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         if (atomic_read(&mm->mm_users) == nr + 1)
 303                 goto done;
 304         /*
 305          * We should find and kill all tasks which use this mm, and we should
 306          * count them correctly into ->nr_threads. We don't take tasklist
 307          * lock, but this is safe wrt:
 308          *
 309          * fork:
 310          *      None of sub-threads can fork after zap_process(leader). All
 311          *      processes which were created before this point should be
 312          *      visible to zap_threads() because copy_process() adds the new
 313          *      process to the tail of init_task.tasks list, and lock/unlock
 314          *      of ->siglock provides a memory barrier.
 315          *
 316          * do_exit:
 317          *      The caller holds mm->mmap_sem. This means that the task which
 318          *      uses this mm can't pass exit_mm(), so it can't exit or clear
 319          *      its ->mm.
 320          *
 321          * de_thread:
 322          *      It does list_replace_rcu(&leader->tasks, &current->tasks),
 323          *      we must see either old or new leader, this does not matter.
 324          *      However, it can change p->sighand, so lock_task_sighand(p)
 325          *      must be used. Since p->mm != NULL and we hold ->mmap_sem
 326          *      it can't fail.
 327          *
 328          *      Note also that "g" can be the old leader with ->mm == NULL
 329          *      and already unhashed and thus removed from ->thread_group.
 330          *      This is OK, __unhash_process()->list_del_rcu() does not
 331          *      clear the ->next pointer, we will find the new leader via
 332          *      next_thread().
 333          */
 334         rcu_read_lock();
 335         for_each_process(g) {
 336                 if (g == tsk->group_leader)
 337                         continue;
 338                 if (g->flags & PF_KTHREAD)
 339                         continue;
 340                 p = g;
 341                 do {
 342                         if (p->mm) {
 343                                 if (unlikely(p->mm == mm)) {
 344                                         lock_task_sighand(p, &flags);
 345                                         nr += zap_process(p, exit_code);
 346                                         p->signal->flags = SIGNAL_GROUP_EXIT;
 347                                         unlock_task_sighand(p, &flags);
 348                                 }
 349                                 break;
 350                         }
 351                 } while_each_thread(g, p);
 352         }
 353         rcu_read_unlock();
 354 done:
 355         atomic_set(&core_state->nr_threads, nr);
 356         return nr;
 357 }
 358
 359 static int coredump_wait(int exit_code, struct core_state *core_state)
 360 {
 361         struct task_struct *tsk = current;
 362         struct mm_struct *mm = tsk->mm;
 363         int core_waiters = -EBUSY;
 364
 365         init_completion(&core_state->startup);
 366         core_state->dumper.task = tsk;
 367         core_state->dumper.next = NULL;
 368
 369         down_write(&mm->mmap_sem);
 370         if (!mm->core_state)
 371                 core_waiters = zap_threads(tsk, mm, core_state, exit_code);
 372         up_write(&mm->mmap_sem);
 373
 374         if (core_waiters > 0) {
 375                 struct core_thread *ptr;
 376
 377                 wait_for_completion(&core_state->startup);
 378                 /*
 379                  * Wait for all the threads to become inactive, so that
 380                  * all the thread context (extended register state, like
 381                  * fpu etc) gets copied to the memory.
 382                  */
 383                 ptr = core_state->dumper.next;
 384                 while (ptr != NULL) {
 385                         wait_task_inactive(ptr->task, 0);
 386                         ptr = ptr->next;
 387                 }
 388         }
 389
 390         return core_waiters;
 391 }
 392
 393 static void coredump_finish(struct mm_struct *mm, bool core_dumped)
 394 {
 395         struct core_thread *curr, *next;
 396         struct task_struct *task;
 397
 398         spin_lock_irq(&current->sighand->siglock);
 399         if (core_dumped && !__fatal_signal_pending(current))
 400                 current->signal->group_exit_code |= 0x80;
 401         current->signal->group_exit_task = NULL;
 402         current->signal->flags = SIGNAL_GROUP_EXIT;
 403         spin_unlock_irq(&current->sighand->siglock);
 404
 405         next = mm->core_state->dumper.next;
 406         while ((curr = next) != NULL) {
 407                 next = curr->next;
 408                 task = curr->task;
 409                 /*
 410                  * see exit_mm(), curr->task must not see
 411                  * ->task == NULL before we read ->next.
 412                  */
 413                 smp_mb();
 414                 curr->task = NULL;
 415                 wake_up_process(task);
 416         }
 417
 418         mm->core_state = NULL;
 419 }
 420
 421 static void wait_for_dump_helpers(struct file *file)
 422 {
 423         struct pipe_inode_info *pipe;
 424
 425         pipe = file_inode(file)->i_pipe;
 426
 427         pipe_lock(pipe);
 428         pipe->readers++;
 429         pipe->writers--;
 430
 431         while ((pipe->readers > 1) && (!signal_pending(current))) {
 432                 wake_up_interruptible_sync(&pipe->wait);
 433                 kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
 434                 pipe_wait(pipe);
 435         }
 436
 437         pipe->readers--;
 438         pipe->writers++;
 439         pipe_unlock(pipe);
 440
 441 }
 442
 443 /*
 444  * umh_pipe_setup
 445  * helper function to customize the process used
 446  * to collect the core in userspace.  Specifically
 447  * it sets up a pipe and installs it as fd 0 (stdin)
 448  * for the process.  Returns 0 on success, or
 449  * PTR_ERR on failure.
 450  * Note that it also sets the core limit to 1.  This
 451  * is a special value that we use to trap recursive
 452  * core dumps
 453  */
 454 static int umh_pipe_setup(struct subprocess_info *info, struct cred *new)
 455 {
 456         struct file *files[2];
 457         struct coredump_params *cp = (struct coredump_params *)info->data;
 458         int err = create_pipe_files(files, 0);
 459         if (err)
 460                 return err;
 461
 462         cp->file = files[1];
 463
 464         err = replace_fd(0, files[0], 0);
 465         fput(files[0]);
 466         /* and disallow core files too */
 467         current->signal->rlim[RLIMIT_CORE] = (struct rlimit){1, 1};
 468
 469         return err;
 470 }
 471
 472 void do_coredump(siginfo_t *siginfo)
 473 {
 474         struct core_state core_state;
 475         struct core_name cn;
 476         struct mm_struct *mm = current->mm;
 477         struct linux_binfmt * binfmt;
 478         const struct cred *old_cred;
 479         struct cred *cred;
 480         int retval = 0;
 481         int flag = 0;
 482         int ispipe;
 483         struct files_struct *displaced;
 484         bool need_nonrelative = false;
 485         bool core_dumped = false;
 486         static atomic_t core_dump_count = ATOMIC_INIT(0);
 487         struct coredump_params cprm = {
 488                 .siginfo = siginfo,
 489                 .regs = signal_pt_regs(),
 490                 .limit = rlimit(RLIMIT_CORE),
 491                 /*
 492                  * We must use the same mm->flags while dumping core to avoid
 493                  * inconsistency of bit flags, since this flag is not protected
 494                  * by any locks.
 495                  */
 496                 .mm_flags = mm->flags,
 497         };
 498
 499         audit_core_dumps(siginfo->si_signo);
 500
 501         binfmt = mm->binfmt;
 502         if (!binfmt || !binfmt->core_dump)
 503                 goto fail;
 504         if (!__get_dumpable(cprm.mm_flags))
 505                 goto fail;
 506
 507         cred = prepare_creds();
 508         if (!cred)
 509                 goto fail;
 510         /*
 511          * We cannot trust fsuid as being the "true" uid of the process
 512          * nor do we know its entire history. We only know it was tainted
 513          * so we dump it as root in mode 2, and only into a controlled
 514          * environment (pipe handler or fully qualified path).
 515          */
 516         if (__get_dumpable(cprm.mm_flags) == SUID_DUMP_ROOT) {
 517                 /* Setuid core dump mode */
 518                 flag = O_EXCL;          /* Stop rewrite attacks */
 519                 cred->fsuid = GLOBAL_ROOT_UID;  /* Dump root private */
 520                 need_nonrelative = true;
 521         }
 522
 523         retval = coredump_wait(siginfo->si_signo, &core_state);
 524         if (retval < 0)
 525                 goto fail_creds;
 526
 527         old_cred = override_creds(cred);
 528
 529         ispipe = format_corename(&cn, &cprm);
 530
 531         if (ispipe) {
 532                 int dump_count;
 533                 char **helper_argv;
 534                 struct subprocess_info *sub_info;
 535
 536                 if (ispipe < 0) {
 537                         printk(KERN_WARNING "format_corename failed\n");
 538                         printk(KERN_WARNING "Aborting core\n");
 539                         goto fail_corename;
 540                 }
 541
 542                 if (cprm.limit == 1) {
 543                         /* See umh_pipe_setup() which sets RLIMIT_CORE = 1.
 544                          *
 545                          * Normally core limits are irrelevant to pipes, since
 546                          * we're not writing to the file system, but we use
 547                          * cprm.limit of 1 here as a speacial value, this is a
 548                          * consistent way to catch recursive crashes.
 549                          * We can still crash if the core_pattern binary sets
 550                          * RLIM_CORE = !1, but it runs as root, and can do
 551                          * lots of stupid things.
 552                          *
 553                          * Note that we use task_tgid_vnr here to grab the pid
 554                          * of the process group leader.  That way we get the
 555                          * right pid if a thread in a multi-threaded
 556                          * core_pattern process dies.
 557                          */
 558                         printk(KERN_WARNING
 559                                 "Process %d(%s) has RLIMIT_CORE set to 1\n",
 560                                 task_tgid_vnr(current), current->comm);
 561                         printk(KERN_WARNING "Aborting core\n");
 562                         goto fail_unlock;
 563                 }
 564                 cprm.limit = RLIM_INFINITY;
 565
 566                 dump_count = atomic_inc_return(&core_dump_count);
 567                 if (core_pipe_limit && (core_pipe_limit < dump_count)) {
 568                         printk(KERN_WARNING "Pid %d(%s) over core_pipe_limit\n",
 569                                task_tgid_vnr(current), current->comm);
 570                         printk(KERN_WARNING "Skipping core dump\n");
 571                         goto fail_dropcount;
 572                 }
 573
 574                 helper_argv = argv_split(GFP_KERNEL, cn.corename+1, NULL);
 575                 if (!helper_argv) {
 576                         printk(KERN_WARNING "%s failed to allocate memory\n",
 577                                __func__);
 578                         goto fail_dropcount;
 579                 }
 580
 581                 retval = -ENOMEM;
 582                 sub_info = call_usermodehelper_setup(helper_argv[0],
 583                                                 helper_argv, NULL, GFP_KERNEL,
 584                                                 umh_pipe_setup, NULL, &cprm);
 585                 if (sub_info)
 586                         retval = call_usermodehelper_exec(sub_info,
 587                                                           UMH_WAIT_EXEC);
 588
 589                 argv_free(helper_argv);
 590                 if (retval) {
 591                         printk(KERN_INFO "Core dump to %s pipe failed\n",
 592                                cn.corename);
 593                         goto close_fail;
 594                 }
 595         } else {
 596                 struct inode *inode;
 597
 598                 if (cprm.limit < binfmt->min_coredump)
 599                         goto fail_unlock;
 600
 601                 if (need_nonrelative && cn.corename[0] != '/') {
 602                         printk(KERN_WARNING "Pid %d(%s) can only dump core "\
 603                                 "to fully qualified path!\n",
 604                                 task_tgid_vnr(current), current->comm);
 605                         printk(KERN_WARNING "Skipping core dump\n");
 606                         goto fail_unlock;
 607                 }
 608
 609                 cprm.file = filp_open(cn.corename,
 610                                  O_CREAT | 2 | O_NOFOLLOW | O_LARGEFILE | flag,
 611                                  0600);
 612                 if (IS_ERR(cprm.file))
 613                         goto fail_unlock;
 614
 615                 inode = file_inode(cprm.file);
 616                 if (inode->i_nlink > 1)
 617                         goto close_fail;
 618                 if (d_unhashed(cprm.file->f_path.dentry))
 619                         goto close_fail;
 620                 /*
 621                  * AK: actually i see no reason to not allow this for named
 622                  * pipes etc, but keep the previous behaviour for now.
 623                  */
 624                 if (!S_ISREG(inode->i_mode))
 625                         goto close_fail;
 626                 /*
 627                  * Dont allow local users get cute and trick others to coredump
 628                  * into their pre-created files.
 629                  */
 630                 if (!uid_eq(inode->i_uid, current_fsuid()))
 631                         goto close_fail;
 632                 if (!cprm.file->f_op || !cprm.file->f_op->write)
 633                         goto close_fail;
 634                 if (do_truncate(cprm.file->f_path.dentry, 0, 0, cprm.file))
 635                         goto close_fail;
 636         }
 637
 638         /* get us an unshared descriptor table; almost always a no-op */
 639         retval = unshare_files(&displaced);
 640         if (retval)
 641                 goto close_fail;
 642         if (displaced)
 643                 put_files_struct(displaced);
 644
 645         core_dumped = binfmt->core_dump(&cprm);
 646
 647         if (ispipe && core_pipe_limit)
 648                 wait_for_dump_helpers(cprm.file);
 649 close_fail:
 650         if (cprm.file)
 651                 filp_close(cprm.file, NULL);
 652 fail_dropcount:
 653         if (ispipe)
 654                 atomic_dec(&core_dump_count);
 655 fail_unlock:
 656         kfree(cn.corename);
 657 fail_corename:
 658         coredump_finish(mm, core_dumped);
 659         revert_creds(old_cred);
 660 fail_creds:
 661         put_cred(cred);
 662 fail:
 663         return;
 664 }
 665
 666 /*
 667  * Core dumping helper functions.  These are the only things you should
 668  * do on a core-file: use only these functions to write out all the
 669  * necessary info.
 670  */
 671 int dump_write(struct file *file, const void *addr, int nr)
 672 {
 673         return access_ok(VERIFY_READ, addr, nr) && file->f_op->write(file, addr, nr, &file->f_pos) == nr;
 674 }
 675 EXPORT_SYMBOL(dump_write);
 676
 677 int dump_seek(struct file *file, loff_t off)
 678 {
 679         int ret = 1;
 680
 681         if (file->f_op->llseek && file->f_op->llseek != no_llseek) {
 682                 if (file->f_op->llseek(file, off, SEEK_CUR) < 0)
 683                         return 0;
 684         } else {
 685                 char *buf = (char *)get_zeroed_page(GFP_KERNEL);
 686
 687                 if (!buf)
 688                         return 0;
 689                 while (off > 0) {
 690                         unsigned long n = off;
 691
 692                         if (n > PAGE_SIZE)
 693                                 n = PAGE_SIZE;
 694                         if (!dump_write(file, buf, n)) {
 695                                 ret = 0;
 696                                 break;
 697                         }
 698                         off -= n;
 699                 }
 700                 free_page((unsigned long)buf);
 701         }
 702         return ret;
 703 }
 704 EXPORT_SYMBOL(dump_seek);