]>
git.ipfire.org Git - thirdparty/systemd.git/blob - src/core/dynamic-user.c
1 /* SPDX-License-Identifier: LGPL-2.1-or-later */
8 #include "dynamic-user.h"
11 #include "format-util.h"
14 #include "nscd-flush.h"
15 #include "parse-util.h"
16 #include "random-util.h"
17 #include "serialize.h"
18 #include "socket-util.h"
19 #include "stdio-util.h"
20 #include "string-util.h"
22 #include "uid-alloc-range.h"
23 #include "user-util.h"
25 /* Takes a value generated randomly or by hashing and turns it into a UID in the right range */
26 #define UID_CLAMP_INTO_RANGE(rnd) (((uid_t) (rnd) % (DYNAMIC_UID_MAX - DYNAMIC_UID_MIN + 1)) + DYNAMIC_UID_MIN)
28 DEFINE_PRIVATE_TRIVIAL_REF_FUNC(DynamicUser
, dynamic_user
);
30 static DynamicUser
* dynamic_user_free(DynamicUser
*d
) {
35 (void) hashmap_remove(d
->manager
->dynamic_users
, d
->name
);
37 safe_close_pair(d
->storage_socket
);
41 static int dynamic_user_add(Manager
*m
, const char *name
, int storage_socket
[static 2], DynamicUser
**ret
) {
47 assert(storage_socket
);
49 r
= hashmap_ensure_allocated(&m
->dynamic_users
, &string_hash_ops
);
53 d
= malloc0(offsetof(DynamicUser
, name
) + strlen(name
) + 1);
57 strcpy(d
->name
, name
);
59 d
->storage_socket
[0] = storage_socket
[0];
60 d
->storage_socket
[1] = storage_socket
[1];
62 r
= hashmap_put(m
->dynamic_users
, d
->name
, d
);
76 static int dynamic_user_acquire(Manager
*m
, const char *name
, DynamicUser
** ret
) {
77 _cleanup_close_pair_
int storage_socket
[2] = { -1, -1 };
84 /* Return the DynamicUser structure for a specific user name. Note that this won't actually allocate a UID for
85 * it, but just prepare the data structure for it. The UID is allocated only on demand, when it's really
86 * needed, and in the child process we fork off, since allocation involves NSS checks which are not OK to do
87 * from PID 1. To allow the children and PID 1 share information about allocated UIDs we use an anonymous
88 * AF_UNIX/SOCK_DGRAM socket (called the "storage socket") that contains at most one datagram with the
89 * allocated UID number, plus an fd referencing the lock file for the UID
90 * (i.e. /run/systemd/dynamic-uid/$UID). Why involve the socket pair? So that PID 1 and all its children can
91 * share the same storage for the UID and lock fd, simply by inheriting the storage socket fds. The socket pair
92 * may exist in three different states:
94 * a) no datagram stored. This is the initial state. In this case the dynamic user was never realized.
96 * b) a datagram containing a UID stored, but no lock fd attached to it. In this case there was already a
97 * statically assigned UID by the same name, which we are reusing.
99 * c) a datagram containing a UID stored, and a lock fd is attached to it. In this case we allocated a dynamic
100 * UID and locked it in the file system, using the lock fd.
102 * As PID 1 and various children might access the socket pair simultaneously, and pop the datagram or push it
103 * back in any time, we also maintain a lock on the socket pair. Note one peculiarity regarding locking here:
104 * the UID lock on disk is protected via a BSD file lock (i.e. an fd-bound lock), so that the lock is kept in
105 * place as long as there's a reference to the fd open. The lock on the storage socket pair however is a POSIX
106 * file lock (i.e. a process-bound lock), as all users share the same fd of this (after all it is anonymous,
107 * nobody else could get any access to it except via our own fd) and we want to synchronize access between all
108 * processes that have access to it. */
110 d
= hashmap_get(m
->dynamic_users
, name
);
113 /* We already have a structure for the dynamic user, let's increase the ref count and reuse it */
120 if (!valid_user_group_name(name
, VALID_USER_ALLOW_NUMERIC
))
123 if (socketpair(AF_UNIX
, SOCK_DGRAM
|SOCK_CLOEXEC
, 0, storage_socket
) < 0)
126 r
= dynamic_user_add(m
, name
, storage_socket
, &d
);
130 storage_socket
[0] = storage_socket
[1] = -1;
140 static int make_uid_symlinks(uid_t uid
, const char *name
, bool b
) {
142 char path1
[STRLEN("/run/systemd/dynamic-uid/direct:") + DECIMAL_STR_MAX(uid_t
) + 1];
146 /* Add direct additional symlinks for direct lookups of dynamic UIDs and their names by userspace code. The
147 * only reason we have this is because dbus-daemon cannot use D-Bus for resolving users and groups (since it
148 * would be its own client then). We hence keep these world-readable symlinks in place, so that the
149 * unprivileged dbus user can read the mappings when it needs them via these symlinks instead of having to go
150 * via the bus. Ideally, we'd use the lock files we keep for this anyway, but we can't since we use BSD locks
151 * on them and as those may be taken by any user with read access we can't make them world-readable. */
153 xsprintf(path1
, "/run/systemd/dynamic-uid/direct:" UID_FMT
, uid
);
154 if (unlink(path1
) < 0 && errno
!= ENOENT
)
157 if (b
&& symlink(name
, path1
) < 0) {
158 k
= log_warning_errno(errno
, "Failed to symlink \"%s\": %m", path1
);
163 path2
= strjoina("/run/systemd/dynamic-uid/direct:", name
);
164 if (unlink(path2
) < 0 && errno
!= ENOENT
) {
170 if (b
&& symlink(path1
+ STRLEN("/run/systemd/dynamic-uid/direct:"), path2
) < 0) {
171 k
= log_warning_errno(errno
, "Failed to symlink \"%s\": %m", path2
);
179 static int pick_uid(char **suggested_paths
, const char *name
, uid_t
*ret_uid
) {
181 /* Find a suitable free UID. We use the following strategy to find a suitable UID:
183 * 1. Initially, we try to read the UID of a number of specified paths. If any of these UIDs works, we use
184 * them. We use in order to increase the chance of UID reuse, if StateDirectory=, CacheDirectory= or
185 * LogsDirectory= are used, as reusing the UID these directories are owned by saves us from having to
186 * recursively chown() them to new users.
188 * 2. If that didn't yield a currently unused UID, we hash the user name, and try to use that. This should be
189 * pretty good, as the use ris by default derived from the unit name, and hence the same service and same
190 * user should usually get the same UID as long as our hashing doesn't clash.
192 * 3. Finally, if that didn't work, we randomly pick UIDs, until we find one that is empty.
194 * Since the dynamic UID space is relatively small we'll stop trying after 100 iterations, giving up. */
197 PHASE_SUGGESTED
, /* the first phase, reusing directory ownership UIDs */
198 PHASE_HASHED
, /* the second phase, deriving a UID from the username by hashing */
199 PHASE_RANDOM
, /* the last phase, randomly picking UIDs */
200 } phase
= PHASE_SUGGESTED
;
202 static const uint8_t hash_key
[] = {
203 0x37, 0x53, 0x7e, 0x31, 0xcf, 0xce, 0x48, 0xf5,
204 0x8a, 0xbb, 0x39, 0x57, 0x8d, 0xd9, 0xec, 0x59
207 unsigned n_tries
= 100, current_suggested
= 0;
210 (void) mkdir("/run/systemd/dynamic-uid", 0755);
213 char lock_path
[STRLEN("/run/systemd/dynamic-uid/") + DECIMAL_STR_MAX(uid_t
) + 1];
214 _cleanup_close_
int lock_fd
= -EBADF
;
218 if (--n_tries
<= 0) /* Give up retrying eventually */
223 case PHASE_SUGGESTED
: {
226 if (!suggested_paths
|| !suggested_paths
[current_suggested
]) {
227 /* We reached the end of the suggested paths list, let's try by hashing the name */
228 phase
= PHASE_HASHED
;
232 if (stat(suggested_paths
[current_suggested
++], &st
) < 0)
233 continue; /* We can't read the UID of this path, but that doesn't matter, just try the next */
235 candidate
= st
.st_uid
;
240 /* A static user by this name does not exist yet. Let's find a free ID then, and use that. We
241 * start with a UID generated as hash from the user name. */
242 candidate
= UID_CLAMP_INTO_RANGE(siphash24(name
, strlen(name
), hash_key
));
244 /* If this one fails, we should proceed with random tries */
245 phase
= PHASE_RANDOM
;
250 /* Pick another random UID, and see if that works for us. */
251 random_bytes(&candidate
, sizeof(candidate
));
252 candidate
= UID_CLAMP_INTO_RANGE(candidate
);
256 assert_not_reached();
259 /* Make sure whatever we picked here actually is in the right range */
260 if (!uid_is_dynamic(candidate
))
263 xsprintf(lock_path
, "/run/systemd/dynamic-uid/" UID_FMT
, candidate
);
268 lock_fd
= open(lock_path
, O_CREAT
|O_RDWR
|O_NOFOLLOW
|O_CLOEXEC
|O_NOCTTY
, 0600);
272 r
= flock(lock_fd
, LOCK_EX
|LOCK_NB
); /* Try to get a BSD file lock on the UID lock file */
274 if (IN_SET(errno
, EBUSY
, EAGAIN
))
275 goto next
; /* already in use */
280 if (fstat(lock_fd
, &st
) < 0)
285 /* Oh, bummer, we got the lock, but the file was unlinked between the time we opened it and
286 * got the lock. Close it, and try again. */
287 lock_fd
= safe_close(lock_fd
);
290 /* Some superficial check whether this UID/GID might already be taken by some static user */
291 if (getpwuid(candidate
) ||
292 getgrgid((gid_t
) candidate
) ||
293 search_ipc(candidate
, (gid_t
) candidate
) != 0) {
294 (void) unlink(lock_path
);
298 /* Let's store the user name in the lock file, so that we can use it for looking up the username for a UID */
301 IOVEC_INIT_STRING(name
),
302 IOVEC_INIT((char[1]) { '\n' }, 1),
306 (void) unlink(lock_path
);
310 (void) ftruncate(lock_fd
, l
);
311 (void) make_uid_symlinks(candidate
, name
, true); /* also add direct lookup symlinks */
313 *ret_uid
= candidate
;
314 return TAKE_FD(lock_fd
);
321 static int dynamic_user_pop(DynamicUser
*d
, uid_t
*ret_uid
, int *ret_lock_fd
) {
322 uid_t uid
= UID_INVALID
;
323 struct iovec iov
= IOVEC_INIT(&uid
, sizeof(uid
));
331 /* Read the UID and lock fd that is stored in the storage AF_UNIX socket. This should be called with
332 * the lock on the socket taken. */
334 k
= receive_one_fd_iov(d
->storage_socket
[0], &iov
, 1, MSG_DONTWAIT
, &lock_fd
);
339 *ret_lock_fd
= lock_fd
;
344 static int dynamic_user_push(DynamicUser
*d
, uid_t uid
, int lock_fd
) {
345 struct iovec iov
= IOVEC_INIT(&uid
, sizeof(uid
));
349 /* Store the UID and lock_fd in the storage socket. This should be called with the socket pair lock taken. */
350 return send_one_fd_iov(d
->storage_socket
[1], lock_fd
, &iov
, 1, MSG_DONTWAIT
);
353 static void unlink_uid_lock(int lock_fd
, uid_t uid
, const char *name
) {
354 char lock_path
[STRLEN("/run/systemd/dynamic-uid/") + DECIMAL_STR_MAX(uid_t
) + 1];
359 xsprintf(lock_path
, "/run/systemd/dynamic-uid/" UID_FMT
, uid
);
360 (void) unlink(lock_path
);
362 (void) make_uid_symlinks(uid
, name
, false); /* remove direct lookup symlinks */
365 static int lockfp(int fd
, int *fd_lock
) {
366 if (lockf(fd
, F_LOCK
, 0) < 0)
372 static void unlockfp(int *fd_lock
) {
375 lockf(*fd_lock
, F_ULOCK
, 0);
379 static int dynamic_user_realize(
381 char **suggested_dirs
,
382 uid_t
*ret_uid
, gid_t
*ret_gid
,
385 _cleanup_(unlockfp
) int storage_socket0_lock
= -1;
386 _cleanup_close_
int uid_lock_fd
= -EBADF
;
387 _cleanup_close_
int etc_passwd_lock_fd
= -EBADF
;
388 uid_t num
= UID_INVALID
; /* a uid if is_user, and a gid otherwise */
389 gid_t gid
= GID_INVALID
; /* a gid if is_user, ignored otherwise */
390 bool flush_cache
= false;
394 assert(is_user
== !!ret_uid
);
397 /* Acquire a UID for the user name. This will allocate a UID for the user name if the user doesn't exist
398 * yet. If it already exists its existing UID/GID will be reused. */
400 r
= lockfp(d
->storage_socket
[0], &storage_socket0_lock
);
404 r
= dynamic_user_pop(d
, &num
, &uid_lock_fd
);
412 /* OK, nothing stored yet, let's try to find something useful. While we are working on this release the
413 * lock however, so that nobody else blocks on our NSS lookups. */
414 unlockfp(&storage_socket0_lock
);
416 /* Let's see if a proper, static user or group by this name exists. Try to take the lock on
417 * /etc/passwd, if that fails with EROFS then /etc is read-only. In that case it's fine if we don't
418 * take the lock, given that users can't be added there anyway in this case. */
419 etc_passwd_lock_fd
= take_etc_passwd_lock(NULL
);
420 if (etc_passwd_lock_fd
< 0 && etc_passwd_lock_fd
!= -EROFS
)
421 return etc_passwd_lock_fd
;
423 /* First, let's parse this as numeric UID */
424 r
= parse_uid(d
->name
, &num
);
430 /* OK, this is not a numeric UID. Let's see if there's a user by this name */
431 p
= getpwnam(d
->name
);
436 /* if the user does not exist but the group with the same name exists, refuse operation */
437 g
= getgrnam(d
->name
);
442 /* Let's see if there's a group by this name */
443 g
= getgrnam(d
->name
);
445 num
= (uid_t
) g
->gr_gid
;
447 /* if the group does not exist but the user with the same name exists, refuse operation */
448 p
= getpwnam(d
->name
);
455 if (num
== UID_INVALID
) {
456 /* No static UID assigned yet, excellent. Let's pick a new dynamic one, and lock it. */
458 uid_lock_fd
= pick_uid(suggested_dirs
, d
->name
, &num
);
463 /* So, we found a working UID/lock combination. Let's see if we actually still need it. */
464 r
= lockfp(d
->storage_socket
[0], &storage_socket0_lock
);
466 unlink_uid_lock(uid_lock_fd
, num
, d
->name
);
470 r
= dynamic_user_pop(d
, &new_uid
, &new_uid_lock_fd
);
473 /* OK, something bad happened, let's get rid of the bits we acquired. */
474 unlink_uid_lock(uid_lock_fd
, num
, d
->name
);
478 /* Great! Nothing is stored here, still. Store our newly acquired data. */
481 /* Hmm, so as it appears there's now something stored in the storage socket. Throw away what we
482 * acquired, and use what's stored now. */
484 unlink_uid_lock(uid_lock_fd
, num
, d
->name
);
485 safe_close(uid_lock_fd
);
488 uid_lock_fd
= new_uid_lock_fd
;
490 } else if (is_user
&& !uid_is_dynamic(num
)) {
493 /* Statically allocated user may have different uid and gid. So, let's obtain the gid. */
497 return errno_or_else(ESRCH
);
502 /* If the UID/GID was already allocated dynamically, push the data we popped out back in. If it was already
503 * allocated statically, push the UID back too, but do not push the lock fd in. If we allocated the UID
504 * dynamically right here, push that in along with the lock fd for it. */
505 r
= dynamic_user_push(d
, num
, uid_lock_fd
);
510 /* If we allocated a new dynamic UID, refresh nscd, so that it forgets about potentially cached
511 * negative entries. But let's do so after we release the /etc/passwd lock, so that there's no
512 * potential for nscd wanting to lock that for completing the invalidation. */
513 etc_passwd_lock_fd
= safe_close(etc_passwd_lock_fd
);
514 (void) nscd_flush_cache(STRV_MAKE("passwd", "group"));
519 *ret_gid
= gid
!= GID_INVALID
? gid
: num
;
526 int dynamic_user_current(DynamicUser
*d
, uid_t
*ret
) {
527 _cleanup_(unlockfp
) int storage_socket0_lock
= -1;
528 _cleanup_close_
int lock_fd
= -EBADF
;
534 /* Get the currently assigned UID for the user, if there's any. This simply pops the data from the
535 * storage socket, and pushes it back in right-away. */
537 r
= lockfp(d
->storage_socket
[0], &storage_socket0_lock
);
541 r
= dynamic_user_pop(d
, &uid
, &lock_fd
);
545 r
= dynamic_user_push(d
, uid
, lock_fd
);
555 static DynamicUser
* dynamic_user_unref(DynamicUser
*d
) {
559 /* Note that this doesn't actually release any resources itself. If a dynamic user should be fully
560 * destroyed and its UID released, use dynamic_user_destroy() instead. NB: the dynamic user table may
561 * contain entries with no references, which is commonly the case right before a daemon reload. */
563 assert(d
->n_ref
> 0);
569 static int dynamic_user_close(DynamicUser
*d
) {
570 _cleanup_(unlockfp
) int storage_socket0_lock
= -1;
571 _cleanup_close_
int lock_fd
= -EBADF
;
575 /* Release the user ID, by releasing the lock on it, and emptying the storage socket. After this the
576 * user is unrealized again, much like it was after it the DynamicUser object was first allocated. */
578 r
= lockfp(d
->storage_socket
[0], &storage_socket0_lock
);
582 r
= dynamic_user_pop(d
, &uid
, &lock_fd
);
584 /* User wasn't realized yet, nothing to do. */
589 /* This dynamic user was realized and dynamically allocated. In this case, let's remove the lock file. */
590 unlink_uid_lock(lock_fd
, uid
, d
->name
);
592 (void) nscd_flush_cache(STRV_MAKE("passwd", "group"));
596 static DynamicUser
* dynamic_user_destroy(DynamicUser
*d
) {
600 /* Drop a reference to a DynamicUser object, and destroy the user completely if this was the last
601 * reference. This is called whenever a service is shut down and wants its dynamic UID gone. Note that
602 * dynamic_user_unref() is what is called whenever a service is simply freed, for example during a reload
603 * cycle, where the dynamic users should not be destroyed, but our datastructures should. */
605 dynamic_user_unref(d
);
610 (void) dynamic_user_close(d
);
611 return dynamic_user_free(d
);
614 int dynamic_user_serialize(Manager
*m
, FILE *f
, FDSet
*fds
) {
621 /* Dump the dynamic user database into the manager serialization, to deal with daemon reloads. */
623 HASHMAP_FOREACH(d
, m
->dynamic_users
) {
626 copy0
= fdset_put_dup(fds
, d
->storage_socket
[0]);
628 return log_error_errno(copy0
, "Failed to add dynamic user storage fd to serialization: %m");
630 copy1
= fdset_put_dup(fds
, d
->storage_socket
[1]);
632 return log_error_errno(copy1
, "Failed to add dynamic user storage fd to serialization: %m");
634 (void) serialize_item_format(f
, "dynamic-user", "%s %i %i", d
->name
, copy0
, copy1
);
640 void dynamic_user_deserialize_one(Manager
*m
, const char *value
, FDSet
*fds
) {
641 _cleanup_free_
char *name
= NULL
, *s0
= NULL
, *s1
= NULL
;
648 /* Parse the serialization again, after a daemon reload */
650 r
= extract_many_words(&value
, NULL
, 0, &name
, &s0
, &s1
, NULL
);
651 if (r
!= 3 || !isempty(value
)) {
652 log_debug("Unable to parse dynamic user line.");
656 if (safe_atoi(s0
, &fd0
) < 0 || !fdset_contains(fds
, fd0
)) {
657 log_debug("Unable to process dynamic user fd specification.");
661 if (safe_atoi(s1
, &fd1
) < 0 || !fdset_contains(fds
, fd1
)) {
662 log_debug("Unable to process dynamic user fd specification.");
666 r
= dynamic_user_add(m
, name
, (int[]) { fd0
, fd1
}, NULL
);
668 log_debug_errno(r
, "Failed to add dynamic user: %m");
672 (void) fdset_remove(fds
, fd0
);
673 (void) fdset_remove(fds
, fd1
);
676 void dynamic_user_vacuum(Manager
*m
, bool close_user
) {
681 /* Empty the dynamic user database, optionally cleaning up orphaned dynamic users, i.e. destroy and free users
682 * to which no reference exist. This is called after a daemon reload finished, in order to destroy users which
683 * might not be referenced anymore. */
685 HASHMAP_FOREACH(d
, m
->dynamic_users
) {
690 log_debug("Removing orphaned dynamic user %s", d
->name
);
691 (void) dynamic_user_close(d
);
694 dynamic_user_free(d
);
698 int dynamic_user_lookup_uid(Manager
*m
, uid_t uid
, char **ret
) {
699 char lock_path
[STRLEN("/run/systemd/dynamic-uid/") + DECIMAL_STR_MAX(uid_t
) + 1];
700 _cleanup_free_
char *user
= NULL
;
707 /* A friendly way to translate a dynamic user's UID into a name. */
708 if (!uid_is_dynamic(uid
))
711 xsprintf(lock_path
, "/run/systemd/dynamic-uid/" UID_FMT
, uid
);
712 r
= read_one_line_file(lock_path
, &user
);
713 if (IN_SET(r
, -ENOENT
, 0))
718 /* The lock file might be stale, hence let's verify the data before we return it */
719 r
= dynamic_user_lookup_name(m
, user
, &check_uid
);
722 if (check_uid
!= uid
) /* lock file doesn't match our own idea */
725 *ret
= TAKE_PTR(user
);
730 int dynamic_user_lookup_name(Manager
*m
, const char *name
, uid_t
*ret
) {
737 /* A friendly call for translating a dynamic user's name into its UID */
739 d
= hashmap_get(m
->dynamic_users
, name
);
743 r
= dynamic_user_current(d
, ret
);
744 if (r
== -EAGAIN
) /* not realized yet? */
750 int dynamic_creds_acquire(DynamicCreds
*creds
, Manager
*m
, const char *user
, const char *group
) {
751 bool acquired
= false;
757 /* A DynamicUser object encapsulates an allocation of both a UID and a GID for a specific name. However, some
758 * services use different user and groups. For cases like that there's DynamicCreds containing a pair of user
759 * and group. This call allocates a pair. */
761 if (!creds
->user
&& user
) {
762 r
= dynamic_user_acquire(m
, user
, &creds
->user
);
771 if (creds
->user
&& (!group
|| streq_ptr(user
, group
)))
772 creds
->group
= dynamic_user_ref(creds
->user
);
774 r
= dynamic_user_acquire(m
, group
, &creds
->group
);
777 creds
->user
= dynamic_user_unref(creds
->user
);
786 int dynamic_creds_realize(DynamicCreds
*creds
, char **suggested_paths
, uid_t
*uid
, gid_t
*gid
) {
787 uid_t u
= UID_INVALID
;
788 gid_t g
= GID_INVALID
;
795 /* Realize both the referenced user and group */
798 r
= dynamic_user_realize(creds
->user
, suggested_paths
, &u
, &g
, true);
803 if (creds
->group
&& creds
->group
!= creds
->user
) {
804 r
= dynamic_user_realize(creds
->group
, suggested_paths
, NULL
, &g
, false);
814 void dynamic_creds_unref(DynamicCreds
*creds
) {
817 creds
->user
= dynamic_user_unref(creds
->user
);
818 creds
->group
= dynamic_user_unref(creds
->group
);
821 void dynamic_creds_destroy(DynamicCreds
*creds
) {
824 creds
->user
= dynamic_user_destroy(creds
->user
);
825 creds
->group
= dynamic_user_destroy(creds
->group
);