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
  44 #include <trace/events/sched.h>
  45
  46 int core_uses_pid;
  47 unsigned int core_pipe_limit;
  48 char core_pattern[CORENAME_MAX_SIZE] = "core";
  49 static int core_name_size = CORENAME_MAX_SIZE;
  50
  51 struct core_name {
  52         char *corename;
  53         int used, size;
  54 };
  55
  56 /* The maximal length of core_pattern is also specified in sysctl.c */
  57
  58 static int expand_corename(struct core_name *cn, int size)
  59 {
  60         char *corename = krealloc(cn->corename, size, GFP_KERNEL);
  61
  62         if (!corename)
  63                 return -ENOMEM;
  64
  65         if (size > core_name_size) /* racy but harmless */
  66                 core_name_size = size;
  67
  68         cn->size = ksize(corename);
  69         cn->corename = corename;
  70         return 0;
  71 }
  72
  73 static int cn_vprintf(struct core_name *cn, const char *fmt, va_list arg)
  74 {
  75         int free, need;
  76         va_list arg_copy;
  77
  78 again:
  79         free = cn->size - cn->used;
  80
  81         va_copy(arg_copy, arg);
  82         need = vsnprintf(cn->corename + cn->used, free, fmt, arg_copy);
  83         va_end(arg_copy);
  84
  85         if (need < free) {
  86                 cn->used += need;
  87                 return 0;
  88         }
  89
  90         if (!expand_corename(cn, cn->size + need - free + 1))
  91                 goto again;
  92
  93         return -ENOMEM;
  94 }
  95
  96 static int cn_printf(struct core_name *cn, const char *fmt, ...)
  97 {
  98         va_list arg;
  99         int ret;
 100
 101         va_start(arg, fmt);
 102         ret = cn_vprintf(cn, fmt, arg);
 103         va_end(arg);
 104
 105         return ret;
 106 }
 107
 108 static int cn_esc_printf(struct core_name *cn, const char *fmt, ...)
 109 {
 110         int cur = cn->used;
 111         va_list arg;
 112         int ret;
 113
 114         va_start(arg, fmt);
 115         ret = cn_vprintf(cn, fmt, arg);
 116         va_end(arg);
 117
 118         for (; cur < cn->used; ++cur) {
 119                 if (cn->corename[cur] == '/')
 120                         cn->corename[cur] = '!';
 121         }
 122         return ret;
 123 }
 124
 125 static int cn_print_exe_file(struct core_name *cn)
 126 {
 127         struct file *exe_file;
 128         char *pathbuf, *path;
 129         int ret;
 130
 131         exe_file = get_mm_exe_file(current->mm);
 132         if (!exe_file)
 133                 return cn_esc_printf(cn, "%s (path unknown)", current->comm);
 134
 135         pathbuf = kmalloc(PATH_MAX, GFP_TEMPORARY);
 136         if (!pathbuf) {
 137                 ret = -ENOMEM;
 138                 goto put_exe_file;
 139         }
 140
 141         path = d_path(&exe_file->f_path, pathbuf, PATH_MAX);
 142         if (IS_ERR(path)) {
 143                 ret = PTR_ERR(path);
 144                 goto free_buf;
 145         }
 146
 147         ret = cn_esc_printf(cn, "%s", path);
 148
 149 free_buf:
 150         kfree(pathbuf);
 151 put_exe_file:
 152         fput(exe_file);
 153         return ret;
 154 }
 155
 156 /* format_corename will inspect the pattern parameter, and output a
 157  * name into corename, which must have space for at least
 158  * CORENAME_MAX_SIZE bytes plus one byte for the zero terminator.
 159  */
 160 static int format_corename(struct core_name *cn, struct coredump_params *cprm)
 161 {
 162         const struct cred *cred = current_cred();
 163         const char *pat_ptr = core_pattern;
 164         int ispipe = (*pat_ptr == '|');
 165         int pid_in_pattern = 0;
 166         int err = 0;
 167
 168         cn->used = 0;
 169         cn->corename = NULL;
 170         if (expand_corename(cn, core_name_size))
 171                 return -ENOMEM;
 172         cn->corename[0] = '\0';
 173
 174         if (ispipe)
 175                 ++pat_ptr;
 176
 177         /* Repeat as long as we have more pattern to process and more output
 178            space */
 179         while (*pat_ptr) {
 180                 if (*pat_ptr != '%') {
 181                         err = cn_printf(cn, "%c", *pat_ptr++);
 182                 } else {
 183                         switch (*++pat_ptr) {
 184                         /* single % at the end, drop that */
 185                         case 0:
 186                                 goto out;
 187                         /* Double percent, output one percent */
 188                         case '%':
 189                                 err = cn_printf(cn, "%c", '%');
 190                                 break;
 191                         /* pid */
 192                         case 'p':
 193                                 pid_in_pattern = 1;
 194                                 err = cn_printf(cn, "%d",
 195                                               task_tgid_vnr(current));
 196                                 break;
 197                         /* global pid */
 198                         case 'P':
 199                                 err = cn_printf(cn, "%d",
 200                                               task_tgid_nr(current));
 201                                 break;
 202                         case 'i':
 203                                 err = cn_printf(cn, "%d",
 204                                               task_pid_vnr(current));
 205                                 break;
 206                         case 'I':
 207                                 err = cn_printf(cn, "%d",
 208                                               task_pid_nr(current));
 209                                 break;
 210                         /* uid */
 211                         case 'u':
 212                                 err = cn_printf(cn, "%d", cred->uid);
 213                                 break;
 214                         /* gid */
 215                         case 'g':
 216                                 err = cn_printf(cn, "%d", cred->gid);
 217                                 break;
 218                         case 'd':
 219                                 err = cn_printf(cn, "%d",
 220                                         __get_dumpable(cprm->mm_flags));
 221                                 break;
 222                         /* signal that caused the coredump */
 223                         case 's':
 224                                 err = cn_printf(cn, "%ld", cprm->siginfo->si_signo);
 225                                 break;
 226                         /* UNIX time of coredump */
 227                         case 't': {
 228                                 struct timeval tv;
 229                                 do_gettimeofday(&tv);
 230                                 err = cn_printf(cn, "%lu", tv.tv_sec);
 231                                 break;
 232                         }
 233                         /* hostname */
 234                         case 'h':
 235                                 down_read(&uts_sem);
 236                                 err = cn_esc_printf(cn, "%s",
 237                                               utsname()->nodename);
 238                                 up_read(&uts_sem);
 239                                 break;
 240                         /* executable */
 241                         case 'e':
 242                                 err = cn_esc_printf(cn, "%s", current->comm);
 243                                 break;
 244                         case 'E':
 245                                 err = cn_print_exe_file(cn);
 246                                 break;
 247                         /* core limit size */
 248                         case 'c':
 249                                 err = cn_printf(cn, "%lu",
 250                                               rlimit(RLIMIT_CORE));
 251                                 break;
 252                         default:
 253                                 break;
 254                         }
 255                         ++pat_ptr;
 256                 }
 257
 258                 if (err)
 259                         return err;
 260         }
 261
 262 out:
 263         /* Backward compatibility with core_uses_pid:
 264          *
 265          * If core_pattern does not include a %p (as is the default)
 266          * and core_uses_pid is set, then .%pid will be appended to
 267          * the filename. Do not do this for piped commands. */
 268         if (!ispipe && !pid_in_pattern && core_uses_pid) {
 269                 err = cn_printf(cn, ".%d", task_tgid_vnr(current));
 270                 if (err)
 271                         return err;
 272         }
 273         return ispipe;
 274 }
 275
 276 static int zap_process(struct task_struct *start, int exit_code)
 277 {
 278         struct task_struct *t;
 279         int nr = 0;
 280
 281         start->signal->group_exit_code = exit_code;
 282         start->signal->group_stop_count = 0;
 283
 284         t = start;
 285         do {
 286                 task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);
 287                 if (t != current && t->mm) {
 288                         sigaddset(&t->pending.signal, SIGKILL);
 289                         signal_wake_up(t, 1);
 290                         nr++;
 291                 }
 292         } while_each_thread(start, t);
 293
 294         return nr;
 295 }
 296
 297 static int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
 298                         struct core_state *core_state, int exit_code)
 299 {
 300         struct task_struct *g, *p;
 301         unsigned long flags;
 302         int nr = -EAGAIN;
 303
 304         spin_lock_irq(&tsk->sighand->siglock);
 305         if (!signal_group_exit(tsk->signal)) {
 306                 mm->core_state = core_state;
 307                 nr = zap_process(tsk, exit_code);
 308                 tsk->signal->group_exit_task = tsk;
 309                 /* ignore all signals except SIGKILL, see prepare_signal() */
 310                 tsk->signal->flags = SIGNAL_GROUP_COREDUMP;
 311                 clear_tsk_thread_flag(tsk, TIF_SIGPENDING);
 312         }
 313         spin_unlock_irq(&tsk->sighand->siglock);
 314         if (unlikely(nr < 0))
 315                 return nr;
 316
 317         tsk->flags |= PF_DUMPCORE;
 318         if (atomic_read(&mm->mm_users) == nr + 1)
 319                 goto done;
 320         /*
 321          * We should find and kill all tasks which use this mm, and we should
 322          * count them correctly into ->nr_threads. We don't take tasklist
 323          * lock, but this is safe wrt:
 324          *
 325          * fork:
 326          *      None of sub-threads can fork after zap_process(leader). All
 327          *      processes which were created before this point should be
 328          *      visible to zap_threads() because copy_process() adds the new
 329          *      process to the tail of init_task.tasks list, and lock/unlock
 330          *      of ->siglock provides a memory barrier.
 331          *
 332          * do_exit:
 333          *      The caller holds mm->mmap_sem. This means that the task which
 334          *      uses this mm can't pass exit_mm(), so it can't exit or clear
 335          *      its ->mm.
 336          *
 337          * de_thread:
 338          *      It does list_replace_rcu(&leader->tasks, &current->tasks),
 339          *      we must see either old or new leader, this does not matter.
 340          *      However, it can change p->sighand, so lock_task_sighand(p)
 341          *      must be used. Since p->mm != NULL and we hold ->mmap_sem
 342          *      it can't fail.
 343          *
 344          *      Note also that "g" can be the old leader with ->mm == NULL
 345          *      and already unhashed and thus removed from ->thread_group.
 346          *      This is OK, __unhash_process()->list_del_rcu() does not
 347          *      clear the ->next pointer, we will find the new leader via
 348          *      next_thread().
 349          */
 350         rcu_read_lock();
 351         for_each_process(g) {
 352                 if (g == tsk->group_leader)
 353                         continue;
 354                 if (g->flags & PF_KTHREAD)
 355                         continue;
 356                 p = g;
 357                 do {
 358                         if (p->mm) {
 359                                 if (unlikely(p->mm == mm)) {
 360                                         lock_task_sighand(p, &flags);
 361                                         nr += zap_process(p, exit_code);
 362                                         p->signal->flags = SIGNAL_GROUP_EXIT;
 363                                         unlock_task_sighand(p, &flags);
 364                                 }
 365                                 break;
 366                         }
 367                 } while_each_thread(g, p);
 368         }
 369         rcu_read_unlock();
 370 done:
 371         atomic_set(&core_state->nr_threads, nr);
 372         return nr;
 373 }
 374
 375 static int coredump_wait(int exit_code, struct core_state *core_state)
 376 {
 377         struct task_struct *tsk = current;
 378         struct mm_struct *mm = tsk->mm;
 379         int core_waiters = -EBUSY;
 380
 381         init_completion(&core_state->startup);
 382         core_state->dumper.task = tsk;
 383         core_state->dumper.next = NULL;
 384
 385         down_write(&mm->mmap_sem);
 386         if (!mm->core_state)
 387                 core_waiters = zap_threads(tsk, mm, core_state, exit_code);
 388         up_write(&mm->mmap_sem);
 389
 390         if (core_waiters > 0) {
 391                 struct core_thread *ptr;
 392
 393                 wait_for_completion(&core_state->startup);
 394                 /*
 395                  * Wait for all the threads to become inactive, so that
 396                  * all the thread context (extended register state, like
 397                  * fpu etc) gets copied to the memory.
 398                  */
 399                 ptr = core_state->dumper.next;
 400                 while (ptr != NULL) {
 401                         wait_task_inactive(ptr->task, 0);
 402                         ptr = ptr->next;
 403                 }
 404         }
 405
 406         return core_waiters;
 407 }
 408
 409 static void coredump_finish(struct mm_struct *mm, bool core_dumped)
 410 {
 411         struct core_thread *curr, *next;
 412         struct task_struct *task;
 413
 414         spin_lock_irq(&current->sighand->siglock);
 415         if (core_dumped && !__fatal_signal_pending(current))
 416                 current->signal->group_exit_code |= 0x80;
 417         current->signal->group_exit_task = NULL;
 418         current->signal->flags = SIGNAL_GROUP_EXIT;
 419         spin_unlock_irq(&current->sighand->siglock);
 420
 421         next = mm->core_state->dumper.next;
 422         while ((curr = next) != NULL) {
 423                 next = curr->next;
 424                 task = curr->task;
 425                 /*
 426                  * see exit_mm(), curr->task must not see
 427                  * ->task == NULL before we read ->next.
 428                  */
 429                 smp_mb();
 430                 curr->task = NULL;
 431                 wake_up_process(task);
 432         }
 433
 434         mm->core_state = NULL;
 435 }
 436
 437 static bool dump_interrupted(void)
 438 {
 439         /*
 440          * SIGKILL or freezing() interrupt the coredumping. Perhaps we
 441          * can do try_to_freeze() and check __fatal_signal_pending(),
 442          * but then we need to teach dump_write() to restart and clear
 443          * TIF_SIGPENDING.
 444          */
 445         return signal_pending(current);
 446 }
 447
 448 static void wait_for_dump_helpers(struct file *file)
 449 {
 450         struct pipe_inode_info *pipe = file->private_data;
 451
 452         pipe_lock(pipe);
 453         pipe->readers++;
 454         pipe->writers--;
 455         wake_up_interruptible_sync(&pipe->wait);
 456         kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
 457         pipe_unlock(pipe);
 458
 459         /*
 460          * We actually want wait_event_freezable() but then we need
 461          * to clear TIF_SIGPENDING and improve dump_interrupted().
 462          */
 463         wait_event_interruptible(pipe->wait, pipe->readers == 1);
 464
 465         pipe_lock(pipe);
 466         pipe->readers--;
 467         pipe->writers++;
 468         pipe_unlock(pipe);
 469 }
 470
 471 /*
 472  * umh_pipe_setup
 473  * helper function to customize the process used
 474  * to collect the core in userspace.  Specifically
 475  * it sets up a pipe and installs it as fd 0 (stdin)
 476  * for the process.  Returns 0 on success, or
 477  * PTR_ERR on failure.
 478  * Note that it also sets the core limit to 1.  This
 479  * is a special value that we use to trap recursive
 480  * core dumps
 481  */
 482 static int umh_pipe_setup(struct subprocess_info *info, struct cred *new)
 483 {
 484         struct file *files[2];
 485         struct coredump_params *cp = (struct coredump_params *)info->data;
 486         int err = create_pipe_files(files, 0);
 487         if (err)
 488                 return err;
 489
 490         cp->file = files[1];
 491
 492         err = replace_fd(0, files[0], 0);
 493         fput(files[0]);
 494         /* and disallow core files too */
 495         current->signal->rlim[RLIMIT_CORE] = (struct rlimit){1, 1};
 496
 497         return err;
 498 }
 499
 500 void do_coredump(const siginfo_t *siginfo)
 501 {
 502         struct core_state core_state;
 503         struct core_name cn;
 504         struct mm_struct *mm = current->mm;
 505         struct linux_binfmt * binfmt;
 506         const struct cred *old_cred;
 507         struct cred *cred;
 508         int retval = 0;
 509         int flag = 0;
 510         int ispipe;
 511         struct files_struct *displaced;
 512         bool need_nonrelative = false;
 513         bool core_dumped = false;
 514         static atomic_t core_dump_count = ATOMIC_INIT(0);
 515         struct coredump_params cprm = {
 516                 .siginfo = siginfo,
 517                 .regs = signal_pt_regs(),
 518                 .limit = rlimit(RLIMIT_CORE),
 519                 /*
 520                  * We must use the same mm->flags while dumping core to avoid
 521                  * inconsistency of bit flags, since this flag is not protected
 522                  * by any locks.
 523                  */
 524                 .mm_flags = mm->flags,
 525         };
 526
 527         audit_core_dumps(siginfo->si_signo);
 528
 529         binfmt = mm->binfmt;
 530         if (!binfmt || !binfmt->core_dump)
 531                 goto fail;
 532         if (!__get_dumpable(cprm.mm_flags))
 533                 goto fail;
 534
 535         cred = prepare_creds();
 536         if (!cred)
 537                 goto fail;
 538         /*
 539          * We cannot trust fsuid as being the "true" uid of the process
 540          * nor do we know its entire history. We only know it was tainted
 541          * so we dump it as root in mode 2, and only into a controlled
 542          * environment (pipe handler or fully qualified path).
 543          */
 544         if (__get_dumpable(cprm.mm_flags) == SUID_DUMP_ROOT) {
 545                 /* Setuid core dump mode */
 546                 flag = O_EXCL;          /* Stop rewrite attacks */
 547                 cred->fsuid = GLOBAL_ROOT_UID;  /* Dump root private */
 548                 need_nonrelative = true;
 549         }
 550
 551         retval = coredump_wait(siginfo->si_signo, &core_state);
 552         if (retval < 0)
 553                 goto fail_creds;
 554
 555         old_cred = override_creds(cred);
 556
 557         ispipe = format_corename(&cn, &cprm);
 558
 559         if (ispipe) {
 560                 int dump_count;
 561                 char **helper_argv;
 562                 struct subprocess_info *sub_info;
 563
 564                 if (ispipe < 0) {
 565                         printk(KERN_WARNING "format_corename failed\n");
 566                         printk(KERN_WARNING "Aborting core\n");
 567                         goto fail_unlock;
 568                 }
 569
 570                 if (cprm.limit == 1) {
 571                         /* See umh_pipe_setup() which sets RLIMIT_CORE = 1.
 572                          *
 573                          * Normally core limits are irrelevant to pipes, since
 574                          * we're not writing to the file system, but we use
 575                          * cprm.limit of 1 here as a speacial value, this is a
 576                          * consistent way to catch recursive crashes.
 577                          * We can still crash if the core_pattern binary sets
 578                          * RLIM_CORE = !1, but it runs as root, and can do
 579                          * lots of stupid things.
 580                          *
 581                          * Note that we use task_tgid_vnr here to grab the pid
 582                          * of the process group leader.  That way we get the
 583                          * right pid if a thread in a multi-threaded
 584                          * core_pattern process dies.
 585                          */
 586                         printk(KERN_WARNING
 587                                 "Process %d(%s) has RLIMIT_CORE set to 1\n",
 588                                 task_tgid_vnr(current), current->comm);
 589                         printk(KERN_WARNING "Aborting core\n");
 590                         goto fail_unlock;
 591                 }
 592                 cprm.limit = RLIM_INFINITY;
 593
 594                 dump_count = atomic_inc_return(&core_dump_count);
 595                 if (core_pipe_limit && (core_pipe_limit < dump_count)) {
 596                         printk(KERN_WARNING "Pid %d(%s) over core_pipe_limit\n",
 597                                task_tgid_vnr(current), current->comm);
 598                         printk(KERN_WARNING "Skipping core dump\n");
 599                         goto fail_dropcount;
 600                 }
 601
 602                 helper_argv = argv_split(GFP_KERNEL, cn.corename, NULL);
 603                 if (!helper_argv) {
 604                         printk(KERN_WARNING "%s failed to allocate memory\n",
 605                                __func__);
 606                         goto fail_dropcount;
 607                 }
 608
 609                 retval = -ENOMEM;
 610                 sub_info = call_usermodehelper_setup(helper_argv[0],
 611                                                 helper_argv, NULL, GFP_KERNEL,
 612                                                 umh_pipe_setup, NULL, &cprm);
 613                 if (sub_info)
 614                         retval = call_usermodehelper_exec(sub_info,
 615                                                           UMH_WAIT_EXEC);
 616
 617                 argv_free(helper_argv);
 618                 if (retval) {
 619                         printk(KERN_INFO "Core dump to |%s pipe failed\n",
 620                                cn.corename);
 621                         goto close_fail;
 622                 }
 623         } else {
 624                 struct inode *inode;
 625
 626                 if (cprm.limit < binfmt->min_coredump)
 627                         goto fail_unlock;
 628
 629                 if (need_nonrelative && cn.corename[0] != '/') {
 630                         printk(KERN_WARNING "Pid %d(%s) can only dump core "\
 631                                 "to fully qualified path!\n",
 632                                 task_tgid_vnr(current), current->comm);
 633                         printk(KERN_WARNING "Skipping core dump\n");
 634                         goto fail_unlock;
 635                 }
 636
 637                 cprm.file = filp_open(cn.corename,
 638                                  O_CREAT | 2 | O_NOFOLLOW | O_LARGEFILE | flag,
 639                                  0600);
 640                 if (IS_ERR(cprm.file))
 641                         goto fail_unlock;
 642
 643                 inode = file_inode(cprm.file);
 644                 if (inode->i_nlink > 1)
 645                         goto close_fail;
 646                 if (d_unhashed(cprm.file->f_path.dentry))
 647                         goto close_fail;
 648                 /*
 649                  * AK: actually i see no reason to not allow this for named
 650                  * pipes etc, but keep the previous behaviour for now.
 651                  */
 652                 if (!S_ISREG(inode->i_mode))
 653                         goto close_fail;
 654                 /*
 655                  * Dont allow local users get cute and trick others to coredump
 656                  * into their pre-created files.
 657                  */
 658                 if (!uid_eq(inode->i_uid, current_fsuid()))
 659                         goto close_fail;
 660                 if (!cprm.file->f_op->write)
 661                         goto close_fail;
 662                 if (do_truncate(cprm.file->f_path.dentry, 0, 0, cprm.file))
 663                         goto close_fail;
 664         }
 665
 666         /* get us an unshared descriptor table; almost always a no-op */
 667         retval = unshare_files(&displaced);
 668         if (retval)
 669                 goto close_fail;
 670         if (displaced)
 671                 put_files_struct(displaced);
 672         if (!dump_interrupted()) {
 673                 file_start_write(cprm.file);
 674                 core_dumped = binfmt->core_dump(&cprm);
 675                 file_end_write(cprm.file);
 676         }
 677         if (ispipe && core_pipe_limit)
 678                 wait_for_dump_helpers(cprm.file);
 679 close_fail:
 680         if (cprm.file)
 681                 filp_close(cprm.file, NULL);
 682 fail_dropcount:
 683         if (ispipe)
 684                 atomic_dec(&core_dump_count);
 685 fail_unlock:
 686         kfree(cn.corename);
 687         coredump_finish(mm, core_dumped);
 688         revert_creds(old_cred);
 689 fail_creds:
 690         put_cred(cred);
 691 fail:
 692         return;
 693 }
 694
 695 /*
 696  * Core dumping helper functions.  These are the only things you should
 697  * do on a core-file: use only these functions to write out all the
 698  * necessary info.
 699  */
 700 int dump_emit(struct coredump_params *cprm, const void *addr, int nr)
 701 {
 702         struct file *file = cprm->file;
 703         loff_t pos = file->f_pos;
 704         ssize_t n;
 705         if (cprm->written + nr > cprm->limit)
 706                 return 0;
 707         while (nr) {
 708                 if (dump_interrupted())
 709                         return 0;
 710                 n = __kernel_write(file, addr, nr, &pos);
 711                 if (n <= 0)
 712                         return 0;
 713                 file->f_pos = pos;
 714                 cprm->written += n;
 715                 nr -= n;
 716         }
 717         return 1;
 718 }
 719 EXPORT_SYMBOL(dump_emit);
 720
 721 int dump_skip(struct coredump_params *cprm, size_t nr)
 722 {
 723         static char zeroes[PAGE_SIZE];
 724         struct file *file = cprm->file;
 725         if (file->f_op->llseek && file->f_op->llseek != no_llseek) {
 726                 if (cprm->written + nr > cprm->limit)
 727                         return 0;
 728                 if (dump_interrupted() ||
 729                     file->f_op->llseek(file, nr, SEEK_CUR) < 0)
 730                         return 0;
 731                 cprm->written += nr;
 732                 return 1;
 733         } else {
 734                 while (nr > PAGE_SIZE) {
 735                         if (!dump_emit(cprm, zeroes, PAGE_SIZE))
 736                                 return 0;
 737                         nr -= PAGE_SIZE;
 738                 }
 739                 return dump_emit(cprm, zeroes, nr);
 740         }
 741 }
 742 EXPORT_SYMBOL(dump_skip);
 743
 744 int dump_align(struct coredump_params *cprm, int align)
 745 {
 746         unsigned mod = cprm->written & (align - 1);
 747         if (align & (align - 1))
 748                 return 0;
 749         return mod ? dump_skip(cprm, align - mod) : 1;
 750 }
 751 EXPORT_SYMBOL(dump_align);