]>
git.ipfire.org Git - thirdparty/systemd.git/blob - src/core/dynamic-user.c
2 This file is part of systemd.
4 Copyright 2016 Lennart Poettering
6 systemd is free software; you can redistribute it and/or modify it
7 under the terms of the GNU Lesser General Public License as published by
8 the Free Software Foundation; either version 2.1 of the License, or
9 (at your option) any later version.
11 systemd is distributed in the hope that it will be useful, but
12 WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Lesser General Public License for more details.
16 You should have received a copy of the GNU Lesser General Public License
17 along with systemd; If not, see <http://www.gnu.org/licenses/>.
24 #include "dynamic-user.h"
27 #include "parse-util.h"
28 #include "random-util.h"
29 #include "stdio-util.h"
30 #include "string-util.h"
31 #include "user-util.h"
34 /* Takes a value generated randomly or by hashing and turns it into a UID in the right range */
35 #define UID_CLAMP_INTO_RANGE(rnd) (((uid_t) (rnd) % (DYNAMIC_UID_MAX - DYNAMIC_UID_MIN + 1)) + DYNAMIC_UID_MIN)
37 static DynamicUser
* dynamic_user_free ( DynamicUser
* d
) {
42 ( void ) hashmap_remove ( d
-> manager
-> dynamic_users
, d
-> name
);
44 safe_close_pair ( d
-> storage_socket
);
48 static int dynamic_user_add ( Manager
* m
, const char * name
, int storage_socket
[ 2 ], DynamicUser
** ret
) {
49 DynamicUser
* d
= NULL
;
54 assert ( storage_socket
);
56 r
= hashmap_ensure_allocated (& m
-> dynamic_users
, & string_hash_ops
);
60 d
= malloc0 ( offsetof ( DynamicUser
, name
) + strlen ( name
) + 1 );
64 strcpy ( d
-> name
, name
);
66 d
-> storage_socket
[ 0 ] = storage_socket
[ 0 ];
67 d
-> storage_socket
[ 1 ] = storage_socket
[ 1 ];
69 r
= hashmap_put ( m
-> dynamic_users
, d
-> name
, d
);
83 int dynamic_user_acquire ( Manager
* m
, const char * name
, DynamicUser
** ret
) {
84 _cleanup_close_pair_
int storage_socket
[ 2 ] = { - 1 , - 1 };
91 /* Return the DynamicUser structure for a specific user name. Note that this won't actually allocate a UID for
92 * it, but just prepare the data structure for it. The UID is allocated only on demand, when it's really
93 * needed, and in the child process we fork off, since allocation involves NSS checks which are not OK to do
94 * from PID 1. To allow the children and PID 1 share information about allocated UIDs we use an anonymous
95 * AF_UNIX/SOCK_DGRAM socket (called the "storage socket") that contains at most one datagram with the
96 * allocated UID number, plus an fd referencing the lock file for the UID
97 * (i.e. /run/systemd/dynamic-uid/$UID). Why involve the socket pair? So that PID 1 and all its children can
98 * share the same storage for the UID and lock fd, simply by inheriting the storage socket fds. The socket pair
99 * may exist in three different states:
101 * a) no datagram stored. This is the initial state. In this case the dynamic user was never realized.
103 * b) a datagram containing a UID stored, but no lock fd attached to it. In this case there was already a
104 * statically assigned UID by the same name, which we are reusing.
106 * c) a datagram containing a UID stored, and a lock fd is attached to it. In this case we allocated a dynamic
107 * UID and locked it in the file system, using the lock fd.
109 * As PID 1 and various children might access the socket pair simultaneously, and pop the datagram or push it
110 * back in any time, we also maintain a lock on the socket pair. Note one peculiarity regarding locking here:
111 * 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
112 * place as long as there's a reference to the fd open. The lock on the storage socket pair however is a POSIX
113 * file lock (i.e. a process-bound lock), as all users share the same fd of this (after all it is anonymous,
114 * nobody else could get any access to it except via our own fd) and we want to synchronize access between all
115 * processes that have access to it. */
117 d
= hashmap_get ( m
-> dynamic_users
, name
);
119 /* We already have a structure for the dynamic user, let's increase the ref count and reuse it */
125 if (! valid_user_group_name_or_id ( name
))
128 if ( socketpair ( AF_UNIX
, SOCK_DGRAM
| SOCK_CLOEXEC
, 0 , storage_socket
) < 0 )
131 r
= dynamic_user_add ( m
, name
, storage_socket
, & d
);
135 storage_socket
[ 0 ] = storage_socket
[ 1 ] = - 1 ;
145 static int make_uid_symlinks ( uid_t uid
, const char * name
, bool b
) {
147 char path1
[ strlen ( "/run/systemd/dynamic-uid/direct:" ) + DECIMAL_STR_MAX ( uid_t
) + 1 ];
151 /* Add direct additional symlinks for direct lookups of dynamic UIDs and their names by userspace code. The
152 * only reason we have this is because dbus-daemon cannot use D-Bus for resolving users and groups (since it
153 * would be its own client then). We hence keep these world-readable symlinks in place, so that the
154 * unprivileged dbus user can read the mappings when it needs them via these symlinks instead of having to go
155 * via the bus. Ideally, we'd use the lock files we keep for this anyway, but we can't since we use BSD locks
156 * on them and as those may be taken by any user with read access we can't make them world-readable. */
158 xsprintf ( path1
, "/run/systemd/dynamic-uid/direct:" UID_FMT
, uid
);
159 if ( unlink ( path1
) < 0 && errno
!= ENOENT
)
162 if ( b
&& symlink ( name
, path1
) < 0 ) {
163 k
= log_warning_errno ( errno
, "Failed to symlink \" %s \" : %m" , path1
);
168 path2
= strjoina ( "/run/systemd/dynamic-uid/direct:" , name
);
169 if ( unlink ( path2
) < 0 && errno
!= ENOENT
) {
175 if ( b
&& symlink ( path1
+ strlen ( "/run/systemd/dynamic-uid/direct:" ), path2
) < 0 ) {
176 k
= log_warning_errno ( errno
, "Failed to symlink \" %s \" : %m" , path2
);
184 static int pick_uid ( const char * name
, uid_t
* ret_uid
) {
186 static const uint8_t hash_key
[] = {
187 0x37 , 0x53 , 0x7e , 0x31 , 0xcf , 0xce , 0x48 , 0xf5 ,
188 0x8a , 0xbb , 0x39 , 0x57 , 0x8d , 0xd9 , 0xec , 0x59
191 unsigned n_tries
= 100 ;
195 /* A static user by this name does not exist yet. Let's find a free ID then, and use that. We start with a UID
196 * generated as hash from the user name. */
197 candidate
= UID_CLAMP_INTO_RANGE ( siphash24 ( name
, strlen ( name
), hash_key
));
199 ( void ) mkdir ( "/run/systemd/dynamic-uid" , 0755 );
202 char lock_path
[ strlen ( "/run/systemd/dynamic-uid/" ) + DECIMAL_STR_MAX ( uid_t
) + 1 ];
203 _cleanup_close_
int lock_fd
= - 1 ;
206 if (-- n_tries
<= 0 ) /* Give up retrying eventually */
209 if (! uid_is_dynamic ( candidate
))
212 xsprintf ( lock_path
, "/run/systemd/dynamic-uid/" UID_FMT
, candidate
);
217 lock_fd
= open ( lock_path
, O_CREAT
| O_RDWR
| O_NOFOLLOW
| O_CLOEXEC
| O_NOCTTY
, 0600 );
221 r
= flock ( lock_fd
, LOCK_EX
| LOCK_NB
); /* Try to get a BSD file lock on the UID lock file */
223 if ( errno
== EBUSY
|| errno
== EAGAIN
)
224 goto next
; /* already in use */
229 if ( fstat ( lock_fd
, & st
) < 0 )
234 /* Oh, bummer, we got the lock, but the file was unlinked between the time we opened it and
235 * got the lock. Close it, and try again. */
236 lock_fd
= safe_close ( lock_fd
);
239 /* Some superficial check whether this UID/GID might already be taken by some static user */
240 if ( getpwuid ( candidate
) || getgrgid (( gid_t
) candidate
)) {
241 ( void ) unlink ( lock_path
);
245 /* Let's store the user name in the lock file, so that we can use it for looking up the username for a UID */
248 { . iov_base
= ( char *) name
, . iov_len
= strlen ( name
) },
249 { . iov_base
= ( char [ 1 ]) { ' \n ' }, . iov_len
= 1 }
252 ( void ) unlink ( lock_path
);
256 ( void ) ftruncate ( lock_fd
, l
);
257 ( void ) make_uid_symlinks ( candidate
, name
, true ); /* also add direct lookup symlinks */
259 * ret_uid
= candidate
;
266 /* Pick another random UID, and see if that works for us. */
267 random_bytes (& candidate
, sizeof ( candidate
));
268 candidate
= UID_CLAMP_INTO_RANGE ( candidate
);
272 static int dynamic_user_pop ( DynamicUser
* d
, uid_t
* ret_uid
, int * ret_lock_fd
) {
273 uid_t uid
= UID_INVALID
;
276 . iov_len
= sizeof ( uid
),
279 struct cmsghdr cmsghdr
;
280 uint8_t buf
[ CMSG_SPACE ( sizeof ( int ))];
283 . msg_control
= & control
,
284 . msg_controllen
= sizeof ( control
),
288 struct cmsghdr
* cmsg
;
297 /* Read the UID and lock fd that is stored in the storage AF_UNIX socket. This should be called with the lock
298 * on the socket taken. */
300 k
= recvmsg ( d
-> storage_socket
[ 0 ], & mh
, MSG_DONTWAIT
| MSG_NOSIGNAL
| MSG_CMSG_CLOEXEC
);
304 cmsg
= cmsg_find (& mh
, SOL_SOCKET
, SCM_RIGHTS
, CMSG_LEN ( sizeof ( int )));
306 lock_fd
= *( int *) CMSG_DATA ( cmsg
);
308 cmsg_close_all (& mh
); /* just in case... */
311 * ret_lock_fd
= lock_fd
;
316 static int dynamic_user_push ( DynamicUser
* d
, uid_t uid
, int lock_fd
) {
319 . iov_len
= sizeof ( uid
),
322 struct cmsghdr cmsghdr
;
323 uint8_t buf
[ CMSG_SPACE ( sizeof ( int ))];
326 . msg_control
= & control
,
327 . msg_controllen
= sizeof ( control
),
335 /* Store the UID and lock_fd in the storage socket. This should be called with the socket pair lock taken. */
338 struct cmsghdr
* cmsg
;
340 cmsg
= CMSG_FIRSTHDR (& mh
);
341 cmsg
-> cmsg_level
= SOL_SOCKET
;
342 cmsg
-> cmsg_type
= SCM_RIGHTS
;
343 cmsg
-> cmsg_len
= CMSG_LEN ( sizeof ( int ));
344 memcpy ( CMSG_DATA ( cmsg
), & lock_fd
, sizeof ( int ));
346 mh
. msg_controllen
= CMSG_SPACE ( sizeof ( int ));
348 mh
. msg_control
= NULL
;
349 mh
. msg_controllen
= 0 ;
352 k
= sendmsg ( d
-> storage_socket
[ 1 ], & mh
, MSG_DONTWAIT
| MSG_NOSIGNAL
);
359 static void unlink_uid_lock ( int lock_fd
, uid_t uid
, const char * name
) {
360 char lock_path
[ strlen ( "/run/systemd/dynamic-uid/" ) + DECIMAL_STR_MAX ( uid_t
) + 1 ];
365 xsprintf ( lock_path
, "/run/systemd/dynamic-uid/" UID_FMT
, uid
);
366 ( void ) unlink ( lock_path
);
368 ( void ) make_uid_symlinks ( uid
, name
, false ); /* remove direct lookup symlinks */
371 int dynamic_user_realize ( DynamicUser
* d
, uid_t
* ret
) {
373 _cleanup_close_
int etc_passwd_lock_fd
= - 1 , uid_lock_fd
= - 1 ;
374 uid_t uid
= UID_INVALID
;
379 /* Acquire a UID for the user name. This will allocate a UID for the user name if the user doesn't exist
380 * yet. If it already exists its existing UID/GID will be reused. */
382 if ( lockf ( d
-> storage_socket
[ 0 ], F_LOCK
, 0 ) < 0 )
385 r
= dynamic_user_pop ( d
, & uid
, & uid_lock_fd
);
393 /* OK, nothing stored yet, let's try to find something useful. While we are working on this release the
394 * lock however, so that nobody else blocks on our NSS lookups. */
395 ( void ) lockf ( d
-> storage_socket
[ 0 ], F_ULOCK
, 0 );
397 /* Let's see if a proper, static user or group by this name exists. Try to take the lock on
398 * /etc/passwd, if that fails with EROFS then /etc is read-only. In that case it's fine if we don't
399 * take the lock, given that users can't be added there anyway in this case. */
400 etc_passwd_lock_fd
= take_etc_passwd_lock ( NULL
);
401 if ( etc_passwd_lock_fd
< 0 && etc_passwd_lock_fd
!= - EROFS
)
402 return etc_passwd_lock_fd
;
404 /* First, let's parse this as numeric UID */
405 r
= parse_uid ( d
-> name
, & uid
);
410 /* OK, this is not a numeric UID. Let's see if there's a user by this name */
411 p
= getpwnam ( d
-> name
);
415 /* Let's see if there's a group by this name */
416 g
= getgrnam ( d
-> name
);
418 /* If the UID/GID of the user/group of the same don't match, refuse operation */
419 if ( uid
!= UID_INVALID
&& uid
!= ( uid_t
) g
-> gr_gid
)
422 uid
= ( uid_t
) g
-> gr_gid
;
426 if ( uid
== UID_INVALID
) {
427 /* No static UID assigned yet, excellent. Let's pick a new dynamic one, and lock it. */
429 uid_lock_fd
= pick_uid ( d
-> name
, & uid
);
434 /* So, we found a working UID/lock combination. Let's see if we actually still need it. */
435 if ( lockf ( d
-> storage_socket
[ 0 ], F_LOCK
, 0 ) < 0 ) {
436 unlink_uid_lock ( uid_lock_fd
, uid
, d
-> name
);
440 r
= dynamic_user_pop ( d
, & new_uid
, & new_uid_lock_fd
);
443 /* OK, something bad happened, let's get rid of the bits we acquired. */
444 unlink_uid_lock ( uid_lock_fd
, uid
, d
-> name
);
448 /* Great! Nothing is stored here, still. Store our newly acquired data. */
450 /* Hmm, so as it appears there's now something stored in the storage socket. Throw away what we
451 * acquired, and use what's stored now. */
453 unlink_uid_lock ( uid_lock_fd
, uid
, d
-> name
);
454 safe_close ( uid_lock_fd
);
457 uid_lock_fd
= new_uid_lock_fd
;
461 /* If the UID/GID was already allocated dynamically, push the data we popped out back in. If it was already
462 * allocated statically, push the UID back too, but do not push the lock fd in. If we allocated the UID
463 * dynamically right here, push that in along with the lock fd for it. */
464 r
= dynamic_user_push ( d
, uid
, uid_lock_fd
);
472 ( void ) lockf ( d
-> storage_socket
[ 0 ], F_ULOCK
, 0 );
476 int dynamic_user_current ( DynamicUser
* d
, uid_t
* ret
) {
477 _cleanup_close_
int lock_fd
= - 1 ;
484 /* Get the currently assigned UID for the user, if there's any. This simply pops the data from the storage socket, and pushes it back in right-away. */
486 if ( lockf ( d
-> storage_socket
[ 0 ], F_LOCK
, 0 ) < 0 )
489 r
= dynamic_user_pop ( d
, & uid
, & lock_fd
);
493 r
= dynamic_user_push ( d
, uid
, lock_fd
);
501 ( void ) lockf ( d
-> storage_socket
[ 0 ], F_ULOCK
, 0 );
505 DynamicUser
* dynamic_user_ref ( DynamicUser
* d
) {
509 assert ( d
-> n_ref
> 0 );
515 DynamicUser
* dynamic_user_unref ( DynamicUser
* d
) {
519 /* Note that this doesn't actually release any resources itself. If a dynamic user should be fully destroyed
520 * and its UID released, use dynamic_user_destroy() instead. NB: the dynamic user table may contain entries
521 * with no references, which is commonly the case right before a daemon reload. */
523 assert ( d
-> n_ref
> 0 );
529 static int dynamic_user_close ( DynamicUser
* d
) {
530 _cleanup_close_
int lock_fd
= - 1 ;
534 /* Release the user ID, by releasing the lock on it, and emptying the storage socket. After this the user is
535 * unrealized again, much like it was after it the DynamicUser object was first allocated. */
537 if ( lockf ( d
-> storage_socket
[ 0 ], F_LOCK
, 0 ) < 0 )
540 r
= dynamic_user_pop ( d
, & uid
, & lock_fd
);
542 /* User wasn't realized yet, nothing to do. */
549 /* This dynamic user was realized and dynamically allocated. In this case, let's remove the lock file. */
550 unlink_uid_lock ( lock_fd
, uid
, d
-> name
);
554 ( void ) lockf ( d
-> storage_socket
[ 0 ], F_ULOCK
, 0 );
558 DynamicUser
* dynamic_user_destroy ( DynamicUser
* d
) {
562 /* Drop a reference to a DynamicUser object, and destroy the user completely if this was the last
563 * reference. This is called whenever a service is shut down and wants its dynamic UID gone. Note that
564 * dynamic_user_unref() is what is called whenever a service is simply freed, for example during a reload
565 * cycle, where the dynamic users should not be destroyed, but our datastructures should. */
567 dynamic_user_unref ( d
);
572 ( void ) dynamic_user_close ( d
);
573 return dynamic_user_free ( d
);
576 int dynamic_user_serialize ( Manager
* m
, FILE * f
, FDSet
* fds
) {
584 /* Dump the dynamic user database into the manager serialization, to deal with daemon reloads. */
586 HASHMAP_FOREACH ( d
, m
-> dynamic_users
, i
) {
589 copy0
= fdset_put_dup ( fds
, d
-> storage_socket
[ 0 ]);
593 copy1
= fdset_put_dup ( fds
, d
-> storage_socket
[ 1 ]);
597 fprintf ( f
, "dynamic-user=%s %i %i \n " , d
-> name
, copy0
, copy1
);
603 void dynamic_user_deserialize_one ( Manager
* m
, const char * value
, FDSet
* fds
) {
604 _cleanup_free_
char * name
= NULL
, * s0
= NULL
, * s1
= NULL
;
611 /* Parse the serialization again, after a daemon reload */
613 r
= extract_many_words (& value
, NULL
, 0 , & name
, & s0
, & s1
, NULL
);
614 if ( r
!= 3 || ! isempty ( value
)) {
615 log_debug ( "Unable to parse dynamic user line." );
619 if ( safe_atoi ( s0
, & fd0
) < 0 || ! fdset_contains ( fds
, fd0
)) {
620 log_debug ( "Unable to process dynamic user fd specification." );
624 if ( safe_atoi ( s1
, & fd1
) < 0 || ! fdset_contains ( fds
, fd1
)) {
625 log_debug ( "Unable to process dynamic user fd specification." );
629 r
= dynamic_user_add ( m
, name
, ( int []) { fd0
, fd1
}, NULL
);
631 log_debug_errno ( r
, "Failed to add dynamic user: %m" );
635 ( void ) fdset_remove ( fds
, fd0
);
636 ( void ) fdset_remove ( fds
, fd1
);
639 void dynamic_user_vacuum ( Manager
* m
, bool close_user
) {
645 /* Empty the dynamic user database, optionally cleaning up orphaned dynamic users, i.e. destroy and free users
646 * to which no reference exist. This is called after a daemon reload finished, in order to destroy users which
647 * might not be referenced anymore. */
649 HASHMAP_FOREACH ( d
, m
-> dynamic_users
, i
) {
654 log_debug ( "Removing orphaned dynamic user %s" , d
-> name
);
655 ( void ) dynamic_user_close ( d
);
658 dynamic_user_free ( d
);
662 int dynamic_user_lookup_uid ( Manager
* m
, uid_t uid
, char ** ret
) {
663 char lock_path
[ strlen ( "/run/systemd/dynamic-uid/" ) + DECIMAL_STR_MAX ( uid_t
) + 1 ];
664 _cleanup_free_
char * user
= NULL
;
671 /* A friendly way to translate a dynamic user's UID into a name. */
672 if (! uid_is_dynamic ( uid
))
675 xsprintf ( lock_path
, "/run/systemd/dynamic-uid/" UID_FMT
, uid
);
676 r
= read_one_line_file ( lock_path
, & user
);
682 /* The lock file might be stale, hence let's verify the data before we return it */
683 r
= dynamic_user_lookup_name ( m
, user
, & check_uid
);
686 if ( check_uid
!= uid
) /* lock file doesn't match our own idea */
695 int dynamic_user_lookup_name ( Manager
* m
, const char * name
, uid_t
* ret
) {
703 /* A friendly call for translating a dynamic user's name into its UID */
705 d
= hashmap_get ( m
-> dynamic_users
, name
);
709 r
= dynamic_user_current ( d
, ret
);
710 if ( r
== - EAGAIN
) /* not realized yet? */
716 int dynamic_creds_acquire ( DynamicCreds
* creds
, Manager
* m
, const char * user
, const char * group
) {
717 bool acquired
= false ;
723 /* A DynamicUser object encapsulates an allocation of both a UID and a GID for a specific name. However, some
724 * services use different user and groups. For cases like that there's DynamicCreds containing a pair of user
725 * and group. This call allocates a pair. */
727 if (! creds
-> user
&& user
) {
728 r
= dynamic_user_acquire ( m
, user
, & creds
-> user
);
737 if ( creds
-> user
&& (! group
|| streq_ptr ( user
, group
)))
738 creds
-> group
= dynamic_user_ref ( creds
-> user
);
740 r
= dynamic_user_acquire ( m
, group
, & creds
-> group
);
743 creds
-> user
= dynamic_user_unref ( creds
-> user
);
752 int dynamic_creds_realize ( DynamicCreds
* creds
, uid_t
* uid
, gid_t
* gid
) {
753 uid_t u
= UID_INVALID
;
754 gid_t g
= GID_INVALID
;
761 /* Realize both the referenced user and group */
764 r
= dynamic_user_realize ( creds
-> user
, & u
);
769 if ( creds
-> group
&& creds
-> group
!= creds
-> user
) {
770 r
= dynamic_user_realize ( creds
-> group
, & g
);
782 void dynamic_creds_unref ( DynamicCreds
* creds
) {
785 creds
-> user
= dynamic_user_unref ( creds
-> user
);
786 creds
-> group
= dynamic_user_unref ( creds
-> group
);
789 void dynamic_creds_destroy ( DynamicCreds
* creds
) {
792 creds
-> user
= dynamic_user_destroy ( creds
-> user
);
793 creds
-> group
= dynamic_user_destroy ( creds
-> group
);