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1// SPDX-License-Identifier: GPL-2.0
2#include <linux/anon_inodes.h>
3#include <linux/exportfs.h>
4#include <linux/file.h>
5#include <linux/fs.h>
6#include <linux/cgroup.h>
7#include <linux/magic.h>
8#include <linux/mount.h>
9#include <linux/pid.h>
10#include <linux/pidfs.h>
11#include <linux/pid_namespace.h>
12#include <linux/poll.h>
13#include <linux/proc_fs.h>
14#include <linux/proc_ns.h>
15#include <linux/pseudo_fs.h>
16#include <linux/ptrace.h>
17#include <linux/seq_file.h>
18#include <uapi/linux/pidfd.h>
19#include <linux/ipc_namespace.h>
20#include <linux/time_namespace.h>
21#include <linux/utsname.h>
22#include <net/net_namespace.h>
23#include <linux/coredump.h>
24#include <linux/xattr.h>
25
26#include "internal.h"
27#include "mount.h"
28
29#define PIDFS_PID_DEAD ERR_PTR(-ESRCH)
30
31static struct kmem_cache *pidfs_attr_cachep __ro_after_init;
32static struct kmem_cache *pidfs_xattr_cachep __ro_after_init;
33
34static struct path pidfs_root_path = {};
35
36void pidfs_get_root(struct path *path)
37{
38 *path = pidfs_root_path;
39 path_get(path);
40}
41
42enum pidfs_attr_mask_bits {
43 PIDFS_ATTR_BIT_EXIT = 0,
44 PIDFS_ATTR_BIT_COREDUMP = 1,
45};
46
47struct pidfs_attr {
48 unsigned long attr_mask;
49 struct simple_xattrs *xattrs;
50 struct /* exit info */ {
51 __u64 cgroupid;
52 __s32 exit_code;
53 };
54 __u32 coredump_mask;
55 __u32 coredump_signal;
56};
57
58static struct rb_root pidfs_ino_tree = RB_ROOT;
59
60#if BITS_PER_LONG == 32
61static inline unsigned long pidfs_ino(u64 ino)
62{
63 return lower_32_bits(ino);
64}
65
66/* On 32 bit the generation number are the upper 32 bits. */
67static inline u32 pidfs_gen(u64 ino)
68{
69 return upper_32_bits(ino);
70}
71
72#else
73
74/* On 64 bit simply return ino. */
75static inline unsigned long pidfs_ino(u64 ino)
76{
77 return ino;
78}
79
80/* On 64 bit the generation number is 0. */
81static inline u32 pidfs_gen(u64 ino)
82{
83 return 0;
84}
85#endif
86
87static int pidfs_ino_cmp(struct rb_node *a, const struct rb_node *b)
88{
89 struct pid *pid_a = rb_entry(a, struct pid, pidfs_node);
90 struct pid *pid_b = rb_entry(b, struct pid, pidfs_node);
91 u64 pid_ino_a = pid_a->ino;
92 u64 pid_ino_b = pid_b->ino;
93
94 if (pid_ino_a < pid_ino_b)
95 return -1;
96 if (pid_ino_a > pid_ino_b)
97 return 1;
98 return 0;
99}
100
101void pidfs_add_pid(struct pid *pid)
102{
103 static u64 pidfs_ino_nr = 2;
104
105 /*
106 * On 64 bit nothing special happens. The 64bit number assigned
107 * to struct pid is the inode number.
108 *
109 * On 32 bit the 64 bit number assigned to struct pid is split
110 * into two 32 bit numbers. The lower 32 bits are used as the
111 * inode number and the upper 32 bits are used as the inode
112 * generation number.
113 *
114 * On 32 bit pidfs_ino() will return the lower 32 bit. When
115 * pidfs_ino() returns zero a wrap around happened. When a
116 * wraparound happens the 64 bit number will be incremented by 2
117 * so inode numbering starts at 2 again.
118 *
119 * On 64 bit comparing two pidfds is as simple as comparing
120 * inode numbers.
121 *
122 * When a wraparound happens on 32 bit multiple pidfds with the
123 * same inode number are likely to exist (This isn't a problem
124 * since before pidfs pidfds used the anonymous inode meaning
125 * all pidfds had the same inode number.). Userspace can
126 * reconstruct the 64 bit identifier by retrieving both the
127 * inode number and the inode generation number to compare or
128 * use file handles.
129 */
130 if (pidfs_ino(ino: pidfs_ino_nr) == 0)
131 pidfs_ino_nr += 2;
132
133 pid->ino = pidfs_ino_nr;
134 pid->stashed = NULL;
135 pid->attr = NULL;
136 pidfs_ino_nr++;
137
138 write_seqcount_begin(&pidmap_lock_seq);
139 rb_find_add_rcu(node: &pid->pidfs_node, tree: &pidfs_ino_tree, cmp: pidfs_ino_cmp);
140 write_seqcount_end(&pidmap_lock_seq);
141}
142
143void pidfs_remove_pid(struct pid *pid)
144{
145 write_seqcount_begin(&pidmap_lock_seq);
146 rb_erase(&pid->pidfs_node, &pidfs_ino_tree);
147 write_seqcount_end(&pidmap_lock_seq);
148}
149
150void pidfs_free_pid(struct pid *pid)
151{
152 struct pidfs_attr *attr __free(kfree) = no_free_ptr(pid->attr);
153 struct simple_xattrs *xattrs __free(kfree) = NULL;
154
155 /*
156 * Any dentry must've been wiped from the pid by now.
157 * Otherwise there's a reference count bug.
158 */
159 VFS_WARN_ON_ONCE(pid->stashed);
160
161 /*
162 * This if an error occurred during e.g., task creation that
163 * causes us to never go through the exit path.
164 */
165 if (unlikely(!attr))
166 return;
167
168 /* This never had a pidfd created. */
169 if (IS_ERR(ptr: attr))
170 return;
171
172 xattrs = no_free_ptr(attr->xattrs);
173 if (xattrs)
174 simple_xattrs_free(xattrs, NULL);
175}
176
177#ifdef CONFIG_PROC_FS
178/**
179 * pidfd_show_fdinfo - print information about a pidfd
180 * @m: proc fdinfo file
181 * @f: file referencing a pidfd
182 *
183 * Pid:
184 * This function will print the pid that a given pidfd refers to in the
185 * pid namespace of the procfs instance.
186 * If the pid namespace of the process is not a descendant of the pid
187 * namespace of the procfs instance 0 will be shown as its pid. This is
188 * similar to calling getppid() on a process whose parent is outside of
189 * its pid namespace.
190 *
191 * NSpid:
192 * If pid namespaces are supported then this function will also print
193 * the pid of a given pidfd refers to for all descendant pid namespaces
194 * starting from the current pid namespace of the instance, i.e. the
195 * Pid field and the first entry in the NSpid field will be identical.
196 * If the pid namespace of the process is not a descendant of the pid
197 * namespace of the procfs instance 0 will be shown as its first NSpid
198 * entry and no others will be shown.
199 * Note that this differs from the Pid and NSpid fields in
200 * /proc/<pid>/status where Pid and NSpid are always shown relative to
201 * the pid namespace of the procfs instance. The difference becomes
202 * obvious when sending around a pidfd between pid namespaces from a
203 * different branch of the tree, i.e. where no ancestral relation is
204 * present between the pid namespaces:
205 * - create two new pid namespaces ns1 and ns2 in the initial pid
206 * namespace (also take care to create new mount namespaces in the
207 * new pid namespace and mount procfs)
208 * - create a process with a pidfd in ns1
209 * - send pidfd from ns1 to ns2
210 * - read /proc/self/fdinfo/<pidfd> and observe that both Pid and NSpid
211 * have exactly one entry, which is 0
212 */
213static void pidfd_show_fdinfo(struct seq_file *m, struct file *f)
214{
215 struct pid *pid = pidfd_pid(file: f);
216 struct pid_namespace *ns;
217 pid_t nr = -1;
218
219 if (likely(pid_has_task(pid, PIDTYPE_PID))) {
220 ns = proc_pid_ns(sb: file_inode(f: m->file)->i_sb);
221 nr = pid_nr_ns(pid, ns);
222 }
223
224 seq_put_decimal_ll(m, delimiter: "Pid:\t", num: nr);
225
226#ifdef CONFIG_PID_NS
227 seq_put_decimal_ll(m, delimiter: "\nNSpid:\t", num: nr);
228 if (nr > 0) {
229 int i;
230
231 /* If nr is non-zero it means that 'pid' is valid and that
232 * ns, i.e. the pid namespace associated with the procfs
233 * instance, is in the pid namespace hierarchy of pid.
234 * Start at one below the already printed level.
235 */
236 for (i = ns->level + 1; i <= pid->level; i++)
237 seq_put_decimal_ll(m, delimiter: "\t", num: pid->numbers[i].nr);
238 }
239#endif
240 seq_putc(m, c: '\n');
241}
242#endif
243
244/*
245 * Poll support for process exit notification.
246 */
247static __poll_t pidfd_poll(struct file *file, struct poll_table_struct *pts)
248{
249 struct pid *pid = pidfd_pid(file);
250 struct task_struct *task;
251 __poll_t poll_flags = 0;
252
253 poll_wait(filp: file, wait_address: &pid->wait_pidfd, p: pts);
254 /*
255 * Don't wake waiters if the thread-group leader exited
256 * prematurely. They either get notified when the last subthread
257 * exits or not at all if one of the remaining subthreads execs
258 * and assumes the struct pid of the old thread-group leader.
259 */
260 guard(rcu)();
261 task = pid_task(pid, PIDTYPE_PID);
262 if (!task)
263 poll_flags = EPOLLIN | EPOLLRDNORM | EPOLLHUP;
264 else if (task->exit_state && !delay_group_leader(task))
265 poll_flags = EPOLLIN | EPOLLRDNORM;
266
267 return poll_flags;
268}
269
270static inline bool pid_in_current_pidns(const struct pid *pid)
271{
272 const struct pid_namespace *ns = task_active_pid_ns(current);
273
274 if (ns->level <= pid->level)
275 return pid->numbers[ns->level].ns == ns;
276
277 return false;
278}
279
280static __u32 pidfs_coredump_mask(unsigned long mm_flags)
281{
282 switch (__get_dumpable(mm_flags)) {
283 case SUID_DUMP_USER:
284 return PIDFD_COREDUMP_USER;
285 case SUID_DUMP_ROOT:
286 return PIDFD_COREDUMP_ROOT;
287 case SUID_DUMP_DISABLE:
288 return PIDFD_COREDUMP_SKIP;
289 default:
290 WARN_ON_ONCE(true);
291 }
292
293 return 0;
294}
295
296/* This must be updated whenever a new flag is added */
297#define PIDFD_INFO_SUPPORTED (PIDFD_INFO_PID | \
298 PIDFD_INFO_CREDS | \
299 PIDFD_INFO_CGROUPID | \
300 PIDFD_INFO_EXIT | \
301 PIDFD_INFO_COREDUMP | \
302 PIDFD_INFO_SUPPORTED_MASK | \
303 PIDFD_INFO_COREDUMP_SIGNAL)
304
305static long pidfd_info(struct file *file, unsigned int cmd, unsigned long arg)
306{
307 struct pidfd_info __user *uinfo = (struct pidfd_info __user *)arg;
308 struct task_struct *task __free(put_task) = NULL;
309 struct pid *pid = pidfd_pid(file);
310 size_t usize = _IOC_SIZE(cmd);
311 struct pidfd_info kinfo = {};
312 struct user_namespace *user_ns;
313 struct pidfs_attr *attr;
314 const struct cred *c;
315 __u64 mask;
316
317 BUILD_BUG_ON(sizeof(struct pidfd_info) != PIDFD_INFO_SIZE_VER2);
318
319 if (!uinfo)
320 return -EINVAL;
321 if (usize < PIDFD_INFO_SIZE_VER0)
322 return -EINVAL; /* First version, no smaller struct possible */
323
324 if (copy_from_user(to: &mask, from: &uinfo->mask, n: sizeof(mask)))
325 return -EFAULT;
326
327 /*
328 * Restrict information retrieval to tasks within the caller's pid
329 * namespace hierarchy.
330 */
331 if (!pid_in_current_pidns(pid))
332 return -ESRCH;
333
334 attr = READ_ONCE(pid->attr);
335 if (mask & PIDFD_INFO_EXIT) {
336 if (test_bit(PIDFS_ATTR_BIT_EXIT, &attr->attr_mask)) {
337 smp_rmb();
338 kinfo.mask |= PIDFD_INFO_EXIT;
339#ifdef CONFIG_CGROUPS
340 kinfo.cgroupid = attr->cgroupid;
341 kinfo.mask |= PIDFD_INFO_CGROUPID;
342#endif
343 kinfo.exit_code = attr->exit_code;
344 }
345 }
346
347 if (mask & PIDFD_INFO_COREDUMP) {
348 if (test_bit(PIDFS_ATTR_BIT_COREDUMP, &attr->attr_mask)) {
349 smp_rmb();
350 kinfo.mask |= PIDFD_INFO_COREDUMP | PIDFD_INFO_COREDUMP_SIGNAL;
351 kinfo.coredump_mask = attr->coredump_mask;
352 kinfo.coredump_signal = attr->coredump_signal;
353 }
354 }
355
356 task = get_pid_task(pid, PIDTYPE_PID);
357 if (!task) {
358 /*
359 * If the task has already been reaped, only exit
360 * information is available
361 */
362 if (!(mask & PIDFD_INFO_EXIT))
363 return -ESRCH;
364
365 goto copy_out;
366 }
367
368 c = get_task_cred(task);
369 if (!c)
370 return -ESRCH;
371
372 if ((mask & PIDFD_INFO_COREDUMP) && !kinfo.coredump_mask) {
373 guard(task_lock)(T: task);
374 if (task->mm) {
375 unsigned long flags = __mm_flags_get_dumpable(mm: task->mm);
376
377 kinfo.coredump_mask = pidfs_coredump_mask(mm_flags: flags);
378 kinfo.mask |= PIDFD_INFO_COREDUMP;
379 /* No coredump actually took place, so no coredump signal. */
380 }
381 }
382
383 /* Unconditionally return identifiers and credentials, the rest only on request */
384
385 user_ns = current_user_ns();
386 kinfo.ruid = from_kuid_munged(to: user_ns, uid: c->uid);
387 kinfo.rgid = from_kgid_munged(to: user_ns, gid: c->gid);
388 kinfo.euid = from_kuid_munged(to: user_ns, uid: c->euid);
389 kinfo.egid = from_kgid_munged(to: user_ns, gid: c->egid);
390 kinfo.suid = from_kuid_munged(to: user_ns, uid: c->suid);
391 kinfo.sgid = from_kgid_munged(to: user_ns, gid: c->sgid);
392 kinfo.fsuid = from_kuid_munged(to: user_ns, uid: c->fsuid);
393 kinfo.fsgid = from_kgid_munged(to: user_ns, gid: c->fsgid);
394 kinfo.mask |= PIDFD_INFO_CREDS;
395 put_cred(cred: c);
396
397#ifdef CONFIG_CGROUPS
398 if (!kinfo.cgroupid) {
399 struct cgroup *cgrp;
400
401 rcu_read_lock();
402 cgrp = task_dfl_cgroup(task);
403 kinfo.cgroupid = cgroup_id(cgrp);
404 kinfo.mask |= PIDFD_INFO_CGROUPID;
405 rcu_read_unlock();
406 }
407#endif
408
409 /*
410 * Copy pid/tgid last, to reduce the chances the information might be
411 * stale. Note that it is not possible to ensure it will be valid as the
412 * task might return as soon as the copy_to_user finishes, but that's ok
413 * and userspace expects that might happen and can act accordingly, so
414 * this is just best-effort. What we can do however is checking that all
415 * the fields are set correctly, or return ESRCH to avoid providing
416 * incomplete information. */
417
418 kinfo.ppid = task_ppid_nr_ns(tsk: task, NULL);
419 kinfo.tgid = task_tgid_vnr(tsk: task);
420 kinfo.pid = task_pid_vnr(tsk: task);
421 kinfo.mask |= PIDFD_INFO_PID;
422
423 if (kinfo.pid == 0 || kinfo.tgid == 0)
424 return -ESRCH;
425
426copy_out:
427 if (mask & PIDFD_INFO_SUPPORTED_MASK) {
428 kinfo.mask |= PIDFD_INFO_SUPPORTED_MASK;
429 kinfo.supported_mask = PIDFD_INFO_SUPPORTED;
430 }
431
432 /* Are there bits in the return mask not present in PIDFD_INFO_SUPPORTED? */
433 WARN_ON_ONCE(~PIDFD_INFO_SUPPORTED & kinfo.mask);
434 /*
435 * If userspace and the kernel have the same struct size it can just
436 * be copied. If userspace provides an older struct, only the bits that
437 * userspace knows about will be copied. If userspace provides a new
438 * struct, only the bits that the kernel knows about will be copied.
439 */
440 return copy_struct_to_user(dst: uinfo, usize, src: &kinfo, ksize: sizeof(kinfo), NULL);
441}
442
443static bool pidfs_ioctl_valid(unsigned int cmd)
444{
445 switch (cmd) {
446 case FS_IOC_GETVERSION:
447 case PIDFD_GET_CGROUP_NAMESPACE:
448 case PIDFD_GET_IPC_NAMESPACE:
449 case PIDFD_GET_MNT_NAMESPACE:
450 case PIDFD_GET_NET_NAMESPACE:
451 case PIDFD_GET_PID_FOR_CHILDREN_NAMESPACE:
452 case PIDFD_GET_TIME_NAMESPACE:
453 case PIDFD_GET_TIME_FOR_CHILDREN_NAMESPACE:
454 case PIDFD_GET_UTS_NAMESPACE:
455 case PIDFD_GET_USER_NAMESPACE:
456 case PIDFD_GET_PID_NAMESPACE:
457 return true;
458 }
459
460 /* Extensible ioctls require some more careful checks. */
461 switch (_IOC_NR(cmd)) {
462 case _IOC_NR(PIDFD_GET_INFO):
463 /*
464 * Try to prevent performing a pidfd ioctl when someone
465 * erronously mistook the file descriptor for a pidfd.
466 * This is not perfect but will catch most cases.
467 */
468 return extensible_ioctl_valid(cmd_a: cmd, PIDFD_GET_INFO, PIDFD_INFO_SIZE_VER0);
469 }
470
471 return false;
472}
473
474static long pidfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
475{
476 struct task_struct *task __free(put_task) = NULL;
477 struct nsproxy *nsp __free(put_nsproxy) = NULL;
478 struct ns_common *ns_common = NULL;
479
480 if (!pidfs_ioctl_valid(cmd))
481 return -ENOIOCTLCMD;
482
483 if (cmd == FS_IOC_GETVERSION) {
484 if (!arg)
485 return -EINVAL;
486
487 __u32 __user *argp = (__u32 __user *)arg;
488 return put_user(file_inode(file)->i_generation, argp);
489 }
490
491 /* Extensible IOCTL that does not open namespace FDs, take a shortcut */
492 if (_IOC_NR(cmd) == _IOC_NR(PIDFD_GET_INFO))
493 return pidfd_info(file, cmd, arg);
494
495 task = get_pid_task(pid: pidfd_pid(file), PIDTYPE_PID);
496 if (!task)
497 return -ESRCH;
498
499 if (arg)
500 return -EINVAL;
501
502 scoped_guard(task_lock, task) {
503 nsp = task->nsproxy;
504 if (nsp)
505 get_nsproxy(ns: nsp);
506 }
507 if (!nsp)
508 return -ESRCH; /* just pretend it didn't exist */
509
510 /*
511 * We're trying to open a file descriptor to the namespace so perform a
512 * filesystem cred ptrace check. Also, we mirror nsfs behavior.
513 */
514 if (!ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS))
515 return -EACCES;
516
517 switch (cmd) {
518 /* Namespaces that hang of nsproxy. */
519 case PIDFD_GET_CGROUP_NAMESPACE:
520#ifdef CONFIG_CGROUPS
521 if (!ns_ref_get(nsp->cgroup_ns))
522 break;
523 ns_common = to_ns_common(nsp->cgroup_ns);
524#endif
525 break;
526 case PIDFD_GET_IPC_NAMESPACE:
527#ifdef CONFIG_IPC_NS
528 if (!ns_ref_get(nsp->ipc_ns))
529 break;
530 ns_common = to_ns_common(nsp->ipc_ns);
531#endif
532 break;
533 case PIDFD_GET_MNT_NAMESPACE:
534 if (!ns_ref_get(nsp->mnt_ns))
535 break;
536 ns_common = to_ns_common(nsp->mnt_ns);
537 break;
538 case PIDFD_GET_NET_NAMESPACE:
539#ifdef CONFIG_NET_NS
540 if (!ns_ref_get(nsp->net_ns))
541 break;
542 ns_common = to_ns_common(nsp->net_ns);
543#endif
544 break;
545 case PIDFD_GET_PID_FOR_CHILDREN_NAMESPACE:
546#ifdef CONFIG_PID_NS
547 if (!ns_ref_get(nsp->pid_ns_for_children))
548 break;
549 ns_common = to_ns_common(nsp->pid_ns_for_children);
550#endif
551 break;
552 case PIDFD_GET_TIME_NAMESPACE:
553#ifdef CONFIG_TIME_NS
554 if (!ns_ref_get(nsp->time_ns))
555 break;
556 ns_common = to_ns_common(nsp->time_ns);
557#endif
558 break;
559 case PIDFD_GET_TIME_FOR_CHILDREN_NAMESPACE:
560#ifdef CONFIG_TIME_NS
561 if (!ns_ref_get(nsp->time_ns_for_children))
562 break;
563 ns_common = to_ns_common(nsp->time_ns_for_children);
564#endif
565 break;
566 case PIDFD_GET_UTS_NAMESPACE:
567#ifdef CONFIG_UTS_NS
568 if (!ns_ref_get(nsp->uts_ns))
569 break;
570 ns_common = to_ns_common(nsp->uts_ns);
571#endif
572 break;
573 /* Namespaces that don't hang of nsproxy. */
574 case PIDFD_GET_USER_NAMESPACE:
575#ifdef CONFIG_USER_NS
576 scoped_guard(rcu) {
577 struct user_namespace *user_ns;
578
579 user_ns = task_cred_xxx(task, user_ns);
580 if (!ns_ref_get(user_ns))
581 break;
582 ns_common = to_ns_common(user_ns);
583 }
584#endif
585 break;
586 case PIDFD_GET_PID_NAMESPACE:
587#ifdef CONFIG_PID_NS
588 scoped_guard(rcu) {
589 struct pid_namespace *pid_ns;
590
591 pid_ns = task_active_pid_ns(tsk: task);
592 if (!ns_ref_get(pid_ns))
593 break;
594 ns_common = to_ns_common(pid_ns);
595 }
596#endif
597 break;
598 default:
599 return -ENOIOCTLCMD;
600 }
601
602 if (!ns_common)
603 return -EOPNOTSUPP;
604
605 /* open_namespace() unconditionally consumes the reference */
606 return open_namespace(ns: ns_common);
607}
608
609static const struct file_operations pidfs_file_operations = {
610 .poll = pidfd_poll,
611#ifdef CONFIG_PROC_FS
612 .show_fdinfo = pidfd_show_fdinfo,
613#endif
614 .unlocked_ioctl = pidfd_ioctl,
615 .compat_ioctl = compat_ptr_ioctl,
616};
617
618struct pid *pidfd_pid(const struct file *file)
619{
620 if (file->f_op != &pidfs_file_operations)
621 return ERR_PTR(error: -EBADF);
622 return file_inode(f: file)->i_private;
623}
624
625/*
626 * We're called from release_task(). We know there's at least one
627 * reference to struct pid being held that won't be released until the
628 * task has been reaped which cannot happen until we're out of
629 * release_task().
630 *
631 * If this struct pid has at least once been referred to by a pidfd then
632 * pid->attr will be allocated. If not we mark the struct pid as dead so
633 * anyone who is trying to register it with pidfs will fail to do so.
634 * Otherwise we would hand out pidfs for reaped tasks without having
635 * exit information available.
636 *
637 * Worst case is that we've filled in the info and the pid gets freed
638 * right away in free_pid() when no one holds a pidfd anymore. Since
639 * pidfs_exit() currently is placed after exit_task_work() we know that
640 * it cannot be us aka the exiting task holding a pidfd to itself.
641 */
642void pidfs_exit(struct task_struct *tsk)
643{
644 struct pid *pid = task_pid(task: tsk);
645 struct pidfs_attr *attr;
646#ifdef CONFIG_CGROUPS
647 struct cgroup *cgrp;
648#endif
649
650 might_sleep();
651
652 /* Synchronize with pidfs_register_pid(). */
653 scoped_guard(spinlock_irq, &pid->wait_pidfd.lock) {
654 attr = pid->attr;
655 if (!attr) {
656 /*
657 * No one ever held a pidfd for this struct pid.
658 * Mark it as dead so no one can add a pidfs
659 * entry anymore. We're about to be reaped and
660 * so no exit information would be available.
661 */
662 pid->attr = PIDFS_PID_DEAD;
663 return;
664 }
665 }
666
667 /*
668 * If @pid->attr is set someone might still legitimately hold a
669 * pidfd to @pid or someone might concurrently still be getting
670 * a reference to an already stashed dentry from @pid->stashed.
671 * So defer cleaning @pid->attr until the last reference to @pid
672 * is put
673 */
674
675#ifdef CONFIG_CGROUPS
676 rcu_read_lock();
677 cgrp = task_dfl_cgroup(task: tsk);
678 attr->cgroupid = cgroup_id(cgrp);
679 rcu_read_unlock();
680#endif
681 attr->exit_code = tsk->exit_code;
682
683 /* Ensure that PIDFD_GET_INFO sees either all or nothing. */
684 smp_wmb();
685 set_bit(nr: PIDFS_ATTR_BIT_EXIT, addr: &attr->attr_mask);
686}
687
688#ifdef CONFIG_COREDUMP
689void pidfs_coredump(const struct coredump_params *cprm)
690{
691 struct pid *pid = cprm->pid;
692 struct pidfs_attr *attr;
693
694 attr = READ_ONCE(pid->attr);
695
696 VFS_WARN_ON_ONCE(!attr);
697 VFS_WARN_ON_ONCE(attr == PIDFS_PID_DEAD);
698
699 /* Note how we were coredumped and that we coredumped. */
700 attr->coredump_mask = pidfs_coredump_mask(mm_flags: cprm->mm_flags) |
701 PIDFD_COREDUMPED;
702 /* If coredumping is set to skip we should never end up here. */
703 VFS_WARN_ON_ONCE(attr->coredump_mask & PIDFD_COREDUMP_SKIP);
704 /* Expose the signal number that caused the coredump. */
705 attr->coredump_signal = cprm->siginfo->si_signo;
706 smp_wmb();
707 set_bit(nr: PIDFS_ATTR_BIT_COREDUMP, addr: &attr->attr_mask);
708}
709#endif
710
711static struct vfsmount *pidfs_mnt __ro_after_init;
712
713/*
714 * The vfs falls back to simple_setattr() if i_op->setattr() isn't
715 * implemented. Let's reject it completely until we have a clean
716 * permission concept for pidfds.
717 */
718static int pidfs_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
719 struct iattr *attr)
720{
721 return anon_inode_setattr(idmap, dentry, attr);
722}
723
724static int pidfs_getattr(struct mnt_idmap *idmap, const struct path *path,
725 struct kstat *stat, u32 request_mask,
726 unsigned int query_flags)
727{
728 return anon_inode_getattr(idmap, path, stat, request_mask, query_flags);
729}
730
731static ssize_t pidfs_listxattr(struct dentry *dentry, char *buf, size_t size)
732{
733 struct inode *inode = d_inode(dentry);
734 struct pid *pid = inode->i_private;
735 struct pidfs_attr *attr = pid->attr;
736 struct simple_xattrs *xattrs;
737
738 xattrs = READ_ONCE(attr->xattrs);
739 if (!xattrs)
740 return 0;
741
742 return simple_xattr_list(inode, xattrs, buffer: buf, size);
743}
744
745static const struct inode_operations pidfs_inode_operations = {
746 .getattr = pidfs_getattr,
747 .setattr = pidfs_setattr,
748 .listxattr = pidfs_listxattr,
749};
750
751static void pidfs_evict_inode(struct inode *inode)
752{
753 struct pid *pid = inode->i_private;
754
755 clear_inode(inode);
756 put_pid(pid);
757}
758
759static const struct super_operations pidfs_sops = {
760 .drop_inode = inode_just_drop,
761 .evict_inode = pidfs_evict_inode,
762 .statfs = simple_statfs,
763};
764
765/*
766 * 'lsof' has knowledge of out historical anon_inode use, and expects
767 * the pidfs dentry name to start with 'anon_inode'.
768 */
769static char *pidfs_dname(struct dentry *dentry, char *buffer, int buflen)
770{
771 return dynamic_dname(buffer, buflen, "anon_inode:[pidfd]");
772}
773
774const struct dentry_operations pidfs_dentry_operations = {
775 .d_dname = pidfs_dname,
776 .d_prune = stashed_dentry_prune,
777};
778
779static int pidfs_encode_fh(struct inode *inode, u32 *fh, int *max_len,
780 struct inode *parent)
781{
782 const struct pid *pid = inode->i_private;
783
784 if (*max_len < 2) {
785 *max_len = 2;
786 return FILEID_INVALID;
787 }
788
789 *max_len = 2;
790 *(u64 *)fh = pid->ino;
791 return FILEID_KERNFS;
792}
793
794static int pidfs_ino_find(const void *key, const struct rb_node *node)
795{
796 const u64 pid_ino = *(u64 *)key;
797 const struct pid *pid = rb_entry(node, struct pid, pidfs_node);
798
799 if (pid_ino < pid->ino)
800 return -1;
801 if (pid_ino > pid->ino)
802 return 1;
803 return 0;
804}
805
806/* Find a struct pid based on the inode number. */
807static struct pid *pidfs_ino_get_pid(u64 ino)
808{
809 struct pid *pid;
810 struct rb_node *node;
811 unsigned int seq;
812
813 guard(rcu)();
814 do {
815 seq = read_seqcount_begin(&pidmap_lock_seq);
816 node = rb_find_rcu(key: &ino, tree: &pidfs_ino_tree, cmp: pidfs_ino_find);
817 if (node)
818 break;
819 } while (read_seqcount_retry(&pidmap_lock_seq, seq));
820
821 if (!node)
822 return NULL;
823
824 pid = rb_entry(node, struct pid, pidfs_node);
825
826 /* Within our pid namespace hierarchy? */
827 if (pid_vnr(pid) == 0)
828 return NULL;
829
830 return get_pid(pid);
831}
832
833static struct dentry *pidfs_fh_to_dentry(struct super_block *sb,
834 struct fid *fid, int fh_len,
835 int fh_type)
836{
837 int ret;
838 u64 pid_ino;
839 struct path path;
840 struct pid *pid;
841
842 if (fh_len < 2)
843 return NULL;
844
845 switch (fh_type) {
846 case FILEID_KERNFS:
847 pid_ino = *(u64 *)fid;
848 break;
849 default:
850 return NULL;
851 }
852
853 pid = pidfs_ino_get_pid(ino: pid_ino);
854 if (!pid)
855 return NULL;
856
857 ret = path_from_stashed(stashed: &pid->stashed, mnt: pidfs_mnt, data: pid, path: &path);
858 if (ret < 0)
859 return ERR_PTR(error: ret);
860
861 VFS_WARN_ON_ONCE(!pid->attr);
862
863 mntput(mnt: path.mnt);
864 return path.dentry;
865}
866
867/*
868 * Make sure that we reject any nonsensical flags that users pass via
869 * open_by_handle_at(). Note that PIDFD_THREAD is defined as O_EXCL, and
870 * PIDFD_NONBLOCK as O_NONBLOCK.
871 */
872#define VALID_FILE_HANDLE_OPEN_FLAGS \
873 (O_RDONLY | O_WRONLY | O_RDWR | O_NONBLOCK | O_CLOEXEC | O_EXCL)
874
875static int pidfs_export_permission(struct handle_to_path_ctx *ctx,
876 unsigned int oflags)
877{
878 if (oflags & ~(VALID_FILE_HANDLE_OPEN_FLAGS | O_LARGEFILE))
879 return -EINVAL;
880
881 /*
882 * pidfd_ino_get_pid() will verify that the struct pid is part
883 * of the caller's pid namespace hierarchy. No further
884 * permission checks are needed.
885 */
886 return 0;
887}
888
889static struct file *pidfs_export_open(const struct path *path, unsigned int oflags)
890{
891 /*
892 * Clear O_LARGEFILE as open_by_handle_at() forces it and raise
893 * O_RDWR as pidfds always are.
894 */
895 oflags &= ~O_LARGEFILE;
896 return dentry_open(path, flags: oflags | O_RDWR, current_cred());
897}
898
899static const struct export_operations pidfs_export_operations = {
900 .encode_fh = pidfs_encode_fh,
901 .fh_to_dentry = pidfs_fh_to_dentry,
902 .open = pidfs_export_open,
903 .permission = pidfs_export_permission,
904};
905
906static int pidfs_init_inode(struct inode *inode, void *data)
907{
908 const struct pid *pid = data;
909
910 inode->i_private = data;
911 inode->i_flags |= S_PRIVATE | S_ANON_INODE;
912 /* We allow to set xattrs. */
913 inode->i_flags &= ~S_IMMUTABLE;
914 inode->i_mode |= S_IRWXU;
915 inode->i_op = &pidfs_inode_operations;
916 inode->i_fop = &pidfs_file_operations;
917 inode->i_ino = pidfs_ino(ino: pid->ino);
918 inode->i_generation = pidfs_gen(ino: pid->ino);
919 return 0;
920}
921
922static void pidfs_put_data(void *data)
923{
924 struct pid *pid = data;
925 put_pid(pid);
926}
927
928/**
929 * pidfs_register_pid - register a struct pid in pidfs
930 * @pid: pid to pin
931 *
932 * Register a struct pid in pidfs.
933 *
934 * Return: On success zero, on error a negative error code is returned.
935 */
936int pidfs_register_pid(struct pid *pid)
937{
938 struct pidfs_attr *new_attr __free(kfree) = NULL;
939 struct pidfs_attr *attr;
940
941 might_sleep();
942
943 if (!pid)
944 return 0;
945
946 attr = READ_ONCE(pid->attr);
947 if (unlikely(attr == PIDFS_PID_DEAD))
948 return PTR_ERR(PIDFS_PID_DEAD);
949 if (attr)
950 return 0;
951
952 new_attr = kmem_cache_zalloc(pidfs_attr_cachep, GFP_KERNEL);
953 if (!new_attr)
954 return -ENOMEM;
955
956 /* Synchronize with pidfs_exit(). */
957 guard(spinlock_irq)(l: &pid->wait_pidfd.lock);
958
959 attr = pid->attr;
960 if (unlikely(attr == PIDFS_PID_DEAD))
961 return PTR_ERR(PIDFS_PID_DEAD);
962 if (unlikely(attr))
963 return 0;
964
965 pid->attr = no_free_ptr(new_attr);
966 return 0;
967}
968
969static struct dentry *pidfs_stash_dentry(struct dentry **stashed,
970 struct dentry *dentry)
971{
972 int ret;
973 struct pid *pid = d_inode(dentry)->i_private;
974
975 VFS_WARN_ON_ONCE(stashed != &pid->stashed);
976
977 ret = pidfs_register_pid(pid);
978 if (ret)
979 return ERR_PTR(error: ret);
980
981 return stash_dentry(stashed, dentry);
982}
983
984static const struct stashed_operations pidfs_stashed_ops = {
985 .stash_dentry = pidfs_stash_dentry,
986 .init_inode = pidfs_init_inode,
987 .put_data = pidfs_put_data,
988};
989
990static int pidfs_xattr_get(const struct xattr_handler *handler,
991 struct dentry *unused, struct inode *inode,
992 const char *suffix, void *value, size_t size)
993{
994 struct pid *pid = inode->i_private;
995 struct pidfs_attr *attr = pid->attr;
996 const char *name;
997 struct simple_xattrs *xattrs;
998
999 xattrs = READ_ONCE(attr->xattrs);
1000 if (!xattrs)
1001 return 0;
1002
1003 name = xattr_full_name(handler, suffix);
1004 return simple_xattr_get(xattrs, name, buffer: value, size);
1005}
1006
1007static int pidfs_xattr_set(const struct xattr_handler *handler,
1008 struct mnt_idmap *idmap, struct dentry *unused,
1009 struct inode *inode, const char *suffix,
1010 const void *value, size_t size, int flags)
1011{
1012 struct pid *pid = inode->i_private;
1013 struct pidfs_attr *attr = pid->attr;
1014 const char *name;
1015 struct simple_xattrs *xattrs;
1016 struct simple_xattr *old_xattr;
1017
1018 /* Ensure we're the only one to set @attr->xattrs. */
1019 WARN_ON_ONCE(!inode_is_locked(inode));
1020
1021 xattrs = READ_ONCE(attr->xattrs);
1022 if (!xattrs) {
1023 xattrs = kmem_cache_zalloc(pidfs_xattr_cachep, GFP_KERNEL);
1024 if (!xattrs)
1025 return -ENOMEM;
1026
1027 simple_xattrs_init(xattrs);
1028 smp_store_release(&pid->attr->xattrs, xattrs);
1029 }
1030
1031 name = xattr_full_name(handler, suffix);
1032 old_xattr = simple_xattr_set(xattrs, name, value, size, flags);
1033 if (IS_ERR(ptr: old_xattr))
1034 return PTR_ERR(ptr: old_xattr);
1035
1036 simple_xattr_free(xattr: old_xattr);
1037 return 0;
1038}
1039
1040static const struct xattr_handler pidfs_trusted_xattr_handler = {
1041 .prefix = XATTR_TRUSTED_PREFIX,
1042 .get = pidfs_xattr_get,
1043 .set = pidfs_xattr_set,
1044};
1045
1046static const struct xattr_handler *const pidfs_xattr_handlers[] = {
1047 &pidfs_trusted_xattr_handler,
1048 NULL
1049};
1050
1051static int pidfs_init_fs_context(struct fs_context *fc)
1052{
1053 struct pseudo_fs_context *ctx;
1054
1055 ctx = init_pseudo(fc, PID_FS_MAGIC);
1056 if (!ctx)
1057 return -ENOMEM;
1058
1059 fc->s_iflags |= SB_I_NOEXEC;
1060 fc->s_iflags |= SB_I_NODEV;
1061 ctx->s_d_flags |= DCACHE_DONTCACHE;
1062 ctx->ops = &pidfs_sops;
1063 ctx->eops = &pidfs_export_operations;
1064 ctx->dops = &pidfs_dentry_operations;
1065 ctx->xattr = pidfs_xattr_handlers;
1066 fc->s_fs_info = (void *)&pidfs_stashed_ops;
1067 return 0;
1068}
1069
1070static struct file_system_type pidfs_type = {
1071 .name = "pidfs",
1072 .init_fs_context = pidfs_init_fs_context,
1073 .kill_sb = kill_anon_super,
1074};
1075
1076struct file *pidfs_alloc_file(struct pid *pid, unsigned int flags)
1077{
1078 struct file *pidfd_file;
1079 struct path path __free(path_put) = {};
1080 int ret;
1081
1082 /*
1083 * Ensure that PIDFD_STALE can be passed as a flag without
1084 * overloading other uapi pidfd flags.
1085 */
1086 BUILD_BUG_ON(PIDFD_STALE == PIDFD_THREAD);
1087 BUILD_BUG_ON(PIDFD_STALE == PIDFD_NONBLOCK);
1088
1089 ret = path_from_stashed(stashed: &pid->stashed, mnt: pidfs_mnt, data: get_pid(pid), path: &path);
1090 if (ret < 0)
1091 return ERR_PTR(error: ret);
1092
1093 VFS_WARN_ON_ONCE(!pid->attr);
1094
1095 flags &= ~PIDFD_STALE;
1096 flags |= O_RDWR;
1097 pidfd_file = dentry_open(path: &path, flags, current_cred());
1098 /* Raise PIDFD_THREAD explicitly as do_dentry_open() strips it. */
1099 if (!IS_ERR(ptr: pidfd_file))
1100 pidfd_file->f_flags |= (flags & PIDFD_THREAD);
1101
1102 return pidfd_file;
1103}
1104
1105void __init pidfs_init(void)
1106{
1107 pidfs_attr_cachep = kmem_cache_create("pidfs_attr_cache", sizeof(struct pidfs_attr), 0,
1108 (SLAB_HWCACHE_ALIGN | SLAB_RECLAIM_ACCOUNT |
1109 SLAB_ACCOUNT | SLAB_PANIC), NULL);
1110
1111 pidfs_xattr_cachep = kmem_cache_create("pidfs_xattr_cache",
1112 sizeof(struct simple_xattrs), 0,
1113 (SLAB_HWCACHE_ALIGN | SLAB_RECLAIM_ACCOUNT |
1114 SLAB_ACCOUNT | SLAB_PANIC), NULL);
1115
1116 pidfs_mnt = kern_mount(&pidfs_type);
1117 if (IS_ERR(ptr: pidfs_mnt))
1118 panic(fmt: "Failed to mount pidfs pseudo filesystem");
1119
1120 pidfs_root_path.mnt = pidfs_mnt;
1121 pidfs_root_path.dentry = pidfs_mnt->mnt_root;
1122}
1123

source code of linux/fs/pidfs.c