fs/coredump.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/slab.h>
   3 #include <linux/file.h>
   4 #include <linux/fdtable.h>
   5 #include <linux/freezer.h>
   6 #include <linux/mm.h>
   7 #include <linux/stat.h>
   8 #include <linux/fcntl.h>
   9 #include <linux/swap.h>
  10 #include <linux/ctype.h>
  11 #include <linux/string.h>
  12 #include <linux/init.h>
  13 #include <linux/pagemap.h>
  14 #include <linux/perf_event.h>
  15 #include <linux/highmem.h>
  16 #include <linux/spinlock.h>
  17 #include <linux/key.h>
  18 #include <linux/personality.h>
  19 #include <linux/binfmts.h>
  20 #include <linux/coredump.h>
  21 #include <linux/sched/coredump.h>
  22 #include <linux/sched/signal.h>
  23 #include <linux/sched/task_stack.h>
  24 #include <linux/utsname.h>
  25 #include <linux/pid_namespace.h>
  26 #include <linux/module.h>
  27 #include <linux/namei.h>
  28 #include <linux/mount.h>
  29 #include <linux/security.h>
  30 #include <linux/syscalls.h>
  31 #include <linux/tsacct_kern.h>
  32 #include <linux/cn_proc.h>
  33 #include <linux/audit.h>
  34 #include <linux/tracehook.h>
  35 #include <linux/kmod.h>
  36 #include <linux/fsnotify.h>
  37 #include <linux/fs_struct.h>
  38 #include <linux/pipe_fs_i.h>
  39 #include <linux/oom.h>
  40 #include <linux/compat.h>
  41 #include <linux/fs.h>
  42 #include <linux/path.h>
  43 #include <linux/timekeeping.h>
  44
  45 #include <linux/uaccess.h>
  46 #include <asm/mmu_context.h>
  47 #include <asm/tlb.h>
  48 #include <asm/exec.h>
  49
  50 #include <trace/events/task.h>
  51 #include "internal.h"
  52
  53 #include <trace/events/sched.h>
  54
  55 int core_uses_pid;
  56 unsigned int core_pipe_limit;
  57 char core_pattern[CORENAME_MAX_SIZE] = "core";
  58 static int core_name_size = CORENAME_MAX_SIZE;
  59
  60 struct core_name {
  61         char *corename;
  62         int used, size;
  63 };
  64
  65 /* The maximal length of core_pattern is also specified in sysctl.c */
  66
  67 static int expand_corename(struct core_name *cn, int size)
  68 {
  69         char *corename = krealloc(cn->corename, size, GFP_KERNEL);
  70
  71         if (!corename)
  72                 return -ENOMEM;
  73
  74         if (size > core_name_size) /* racy but harmless */
  75                 core_name_size = size;
  76
  77         cn->size = ksize(corename);
  78         cn->corename = corename;
  79         return 0;
  80 }
  81
  82 static __printf(2, 0) int cn_vprintf(struct core_name *cn, const char *fmt,
  83                                      va_list arg)
  84 {
  85         int free, need;
  86         va_list arg_copy;
  87
  88 again:
  89         free = cn->size - cn->used;
  90
  91         va_copy(arg_copy, arg);
  92         need = vsnprintf(cn->corename + cn->used, free, fmt, arg_copy);
  93         va_end(arg_copy);
  94
  95         if (need < free) {
  96                 cn->used += need;
  97                 return 0;
  98         }
  99
 100         if (!expand_corename(cn, cn->size + need - free + 1))
 101                 goto again;
 102
 103         return -ENOMEM;
 104 }
 105
 106 static __printf(2, 3) int cn_printf(struct core_name *cn, const char *fmt, ...)
 107 {
 108         va_list arg;
 109         int ret;
 110
 111         va_start(arg, fmt);
 112         ret = cn_vprintf(cn, fmt, arg);
 113         va_end(arg);
 114
 115         return ret;
 116 }
 117
 118 static __printf(2, 3)
 119 int cn_esc_printf(struct core_name *cn, const char *fmt, ...)
 120 {
 121         int cur = cn->used;
 122         va_list arg;
 123         int ret;
 124
 125         va_start(arg, fmt);
 126         ret = cn_vprintf(cn, fmt, arg);
 127         va_end(arg);
 128
 129         if (ret == 0) {
 130                 /*
 131                  * Ensure that this coredump name component can't cause the
 132                  * resulting corefile path to consist of a ".." or ".".
 133                  */
 134                 if ((cn->used - cur == 1 && cn->corename[cur] == '.') ||
 135                                 (cn->used - cur == 2 && cn->corename[cur] == '.'
 136                                 && cn->corename[cur+1] == '.'))
 137                         cn->corename[cur] = '!';
 138
 139                 /*
 140                  * Empty names are fishy and could be used to create a "//" in a
 141                  * corefile name, causing the coredump to happen one directory
 142                  * level too high. Enforce that all components of the core
 143                  * pattern are at least one character long.
 144                  */
 145                 if (cn->used == cur)
 146                         ret = cn_printf(cn, "!");
 147         }
 148
 149         for (; cur < cn->used; ++cur) {
 150                 if (cn->corename[cur] == '/')
 151                         cn->corename[cur] = '!';
 152         }
 153         return ret;
 154 }
 155
 156 static int cn_print_exe_file(struct core_name *cn)
 157 {
 158         struct file *exe_file;
 159         char *pathbuf, *path;
 160         int ret;
 161
 162         exe_file = get_mm_exe_file(current->mm);
 163         if (!exe_file)
 164                 return cn_esc_printf(cn, "%s (path unknown)", current->comm);
 165
 166         pathbuf = kmalloc(PATH_MAX, GFP_KERNEL);
 167         if (!pathbuf) {
 168                 ret = -ENOMEM;
 169                 goto put_exe_file;
 170         }
 171
 172         path = file_path(exe_file, pathbuf, PATH_MAX);
 173         if (IS_ERR(path)) {
 174                 ret = PTR_ERR(path);
 175                 goto free_buf;
 176         }
 177
 178         ret = cn_esc_printf(cn, "%s", path);
 179
 180 free_buf:
 181         kfree(pathbuf);
 182 put_exe_file:
 183         fput(exe_file);
 184         return ret;
 185 }
 186
 187 /* format_corename will inspect the pattern parameter, and output a
 188  * name into corename, which must have space for at least
 189  * CORENAME_MAX_SIZE bytes plus one byte for the zero terminator.
 190  */
 191 static int format_corename(struct core_name *cn, struct coredump_params *cprm,
 192                            size_t **argv, int *argc)
 193 {
 194         const struct cred *cred = current_cred();
 195         const char *pat_ptr = core_pattern;
 196         int ispipe = (*pat_ptr == '|');
 197         bool was_space = false;
 198         int pid_in_pattern = 0;
 199         int err = 0;
 200
 201         cn->used = 0;
 202         cn->corename = NULL;
 203         if (expand_corename(cn, core_name_size))
 204                 return -ENOMEM;
 205         cn->corename[0] = '\0';
 206
 207         if (ispipe) {
 208                 int argvs = sizeof(core_pattern) / 2;
 209                 (*argv) = kmalloc_array(argvs, sizeof(**argv), GFP_KERNEL);
 210                 if (!(*argv))
 211                         return -ENOMEM;
 212                 (*argv)[(*argc)++] = 0;
 213                 ++pat_ptr;
 214         }
 215
 216         /* Repeat as long as we have more pattern to process and more output
 217            space */
 218         while (*pat_ptr) {
 219                 /*
 220                  * Split on spaces before doing template expansion so that
 221                  * %e and %E don't get split if they have spaces in them
 222                  */
 223                 if (ispipe) {
 224                         if (isspace(*pat_ptr)) {
 225                                 was_space = true;
 226                                 pat_ptr++;
 227                                 continue;
 228                         } else if (was_space) {
 229                                 was_space = false;
 230                                 err = cn_printf(cn, "%c", '\0');
 231                                 if (err)
 232                                         return err;
 233                                 (*argv)[(*argc)++] = cn->used;
 234                         }
 235                 }
 236                 if (*pat_ptr != '%') {
 237                         err = cn_printf(cn, "%c", *pat_ptr++);
 238                 } else {
 239                         switch (*++pat_ptr) {
 240                         /* single % at the end, drop that */
 241                         case 0:
 242                                 goto out;
 243                         /* Double percent, output one percent */
 244                         case '%':
 245                                 err = cn_printf(cn, "%c", '%');
 246                                 break;
 247                         /* pid */
 248                         case 'p':
 249                                 pid_in_pattern = 1;
 250                                 err = cn_printf(cn, "%d",
 251                                               task_tgid_vnr(current));
 252                                 break;
 253                         /* global pid */
 254                         case 'P':
 255                                 err = cn_printf(cn, "%d",
 256                                               task_tgid_nr(current));
 257                                 break;
 258                         case 'i':
 259                                 err = cn_printf(cn, "%d",
 260                                               task_pid_vnr(current));
 261                                 break;
 262                         case 'I':
 263                                 err = cn_printf(cn, "%d",
 264                                               task_pid_nr(current));
 265                                 break;
 266                         /* uid */
 267                         case 'u':
 268                                 err = cn_printf(cn, "%u",
 269                                                 from_kuid(&init_user_ns,
 270                                                           cred->uid));
 271                                 break;
 272                         /* gid */
 273                         case 'g':
 274                                 err = cn_printf(cn, "%u",
 275                                                 from_kgid(&init_user_ns,
 276                                                           cred->gid));
 277                                 break;
 278                         case 'd':
 279                                 err = cn_printf(cn, "%d",
 280                                         __get_dumpable(cprm->mm_flags));
 281                                 break;
 282                         /* signal that caused the coredump */
 283                         case 's':
 284                                 err = cn_printf(cn, "%d",
 285                                                 cprm->siginfo->si_signo);
 286                                 break;
 287                         /* UNIX time of coredump */
 288                         case 't': {
 289                                 time64_t time;
 290
 291                                 time = ktime_get_real_seconds();
 292                                 err = cn_printf(cn, "%lld", time);
 293                                 break;
 294                         }
 295                         /* hostname */
 296                         case 'h':
 297                                 down_read(&uts_sem);
 298                                 err = cn_esc_printf(cn, "%s",
 299                                               utsname()->nodename);
 300                                 up_read(&uts_sem);
 301                                 break;
 302                         /* executable */
 303                         case 'e':
 304                                 err = cn_esc_printf(cn, "%s", current->comm);
 305                                 break;
 306                         case 'E':
 307                                 err = cn_print_exe_file(cn);
 308                                 break;
 309                         /* core limit size */
 310                         case 'c':
 311                                 err = cn_printf(cn, "%lu",
 312                                               rlimit(RLIMIT_CORE));
 313                                 break;
 314                         default:
 315                                 break;
 316                         }
 317                         ++pat_ptr;
 318                 }
 319
 320                 if (err)
 321                         return err;
 322         }
 323
 324 out:
 325         /* Backward compatibility with core_uses_pid:
 326          *
 327          * If core_pattern does not include a %p (as is the default)
 328          * and core_uses_pid is set, then .%pid will be appended to
 329          * the filename. Do not do this for piped commands. */
 330         if (!ispipe && !pid_in_pattern && core_uses_pid) {
 331                 err = cn_printf(cn, ".%d", task_tgid_vnr(current));
 332                 if (err)
 333                         return err;
 334         }
 335         return ispipe;
 336 }
 337
 338 static int zap_process(struct task_struct *start, int exit_code, int flags)
 339 {
 340         struct task_struct *t;
 341         int nr = 0;
 342
 343         /* ignore all signals except SIGKILL, see prepare_signal() */
 344         start->signal->flags = SIGNAL_GROUP_COREDUMP | flags;
 345         start->signal->group_exit_code = exit_code;
 346         start->signal->group_stop_count = 0;
 347
 348         for_each_thread(start, t) {
 349                 task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);
 350                 if (t != current && t->mm) {
 351                         sigaddset(&t->pending.signal, SIGKILL);
 352                         signal_wake_up(t, 1);
 353                         nr++;
 354                 }
 355         }
 356
 357         return nr;
 358 }
 359
 360 static int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
 361                         struct core_state *core_state, int exit_code)
 362 {
 363         struct task_struct *g, *p;
 364         unsigned long flags;
 365         int nr = -EAGAIN;
 366
 367         spin_lock_irq(&tsk->sighand->siglock);
 368         if (!signal_group_exit(tsk->signal)) {
 369                 mm->core_state = core_state;
 370                 tsk->signal->group_exit_task = tsk;
 371                 nr = zap_process(tsk, exit_code, 0);
 372                 clear_tsk_thread_flag(tsk, TIF_SIGPENDING);
 373         }
 374         spin_unlock_irq(&tsk->sighand->siglock);
 375         if (unlikely(nr < 0))
 376                 return nr;
 377
 378         tsk->flags |= PF_DUMPCORE;
 379         if (atomic_read(&mm->mm_users) == nr + 1)
 380                 goto done;
 381         /*
 382          * We should find and kill all tasks which use this mm, and we should
 383          * count them correctly into ->nr_threads. We don't take tasklist
 384          * lock, but this is safe wrt:
 385          *
 386          * fork:
 387          *      None of sub-threads can fork after zap_process(leader). All
 388          *      processes which were created before this point should be
 389          *      visible to zap_threads() because copy_process() adds the new
 390          *      process to the tail of init_task.tasks list, and lock/unlock
 391          *      of ->siglock provides a memory barrier.
 392          *
 393          * do_exit:
 394          *      The caller holds mm->mmap_sem. This means that the task which
 395          *      uses this mm can't pass exit_mm(), so it can't exit or clear
 396          *      its ->mm.
 397          *
 398          * de_thread:
 399          *      It does list_replace_rcu(&leader->tasks, &current->tasks),
 400          *      we must see either old or new leader, this does not matter.
 401          *      However, it can change p->sighand, so lock_task_sighand(p)
 402          *      must be used. Since p->mm != NULL and we hold ->mmap_sem
 403          *      it can't fail.
 404          *
 405          *      Note also that "g" can be the old leader with ->mm == NULL
 406          *      and already unhashed and thus removed from ->thread_group.
 407          *      This is OK, __unhash_process()->list_del_rcu() does not
 408          *      clear the ->next pointer, we will find the new leader via
 409          *      next_thread().
 410          */
 411         rcu_read_lock();
 412         for_each_process(g) {
 413                 if (g == tsk->group_leader)
 414                         continue;
 415                 if (g->flags & PF_KTHREAD)
 416                         continue;
 417
 418                 for_each_thread(g, p) {
 419                         if (unlikely(!p->mm))
 420                                 continue;
 421                         if (unlikely(p->mm == mm)) {
 422                                 lock_task_sighand(p, &flags);
 423                                 nr += zap_process(p, exit_code,
 424                                                         SIGNAL_GROUP_EXIT);
 425                                 unlock_task_sighand(p, &flags);
 426                         }
 427                         break;
 428                 }
 429         }
 430         rcu_read_unlock();
 431 done:
 432         atomic_set(&core_state->nr_threads, nr);
 433         return nr;
 434 }
 435
 436 static int coredump_wait(int exit_code, struct core_state *core_state)
 437 {
 438         struct task_struct *tsk = current;
 439         struct mm_struct *mm = tsk->mm;
 440         int core_waiters = -EBUSY;
 441
 442         init_completion(&core_state->startup);
 443         core_state->dumper.task = tsk;
 444         core_state->dumper.next = NULL;
 445
 446         if (down_write_killable(&mm->mmap_sem))
 447                 return -EINTR;
 448
 449         if (!mm->core_state)
 450                 core_waiters = zap_threads(tsk, mm, core_state, exit_code);
 451         up_write(&mm->mmap_sem);
 452
 453         if (core_waiters > 0) {
 454                 struct core_thread *ptr;
 455
 456                 freezer_do_not_count();
 457                 wait_for_completion(&core_state->startup);
 458                 freezer_count();
 459                 /*
 460                  * Wait for all the threads to become inactive, so that
 461                  * all the thread context (extended register state, like
 462                  * fpu etc) gets copied to the memory.
 463                  */
 464                 ptr = core_state->dumper.next;
 465                 while (ptr != NULL) {
 466                         wait_task_inactive(ptr->task, 0);
 467                         ptr = ptr->next;
 468                 }
 469         }
 470
 471         return core_waiters;
 472 }
 473
 474 static void coredump_finish(struct mm_struct *mm, bool core_dumped)
 475 {
 476         struct core_thread *curr, *next;
 477         struct task_struct *task;
 478
 479         spin_lock_irq(&current->sighand->siglock);
 480         if (core_dumped && !__fatal_signal_pending(current))
 481                 current->signal->group_exit_code |= 0x80;
 482         current->signal->group_exit_task = NULL;
 483         current->signal->flags = SIGNAL_GROUP_EXIT;
 484         spin_unlock_irq(&current->sighand->siglock);
 485
 486         next = mm->core_state->dumper.next;
 487         while ((curr = next) != NULL) {
 488                 next = curr->next;
 489                 task = curr->task;
 490                 /*
 491                  * see exit_mm(), curr->task must not see
 492                  * ->task == NULL before we read ->next.
 493                  */
 494                 smp_mb();
 495                 curr->task = NULL;
 496                 wake_up_process(task);
 497         }
 498
 499         mm->core_state = NULL;
 500 }
 501
 502 static bool dump_interrupted(void)
 503 {
 504         /*
 505          * SIGKILL or freezing() interrupt the coredumping. Perhaps we
 506          * can do try_to_freeze() and check __fatal_signal_pending(),
 507          * but then we need to teach dump_write() to restart and clear
 508          * TIF_SIGPENDING.
 509          */
 510         return signal_pending(current);
 511 }
 512
 513 static void wait_for_dump_helpers(struct file *file)
 514 {
 515         struct pipe_inode_info *pipe = file->private_data;
 516
 517         pipe_lock(pipe);
 518         pipe->readers++;
 519         pipe->writers--;
 520         wake_up_interruptible_sync(&pipe->wait);
 521         kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
 522         pipe_unlock(pipe);
 523
 524         /*
 525          * We actually want wait_event_freezable() but then we need
 526          * to clear TIF_SIGPENDING and improve dump_interrupted().
 527          */
 528         wait_event_interruptible(pipe->wait, pipe->readers == 1);
 529
 530         pipe_lock(pipe);
 531         pipe->readers--;
 532         pipe->writers++;
 533         pipe_unlock(pipe);
 534 }
 535
 536 /*
 537  * umh_pipe_setup
 538  * helper function to customize the process used
 539  * to collect the core in userspace.  Specifically
 540  * it sets up a pipe and installs it as fd 0 (stdin)
 541  * for the process.  Returns 0 on success, or
 542  * PTR_ERR on failure.
 543  * Note that it also sets the core limit to 1.  This
 544  * is a special value that we use to trap recursive
 545  * core dumps
 546  */
 547 static int umh_pipe_setup(struct subprocess_info *info, struct cred *new)
 548 {
 549         struct file *files[2];
 550         struct coredump_params *cp = (struct coredump_params *)info->data;
 551         int err = create_pipe_files(files, 0);
 552         if (err)
 553                 return err;
 554
 555         cp->file = files[1];
 556
 557         err = replace_fd(0, files[0], 0);
 558         fput(files[0]);
 559         /* and disallow core files too */
 560         current->signal->rlim[RLIMIT_CORE] = (struct rlimit){1, 1};
 561
 562         return err;
 563 }
 564
 565 void do_coredump(const kernel_siginfo_t *siginfo)
 566 {
 567         struct core_state core_state;
 568         struct core_name cn;
 569         struct mm_struct *mm = current->mm;
 570         struct linux_binfmt * binfmt;
 571         const struct cred *old_cred;
 572         struct cred *cred;
 573         int retval = 0;
 574         int ispipe;
 575         size_t *argv = NULL;
 576         int argc = 0;
 577         struct files_struct *displaced;
 578         /* require nonrelative corefile path and be extra careful */
 579         bool need_suid_safe = false;
 580         bool core_dumped = false;
 581         static atomic_t core_dump_count = ATOMIC_INIT(0);
 582         struct coredump_params cprm = {
 583                 .siginfo = siginfo,
 584                 .regs = signal_pt_regs(),
 585                 .limit = rlimit(RLIMIT_CORE),
 586                 /*
 587                  * We must use the same mm->flags while dumping core to avoid
 588                  * inconsistency of bit flags, since this flag is not protected
 589                  * by any locks.
 590                  */
 591                 .mm_flags = mm->flags,
 592         };
 593
 594         audit_core_dumps(siginfo->si_signo);
 595
 596         binfmt = mm->binfmt;
 597         if (!binfmt || !binfmt->core_dump)
 598                 goto fail;
 599         if (!__get_dumpable(cprm.mm_flags))
 600                 goto fail;
 601
 602         cred = prepare_creds();
 603         if (!cred)
 604                 goto fail;
 605         /*
 606          * We cannot trust fsuid as being the "true" uid of the process
 607          * nor do we know its entire history. We only know it was tainted
 608          * so we dump it as root in mode 2, and only into a controlled
 609          * environment (pipe handler or fully qualified path).
 610          */
 611         if (__get_dumpable(cprm.mm_flags) == SUID_DUMP_ROOT) {
 612                 /* Setuid core dump mode */
 613                 cred->fsuid = GLOBAL_ROOT_UID;  /* Dump root private */
 614                 need_suid_safe = true;
 615         }
 616
 617         retval = coredump_wait(siginfo->si_signo, &core_state);
 618         if (retval < 0)
 619                 goto fail_creds;
 620
 621         old_cred = override_creds(cred);
 622
 623         ispipe = format_corename(&cn, &cprm, &argv, &argc);
 624
 625         if (ispipe) {
 626                 int argi;
 627                 int dump_count;
 628                 char **helper_argv;
 629                 struct subprocess_info *sub_info;
 630
 631                 if (ispipe < 0) {
 632                         printk(KERN_WARNING "format_corename failed\n");
 633                         printk(KERN_WARNING "Aborting core\n");
 634                         goto fail_unlock;
 635                 }
 636
 637                 if (cprm.limit == 1) {
 638                         /* See umh_pipe_setup() which sets RLIMIT_CORE = 1.
 639                          *
 640                          * Normally core limits are irrelevant to pipes, since
 641                          * we're not writing to the file system, but we use
 642                          * cprm.limit of 1 here as a special value, this is a
 643                          * consistent way to catch recursive crashes.
 644                          * We can still crash if the core_pattern binary sets
 645                          * RLIM_CORE = !1, but it runs as root, and can do
 646                          * lots of stupid things.
 647                          *
 648                          * Note that we use task_tgid_vnr here to grab the pid
 649                          * of the process group leader.  That way we get the
 650                          * right pid if a thread in a multi-threaded
 651                          * core_pattern process dies.
 652                          */
 653                         printk(KERN_WARNING
 654                                 "Process %d(%s) has RLIMIT_CORE set to 1\n",
 655                                 task_tgid_vnr(current), current->comm);
 656                         printk(KERN_WARNING "Aborting core\n");
 657                         goto fail_unlock;
 658                 }
 659                 cprm.limit = RLIM_INFINITY;
 660
 661                 dump_count = atomic_inc_return(&core_dump_count);
 662                 if (core_pipe_limit && (core_pipe_limit < dump_count)) {
 663                         printk(KERN_WARNING "Pid %d(%s) over core_pipe_limit\n",
 664                                task_tgid_vnr(current), current->comm);
 665                         printk(KERN_WARNING "Skipping core dump\n");
 666                         goto fail_dropcount;
 667                 }
 668
 669                 helper_argv = kmalloc_array(argc + 1, sizeof(*helper_argv),
 670                                             GFP_KERNEL);
 671                 if (!helper_argv) {
 672                         printk(KERN_WARNING "%s failed to allocate memory\n",
 673                                __func__);
 674                         goto fail_dropcount;
 675                 }
 676                 for (argi = 0; argi < argc; argi++)
 677                         helper_argv[argi] = cn.corename + argv[argi];
 678                 helper_argv[argi] = NULL;
 679
 680                 retval = -ENOMEM;
 681                 sub_info = call_usermodehelper_setup(helper_argv[0],
 682                                                 helper_argv, NULL, GFP_KERNEL,
 683                                                 umh_pipe_setup, NULL, &cprm);
 684                 if (sub_info)
 685                         retval = call_usermodehelper_exec(sub_info,
 686                                                           UMH_WAIT_EXEC);
 687
 688                 kfree(helper_argv);
 689                 if (retval) {
 690                         printk(KERN_INFO "Core dump to |%s pipe failed\n",
 691                                cn.corename);
 692                         goto close_fail;
 693                 }
 694         } else {
 695                 struct inode *inode;
 696                 int open_flags = O_CREAT | O_RDWR | O_NOFOLLOW |
 697                                  O_LARGEFILE | O_EXCL;
 698
 699                 if (cprm.limit < binfmt->min_coredump)
 700                         goto fail_unlock;
 701
 702                 if (need_suid_safe && cn.corename[0] != '/') {
 703                         printk(KERN_WARNING "Pid %d(%s) can only dump core "\
 704                                 "to fully qualified path!\n",
 705                                 task_tgid_vnr(current), current->comm);
 706                         printk(KERN_WARNING "Skipping core dump\n");
 707                         goto fail_unlock;
 708                 }
 709
 710                 /*
 711                  * Unlink the file if it exists unless this is a SUID
 712                  * binary - in that case, we're running around with root
 713                  * privs and don't want to unlink another user's coredump.
 714                  */
 715                 if (!need_suid_safe) {
 716                         /*
 717                          * If it doesn't exist, that's fine. If there's some
 718                          * other problem, we'll catch it at the filp_open().
 719                          */
 720                         do_unlinkat(AT_FDCWD, getname_kernel(cn.corename));
 721                 }
 722
 723                 /*
 724                  * There is a race between unlinking and creating the
 725                  * file, but if that causes an EEXIST here, that's
 726                  * fine - another process raced with us while creating
 727                  * the corefile, and the other process won. To userspace,
 728                  * what matters is that at least one of the two processes
 729                  * writes its coredump successfully, not which one.
 730                  */
 731                 if (need_suid_safe) {
 732                         /*
 733                          * Using user namespaces, normal user tasks can change
 734                          * their current->fs->root to point to arbitrary
 735                          * directories. Since the intention of the "only dump
 736                          * with a fully qualified path" rule is to control where
 737                          * coredumps may be placed using root privileges,
 738                          * current->fs->root must not be used. Instead, use the
 739                          * root directory of init_task.
 740                          */
 741                         struct path root;
 742
 743                         task_lock(&init_task);
 744                         get_fs_root(init_task.fs, &root);
 745                         task_unlock(&init_task);
 746                         cprm.file = file_open_root(root.dentry, root.mnt,
 747                                 cn.corename, open_flags, 0600);
 748                         path_put(&root);
 749                 } else {
 750                         cprm.file = filp_open(cn.corename, open_flags, 0600);
 751                 }
 752                 if (IS_ERR(cprm.file))
 753                         goto fail_unlock;
 754
 755                 inode = file_inode(cprm.file);
 756                 if (inode->i_nlink > 1)
 757                         goto close_fail;
 758                 if (d_unhashed(cprm.file->f_path.dentry))
 759                         goto close_fail;
 760                 /*
 761                  * AK: actually i see no reason to not allow this for named
 762                  * pipes etc, but keep the previous behaviour for now.
 763                  */
 764                 if (!S_ISREG(inode->i_mode))
 765                         goto close_fail;
 766                 /*
 767                  * Don't dump core if the filesystem changed owner or mode
 768                  * of the file during file creation. This is an issue when
 769                  * a process dumps core while its cwd is e.g. on a vfat
 770                  * filesystem.
 771                  */
 772                 if (!uid_eq(inode->i_uid, current_fsuid()))
 773                         goto close_fail;
 774                 if ((inode->i_mode & 0677) != 0600)
 775                         goto close_fail;
 776                 if (!(cprm.file->f_mode & FMODE_CAN_WRITE))
 777                         goto close_fail;
 778                 if (do_truncate(cprm.file->f_path.dentry, 0, 0, cprm.file))
 779                         goto close_fail;
 780         }
 781
 782         /* get us an unshared descriptor table; almost always a no-op */
 783         retval = unshare_files(&displaced);
 784         if (retval)
 785                 goto close_fail;
 786         if (displaced)
 787                 put_files_struct(displaced);
 788         if (!dump_interrupted()) {
 789                 file_start_write(cprm.file);
 790                 core_dumped = binfmt->core_dump(&cprm);
 791                 file_end_write(cprm.file);
 792         }
 793         if (ispipe && core_pipe_limit)
 794                 wait_for_dump_helpers(cprm.file);
 795 close_fail:
 796         if (cprm.file)
 797                 filp_close(cprm.file, NULL);
 798 fail_dropcount:
 799         if (ispipe)
 800                 atomic_dec(&core_dump_count);
 801 fail_unlock:
 802         kfree(argv);
 803         kfree(cn.corename);
 804         coredump_finish(mm, core_dumped);
 805         revert_creds(old_cred);
 806 fail_creds:
 807         put_cred(cred);
 808 fail:
 809         return;
 810 }
 811
 812 /*
 813  * Core dumping helper functions.  These are the only things you should
 814  * do on a core-file: use only these functions to write out all the
 815  * necessary info.
 816  */
 817 int dump_emit(struct coredump_params *cprm, const void *addr, int nr)
 818 {
 819         struct file *file = cprm->file;
 820         loff_t pos = file->f_pos;
 821         ssize_t n;
 822         if (cprm->written + nr > cprm->limit)
 823                 return 0;
 824         while (nr) {
 825                 if (dump_interrupted())
 826                         return 0;
 827                 n = __kernel_write(file, addr, nr, &pos);
 828                 if (n <= 0)
 829                         return 0;
 830                 file->f_pos = pos;
 831                 cprm->written += n;
 832                 cprm->pos += n;
 833                 nr -= n;
 834         }
 835         return 1;
 836 }
 837 EXPORT_SYMBOL(dump_emit);
 838
 839 int dump_skip(struct coredump_params *cprm, size_t nr)
 840 {
 841         static char zeroes[PAGE_SIZE];
 842         struct file *file = cprm->file;
 843         if (file->f_op->llseek && file->f_op->llseek != no_llseek) {
 844                 if (dump_interrupted() ||
 845                     file->f_op->llseek(file, nr, SEEK_CUR) < 0)
 846                         return 0;
 847                 cprm->pos += nr;
 848                 return 1;
 849         } else {
 850                 while (nr > PAGE_SIZE) {
 851                         if (!dump_emit(cprm, zeroes, PAGE_SIZE))
 852                                 return 0;
 853                         nr -= PAGE_SIZE;
 854                 }
 855                 return dump_emit(cprm, zeroes, nr);
 856         }
 857 }
 858 EXPORT_SYMBOL(dump_skip);
 859
 860 int dump_align(struct coredump_params *cprm, int align)
 861 {
 862         unsigned mod = cprm->pos & (align - 1);
 863         if (align & (align - 1))
 864                 return 0;
 865         return mod ? dump_skip(cprm, align - mod) : 1;
 866 }
 867 EXPORT_SYMBOL(dump_align);
 868
 869 /*
 870  * Ensures that file size is big enough to contain the current file
 871  * postion. This prevents gdb from complaining about a truncated file
 872  * if the last "write" to the file was dump_skip.
 873  */
 874 void dump_truncate(struct coredump_params *cprm)
 875 {
 876         struct file *file = cprm->file;
 877         loff_t offset;
 878
 879         if (file->f_op->llseek && file->f_op->llseek != no_llseek) {
 880                 offset = file->f_op->llseek(file, 0, SEEK_CUR);
 881                 if (i_size_read(file->f_mapping->host) < offset)
 882                         do_truncate(file->f_path.dentry, offset, 0, file);
 883         }
 884 }
 885 EXPORT_SYMBOL(dump_truncate);