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Diffstat (limited to 'src/core/dynamic-user.c')
| -rw-r--r-- | src/core/dynamic-user.c | 763 |
1 files changed, 763 insertions, 0 deletions
diff --git a/src/core/dynamic-user.c b/src/core/dynamic-user.c new file mode 100644 index 0000000000..8035bee231 --- /dev/null +++ b/src/core/dynamic-user.c @@ -0,0 +1,763 @@ +/*** + This file is part of systemd. + + Copyright 2016 Lennart Poettering + + systemd is free software; you can redistribute it and/or modify it + under the terms of the GNU Lesser General Public License as published by + the Free Software Foundation; either version 2.1 of the License, or + (at your option) any later version. + + systemd is distributed in the hope that it will be useful, but + WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public License + along with systemd; If not, see <http://www.gnu.org/licenses/>. +***/ + +#include <grp.h> +#include <pwd.h> +#include <sys/file.h> + +#include "dynamic-user.h" +#include "fd-util.h" +#include "fs-util.h" +#include "parse-util.h" +#include "random-util.h" +#include "stdio-util.h" +#include "string-util.h" +#include "user-util.h" +#include "fileio.h" + +/* Let's pick a UIDs within the 16bit range, so that we are compatible with containers using 16bit user namespacing. At + * least on Fedora normal users are allocated until UID 60000, hence do not allocate from below this. Also stay away + * from the upper end of the range as that is often used for overflow/nobody users. */ +#define UID_PICK_MIN ((uid_t) UINT32_C(0x0000EF00)) +#define UID_PICK_MAX ((uid_t) UINT32_C(0x0000FFEF)) + +/* Takes a value generated randomly or by hashing and turns it into a UID in the right range */ +#define UID_CLAMP_INTO_RANGE(rnd) (((uid_t) (rnd) % (UID_PICK_MAX - UID_PICK_MIN + 1)) + UID_PICK_MIN) + +static DynamicUser* dynamic_user_free(DynamicUser *d) { + if (!d) + return NULL; + + if (d->manager) + (void) hashmap_remove(d->manager->dynamic_users, d->name); + + safe_close_pair(d->storage_socket); + free(d); + + return NULL; +} + +static int dynamic_user_add(Manager *m, const char *name, int storage_socket[2], DynamicUser **ret) { + DynamicUser *d = NULL; + int r; + + assert(m); + assert(name); + assert(storage_socket); + + r = hashmap_ensure_allocated(&m->dynamic_users, &string_hash_ops); + if (r < 0) + return r; + + d = malloc0(offsetof(DynamicUser, name) + strlen(name) + 1); + if (!d) + return -ENOMEM; + + strcpy(d->name, name); + + d->storage_socket[0] = storage_socket[0]; + d->storage_socket[1] = storage_socket[1]; + + r = hashmap_put(m->dynamic_users, d->name, d); + if (r < 0) { + free(d); + return r; + } + + d->manager = m; + + if (ret) + *ret = d; + + return 0; +} + +int dynamic_user_acquire(Manager *m, const char *name, DynamicUser** ret) { + _cleanup_close_pair_ int storage_socket[2] = { -1, -1 }; + DynamicUser *d; + int r; + + assert(m); + assert(name); + + /* Return the DynamicUser structure for a specific user name. Note that this won't actually allocate a UID for + * it, but just prepare the data structure for it. The UID is allocated only on demand, when it's really + * needed, and in the child process we fork off, since allocation involves NSS checks which are not OK to do + * from PID 1. To allow the children and PID 1 share information about allocated UIDs we use an anonymous + * AF_UNIX/SOCK_DGRAM socket (called the "storage socket") that contains at most one datagram with the + * allocated UID number, plus an fd referencing the lock file for the UID + * (i.e. /run/systemd/dynamic-uid/$UID). Why involve the socket pair? So that PID 1 and all its children can + * share the same storage for the UID and lock fd, simply by inheriting the storage socket fds. The socket pair + * may exist in three different states: + * + * a) no datagram stored. This is the initial state. In this case the dynamic user was never realized. + * + * b) a datagram containing a UID stored, but no lock fd attached to it. In this case there was already a + * statically assigned UID by the same name, which we are reusing. + * + * c) a datagram containing a UID stored, and a lock fd is attached to it. In this case we allocated a dynamic + * UID and locked it in the file system, using the lock fd. + * + * As PID 1 and various children might access the socket pair simultaneously, and pop the datagram or push it + * back in any time, we also maintain a lock on the socket pair. Note one peculiarity regarding locking here: + * 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 + * place as long as there's a reference to the fd open. The lock on the storage socket pair however is a POSIX + * file lock (i.e. a process-bound lock), as all users share the same fd of this (after all it is anonymous, + * nobody else could get any access to it except via our own fd) and we want to synchronize access between all + * processes that have access to it. */ + + d = hashmap_get(m->dynamic_users, name); + if (d) { + /* We already have a structure for the dynamic user, let's increase the ref count and reuse it */ + d->n_ref++; + *ret = d; + return 0; + } + + if (!valid_user_group_name_or_id(name)) + return -EINVAL; + + if (socketpair(AF_UNIX, SOCK_DGRAM|SOCK_CLOEXEC, 0, storage_socket) < 0) + return -errno; + + r = dynamic_user_add(m, name, storage_socket, &d); + if (r < 0) + return r; + + storage_socket[0] = storage_socket[1] = -1; + + if (ret) { + d->n_ref++; + *ret = d; + } + + return 1; +} + +static int pick_uid(const char *name, uid_t *ret_uid) { + + static const uint8_t hash_key[] = { + 0x37, 0x53, 0x7e, 0x31, 0xcf, 0xce, 0x48, 0xf5, + 0x8a, 0xbb, 0x39, 0x57, 0x8d, 0xd9, 0xec, 0x59 + }; + + unsigned n_tries = 100; + uid_t candidate; + int r; + + /* 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 + * generated as hash from the user name. */ + candidate = UID_CLAMP_INTO_RANGE(siphash24(name, strlen(name), hash_key)); + + (void) mkdir("/run/systemd/dynamic-uid", 0755); + + for (;;) { + char lock_path[strlen("/run/systemd/dynamic-uid/") + DECIMAL_STR_MAX(uid_t) + 1]; + _cleanup_close_ int lock_fd = -1; + ssize_t l; + + if (--n_tries <= 0) /* Give up retrying eventually */ + return -EBUSY; + + if (candidate < UID_PICK_MIN || candidate > UID_PICK_MAX) + goto next; + + xsprintf(lock_path, "/run/systemd/dynamic-uid/" UID_FMT, candidate); + + for (;;) { + struct stat st; + + lock_fd = open(lock_path, O_CREAT|O_RDWR|O_NOFOLLOW|O_CLOEXEC|O_NOCTTY, 0600); + if (lock_fd < 0) + return -errno; + + r = flock(lock_fd, LOCK_EX|LOCK_NB); /* Try to get a BSD file lock on the UID lock file */ + if (r < 0) { + if (errno == EBUSY || errno == EAGAIN) + goto next; /* already in use */ + + return -errno; + } + + if (fstat(lock_fd, &st) < 0) + return -errno; + if (st.st_nlink > 0) + break; + + /* Oh, bummer, we got got the lock, but the file was unlinked between the time we opened it and + * got the lock. Close it, and try again. */ + lock_fd = safe_close(lock_fd); + } + + /* Some superficial check whether this UID/GID might already be taken by some static user */ + if (getpwuid(candidate) || getgrgid((gid_t) candidate)) { + (void) unlink(lock_path); + goto next; + } + + /* Let's store the user name in the lock file, so that we can use it for looking up the username for a UID */ + l = pwritev(lock_fd, + (struct iovec[2]) { + { .iov_base = (char*) name, .iov_len = strlen(name) }, + { .iov_base = (char[1]) { '\n' }, .iov_len = 1 } + }, 2, 0); + if (l < 0) { + (void) unlink(lock_path); + return -errno; + } + + (void) ftruncate(lock_fd, l); + + *ret_uid = candidate; + r = lock_fd; + lock_fd = -1; + + return r; + + next: + /* Pick another random UID, and see if that works for us. */ + random_bytes(&candidate, sizeof(candidate)); + candidate = UID_CLAMP_INTO_RANGE(candidate); + } +} + +static int dynamic_user_pop(DynamicUser *d, uid_t *ret_uid, int *ret_lock_fd) { + uid_t uid = UID_INVALID; + struct iovec iov = { + .iov_base = &uid, + .iov_len = sizeof(uid), + }; + union { + struct cmsghdr cmsghdr; + uint8_t buf[CMSG_SPACE(sizeof(int))]; + } control = {}; + struct msghdr mh = { + .msg_control = &control, + .msg_controllen = sizeof(control), + .msg_iov = &iov, + .msg_iovlen = 1, + }; + struct cmsghdr *cmsg; + + ssize_t k; + int lock_fd = -1; + + assert(d); + assert(ret_uid); + assert(ret_lock_fd); + + /* Read the UID and lock fd that is stored in the storage AF_UNIX socket. This should be called with the lock + * on the socket taken. */ + + k = recvmsg(d->storage_socket[0], &mh, MSG_DONTWAIT|MSG_NOSIGNAL|MSG_CMSG_CLOEXEC); + if (k < 0) + return -errno; + + cmsg = cmsg_find(&mh, SOL_SOCKET, SCM_RIGHTS, CMSG_LEN(sizeof(int))); + if (cmsg) + lock_fd = *(int*) CMSG_DATA(cmsg); + else + cmsg_close_all(&mh); /* just in case... */ + + *ret_uid = uid; + *ret_lock_fd = lock_fd; + + return 0; +} + +static int dynamic_user_push(DynamicUser *d, uid_t uid, int lock_fd) { + struct iovec iov = { + .iov_base = &uid, + .iov_len = sizeof(uid), + }; + union { + struct cmsghdr cmsghdr; + uint8_t buf[CMSG_SPACE(sizeof(int))]; + } control = {}; + struct msghdr mh = { + .msg_control = &control, + .msg_controllen = sizeof(control), + .msg_iov = &iov, + .msg_iovlen = 1, + }; + ssize_t k; + + assert(d); + + /* Store the UID and lock_fd in the storage socket. This should be called with the socket pair lock taken. */ + + if (lock_fd >= 0) { + struct cmsghdr *cmsg; + + cmsg = CMSG_FIRSTHDR(&mh); + cmsg->cmsg_level = SOL_SOCKET; + cmsg->cmsg_type = SCM_RIGHTS; + cmsg->cmsg_len = CMSG_LEN(sizeof(int)); + memcpy(CMSG_DATA(cmsg), &lock_fd, sizeof(int)); + + mh.msg_controllen = CMSG_SPACE(sizeof(int)); + } else { + mh.msg_control = NULL; + mh.msg_controllen = 0; + } + + k = sendmsg(d->storage_socket[1], &mh, MSG_DONTWAIT|MSG_NOSIGNAL); + if (k < 0) + return -errno; + + return 0; +} + +static void unlink_uid_lock(int lock_fd, uid_t uid) { + char lock_path[strlen("/run/systemd/dynamic-uid/") + DECIMAL_STR_MAX(uid_t) + 1]; + + if (lock_fd < 0) + return; + + xsprintf(lock_path, "/run/systemd/dynamic-uid/" UID_FMT, uid); + (void) unlink_noerrno(lock_path); +} + +int dynamic_user_realize(DynamicUser *d, uid_t *ret) { + + _cleanup_close_ int etc_passwd_lock_fd = -1, uid_lock_fd = -1; + uid_t uid = UID_INVALID; + int r; + + assert(d); + + /* Acquire a UID for the user name. This will allocate a UID for the user name if the user doesn't exist + * yet. If it already exists its existing UID/GID will be reused. */ + + if (lockf(d->storage_socket[0], F_LOCK, 0) < 0) + return -errno; + + r = dynamic_user_pop(d, &uid, &uid_lock_fd); + if (r < 0) { + int new_uid_lock_fd; + uid_t new_uid; + + if (r != -EAGAIN) + goto finish; + + /* OK, nothing stored yet, let's try to find something useful. While we are working on this release the + * lock however, so that nobody else blocks on our NSS lookups. */ + (void) lockf(d->storage_socket[0], F_ULOCK, 0); + + /* Let's see if a proper, static user or group by this name exists. Try to take the lock on + * /etc/passwd, if that fails with EROFS then /etc is read-only. In that case it's fine if we don't + * take the lock, given that users can't be added there anyway in this case. */ + etc_passwd_lock_fd = take_etc_passwd_lock(NULL); + if (etc_passwd_lock_fd < 0 && etc_passwd_lock_fd != -EROFS) + return etc_passwd_lock_fd; + + /* First, let's parse this as numeric UID */ + r = parse_uid(d->name, &uid); + if (r < 0) { + struct passwd *p; + struct group *g; + + /* OK, this is not a numeric UID. Let's see if there's a user by this name */ + p = getpwnam(d->name); + if (p) + uid = p->pw_uid; + + /* Let's see if there's a group by this name */ + g = getgrnam(d->name); + if (g) { + /* If the UID/GID of the user/group of the same don't match, refuse operation */ + if (uid != UID_INVALID && uid != (uid_t) g->gr_gid) + return -EILSEQ; + + uid = (uid_t) g->gr_gid; + } + } + + if (uid == UID_INVALID) { + /* No static UID assigned yet, excellent. Let's pick a new dynamic one, and lock it. */ + + uid_lock_fd = pick_uid(d->name, &uid); + if (uid_lock_fd < 0) + return uid_lock_fd; + } + + /* So, we found a working UID/lock combination. Let's see if we actually still need it. */ + if (lockf(d->storage_socket[0], F_LOCK, 0) < 0) { + unlink_uid_lock(uid_lock_fd, uid); + return -errno; + } + + r = dynamic_user_pop(d, &new_uid, &new_uid_lock_fd); + if (r < 0) { + if (r != -EAGAIN) { + /* OK, something bad happened, let's get rid of the bits we acquired. */ + unlink_uid_lock(uid_lock_fd, uid); + goto finish; + } + + /* Great! Nothing is stored here, still. Store our newly acquired data. */ + } else { + /* Hmm, so as it appears there's now something stored in the storage socket. Throw away what we + * acquired, and use what's stored now. */ + + unlink_uid_lock(uid_lock_fd, uid); + safe_close(uid_lock_fd); + + uid = new_uid; + uid_lock_fd = new_uid_lock_fd; + } + } + + /* If the UID/GID was already allocated dynamically, push the data we popped out back in. If it was already + * allocated statically, push the UID back too, but do not push the lock fd in. If we allocated the UID + * dynamically right here, push that in along with the lock fd for it. */ + r = dynamic_user_push(d, uid, uid_lock_fd); + if (r < 0) + goto finish; + + *ret = uid; + r = 0; + +finish: + (void) lockf(d->storage_socket[0], F_ULOCK, 0); + return r; +} + +int dynamic_user_current(DynamicUser *d, uid_t *ret) { + _cleanup_close_ int lock_fd = -1; + uid_t uid; + int r; + + assert(d); + assert(ret); + + /* 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. */ + + if (lockf(d->storage_socket[0], F_LOCK, 0) < 0) + return -errno; + + r = dynamic_user_pop(d, &uid, &lock_fd); + if (r < 0) + goto finish; + + r = dynamic_user_push(d, uid, lock_fd); + if (r < 0) + goto finish; + + *ret = uid; + r = 0; + +finish: + (void) lockf(d->storage_socket[0], F_ULOCK, 0); + return r; +} + +DynamicUser* dynamic_user_ref(DynamicUser *d) { + if (!d) + return NULL; + + assert(d->n_ref > 0); + d->n_ref++; + + return d; +} + +DynamicUser* dynamic_user_unref(DynamicUser *d) { + if (!d) + return NULL; + + /* Note that this doesn't actually release any resources itself. If a dynamic user should be fully destroyed + * and its UID released, use dynamic_user_destroy() instead. NB: the dynamic user table may contain entries + * with no references, which is commonly the case right before a daemon reload. */ + + assert(d->n_ref > 0); + d->n_ref--; + + return NULL; +} + +static int dynamic_user_close(DynamicUser *d) { + _cleanup_close_ int lock_fd = -1; + uid_t uid; + int r; + + /* Release the user ID, by releasing the lock on it, and emptying the storage socket. After this the user is + * unrealized again, much like it was after it the DynamicUser object was first allocated. */ + + if (lockf(d->storage_socket[0], F_LOCK, 0) < 0) + return -errno; + + r = dynamic_user_pop(d, &uid, &lock_fd); + if (r == -EAGAIN) { + /* User wasn't realized yet, nothing to do. */ + r = 0; + goto finish; + } + if (r < 0) + goto finish; + + /* This dynamic user was realized and dynamically allocated. In this case, let's remove the lock file. */ + unlink_uid_lock(lock_fd, uid); + r = 1; + +finish: + (void) lockf(d->storage_socket[0], F_ULOCK, 0); + return r; +} + +DynamicUser* dynamic_user_destroy(DynamicUser *d) { + if (!d) + return NULL; + + /* Drop a reference to a DynamicUser object, and destroy the user completely if this was the last + * reference. This is called whenever a service is shut down and wants its dynamic UID gone. Note that + * dynamic_user_unref() is what is called whenever a service is simply freed, for example during a reload + * cycle, where the dynamic users should not be destroyed, but our datastructures should. */ + + dynamic_user_unref(d); + + if (d->n_ref > 0) + return NULL; + + (void) dynamic_user_close(d); + return dynamic_user_free(d); +} + +int dynamic_user_serialize(Manager *m, FILE *f, FDSet *fds) { + DynamicUser *d; + Iterator i; + + assert(m); + assert(f); + assert(fds); + + /* Dump the dynamic user database into the manager serialization, to deal with daemon reloads. */ + + HASHMAP_FOREACH(d, m->dynamic_users, i) { + int copy0, copy1; + + copy0 = fdset_put_dup(fds, d->storage_socket[0]); + if (copy0 < 0) + return copy0; + + copy1 = fdset_put_dup(fds, d->storage_socket[1]); + if (copy1 < 0) + return copy1; + + fprintf(f, "dynamic-user=%s %i %i\n", d->name, copy0, copy1); + } + + return 0; +} + +void dynamic_user_deserialize_one(Manager *m, const char *value, FDSet *fds) { + _cleanup_free_ char *name = NULL, *s0 = NULL, *s1 = NULL; + int r, fd0, fd1; + + assert(m); + assert(value); + assert(fds); + + /* Parse the serialization again, after a daemon reload */ + + r = extract_many_words(&value, NULL, 0, &name, &s0, &s1, NULL); + if (r != 3 || !isempty(value)) { + log_debug("Unable to parse dynamic user line."); + return; + } + + if (safe_atoi(s0, &fd0) < 0 || !fdset_contains(fds, fd0)) { + log_debug("Unable to process dynamic user fd specification."); + return; + } + + if (safe_atoi(s1, &fd1) < 0 || !fdset_contains(fds, fd1)) { + log_debug("Unable to process dynamic user fd specification."); + return; + } + + r = dynamic_user_add(m, name, (int[]) { fd0, fd1 }, NULL); + if (r < 0) { + log_debug_errno(r, "Failed to add dynamic user: %m"); + return; + } + + (void) fdset_remove(fds, fd0); + (void) fdset_remove(fds, fd1); +} + +void dynamic_user_vacuum(Manager *m, bool close_user) { + DynamicUser *d; + Iterator i; + + assert(m); + + /* Empty the dynamic user database, optionally cleaning up orphaned dynamic users, i.e. destroy and free users + * to which no reference exist. This is called after a daemon reload finished, in order to destroy users which + * might not be referenced anymore. */ + + HASHMAP_FOREACH(d, m->dynamic_users, i) { + if (d->n_ref > 0) + continue; + + if (close_user) { + log_debug("Removing orphaned dynamic user %s", d->name); + (void) dynamic_user_close(d); + } + + dynamic_user_free(d); + } +} + +int dynamic_user_lookup_uid(Manager *m, uid_t uid, char **ret) { + char lock_path[strlen("/run/systemd/dynamic-uid/") + DECIMAL_STR_MAX(uid_t) + 1]; + _cleanup_free_ char *user = NULL; + uid_t check_uid; + int r; + + assert(m); + assert(ret); + + /* A friendly way to translate a dynamic user's UID into a his name. */ + + if (uid < UID_PICK_MIN) + return -ESRCH; + if (uid > UID_PICK_MAX) + return -ESRCH; + + xsprintf(lock_path, "/run/systemd/dynamic-uid/" UID_FMT, uid); + r = read_one_line_file(lock_path, &user); + if (r == -ENOENT) + return -ESRCH; + if (r < 0) + return r; + + /* The lock file might be stale, hence let's verify the data before we return it */ + r = dynamic_user_lookup_name(m, user, &check_uid); + if (r < 0) + return r; + if (check_uid != uid) /* lock file doesn't match our own idea */ + return -ESRCH; + + *ret = user; + user = NULL; + + return 0; +} + +int dynamic_user_lookup_name(Manager *m, const char *name, uid_t *ret) { + DynamicUser *d; + int r; + + assert(m); + assert(name); + assert(ret); + + /* A friendly call for translating a dynamic user's name into its UID */ + + d = hashmap_get(m->dynamic_users, name); + if (!d) + return -ESRCH; + + r = dynamic_user_current(d, ret); + if (r == -EAGAIN) /* not realized yet? */ + return -ESRCH; + + return r; +} + +int dynamic_creds_acquire(DynamicCreds *creds, Manager *m, const char *user, const char *group) { + bool acquired = false; + int r; + + assert(creds); + assert(m); + + /* A DynamicUser object encapsulates an allocation of both a UID and a GID for a specific name. However, some + * services use different user and groups. For cases like that there's DynamicCreds containing a pair of user + * and group. This call allocates a pair. */ + + if (!creds->user && user) { + r = dynamic_user_acquire(m, user, &creds->user); + if (r < 0) + return r; + + acquired = true; + } + + if (!creds->group) { + + if (creds->user && (!group || streq_ptr(user, group))) + creds->group = dynamic_user_ref(creds->user); + else { + r = dynamic_user_acquire(m, group, &creds->group); + if (r < 0) { + if (acquired) + creds->user = dynamic_user_unref(creds->user); + return r; + } + } + } + + return 0; +} + +int dynamic_creds_realize(DynamicCreds *creds, uid_t *uid, gid_t *gid) { + uid_t u = UID_INVALID; + gid_t g = GID_INVALID; + int r; + + assert(creds); + assert(uid); + assert(gid); + + /* Realize both the referenced user and group */ + + if (creds->user) { + r = dynamic_user_realize(creds->user, &u); + if (r < 0) + return r; + } + + if (creds->group && creds->group != creds->user) { + r = dynamic_user_realize(creds->group, &g); + if (r < 0) + return r; + } else + g = u; + + *uid = u; + *gid = g; + + return 0; +} + +void dynamic_creds_unref(DynamicCreds *creds) { + assert(creds); + + creds->user = dynamic_user_unref(creds->user); + creds->group = dynamic_user_unref(creds->group); +} + +void dynamic_creds_destroy(DynamicCreds *creds) { + assert(creds); + + creds->user = dynamic_user_destroy(creds->user); + creds->group = dynamic_user_destroy(creds->group); +} |