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         va_list arg_copy;
  78
  79 again:
  80         free = cn->size - cn->used;
  81
  82         va_copy(arg_copy, arg);
  83         need = vsnprintf(cn->corename + cn->used, free, fmt, arg_copy);
  84         va_end(arg_copy);
  85
  86         if (need < free) {
  87                 cn->used += need;
  88                 return 0;
  89         }
  90
  91         if (!expand_corename(cn, cn->size + need - free + 1))
  92                 goto again;
  93
  94         return -ENOMEM;
  95 }
  96
  97 static int cn_printf(struct core_name *cn, const char *fmt, ...)
  98 {
  99         va_list arg;
 100         int ret;
 101
 102         va_start(arg, fmt);
 103         ret = cn_vprintf(cn, fmt, arg);
 104         va_end(arg);
 105
 106         return ret;
 107 }
 108
 109 static int cn_esc_printf(struct core_name *cn, const char *fmt, ...)
 110 {
 111         int cur = cn->used;
 112         va_list arg;
 113         int ret;
 114
 115         va_start(arg, fmt);
 116         ret = cn_vprintf(cn, fmt, arg);
 117         va_end(arg);
 118
 119         for (; cur < cn->used; ++cur) {
 120                 if (cn->corename[cur] == '/')
 121                         cn->corename[cur] = '!';
 122         }
 123         return ret;
 124 }
 125
 126 static int cn_print_exe_file(struct core_name *cn)
 127 {
 128         struct file *exe_file;
 129         char *pathbuf, *path;
 130         int ret;
 131
 132         exe_file = get_mm_exe_file(current->mm);
 133         if (!exe_file)
 134                 return cn_esc_printf(cn, "%s (path unknown)", current->comm);
 135
 136         pathbuf = kmalloc(PATH_MAX, GFP_TEMPORARY);
 137         if (!pathbuf) {
 138                 ret = -ENOMEM;
 139                 goto put_exe_file;
 140         }
 141
 142         path = d_path(&exe_file->f_path, pathbuf, PATH_MAX);
 143         if (IS_ERR(path)) {
 144                 ret = PTR_ERR(path);
 145                 goto free_buf;
 146         }
 147
 148         ret = cn_esc_printf(cn, "%s", path);
 149
 150 free_buf:
 151         kfree(pathbuf);
 152 put_exe_file:
 153         fput(exe_file);
 154         return ret;
 155 }
 156
 157 /* format_corename will inspect the pattern parameter, and output a
 158  * name into corename, which must have space for at least
 159  * CORENAME_MAX_SIZE bytes plus one byte for the zero terminator.
 160  */
 161 static int format_corename(struct core_name *cn, struct coredump_params *cprm)
 162 {
 163         const struct cred *cred = current_cred();
 164         const char *pat_ptr = core_pattern;
 165         int ispipe = (*pat_ptr == '|');
 166         int pid_in_pattern = 0;
 167         int err = 0;
 168
 169         cn->used = 0;
 170         cn->corename = NULL;
 171         if (expand_corename(cn, core_name_size))
 172                 return -ENOMEM;
 173         cn->corename[0] = '\0';
 174
 175         if (ispipe)
 176                 ++pat_ptr;
 177
 178         /* Repeat as long as we have more pattern to process and more output
 179            space */
 180         while (*pat_ptr) {
 181                 if (*pat_ptr != '%') {
 182                         err = cn_printf(cn, "%c", *pat_ptr++);
 183                 } else {
 184                         switch (*++pat_ptr) {
 185                         /* single % at the end, drop that */
 186                         case 0:
 187                                 goto out;
 188                         /* Double percent, output one percent */
 189                         case '%':
 190                                 err = cn_printf(cn, "%c", '%');
 191                                 break;
 192                         /* pid */
 193                         case 'p':
 194                                 pid_in_pattern = 1;
 195                                 err = cn_printf(cn, "%d",
 196                                               task_tgid_vnr(current));
 197                                 break;
 198                         /* global pid */
 199                         case 'P':
 200                                 err = cn_printf(cn, "%d",
 201                                               task_tgid_nr(current));
 202                                 break;
 203                         /* uid */
 204                         case 'u':
 205                                 err = cn_printf(cn, "%d", cred->uid);
 206                                 break;
 207                         /* gid */
 208                         case 'g':
 209                                 err = cn_printf(cn, "%d", cred->gid);
 210                                 break;
 211                         case 'd':
 212                                 err = cn_printf(cn, "%d",
 213                                         __get_dumpable(cprm->mm_flags));
 214                                 break;
 215                         /* signal that caused the coredump */
 216                         case 's':
 217                                 err = cn_printf(cn, "%ld", cprm->siginfo->si_signo);
 218                                 break;
 219                         /* UNIX time of coredump */
 220                         case 't': {
 221                                 struct timeval tv;
 222                                 do_gettimeofday(&tv);
 223                                 err = cn_printf(cn, "%lu", tv.tv_sec);
 224                                 break;
 225                         }
 226                         /* hostname */
 227                         case 'h':
 228                                 down_read(&uts_sem);
 229                                 err = cn_esc_printf(cn, "%s",
 230                                               utsname()->nodename);
 231                                 up_read(&uts_sem);
 232                                 break;
 233                         /* executable */
 234                         case 'e':
 235                                 err = cn_esc_printf(cn, "%s", current->comm);
 236                                 break;
 237                         case 'E':
 238                                 err = cn_print_exe_file(cn);
 239                                 break;
 240                         /* core limit size */
 241                         case 'c':
 242                                 err = cn_printf(cn, "%lu",
 243                                               rlimit(RLIMIT_CORE));
 244                                 break;
 245                         default:
 246                                 break;
 247                         }
 248                         ++pat_ptr;
 249                 }
 250
 251                 if (err)
 252                         return err;
 253         }
 254
 255 out:
 256         /* Backward compatibility with core_uses_pid:
 257          *
 258          * If core_pattern does not include a %p (as is the default)
 259          * and core_uses_pid is set, then .%pid will be appended to
 260          * the filename. Do not do this for piped commands. */
 261         if (!ispipe && !pid_in_pattern && core_uses_pid) {
 262                 err = cn_printf(cn, ".%d", task_tgid_vnr(current));
 263                 if (err)
 264                         return err;
 265         }
 266         return ispipe;
 267 }
 268
 269 static int zap_process(struct task_struct *start, int exit_code)
 270 {
 271         struct task_struct *t;
 272         int nr = 0;
 273
 274         start->signal->group_exit_code = exit_code;
 275         start->signal->group_stop_count = 0;
 276
 277         t = start;
 278         do {
 279                 task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);
 280                 if (t != current && t->mm) {
 281                         sigaddset(&t->pending.signal, SIGKILL);
 282                         signal_wake_up(t, 1);
 283                         nr++;
 284                 }
 285         } while_each_thread(start, t);
 286
 287         return nr;
 288 }
 289
 290 static int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
 291                         struct core_state *core_state, int exit_code)
 292 {
 293         struct task_struct *g, *p;
 294         unsigned long flags;
 295         int nr = -EAGAIN;
 296
 297         spin_lock_irq(&tsk->sighand->siglock);
 298         if (!signal_group_exit(tsk->signal)) {
 299                 mm->core_state = core_state;
 300                 nr = zap_process(tsk, exit_code);
 301                 tsk->signal->group_exit_task = tsk;
 302                 /* ignore all signals except SIGKILL, see prepare_signal() */
 303                 tsk->signal->flags = SIGNAL_GROUP_COREDUMP;
 304                 clear_tsk_thread_flag(tsk, TIF_SIGPENDING);
 305         }
 306         spin_unlock_irq(&tsk->sighand->siglock);
 307         if (unlikely(nr < 0))
 308                 return nr;
 309
 310         tsk->flags |= PF_DUMPCORE;
 311         if (atomic_read(&mm->mm_users) == nr + 1)
 312                 goto done;
 313         /*
 314          * We should find and kill all tasks which use this mm, and we should
 315          * count them correctly into ->nr_threads. We don't take tasklist
 316          * lock, but this is safe wrt:
 317          *
 318          * fork:
 319          *      None of sub-threads can fork after zap_process(leader). All
 320          *      processes which were created before this point should be
 321          *      visible to zap_threads() because copy_process() adds the new
 322          *      process to the tail of init_task.tasks list, and lock/unlock
 323          *      of ->siglock provides a memory barrier.
 324          *
 325          * do_exit:
 326          *      The caller holds mm->mmap_sem. This means that the task which
 327          *      uses this mm can't pass exit_mm(), so it can't exit or clear
 328          *      its ->mm.
 329          *
 330          * de_thread:
 331          *      It does list_replace_rcu(&leader->tasks, &current->tasks),
 332          *      we must see either old or new leader, this does not matter.
 333          *      However, it can change p->sighand, so lock_task_sighand(p)
 334          *      must be used. Since p->mm != NULL and we hold ->mmap_sem
 335          *      it can't fail.
 336          *
 337          *      Note also that "g" can be the old leader with ->mm == NULL
 338          *      and already unhashed and thus removed from ->thread_group.
 339          *      This is OK, __unhash_process()->list_del_rcu() does not
 340          *      clear the ->next pointer, we will find the new leader via
 341          *      next_thread().
 342          */
 343         rcu_read_lock();
 344         for_each_process(g) {
 345                 if (g == tsk->group_leader)
 346                         continue;
 347                 if (g->flags & PF_KTHREAD)
 348                         continue;
 349                 p = g;
 350                 do {
 351                         if (p->mm) {
 352                                 if (unlikely(p->mm == mm)) {
 353                                         lock_task_sighand(p, &flags);
 354                                         nr += zap_process(p, exit_code);
 355                                         p->signal->flags = SIGNAL_GROUP_EXIT;
 356                                         unlock_task_sighand(p, &flags);
 357                                 }
 358                                 break;
 359                         }
 360                 } while_each_thread(g, p);
 361         }
 362         rcu_read_unlock();
 363 done:
 364         atomic_set(&core_state->nr_threads, nr);
 365         return nr;
 366 }
 367
 368 static int coredump_wait(int exit_code, struct core_state *core_state)
 369 {
 370         struct task_struct *tsk = current;
 371         struct mm_struct *mm = tsk->mm;
 372         int core_waiters = -EBUSY;
 373
 374         init_completion(&core_state->startup);
 375         core_state->dumper.task = tsk;
 376         core_state->dumper.next = NULL;
 377
 378         down_write(&mm->mmap_sem);
 379         if (!mm->core_state)
 380                 core_waiters = zap_threads(tsk, mm, core_state, exit_code);
 381         up_write(&mm->mmap_sem);
 382
 383         if (core_waiters > 0) {
 384                 struct core_thread *ptr;
 385
 386                 wait_for_completion(&core_state->startup);
 387                 /*
 388                  * Wait for all the threads to become inactive, so that
 389                  * all the thread context (extended register state, like
 390                  * fpu etc) gets copied to the memory.
 391                  */
 392                 ptr = core_state->dumper.next;
 393                 while (ptr != NULL) {
 394                         wait_task_inactive(ptr->task, 0);
 395                         ptr = ptr->next;
 396                 }
 397         }
 398
 399         return core_waiters;
 400 }
 401
 402 static void coredump_finish(struct mm_struct *mm, bool core_dumped)
 403 {
 404         struct core_thread *curr, *next;
 405         struct task_struct *task;
 406
 407         spin_lock_irq(&current->sighand->siglock);
 408         if (core_dumped && !__fatal_signal_pending(current))
 409                 current->signal->group_exit_code |= 0x80;
 410         current->signal->group_exit_task = NULL;
 411         current->signal->flags = SIGNAL_GROUP_EXIT;
 412         spin_unlock_irq(&current->sighand->siglock);
 413
 414         next = mm->core_state->dumper.next;
 415         while ((curr = next) != NULL) {
 416                 next = curr->next;
 417                 task = curr->task;
 418                 /*
 419                  * see exit_mm(), curr->task must not see
 420                  * ->task == NULL before we read ->next.
 421                  */
 422                 smp_mb();
 423                 curr->task = NULL;
 424                 wake_up_process(task);
 425         }
 426
 427         mm->core_state = NULL;
 428 }
 429
 430 static bool dump_interrupted(void)
 431 {
 432         /*
 433          * SIGKILL or freezing() interrupt the coredumping. Perhaps we
 434          * can do try_to_freeze() and check __fatal_signal_pending(),
 435          * but then we need to teach dump_write() to restart and clear
 436          * TIF_SIGPENDING.
 437          */
 438         return signal_pending(current);
 439 }
 440
 441 static void wait_for_dump_helpers(struct file *file)
 442 {
 443         struct pipe_inode_info *pipe = file->private_data;
 444
 445         pipe_lock(pipe);
 446         pipe->readers++;
 447         pipe->writers--;
 448         wake_up_interruptible_sync(&pipe->wait);
 449         kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
 450         pipe_unlock(pipe);
 451
 452         /*
 453          * We actually want wait_event_freezable() but then we need
 454          * to clear TIF_SIGPENDING and improve dump_interrupted().
 455          */
 456         wait_event_interruptible(pipe->wait, pipe->readers == 1);
 457
 458         pipe_lock(pipe);
 459         pipe->readers--;
 460         pipe->writers++;
 461         pipe_unlock(pipe);
 462 }
 463
 464 /*
 465  * umh_pipe_setup
 466  * helper function to customize the process used
 467  * to collect the core in userspace.  Specifically
 468  * it sets up a pipe and installs it as fd 0 (stdin)
 469  * for the process.  Returns 0 on success, or
 470  * PTR_ERR on failure.
 471  * Note that it also sets the core limit to 1.  This
 472  * is a special value that we use to trap recursive
 473  * core dumps
 474  */
 475 static int umh_pipe_setup(struct subprocess_info *info, struct cred *new)
 476 {
 477         struct file *files[2];
 478         struct coredump_params *cp = (struct coredump_params *)info->data;
 479         int err = create_pipe_files(files, 0);
 480         if (err)
 481                 return err;
 482
 483         cp->file = files[1];
 484
 485         err = replace_fd(0, files[0], 0);
 486         fput(files[0]);
 487         /* and disallow core files too */
 488         current->signal->rlim[RLIMIT_CORE] = (struct rlimit){1, 1};
 489
 490         return err;
 491 }
 492
 493 void do_coredump(siginfo_t *siginfo)
 494 {
 495         struct core_state core_state;
 496         struct core_name cn;
 497         struct mm_struct *mm = current->mm;
 498         struct linux_binfmt * binfmt;
 499         const struct cred *old_cred;
 500         struct cred *cred;
 501         int retval = 0;
 502         int flag = 0;
 503         int ispipe;
 504         struct files_struct *displaced;
 505         bool need_nonrelative = false;
 506         bool core_dumped = false;
 507         static atomic_t core_dump_count = ATOMIC_INIT(0);
 508         struct coredump_params cprm = {
 509                 .siginfo = siginfo,
 510                 .regs = signal_pt_regs(),
 511                 .limit = rlimit(RLIMIT_CORE),
 512                 /*
 513                  * We must use the same mm->flags while dumping core to avoid
 514                  * inconsistency of bit flags, since this flag is not protected
 515                  * by any locks.
 516                  */
 517                 .mm_flags = mm->flags,
 518         };
 519
 520         audit_core_dumps(siginfo->si_signo);
 521
 522         binfmt = mm->binfmt;
 523         if (!binfmt || !binfmt->core_dump)
 524                 goto fail;
 525         if (!__get_dumpable(cprm.mm_flags))
 526                 goto fail;
 527
 528         cred = prepare_creds();
 529         if (!cred)
 530                 goto fail;
 531         /*
 532          * We cannot trust fsuid as being the "true" uid of the process
 533          * nor do we know its entire history. We only know it was tainted
 534          * so we dump it as root in mode 2, and only into a controlled
 535          * environment (pipe handler or fully qualified path).
 536          */
 537         if (__get_dumpable(cprm.mm_flags) == SUID_DUMP_ROOT) {
 538                 /* Setuid core dump mode */
 539                 flag = O_EXCL;          /* Stop rewrite attacks */
 540                 cred->fsuid = GLOBAL_ROOT_UID;  /* Dump root private */
 541                 need_nonrelative = true;
 542         }
 543
 544         retval = coredump_wait(siginfo->si_signo, &core_state);
 545         if (retval < 0)
 546                 goto fail_creds;
 547
 548         old_cred = override_creds(cred);
 549
 550         ispipe = format_corename(&cn, &cprm);
 551
 552         if (ispipe) {
 553                 int dump_count;
 554                 char **helper_argv;
 555                 struct subprocess_info *sub_info;
 556
 557                 if (ispipe < 0) {
 558                         printk(KERN_WARNING "format_corename failed\n");
 559                         printk(KERN_WARNING "Aborting core\n");
 560                         goto fail_unlock;
 561                 }
 562
 563                 if (cprm.limit == 1) {
 564                         /* See umh_pipe_setup() which sets RLIMIT_CORE = 1.
 565                          *
 566                          * Normally core limits are irrelevant to pipes, since
 567                          * we're not writing to the file system, but we use
 568                          * cprm.limit of 1 here as a speacial value, this is a
 569                          * consistent way to catch recursive crashes.
 570                          * We can still crash if the core_pattern binary sets
 571                          * RLIM_CORE = !1, but it runs as root, and can do
 572                          * lots of stupid things.
 573                          *
 574                          * Note that we use task_tgid_vnr here to grab the pid
 575                          * of the process group leader.  That way we get the
 576                          * right pid if a thread in a multi-threaded
 577                          * core_pattern process dies.
 578                          */
 579                         printk(KERN_WARNING
 580                                 "Process %d(%s) has RLIMIT_CORE set to 1\n",
 581                                 task_tgid_vnr(current), current->comm);
 582                         printk(KERN_WARNING "Aborting core\n");
 583                         goto fail_unlock;
 584                 }
 585                 cprm.limit = RLIM_INFINITY;
 586
 587                 dump_count = atomic_inc_return(&core_dump_count);
 588                 if (core_pipe_limit && (core_pipe_limit < dump_count)) {
 589                         printk(KERN_WARNING "Pid %d(%s) over core_pipe_limit\n",
 590                                task_tgid_vnr(current), current->comm);
 591                         printk(KERN_WARNING "Skipping core dump\n");
 592                         goto fail_dropcount;
 593                 }
 594
 595                 helper_argv = argv_split(GFP_KERNEL, cn.corename, NULL);
 596                 if (!helper_argv) {
 597                         printk(KERN_WARNING "%s failed to allocate memory\n",
 598                                __func__);
 599                         goto fail_dropcount;
 600                 }
 601
 602                 retval = -ENOMEM;
 603                 sub_info = call_usermodehelper_setup(helper_argv[0],
 604                                                 helper_argv, NULL, GFP_KERNEL,
 605                                                 umh_pipe_setup, NULL, &cprm);
 606                 if (sub_info)
 607                         retval = call_usermodehelper_exec(sub_info,
 608                                                           UMH_WAIT_EXEC);
 609
 610                 argv_free(helper_argv);
 611                 if (retval) {
 612                         printk(KERN_INFO "Core dump to |%s pipe failed\n",
 613                                cn.corename);
 614                         goto close_fail;
 615                 }
 616         } else {
 617                 struct inode *inode;
 618
 619                 if (cprm.limit < binfmt->min_coredump)
 620                         goto fail_unlock;
 621
 622                 if (need_nonrelative && cn.corename[0] != '/') {
 623                         printk(KERN_WARNING "Pid %d(%s) can only dump core "\
 624                                 "to fully qualified path!\n",
 625                                 task_tgid_vnr(current), current->comm);
 626                         printk(KERN_WARNING "Skipping core dump\n");
 627                         goto fail_unlock;
 628                 }
 629
 630                 cprm.file = filp_open(cn.corename,
 631                                  O_CREAT | 2 | O_NOFOLLOW | O_LARGEFILE | flag,
 632                                  0600);
 633                 if (IS_ERR(cprm.file))
 634                         goto fail_unlock;
 635
 636                 inode = file_inode(cprm.file);
 637                 if (inode->i_nlink > 1)
 638                         goto close_fail;
 639                 if (d_unhashed(cprm.file->f_path.dentry))
 640                         goto close_fail;
 641                 /*
 642                  * AK: actually i see no reason to not allow this for named
 643                  * pipes etc, but keep the previous behaviour for now.
 644                  */
 645                 if (!S_ISREG(inode->i_mode))
 646                         goto close_fail;
 647                 /*
 648                  * Dont allow local users get cute and trick others to coredump
 649                  * into their pre-created files.
 650                  */
 651                 if (!uid_eq(inode->i_uid, current_fsuid()))
 652                         goto close_fail;
 653                 if (!cprm.file->f_op || !cprm.file->f_op->write)
 654                         goto close_fail;
 655                 if (do_truncate(cprm.file->f_path.dentry, 0, 0, cprm.file))
 656                         goto close_fail;
 657         }
 658
 659         /* get us an unshared descriptor table; almost always a no-op */
 660         retval = unshare_files(&displaced);
 661         if (retval)
 662                 goto close_fail;
 663         if (displaced)
 664                 put_files_struct(displaced);
 665         if (!dump_interrupted()) {
 666                 file_start_write(cprm.file);
 667                 core_dumped = binfmt->core_dump(&cprm);
 668                 file_end_write(cprm.file);
 669         }
 670         if (ispipe && core_pipe_limit)
 671                 wait_for_dump_helpers(cprm.file);
 672 close_fail:
 673         if (cprm.file)
 674                 filp_close(cprm.file, NULL);
 675 fail_dropcount:
 676         if (ispipe)
 677                 atomic_dec(&core_dump_count);
 678 fail_unlock:
 679         kfree(cn.corename);
 680         coredump_finish(mm, core_dumped);
 681         revert_creds(old_cred);
 682 fail_creds:
 683         put_cred(cred);
 684 fail:
 685         return;
 686 }
 687
 688 /*
 689  * Core dumping helper functions.  These are the only things you should
 690  * do on a core-file: use only these functions to write out all the
 691  * necessary info.
 692  */
 693 int dump_write(struct file *file, const void *addr, int nr)
 694 {
 695         return !dump_interrupted() &&
 696                 access_ok(VERIFY_READ, addr, nr) &&
 697                 file->f_op->write(file, addr, nr, &file->f_pos) == nr;
 698 }
 699 EXPORT_SYMBOL(dump_write);
 700
 701 int dump_seek(struct file *file, loff_t off)
 702 {
 703         int ret = 1;
 704
 705         if (file->f_op->llseek && file->f_op->llseek != no_llseek) {
 706                 if (dump_interrupted() ||
 707                     file->f_op->llseek(file, off, SEEK_CUR) < 0)
 708                         return 0;
 709         } else {
 710                 char *buf = (char *)get_zeroed_page(GFP_KERNEL);
 711
 712                 if (!buf)
 713                         return 0;
 714                 while (off > 0) {
 715                         unsigned long n = off;
 716
 717                         if (n > PAGE_SIZE)
 718                                 n = PAGE_SIZE;
 719                         if (!dump_write(file, buf, n)) {
 720                                 ret = 0;
 721                                 break;
 722                         }
 723                         off -= n;
 724                 }
 725                 free_page((unsigned long)buf);
 726         }
 727         return ret;
 728 }
 729 EXPORT_SYMBOL(dump_seek);