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 #include <linux/sched.h>
  36 #include <linux/fs.h>
  37 #include <linux/path.h>
  38 #include <linux/timekeeping.h>
  39
  40 #include <asm/uaccess.h>
  41 #include <asm/mmu_context.h>
  42 #include <asm/tlb.h>
  43 #include <asm/exec.h>
  44
  45 #include <trace/events/task.h>
  46 #include "internal.h"
  47
  48 #include <trace/events/sched.h>
  49
  50 int core_uses_pid;
  51 unsigned int core_pipe_limit;
  52 char core_pattern[CORENAME_MAX_SIZE] = "core";
  53 static int core_name_size = CORENAME_MAX_SIZE;
  54
  55 struct core_name {
  56         char *corename;
  57         int used, size;
  58 };
  59
  60 /* The maximal length of core_pattern is also specified in sysctl.c */
  61
  62 static int expand_corename(struct core_name *cn, int size)
  63 {
  64         char *corename = krealloc(cn->corename, size, GFP_KERNEL);
  65
  66         if (!corename)
  67                 return -ENOMEM;
  68
  69         if (size > core_name_size) /* racy but harmless */
  70                 core_name_size = size;
  71
  72         cn->size = ksize(corename);
  73         cn->corename = corename;
  74         return 0;
  75 }
  76
  77 static __printf(2, 0) int cn_vprintf(struct core_name *cn, const char *fmt,
  78                                      va_list arg)
  79 {
  80         int free, need;
  81         va_list arg_copy;
  82
  83 again:
  84         free = cn->size - cn->used;
  85
  86         va_copy(arg_copy, arg);
  87         need = vsnprintf(cn->corename + cn->used, free, fmt, arg_copy);
  88         va_end(arg_copy);
  89
  90         if (need < free) {
  91                 cn->used += need;
  92                 return 0;
  93         }
  94
  95         if (!expand_corename(cn, cn->size + need - free + 1))
  96                 goto again;
  97
  98         return -ENOMEM;
  99 }
 100
 101 static __printf(2, 3) int cn_printf(struct core_name *cn, const char *fmt, ...)
 102 {
 103         va_list arg;
 104         int ret;
 105
 106         va_start(arg, fmt);
 107         ret = cn_vprintf(cn, fmt, arg);
 108         va_end(arg);
 109
 110         return ret;
 111 }
 112
 113 static __printf(2, 3)
 114 int cn_esc_printf(struct core_name *cn, const char *fmt, ...)
 115 {
 116         int cur = cn->used;
 117         va_list arg;
 118         int ret;
 119
 120         va_start(arg, fmt);
 121         ret = cn_vprintf(cn, fmt, arg);
 122         va_end(arg);
 123
 124         if (ret == 0) {
 125                 /*
 126                  * Ensure that this coredump name component can't cause the
 127                  * resulting corefile path to consist of a ".." or ".".
 128                  */
 129                 if ((cn->used - cur == 1 && cn->corename[cur] == '.') ||
 130                                 (cn->used - cur == 2 && cn->corename[cur] == '.'
 131                                 && cn->corename[cur+1] == '.'))
 132                         cn->corename[cur] = '!';
 133
 134                 /*
 135                  * Empty names are fishy and could be used to create a "//" in a
 136                  * corefile name, causing the coredump to happen one directory
 137                  * level too high. Enforce that all components of the core
 138                  * pattern are at least one character long.
 139                  */
 140                 if (cn->used == cur)
 141                         ret = cn_printf(cn, "!");
 142         }
 143
 144         for (; cur < cn->used; ++cur) {
 145                 if (cn->corename[cur] == '/')
 146                         cn->corename[cur] = '!';
 147         }
 148         return ret;
 149 }
 150
 151 static int cn_print_exe_file(struct core_name *cn)
 152 {
 153         struct file *exe_file;
 154         char *pathbuf, *path;
 155         int ret;
 156
 157         exe_file = get_mm_exe_file(current->mm);
 158         if (!exe_file)
 159                 return cn_esc_printf(cn, "%s (path unknown)", current->comm);
 160
 161         pathbuf = kmalloc(PATH_MAX, GFP_TEMPORARY);
 162         if (!pathbuf) {
 163                 ret = -ENOMEM;
 164                 goto put_exe_file;
 165         }
 166
 167         path = file_path(exe_file, pathbuf, PATH_MAX);
 168         if (IS_ERR(path)) {
 169                 ret = PTR_ERR(path);
 170                 goto free_buf;
 171         }
 172
 173         ret = cn_esc_printf(cn, "%s", path);
 174
 175 free_buf:
 176         kfree(pathbuf);
 177 put_exe_file:
 178         fput(exe_file);
 179         return ret;
 180 }
 181
 182 /* format_corename will inspect the pattern parameter, and output a
 183  * name into corename, which must have space for at least
 184  * CORENAME_MAX_SIZE bytes plus one byte for the zero terminator.
 185  */
 186 static int format_corename(struct core_name *cn, struct coredump_params *cprm)
 187 {
 188         const struct cred *cred = current_cred();
 189         const char *pat_ptr = core_pattern;
 190         int ispipe = (*pat_ptr == '|');
 191         int pid_in_pattern = 0;
 192         int err = 0;
 193
 194         cn->used = 0;
 195         cn->corename = NULL;
 196         if (expand_corename(cn, core_name_size))
 197                 return -ENOMEM;
 198         cn->corename[0] = '\0';
 199
 200         if (ispipe)
 201                 ++pat_ptr;
 202
 203         /* Repeat as long as we have more pattern to process and more output
 204            space */
 205         while (*pat_ptr) {
 206                 if (*pat_ptr != '%') {
 207                         err = cn_printf(cn, "%c", *pat_ptr++);
 208                 } else {
 209                         switch (*++pat_ptr) {
 210                         /* single % at the end, drop that */
 211                         case 0:
 212                                 goto out;
 213                         /* Double percent, output one percent */
 214                         case '%':
 215                                 err = cn_printf(cn, "%c", '%');
 216                                 break;
 217                         /* pid */
 218                         case 'p':
 219                                 pid_in_pattern = 1;
 220                                 err = cn_printf(cn, "%d",
 221                                               task_tgid_vnr(current));
 222                                 break;
 223                         /* global pid */
 224                         case 'P':
 225                                 err = cn_printf(cn, "%d",
 226                                               task_tgid_nr(current));
 227                                 break;
 228                         case 'i':
 229                                 err = cn_printf(cn, "%d",
 230                                               task_pid_vnr(current));
 231                                 break;
 232                         case 'I':
 233                                 err = cn_printf(cn, "%d",
 234                                               task_pid_nr(current));
 235                                 break;
 236                         /* uid */
 237                         case 'u':
 238                                 err = cn_printf(cn, "%u",
 239                                                 from_kuid(&init_user_ns,
 240                                                           cred->uid));
 241                                 break;
 242                         /* gid */
 243                         case 'g':
 244                                 err = cn_printf(cn, "%u",
 245                                                 from_kgid(&init_user_ns,
 246                                                           cred->gid));
 247                                 break;
 248                         case 'd':
 249                                 err = cn_printf(cn, "%d",
 250                                         __get_dumpable(cprm->mm_flags));
 251                                 break;
 252                         /* signal that caused the coredump */
 253                         case 's':
 254                                 err = cn_printf(cn, "%d",
 255                                                 cprm->siginfo->si_signo);
 256                                 break;
 257                         /* UNIX time of coredump */
 258                         case 't': {
 259                                 time64_t time;
 260
 261                                 time = ktime_get_real_seconds();
 262                                 err = cn_printf(cn, "%lld", time);
 263                                 break;
 264                         }
 265                         /* hostname */
 266                         case 'h':
 267                                 down_read(&uts_sem);
 268                                 err = cn_esc_printf(cn, "%s",
 269                                               utsname()->nodename);
 270                                 up_read(&uts_sem);
 271                                 break;
 272                         /* executable */
 273                         case 'e':
 274                                 err = cn_esc_printf(cn, "%s", current->comm);
 275                                 break;
 276                         case 'E':
 277                                 err = cn_print_exe_file(cn);
 278                                 break;
 279                         /* core limit size */
 280                         case 'c':
 281                                 err = cn_printf(cn, "%lu",
 282                                               rlimit(RLIMIT_CORE));
 283                                 break;
 284                         default:
 285                                 break;
 286                         }
 287                         ++pat_ptr;
 288                 }
 289
 290                 if (err)
 291                         return err;
 292         }
 293
 294 out:
 295         /* Backward compatibility with core_uses_pid:
 296          *
 297          * If core_pattern does not include a %p (as is the default)
 298          * and core_uses_pid is set, then .%pid will be appended to
 299          * the filename. Do not do this for piped commands. */
 300         if (!ispipe && !pid_in_pattern && core_uses_pid) {
 301                 err = cn_printf(cn, ".%d", task_tgid_vnr(current));
 302                 if (err)
 303                         return err;
 304         }
 305         return ispipe;
 306 }
 307
 308 static int zap_process(struct task_struct *start, int exit_code, int flags)
 309 {
 310         struct task_struct *t;
 311         int nr = 0;
 312
 313         /* ignore all signals except SIGKILL, see prepare_signal() */
 314         start->signal->flags = SIGNAL_GROUP_COREDUMP | flags;
 315         start->signal->group_exit_code = exit_code;
 316         start->signal->group_stop_count = 0;
 317
 318         for_each_thread(start, t) {
 319                 task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);
 320                 if (t != current && t->mm) {
 321                         sigaddset(&t->pending.signal, SIGKILL);
 322                         signal_wake_up(t, 1);
 323                         nr++;
 324                 }
 325         }
 326
 327         return nr;
 328 }
 329
 330 static int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
 331                         struct core_state *core_state, int exit_code)
 332 {
 333         struct task_struct *g, *p;
 334         unsigned long flags;
 335         int nr = -EAGAIN;
 336
 337         spin_lock_irq(&tsk->sighand->siglock);
 338         if (!signal_group_exit(tsk->signal)) {
 339                 mm->core_state = core_state;
 340                 tsk->signal->group_exit_task = tsk;
 341                 nr = zap_process(tsk, exit_code, 0);
 342                 clear_tsk_thread_flag(tsk, TIF_SIGPENDING);
 343         }
 344         spin_unlock_irq(&tsk->sighand->siglock);
 345         if (unlikely(nr < 0))
 346                 return nr;
 347
 348         tsk->flags |= PF_DUMPCORE;
 349         if (atomic_read(&mm->mm_users) == nr + 1)
 350                 goto done;
 351         /*
 352          * We should find and kill all tasks which use this mm, and we should
 353          * count them correctly into ->nr_threads. We don't take tasklist
 354          * lock, but this is safe wrt:
 355          *
 356          * fork:
 357          *      None of sub-threads can fork after zap_process(leader). All
 358          *      processes which were created before this point should be
 359          *      visible to zap_threads() because copy_process() adds the new
 360          *      process to the tail of init_task.tasks list, and lock/unlock
 361          *      of ->siglock provides a memory barrier.
 362          *
 363          * do_exit:
 364          *      The caller holds mm->mmap_sem. This means that the task which
 365          *      uses this mm can't pass exit_mm(), so it can't exit or clear
 366          *      its ->mm.
 367          *
 368          * de_thread:
 369          *      It does list_replace_rcu(&leader->tasks, &current->tasks),
 370          *      we must see either old or new leader, this does not matter.
 371          *      However, it can change p->sighand, so lock_task_sighand(p)
 372          *      must be used. Since p->mm != NULL and we hold ->mmap_sem
 373          *      it can't fail.
 374          *
 375          *      Note also that "g" can be the old leader with ->mm == NULL
 376          *      and already unhashed and thus removed from ->thread_group.
 377          *      This is OK, __unhash_process()->list_del_rcu() does not
 378          *      clear the ->next pointer, we will find the new leader via
 379          *      next_thread().
 380          */
 381         rcu_read_lock();
 382         for_each_process(g) {
 383                 if (g == tsk->group_leader)
 384                         continue;
 385                 if (g->flags & PF_KTHREAD)
 386                         continue;
 387
 388                 for_each_thread(g, p) {
 389                         if (unlikely(!p->mm))
 390                                 continue;
 391                         if (unlikely(p->mm == mm)) {
 392                                 lock_task_sighand(p, &flags);
 393                                 nr += zap_process(p, exit_code,
 394                                                         SIGNAL_GROUP_EXIT);
 395                                 unlock_task_sighand(p, &flags);
 396                         }
 397                         break;
 398                 }
 399         }
 400         rcu_read_unlock();
 401 done:
 402         atomic_set(&core_state->nr_threads, nr);
 403         return nr;
 404 }
 405
 406 static int coredump_wait(int exit_code, struct core_state *core_state)
 407 {
 408         struct task_struct *tsk = current;
 409         struct mm_struct *mm = tsk->mm;
 410         int core_waiters = -EBUSY;
 411
 412         init_completion(&core_state->startup);
 413         core_state->dumper.task = tsk;
 414         core_state->dumper.next = NULL;
 415
 416         if (down_write_killable(&mm->mmap_sem))
 417                 return -EINTR;
 418
 419         if (!mm->core_state)
 420                 core_waiters = zap_threads(tsk, mm, core_state, exit_code);
 421         up_write(&mm->mmap_sem);
 422
 423         if (core_waiters > 0) {
 424                 struct core_thread *ptr;
 425
 426                 wait_for_completion(&core_state->startup);
 427                 /*
 428                  * Wait for all the threads to become inactive, so that
 429                  * all the thread context (extended register state, like
 430                  * fpu etc) gets copied to the memory.
 431                  */
 432                 ptr = core_state->dumper.next;
 433                 while (ptr != NULL) {
 434                         wait_task_inactive(ptr->task, 0);
 435                         ptr = ptr->next;
 436                 }
 437         }
 438
 439         return core_waiters;
 440 }
 441
 442 static void coredump_finish(struct mm_struct *mm, bool core_dumped)
 443 {
 444         struct core_thread *curr, *next;
 445         struct task_struct *task;
 446
 447         spin_lock_irq(&current->sighand->siglock);
 448         if (core_dumped && !__fatal_signal_pending(current))
 449                 current->signal->group_exit_code |= 0x80;
 450         current->signal->group_exit_task = NULL;
 451         current->signal->flags = SIGNAL_GROUP_EXIT;
 452         spin_unlock_irq(&current->sighand->siglock);
 453
 454         next = mm->core_state->dumper.next;
 455         while ((curr = next) != NULL) {
 456                 next = curr->next;
 457                 task = curr->task;
 458                 /*
 459                  * see exit_mm(), curr->task must not see
 460                  * ->task == NULL before we read ->next.
 461                  */
 462                 smp_mb();
 463                 curr->task = NULL;
 464                 wake_up_process(task);
 465         }
 466
 467         mm->core_state = NULL;
 468 }
 469
 470 static bool dump_interrupted(void)
 471 {
 472         /*
 473          * SIGKILL or freezing() interrupt the coredumping. Perhaps we
 474          * can do try_to_freeze() and check __fatal_signal_pending(),
 475          * but then we need to teach dump_write() to restart and clear
 476          * TIF_SIGPENDING.
 477          */
 478         return signal_pending(current);
 479 }
 480
 481 static void wait_for_dump_helpers(struct file *file)
 482 {
 483         struct pipe_inode_info *pipe = file->private_data;
 484
 485         pipe_lock(pipe);
 486         pipe->readers++;
 487         pipe->writers--;
 488         wake_up_interruptible_sync(&pipe->wait);
 489         kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
 490         pipe_unlock(pipe);
 491
 492         /*
 493          * We actually want wait_event_freezable() but then we need
 494          * to clear TIF_SIGPENDING and improve dump_interrupted().
 495          */
 496         wait_event_interruptible(pipe->wait, pipe->readers == 1);
 497
 498         pipe_lock(pipe);
 499         pipe->readers--;
 500         pipe->writers++;
 501         pipe_unlock(pipe);
 502 }
 503
 504 /*
 505  * umh_pipe_setup
 506  * helper function to customize the process used
 507  * to collect the core in userspace.  Specifically
 508  * it sets up a pipe and installs it as fd 0 (stdin)
 509  * for the process.  Returns 0 on success, or
 510  * PTR_ERR on failure.
 511  * Note that it also sets the core limit to 1.  This
 512  * is a special value that we use to trap recursive
 513  * core dumps
 514  */
 515 static int umh_pipe_setup(struct subprocess_info *info, struct cred *new)
 516 {
 517         struct file *files[2];
 518         struct coredump_params *cp = (struct coredump_params *)info->data;
 519         int err = create_pipe_files(files, 0);
 520         if (err)
 521                 return err;
 522
 523         cp->file = files[1];
 524
 525         err = replace_fd(0, files[0], 0);
 526         fput(files[0]);
 527         /* and disallow core files too */
 528         current->signal->rlim[RLIMIT_CORE] = (struct rlimit){1, 1};
 529
 530         return err;
 531 }
 532
 533 void do_coredump(const siginfo_t *siginfo)
 534 {
 535         struct core_state core_state;
 536         struct core_name cn;
 537         struct mm_struct *mm = current->mm;
 538         struct linux_binfmt * binfmt;
 539         const struct cred *old_cred;
 540         struct cred *cred;
 541         int retval = 0;
 542         int ispipe;
 543         struct files_struct *displaced;
 544         /* require nonrelative corefile path and be extra careful */
 545         bool need_suid_safe = false;
 546         bool core_dumped = false;
 547         static atomic_t core_dump_count = ATOMIC_INIT(0);
 548         struct coredump_params cprm = {
 549                 .siginfo = siginfo,
 550                 .regs = signal_pt_regs(),
 551                 .limit = rlimit(RLIMIT_CORE),
 552                 /*
 553                  * We must use the same mm->flags while dumping core to avoid
 554                  * inconsistency of bit flags, since this flag is not protected
 555                  * by any locks.
 556                  */
 557                 .mm_flags = mm->flags,
 558         };
 559
 560         audit_core_dumps(siginfo->si_signo);
 561
 562         binfmt = mm->binfmt;
 563         if (!binfmt || !binfmt->core_dump)
 564                 goto fail;
 565         if (!__get_dumpable(cprm.mm_flags))
 566                 goto fail;
 567
 568         cred = prepare_creds();
 569         if (!cred)
 570                 goto fail;
 571         /*
 572          * We cannot trust fsuid as being the "true" uid of the process
 573          * nor do we know its entire history. We only know it was tainted
 574          * so we dump it as root in mode 2, and only into a controlled
 575          * environment (pipe handler or fully qualified path).
 576          */
 577         if (__get_dumpable(cprm.mm_flags) == SUID_DUMP_ROOT) {
 578                 /* Setuid core dump mode */
 579                 cred->fsuid = GLOBAL_ROOT_UID;  /* Dump root private */
 580                 need_suid_safe = true;
 581         }
 582
 583         retval = coredump_wait(siginfo->si_signo, &core_state);
 584         if (retval < 0)
 585                 goto fail_creds;
 586
 587         old_cred = override_creds(cred);
 588
 589         ispipe = format_corename(&cn, &cprm);
 590
 591         if (ispipe) {
 592                 int dump_count;
 593                 char **helper_argv;
 594                 struct subprocess_info *sub_info;
 595
 596                 if (ispipe < 0) {
 597                         printk(KERN_WARNING "format_corename failed\n");
 598                         printk(KERN_WARNING "Aborting core\n");
 599                         goto fail_unlock;
 600                 }
 601
 602                 if (cprm.limit == 1) {
 603                         /* See umh_pipe_setup() which sets RLIMIT_CORE = 1.
 604                          *
 605                          * Normally core limits are irrelevant to pipes, since
 606                          * we're not writing to the file system, but we use
 607                          * cprm.limit of 1 here as a special value, this is a
 608                          * consistent way to catch recursive crashes.
 609                          * We can still crash if the core_pattern binary sets
 610                          * RLIM_CORE = !1, but it runs as root, and can do
 611                          * lots of stupid things.
 612                          *
 613                          * Note that we use task_tgid_vnr here to grab the pid
 614                          * of the process group leader.  That way we get the
 615                          * right pid if a thread in a multi-threaded
 616                          * core_pattern process dies.
 617                          */
 618                         printk(KERN_WARNING
 619                                 "Process %d(%s) has RLIMIT_CORE set to 1\n",
 620                                 task_tgid_vnr(current), current->comm);
 621                         printk(KERN_WARNING "Aborting core\n");
 622                         goto fail_unlock;
 623                 }
 624                 cprm.limit = RLIM_INFINITY;
 625
 626                 dump_count = atomic_inc_return(&core_dump_count);
 627                 if (core_pipe_limit && (core_pipe_limit < dump_count)) {
 628                         printk(KERN_WARNING "Pid %d(%s) over core_pipe_limit\n",
 629                                task_tgid_vnr(current), current->comm);
 630                         printk(KERN_WARNING "Skipping core dump\n");
 631                         goto fail_dropcount;
 632                 }
 633
 634                 helper_argv = argv_split(GFP_KERNEL, cn.corename, NULL);
 635                 if (!helper_argv) {
 636                         printk(KERN_WARNING "%s failed to allocate memory\n",
 637                                __func__);
 638                         goto fail_dropcount;
 639                 }
 640
 641                 retval = -ENOMEM;
 642                 sub_info = call_usermodehelper_setup(helper_argv[0],
 643                                                 helper_argv, NULL, GFP_KERNEL,
 644                                                 umh_pipe_setup, NULL, &cprm);
 645                 if (sub_info)
 646                         retval = call_usermodehelper_exec(sub_info,
 647                                                           UMH_WAIT_EXEC);
 648
 649                 argv_free(helper_argv);
 650                 if (retval) {
 651                         printk(KERN_INFO "Core dump to |%s pipe failed\n",
 652                                cn.corename);
 653                         goto close_fail;
 654                 }
 655         } else {
 656                 struct inode *inode;
 657                 int open_flags = O_CREAT | O_RDWR | O_NOFOLLOW |
 658                                  O_LARGEFILE | O_EXCL;
 659
 660                 if (cprm.limit < binfmt->min_coredump)
 661                         goto fail_unlock;
 662
 663                 if (need_suid_safe && cn.corename[0] != '/') {
 664                         printk(KERN_WARNING "Pid %d(%s) can only dump core "\
 665                                 "to fully qualified path!\n",
 666                                 task_tgid_vnr(current), current->comm);
 667                         printk(KERN_WARNING "Skipping core dump\n");
 668                         goto fail_unlock;
 669                 }
 670
 671                 /*
 672                  * Unlink the file if it exists unless this is a SUID
 673                  * binary - in that case, we're running around with root
 674                  * privs and don't want to unlink another user's coredump.
 675                  */
 676                 if (!need_suid_safe) {
 677                         mm_segment_t old_fs;
 678
 679                         old_fs = get_fs();
 680                         set_fs(KERNEL_DS);
 681                         /*
 682                          * If it doesn't exist, that's fine. If there's some
 683                          * other problem, we'll catch it at the filp_open().
 684                          */
 685                         (void) sys_unlink((const char __user *)cn.corename);
 686                         set_fs(old_fs);
 687                 }
 688
 689                 /*
 690                  * There is a race between unlinking and creating the
 691                  * file, but if that causes an EEXIST here, that's
 692                  * fine - another process raced with us while creating
 693                  * the corefile, and the other process won. To userspace,
 694                  * what matters is that at least one of the two processes
 695                  * writes its coredump successfully, not which one.
 696                  */
 697                 if (need_suid_safe) {
 698                         /*
 699                          * Using user namespaces, normal user tasks can change
 700                          * their current->fs->root to point to arbitrary
 701                          * directories. Since the intention of the "only dump
 702                          * with a fully qualified path" rule is to control where
 703                          * coredumps may be placed using root privileges,
 704                          * current->fs->root must not be used. Instead, use the
 705                          * root directory of init_task.
 706                          */
 707                         struct path root;
 708
 709                         task_lock(&init_task);
 710                         get_fs_root(init_task.fs, &root);
 711                         task_unlock(&init_task);
 712                         cprm.file = file_open_root(root.dentry, root.mnt,
 713                                 cn.corename, open_flags, 0600);
 714                         path_put(&root);
 715                 } else {
 716                         cprm.file = filp_open(cn.corename, open_flags, 0600);
 717                 }
 718                 if (IS_ERR(cprm.file))
 719                         goto fail_unlock;
 720
 721                 inode = file_inode(cprm.file);
 722                 if (inode->i_nlink > 1)
 723                         goto close_fail;
 724                 if (d_unhashed(cprm.file->f_path.dentry))
 725                         goto close_fail;
 726                 /*
 727                  * AK: actually i see no reason to not allow this for named
 728                  * pipes etc, but keep the previous behaviour for now.
 729                  */
 730                 if (!S_ISREG(inode->i_mode))
 731                         goto close_fail;
 732                 /*
 733                  * Don't dump core if the filesystem changed owner or mode
 734                  * of the file during file creation. This is an issue when
 735                  * a process dumps core while its cwd is e.g. on a vfat
 736                  * filesystem.
 737                  */
 738                 if (!uid_eq(inode->i_uid, current_fsuid()))
 739                         goto close_fail;
 740                 if ((inode->i_mode & 0677) != 0600)
 741                         goto close_fail;
 742                 if (!(cprm.file->f_mode & FMODE_CAN_WRITE))
 743                         goto close_fail;
 744                 if (do_truncate(cprm.file->f_path.dentry, 0, 0, cprm.file))
 745                         goto close_fail;
 746         }
 747
 748         /* get us an unshared descriptor table; almost always a no-op */
 749         retval = unshare_files(&displaced);
 750         if (retval)
 751                 goto close_fail;
 752         if (displaced)
 753                 put_files_struct(displaced);
 754         if (!dump_interrupted()) {
 755                 file_start_write(cprm.file);
 756                 core_dumped = binfmt->core_dump(&cprm);
 757                 file_end_write(cprm.file);
 758         }
 759         if (ispipe && core_pipe_limit)
 760                 wait_for_dump_helpers(cprm.file);
 761 close_fail:
 762         if (cprm.file)
 763                 filp_close(cprm.file, NULL);
 764 fail_dropcount:
 765         if (ispipe)
 766                 atomic_dec(&core_dump_count);
 767 fail_unlock:
 768         kfree(cn.corename);
 769         coredump_finish(mm, core_dumped);
 770         revert_creds(old_cred);
 771 fail_creds:
 772         put_cred(cred);
 773 fail:
 774         return;
 775 }
 776
 777 /*
 778  * Core dumping helper functions.  These are the only things you should
 779  * do on a core-file: use only these functions to write out all the
 780  * necessary info.
 781  */
 782 int dump_emit(struct coredump_params *cprm, const void *addr, int nr)
 783 {
 784         struct file *file = cprm->file;
 785         loff_t pos = file->f_pos;
 786         ssize_t n;
 787         if (cprm->written + nr > cprm->limit)
 788                 return 0;
 789         while (nr) {
 790                 if (dump_interrupted())
 791                         return 0;
 792                 n = __kernel_write(file, addr, nr, &pos);
 793                 if (n <= 0)
 794                         return 0;
 795                 file->f_pos = pos;
 796                 cprm->written += n;
 797                 cprm->pos += n;
 798                 nr -= n;
 799         }
 800         return 1;
 801 }
 802 EXPORT_SYMBOL(dump_emit);
 803
 804 int dump_skip(struct coredump_params *cprm, size_t nr)
 805 {
 806         static char zeroes[PAGE_SIZE];
 807         struct file *file = cprm->file;
 808         if (file->f_op->llseek && file->f_op->llseek != no_llseek) {
 809                 if (dump_interrupted() ||
 810                     file->f_op->llseek(file, nr, SEEK_CUR) < 0)
 811                         return 0;
 812                 cprm->pos += nr;
 813                 return 1;
 814         } else {
 815                 while (nr > PAGE_SIZE) {
 816                         if (!dump_emit(cprm, zeroes, PAGE_SIZE))
 817                                 return 0;
 818                         nr -= PAGE_SIZE;
 819                 }
 820                 return dump_emit(cprm, zeroes, nr);
 821         }
 822 }
 823 EXPORT_SYMBOL(dump_skip);
 824
 825 int dump_align(struct coredump_params *cprm, int align)
 826 {
 827         unsigned mod = cprm->pos & (align - 1);
 828         if (align & (align - 1))
 829                 return 0;
 830         return mod ? dump_skip(cprm, align - mod) : 1;
 831 }
 832 EXPORT_SYMBOL(dump_align);