Merge tag 'drm-misc-fixes-2020-08-12' of git://anongit.freedesktop.org/drm/drm-misc...
[linux-2.6-microblaze.git] / 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, bool name_only)
157 {
158         struct file *exe_file;
159         char *pathbuf, *path, *ptr;
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         if (name_only) {
179                 ptr = strrchr(path, '/');
180                 if (ptr)
181                         path = ptr + 1;
182         }
183         ret = cn_esc_printf(cn, "%s", path);
184
185 free_buf:
186         kfree(pathbuf);
187 put_exe_file:
188         fput(exe_file);
189         return ret;
190 }
191
192 /* format_corename will inspect the pattern parameter, and output a
193  * name into corename, which must have space for at least
194  * CORENAME_MAX_SIZE bytes plus one byte for the zero terminator.
195  */
196 static int format_corename(struct core_name *cn, struct coredump_params *cprm,
197                            size_t **argv, int *argc)
198 {
199         const struct cred *cred = current_cred();
200         const char *pat_ptr = core_pattern;
201         int ispipe = (*pat_ptr == '|');
202         bool was_space = false;
203         int pid_in_pattern = 0;
204         int err = 0;
205
206         cn->used = 0;
207         cn->corename = NULL;
208         if (expand_corename(cn, core_name_size))
209                 return -ENOMEM;
210         cn->corename[0] = '\0';
211
212         if (ispipe) {
213                 int argvs = sizeof(core_pattern) / 2;
214                 (*argv) = kmalloc_array(argvs, sizeof(**argv), GFP_KERNEL);
215                 if (!(*argv))
216                         return -ENOMEM;
217                 (*argv)[(*argc)++] = 0;
218                 ++pat_ptr;
219                 if (!(*pat_ptr))
220                         return -ENOMEM;
221         }
222
223         /* Repeat as long as we have more pattern to process and more output
224            space */
225         while (*pat_ptr) {
226                 /*
227                  * Split on spaces before doing template expansion so that
228                  * %e and %E don't get split if they have spaces in them
229                  */
230                 if (ispipe) {
231                         if (isspace(*pat_ptr)) {
232                                 was_space = true;
233                                 pat_ptr++;
234                                 continue;
235                         } else if (was_space) {
236                                 was_space = false;
237                                 err = cn_printf(cn, "%c", '\0');
238                                 if (err)
239                                         return err;
240                                 (*argv)[(*argc)++] = cn->used;
241                         }
242                 }
243                 if (*pat_ptr != '%') {
244                         err = cn_printf(cn, "%c", *pat_ptr++);
245                 } else {
246                         switch (*++pat_ptr) {
247                         /* single % at the end, drop that */
248                         case 0:
249                                 goto out;
250                         /* Double percent, output one percent */
251                         case '%':
252                                 err = cn_printf(cn, "%c", '%');
253                                 break;
254                         /* pid */
255                         case 'p':
256                                 pid_in_pattern = 1;
257                                 err = cn_printf(cn, "%d",
258                                               task_tgid_vnr(current));
259                                 break;
260                         /* global pid */
261                         case 'P':
262                                 err = cn_printf(cn, "%d",
263                                               task_tgid_nr(current));
264                                 break;
265                         case 'i':
266                                 err = cn_printf(cn, "%d",
267                                               task_pid_vnr(current));
268                                 break;
269                         case 'I':
270                                 err = cn_printf(cn, "%d",
271                                               task_pid_nr(current));
272                                 break;
273                         /* uid */
274                         case 'u':
275                                 err = cn_printf(cn, "%u",
276                                                 from_kuid(&init_user_ns,
277                                                           cred->uid));
278                                 break;
279                         /* gid */
280                         case 'g':
281                                 err = cn_printf(cn, "%u",
282                                                 from_kgid(&init_user_ns,
283                                                           cred->gid));
284                                 break;
285                         case 'd':
286                                 err = cn_printf(cn, "%d",
287                                         __get_dumpable(cprm->mm_flags));
288                                 break;
289                         /* signal that caused the coredump */
290                         case 's':
291                                 err = cn_printf(cn, "%d",
292                                                 cprm->siginfo->si_signo);
293                                 break;
294                         /* UNIX time of coredump */
295                         case 't': {
296                                 time64_t time;
297
298                                 time = ktime_get_real_seconds();
299                                 err = cn_printf(cn, "%lld", time);
300                                 break;
301                         }
302                         /* hostname */
303                         case 'h':
304                                 down_read(&uts_sem);
305                                 err = cn_esc_printf(cn, "%s",
306                                               utsname()->nodename);
307                                 up_read(&uts_sem);
308                                 break;
309                         /* executable, could be changed by prctl PR_SET_NAME etc */
310                         case 'e':
311                                 err = cn_esc_printf(cn, "%s", current->comm);
312                                 break;
313                         /* file name of executable */
314                         case 'f':
315                                 err = cn_print_exe_file(cn, true);
316                                 break;
317                         case 'E':
318                                 err = cn_print_exe_file(cn, false);
319                                 break;
320                         /* core limit size */
321                         case 'c':
322                                 err = cn_printf(cn, "%lu",
323                                               rlimit(RLIMIT_CORE));
324                                 break;
325                         default:
326                                 break;
327                         }
328                         ++pat_ptr;
329                 }
330
331                 if (err)
332                         return err;
333         }
334
335 out:
336         /* Backward compatibility with core_uses_pid:
337          *
338          * If core_pattern does not include a %p (as is the default)
339          * and core_uses_pid is set, then .%pid will be appended to
340          * the filename. Do not do this for piped commands. */
341         if (!ispipe && !pid_in_pattern && core_uses_pid) {
342                 err = cn_printf(cn, ".%d", task_tgid_vnr(current));
343                 if (err)
344                         return err;
345         }
346         return ispipe;
347 }
348
349 static int zap_process(struct task_struct *start, int exit_code, int flags)
350 {
351         struct task_struct *t;
352         int nr = 0;
353
354         /* ignore all signals except SIGKILL, see prepare_signal() */
355         start->signal->flags = SIGNAL_GROUP_COREDUMP | flags;
356         start->signal->group_exit_code = exit_code;
357         start->signal->group_stop_count = 0;
358
359         for_each_thread(start, t) {
360                 task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);
361                 if (t != current && t->mm) {
362                         sigaddset(&t->pending.signal, SIGKILL);
363                         signal_wake_up(t, 1);
364                         nr++;
365                 }
366         }
367
368         return nr;
369 }
370
371 static int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
372                         struct core_state *core_state, int exit_code)
373 {
374         struct task_struct *g, *p;
375         unsigned long flags;
376         int nr = -EAGAIN;
377
378         spin_lock_irq(&tsk->sighand->siglock);
379         if (!signal_group_exit(tsk->signal)) {
380                 mm->core_state = core_state;
381                 tsk->signal->group_exit_task = tsk;
382                 nr = zap_process(tsk, exit_code, 0);
383                 clear_tsk_thread_flag(tsk, TIF_SIGPENDING);
384         }
385         spin_unlock_irq(&tsk->sighand->siglock);
386         if (unlikely(nr < 0))
387                 return nr;
388
389         tsk->flags |= PF_DUMPCORE;
390         if (atomic_read(&mm->mm_users) == nr + 1)
391                 goto done;
392         /*
393          * We should find and kill all tasks which use this mm, and we should
394          * count them correctly into ->nr_threads. We don't take tasklist
395          * lock, but this is safe wrt:
396          *
397          * fork:
398          *      None of sub-threads can fork after zap_process(leader). All
399          *      processes which were created before this point should be
400          *      visible to zap_threads() because copy_process() adds the new
401          *      process to the tail of init_task.tasks list, and lock/unlock
402          *      of ->siglock provides a memory barrier.
403          *
404          * do_exit:
405          *      The caller holds mm->mmap_lock. This means that the task which
406          *      uses this mm can't pass exit_mm(), so it can't exit or clear
407          *      its ->mm.
408          *
409          * de_thread:
410          *      It does list_replace_rcu(&leader->tasks, &current->tasks),
411          *      we must see either old or new leader, this does not matter.
412          *      However, it can change p->sighand, so lock_task_sighand(p)
413          *      must be used. Since p->mm != NULL and we hold ->mmap_lock
414          *      it can't fail.
415          *
416          *      Note also that "g" can be the old leader with ->mm == NULL
417          *      and already unhashed and thus removed from ->thread_group.
418          *      This is OK, __unhash_process()->list_del_rcu() does not
419          *      clear the ->next pointer, we will find the new leader via
420          *      next_thread().
421          */
422         rcu_read_lock();
423         for_each_process(g) {
424                 if (g == tsk->group_leader)
425                         continue;
426                 if (g->flags & PF_KTHREAD)
427                         continue;
428
429                 for_each_thread(g, p) {
430                         if (unlikely(!p->mm))
431                                 continue;
432                         if (unlikely(p->mm == mm)) {
433                                 lock_task_sighand(p, &flags);
434                                 nr += zap_process(p, exit_code,
435                                                         SIGNAL_GROUP_EXIT);
436                                 unlock_task_sighand(p, &flags);
437                         }
438                         break;
439                 }
440         }
441         rcu_read_unlock();
442 done:
443         atomic_set(&core_state->nr_threads, nr);
444         return nr;
445 }
446
447 static int coredump_wait(int exit_code, struct core_state *core_state)
448 {
449         struct task_struct *tsk = current;
450         struct mm_struct *mm = tsk->mm;
451         int core_waiters = -EBUSY;
452
453         init_completion(&core_state->startup);
454         core_state->dumper.task = tsk;
455         core_state->dumper.next = NULL;
456
457         if (mmap_write_lock_killable(mm))
458                 return -EINTR;
459
460         if (!mm->core_state)
461                 core_waiters = zap_threads(tsk, mm, core_state, exit_code);
462         mmap_write_unlock(mm);
463
464         if (core_waiters > 0) {
465                 struct core_thread *ptr;
466
467                 freezer_do_not_count();
468                 wait_for_completion(&core_state->startup);
469                 freezer_count();
470                 /*
471                  * Wait for all the threads to become inactive, so that
472                  * all the thread context (extended register state, like
473                  * fpu etc) gets copied to the memory.
474                  */
475                 ptr = core_state->dumper.next;
476                 while (ptr != NULL) {
477                         wait_task_inactive(ptr->task, 0);
478                         ptr = ptr->next;
479                 }
480         }
481
482         return core_waiters;
483 }
484
485 static void coredump_finish(struct mm_struct *mm, bool core_dumped)
486 {
487         struct core_thread *curr, *next;
488         struct task_struct *task;
489
490         spin_lock_irq(&current->sighand->siglock);
491         if (core_dumped && !__fatal_signal_pending(current))
492                 current->signal->group_exit_code |= 0x80;
493         current->signal->group_exit_task = NULL;
494         current->signal->flags = SIGNAL_GROUP_EXIT;
495         spin_unlock_irq(&current->sighand->siglock);
496
497         next = mm->core_state->dumper.next;
498         while ((curr = next) != NULL) {
499                 next = curr->next;
500                 task = curr->task;
501                 /*
502                  * see exit_mm(), curr->task must not see
503                  * ->task == NULL before we read ->next.
504                  */
505                 smp_mb();
506                 curr->task = NULL;
507                 wake_up_process(task);
508         }
509
510         mm->core_state = NULL;
511 }
512
513 static bool dump_interrupted(void)
514 {
515         /*
516          * SIGKILL or freezing() interrupt the coredumping. Perhaps we
517          * can do try_to_freeze() and check __fatal_signal_pending(),
518          * but then we need to teach dump_write() to restart and clear
519          * TIF_SIGPENDING.
520          */
521         return signal_pending(current);
522 }
523
524 static void wait_for_dump_helpers(struct file *file)
525 {
526         struct pipe_inode_info *pipe = file->private_data;
527
528         pipe_lock(pipe);
529         pipe->readers++;
530         pipe->writers--;
531         wake_up_interruptible_sync(&pipe->rd_wait);
532         kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
533         pipe_unlock(pipe);
534
535         /*
536          * We actually want wait_event_freezable() but then we need
537          * to clear TIF_SIGPENDING and improve dump_interrupted().
538          */
539         wait_event_interruptible(pipe->rd_wait, pipe->readers == 1);
540
541         pipe_lock(pipe);
542         pipe->readers--;
543         pipe->writers++;
544         pipe_unlock(pipe);
545 }
546
547 /*
548  * umh_pipe_setup
549  * helper function to customize the process used
550  * to collect the core in userspace.  Specifically
551  * it sets up a pipe and installs it as fd 0 (stdin)
552  * for the process.  Returns 0 on success, or
553  * PTR_ERR on failure.
554  * Note that it also sets the core limit to 1.  This
555  * is a special value that we use to trap recursive
556  * core dumps
557  */
558 static int umh_pipe_setup(struct subprocess_info *info, struct cred *new)
559 {
560         struct file *files[2];
561         struct coredump_params *cp = (struct coredump_params *)info->data;
562         int err = create_pipe_files(files, 0);
563         if (err)
564                 return err;
565
566         cp->file = files[1];
567
568         err = replace_fd(0, files[0], 0);
569         fput(files[0]);
570         /* and disallow core files too */
571         current->signal->rlim[RLIMIT_CORE] = (struct rlimit){1, 1};
572
573         return err;
574 }
575
576 void do_coredump(const kernel_siginfo_t *siginfo)
577 {
578         struct core_state core_state;
579         struct core_name cn;
580         struct mm_struct *mm = current->mm;
581         struct linux_binfmt * binfmt;
582         const struct cred *old_cred;
583         struct cred *cred;
584         int retval = 0;
585         int ispipe;
586         size_t *argv = NULL;
587         int argc = 0;
588         struct files_struct *displaced;
589         /* require nonrelative corefile path and be extra careful */
590         bool need_suid_safe = false;
591         bool core_dumped = false;
592         static atomic_t core_dump_count = ATOMIC_INIT(0);
593         struct coredump_params cprm = {
594                 .siginfo = siginfo,
595                 .regs = signal_pt_regs(),
596                 .limit = rlimit(RLIMIT_CORE),
597                 /*
598                  * We must use the same mm->flags while dumping core to avoid
599                  * inconsistency of bit flags, since this flag is not protected
600                  * by any locks.
601                  */
602                 .mm_flags = mm->flags,
603         };
604
605         audit_core_dumps(siginfo->si_signo);
606
607         binfmt = mm->binfmt;
608         if (!binfmt || !binfmt->core_dump)
609                 goto fail;
610         if (!__get_dumpable(cprm.mm_flags))
611                 goto fail;
612
613         cred = prepare_creds();
614         if (!cred)
615                 goto fail;
616         /*
617          * We cannot trust fsuid as being the "true" uid of the process
618          * nor do we know its entire history. We only know it was tainted
619          * so we dump it as root in mode 2, and only into a controlled
620          * environment (pipe handler or fully qualified path).
621          */
622         if (__get_dumpable(cprm.mm_flags) == SUID_DUMP_ROOT) {
623                 /* Setuid core dump mode */
624                 cred->fsuid = GLOBAL_ROOT_UID;  /* Dump root private */
625                 need_suid_safe = true;
626         }
627
628         retval = coredump_wait(siginfo->si_signo, &core_state);
629         if (retval < 0)
630                 goto fail_creds;
631
632         old_cred = override_creds(cred);
633
634         ispipe = format_corename(&cn, &cprm, &argv, &argc);
635
636         if (ispipe) {
637                 int argi;
638                 int dump_count;
639                 char **helper_argv;
640                 struct subprocess_info *sub_info;
641
642                 if (ispipe < 0) {
643                         printk(KERN_WARNING "format_corename failed\n");
644                         printk(KERN_WARNING "Aborting core\n");
645                         goto fail_unlock;
646                 }
647
648                 if (cprm.limit == 1) {
649                         /* See umh_pipe_setup() which sets RLIMIT_CORE = 1.
650                          *
651                          * Normally core limits are irrelevant to pipes, since
652                          * we're not writing to the file system, but we use
653                          * cprm.limit of 1 here as a special value, this is a
654                          * consistent way to catch recursive crashes.
655                          * We can still crash if the core_pattern binary sets
656                          * RLIM_CORE = !1, but it runs as root, and can do
657                          * lots of stupid things.
658                          *
659                          * Note that we use task_tgid_vnr here to grab the pid
660                          * of the process group leader.  That way we get the
661                          * right pid if a thread in a multi-threaded
662                          * core_pattern process dies.
663                          */
664                         printk(KERN_WARNING
665                                 "Process %d(%s) has RLIMIT_CORE set to 1\n",
666                                 task_tgid_vnr(current), current->comm);
667                         printk(KERN_WARNING "Aborting core\n");
668                         goto fail_unlock;
669                 }
670                 cprm.limit = RLIM_INFINITY;
671
672                 dump_count = atomic_inc_return(&core_dump_count);
673                 if (core_pipe_limit && (core_pipe_limit < dump_count)) {
674                         printk(KERN_WARNING "Pid %d(%s) over core_pipe_limit\n",
675                                task_tgid_vnr(current), current->comm);
676                         printk(KERN_WARNING "Skipping core dump\n");
677                         goto fail_dropcount;
678                 }
679
680                 helper_argv = kmalloc_array(argc + 1, sizeof(*helper_argv),
681                                             GFP_KERNEL);
682                 if (!helper_argv) {
683                         printk(KERN_WARNING "%s failed to allocate memory\n",
684                                __func__);
685                         goto fail_dropcount;
686                 }
687                 for (argi = 0; argi < argc; argi++)
688                         helper_argv[argi] = cn.corename + argv[argi];
689                 helper_argv[argi] = NULL;
690
691                 retval = -ENOMEM;
692                 sub_info = call_usermodehelper_setup(helper_argv[0],
693                                                 helper_argv, NULL, GFP_KERNEL,
694                                                 umh_pipe_setup, NULL, &cprm);
695                 if (sub_info)
696                         retval = call_usermodehelper_exec(sub_info,
697                                                           UMH_WAIT_EXEC);
698
699                 kfree(helper_argv);
700                 if (retval) {
701                         printk(KERN_INFO "Core dump to |%s pipe failed\n",
702                                cn.corename);
703                         goto close_fail;
704                 }
705         } else {
706                 struct inode *inode;
707                 int open_flags = O_CREAT | O_RDWR | O_NOFOLLOW |
708                                  O_LARGEFILE | O_EXCL;
709
710                 if (cprm.limit < binfmt->min_coredump)
711                         goto fail_unlock;
712
713                 if (need_suid_safe && cn.corename[0] != '/') {
714                         printk(KERN_WARNING "Pid %d(%s) can only dump core "\
715                                 "to fully qualified path!\n",
716                                 task_tgid_vnr(current), current->comm);
717                         printk(KERN_WARNING "Skipping core dump\n");
718                         goto fail_unlock;
719                 }
720
721                 /*
722                  * Unlink the file if it exists unless this is a SUID
723                  * binary - in that case, we're running around with root
724                  * privs and don't want to unlink another user's coredump.
725                  */
726                 if (!need_suid_safe) {
727                         /*
728                          * If it doesn't exist, that's fine. If there's some
729                          * other problem, we'll catch it at the filp_open().
730                          */
731                         do_unlinkat(AT_FDCWD, getname_kernel(cn.corename));
732                 }
733
734                 /*
735                  * There is a race between unlinking and creating the
736                  * file, but if that causes an EEXIST here, that's
737                  * fine - another process raced with us while creating
738                  * the corefile, and the other process won. To userspace,
739                  * what matters is that at least one of the two processes
740                  * writes its coredump successfully, not which one.
741                  */
742                 if (need_suid_safe) {
743                         /*
744                          * Using user namespaces, normal user tasks can change
745                          * their current->fs->root to point to arbitrary
746                          * directories. Since the intention of the "only dump
747                          * with a fully qualified path" rule is to control where
748                          * coredumps may be placed using root privileges,
749                          * current->fs->root must not be used. Instead, use the
750                          * root directory of init_task.
751                          */
752                         struct path root;
753
754                         task_lock(&init_task);
755                         get_fs_root(init_task.fs, &root);
756                         task_unlock(&init_task);
757                         cprm.file = file_open_root(root.dentry, root.mnt,
758                                 cn.corename, open_flags, 0600);
759                         path_put(&root);
760                 } else {
761                         cprm.file = filp_open(cn.corename, open_flags, 0600);
762                 }
763                 if (IS_ERR(cprm.file))
764                         goto fail_unlock;
765
766                 inode = file_inode(cprm.file);
767                 if (inode->i_nlink > 1)
768                         goto close_fail;
769                 if (d_unhashed(cprm.file->f_path.dentry))
770                         goto close_fail;
771                 /*
772                  * AK: actually i see no reason to not allow this for named
773                  * pipes etc, but keep the previous behaviour for now.
774                  */
775                 if (!S_ISREG(inode->i_mode))
776                         goto close_fail;
777                 /*
778                  * Don't dump core if the filesystem changed owner or mode
779                  * of the file during file creation. This is an issue when
780                  * a process dumps core while its cwd is e.g. on a vfat
781                  * filesystem.
782                  */
783                 if (!uid_eq(inode->i_uid, current_fsuid()))
784                         goto close_fail;
785                 if ((inode->i_mode & 0677) != 0600)
786                         goto close_fail;
787                 if (!(cprm.file->f_mode & FMODE_CAN_WRITE))
788                         goto close_fail;
789                 if (do_truncate(cprm.file->f_path.dentry, 0, 0, cprm.file))
790                         goto close_fail;
791         }
792
793         /* get us an unshared descriptor table; almost always a no-op */
794         retval = unshare_files(&displaced);
795         if (retval)
796                 goto close_fail;
797         if (displaced)
798                 put_files_struct(displaced);
799         if (!dump_interrupted()) {
800                 /*
801                  * umh disabled with CONFIG_STATIC_USERMODEHELPER_PATH="" would
802                  * have this set to NULL.
803                  */
804                 if (!cprm.file) {
805                         pr_info("Core dump to |%s disabled\n", cn.corename);
806                         goto close_fail;
807                 }
808                 file_start_write(cprm.file);
809                 core_dumped = binfmt->core_dump(&cprm);
810                 file_end_write(cprm.file);
811         }
812         if (ispipe && core_pipe_limit)
813                 wait_for_dump_helpers(cprm.file);
814 close_fail:
815         if (cprm.file)
816                 filp_close(cprm.file, NULL);
817 fail_dropcount:
818         if (ispipe)
819                 atomic_dec(&core_dump_count);
820 fail_unlock:
821         kfree(argv);
822         kfree(cn.corename);
823         coredump_finish(mm, core_dumped);
824         revert_creds(old_cred);
825 fail_creds:
826         put_cred(cred);
827 fail:
828         return;
829 }
830
831 /*
832  * Core dumping helper functions.  These are the only things you should
833  * do on a core-file: use only these functions to write out all the
834  * necessary info.
835  */
836 int dump_emit(struct coredump_params *cprm, const void *addr, int nr)
837 {
838         struct file *file = cprm->file;
839         loff_t pos = file->f_pos;
840         ssize_t n;
841         if (cprm->written + nr > cprm->limit)
842                 return 0;
843         while (nr) {
844                 if (dump_interrupted())
845                         return 0;
846                 n = __kernel_write(file, addr, nr, &pos);
847                 if (n <= 0)
848                         return 0;
849                 file->f_pos = pos;
850                 cprm->written += n;
851                 cprm->pos += n;
852                 nr -= n;
853         }
854         return 1;
855 }
856 EXPORT_SYMBOL(dump_emit);
857
858 int dump_skip(struct coredump_params *cprm, size_t nr)
859 {
860         static char zeroes[PAGE_SIZE];
861         struct file *file = cprm->file;
862         if (file->f_op->llseek && file->f_op->llseek != no_llseek) {
863                 if (dump_interrupted() ||
864                     file->f_op->llseek(file, nr, SEEK_CUR) < 0)
865                         return 0;
866                 cprm->pos += nr;
867                 return 1;
868         } else {
869                 while (nr > PAGE_SIZE) {
870                         if (!dump_emit(cprm, zeroes, PAGE_SIZE))
871                                 return 0;
872                         nr -= PAGE_SIZE;
873                 }
874                 return dump_emit(cprm, zeroes, nr);
875         }
876 }
877 EXPORT_SYMBOL(dump_skip);
878
879 int dump_align(struct coredump_params *cprm, int align)
880 {
881         unsigned mod = cprm->pos & (align - 1);
882         if (align & (align - 1))
883                 return 0;
884         return mod ? dump_skip(cprm, align - mod) : 1;
885 }
886 EXPORT_SYMBOL(dump_align);
887
888 /*
889  * Ensures that file size is big enough to contain the current file
890  * postion. This prevents gdb from complaining about a truncated file
891  * if the last "write" to the file was dump_skip.
892  */
893 void dump_truncate(struct coredump_params *cprm)
894 {
895         struct file *file = cprm->file;
896         loff_t offset;
897
898         if (file->f_op->llseek && file->f_op->llseek != no_llseek) {
899                 offset = file->f_op->llseek(file, 0, SEEK_CUR);
900                 if (i_size_read(file->f_mapping->host) < offset)
901                         do_truncate(file->f_path.dentry, offset, 0, file);
902         }
903 }
904 EXPORT_SYMBOL(dump_truncate);