "Skipping core dump\n");
 584                         goto fail_dropcount;
 585                 }
 586
 587                 helper_argv = argv_split(GFP_KERNEL, cn.corename+1, NULL);
 588                 if (!helper_argv) {
 589                         printk(KERN_WARNING "%s failed to allocate memory\n",
 590                                __func__);
 591                         goto fail_dropcount;
 592                 }
 593
 594                 retval = -ENOMEM;
 595                 sub_info = call_usermodehelper_setup(helper_argv[0],
 596                                                 helper_argv, NULL, GFP_KERNEL,
 597                                                 umh_pipe_setup, NULL, &cprm);
 598                 if (sub_info)
 599                         retval = call_usermodehelper_exec(sub_info,
 600                                                           UMH_WAIT_EXEC);
 601
 602                 argv_free(helper_argv);
 603                 if (retval) {
 604                         printk(KERN_INFO "Core dump to %s pipe failed\n",
 605                                cn.corename);
 606                         goto close_fail;
 607                 }
 608         } else {
 609                 struct inode *inode;
 610
 611                 if (cprm.limit < binfmt->min_coredump)
 612                         goto fail_unlock;
 613
 614                 if (need_nonrelative && cn.corename[0] != '/') {
 615                         printk(KERN_WARNING "Pid %d(%s) can only dump core "\
 616                                 "to fully qualified path!\n",
 617                                 task_tgid_vnr(current), current->comm);
 618                         printk(KERN_WARNING "Skipping core dump\n");
 619                         goto fail_unlock;
 620                 }
 621
 622                 cprm.file = filp_open(cn.corename,
 623                                  O_CREAT | 2 | O_NOFOLLOW | O_LARGEFILE | flag,
 624                                  0600);
 625                 if (IS_ERR(cprm.file))
 626                         goto fail_unlock;
 627
 628                 inode = file_inode(cprm.file);
 629                 if (inode->i_nlink > 1)
 630                         goto close_fail;
 631                 if (d_unhashed(cprm.file->f_path.dentry))
 632                         goto close_fail;
 633                 /*
 634                  * AK: actually i see no reason to not allow this for named
 635                  * pipes etc, but keep the previous behaviour for now.
 636                  */
 637                 if (!S_ISREG(inode->i_mode))
 638                         goto close_fail;
 639                 /*
 640                  * Dont allow local users get cute and trick others to coredump
 641                  * into their pre-created files.
 642                  */
 643                 if (!uid_eq(inode->i_uid, current_fsuid()))
 644                         goto close_fail;
 645                 if (!cprm.file->f_op || !cprm.file->f_op->write)
 646                         goto close_fail;
 647                 if (do_truncate(cprm.file->f_path.dentry, 0, 0, cprm.file))
 648                         goto close_fail;
 649         }
 650
 651         /* get us an unshared descriptor table; almost always a no-op */
 652         retval = unshare_files(&displaced);
 653         if (retval)
 654                 goto close_fail;
 655         if (displaced)
 656                 put_files_struct(displaced);
 657         if (!dump_interrupted()) {
 658                 file_start_write(cprm.file);
 659                 core_dumped = binfmt->core_dump(&cprm);
 660                 file_end_write(cprm.file);
 661         }
 662         if (ispipe && core_pipe_limit)
 663                 wait_for_dump_helpers(cprm.file);
 664 close_fail:
 665         if (cprm.file)
 666                 filp_close(cprm.file, NULL);
 667 fail_dropcount:
 668         if (ispipe)
 669                 atomic_dec(&core_dump_count);
 670 fail_unlock:
 671         kfree(cn.corename);
 672 fail_corename:
 673         coredump_finish(mm, core_dumped);
 674         revert_creds(old_cred);
 675 fail_creds:
 676         put_cred(cred);
 677 fail:
 678         return;
 679 }
 680
 681 /*
 682  * Core dumping helper functions.  These are the only things you should
 683  * do on a core-file: use only these functions to write out all the
 684  * necessary info.
 685  */
 686 int dump_write(struct file *file, const void *addr, int nr)
 687 {
 688         return !dump_interrupted() &&
 689                 access_ok(VERIFY_READ, addr, nr) &&
 690                 file->f_op->write(file, addr, nr, &file->f_pos) == nr;
 691 }
 692 EXPORT_SYMBOL(dump_write);
 693
 694 int dump_seek(struct file *file, loff_t off)
 695 {
 696         int ret = 1;
 697
 698         if (file->f_op->llseek && file->f_op->llseek != no_llseek) {
 699                 if (dump_interrupted() ||
 700                     file->f_op->llseek(file, off, SEEK_CUR) < 0)
 701                         return 0;
 702         } else {
 703                 char *buf = (char *)get_zeroed_page(GFP_KERNEL);
 704
 705                 if (!buf)
 706                         return 0;
 707                 while (off > 0) {
 708                         unsigned long n = off;
 709
 710                         if (n > PAGE_SIZE)
 711                                 n = PAGE_SIZE;
 712                         if (!dump_write(file, buf, n)) {
 713                                 ret = 0;
 714                                 break;
 715                         }
 716                         off -= n;
 717                 }
 718                 free_page((unsigned long)buf);
 719         }
 720         return ret;
 721 }
 722 EXPORT_SYMBOL(dump_seek);