15263807472

/* SPDX-License-Identifier: LGPL-2.1-or-later */

#include <fcntl.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/file.h>

#include "alloc-util.h"
#include "errno-util.h"
#include "fd-util.h"
#include "fs-util.h"
#include "lock-util.h"
#include "log.h"
#include "path-util.h"
#include "process-util.h"
#include "string-util.h"
#include "time-util.h"

int make_lock_file_at(int dir_fd, const char *p, int operation, LockFile *ret) {
        _cleanup_close_ int fd = -EBADF, dfd = -EBADF;
        _cleanup_free_ char *t = NULL;

        assert(dir_fd >= 0 || dir_fd == AT_FDCWD);
        assert(p);
        assert(IN_SET(operation & ~LOCK_NB, LOCK_EX, LOCK_SH));
        assert(ret);

        if (isempty(p))
                return -EINVAL;

        /* We use UNPOSIX locks as they have nice semantics, and are mostly compatible with NFS. */

        dfd = fd_reopen(dir_fd, O_CLOEXEC|O_PATH|O_DIRECTORY);
        if (dfd < 0)
                return dfd;

        t = strdup(p);
        if (!t)
                return -ENOMEM;

        fd = xopenat_lock_full(dfd,
                               p,
                               O_CREAT|O_RDWR|O_NOFOLLOW|O_CLOEXEC|O_NOCTTY,
                               /* xopen_flags = */ 0,
                               0600,
                               LOCK_UNPOSIX,
                               operation);
        if (fd < 0)
                return fd == -EAGAIN ? -EBUSY : fd;

        *ret = (LockFile) {
                .dir_fd = TAKE_FD(dfd),
                .path = TAKE_PTR(t),
                .fd = TAKE_FD(fd),
                .operation = operation,
        };

        return 0;
}

int make_lock_file_for(const char *p, int operation, LockFile *ret) {
        _cleanup_free_ char *fn = NULL, *dn = NULL, *t = NULL;
        int r;

        assert(p);
        assert(ret);

        r = path_extract_filename(p, &fn);
        if (r < 0)
                return r;

        r = path_extract_directory(p, &dn);
        if (r < 0)
                return r;

        t = strjoin(dn, "/.#", fn, ".lck");
        if (!t)
                return -ENOMEM;

        return make_lock_file(t, operation, ret);
}

void release_lock_file(LockFile *f) {
        if (!f)
                return;

        if (f->path) {

                /* If we are the exclusive owner we can safely delete
                 * the lock file itself. If we are not the exclusive
                 * owner, we can try becoming it. */

                if (f->fd >= 0 &&
                    (f->operation & ~LOCK_NB) == LOCK_SH &&
                    unposix_lock(f->fd, LOCK_EX|LOCK_NB) >= 0)
                        f->operation = LOCK_EX|LOCK_NB;

                if ((f->operation & ~LOCK_NB) == LOCK_EX)
                        (void) unlinkat(f->dir_fd, f->path, 0);

                f->path = mfree(f->path);
        }

        f->dir_fd = safe_close(f->dir_fd);
        f->fd = safe_close(f->fd);
        f->operation = 0;
}

static int fcntl_lock(int fd, int operation, bool ofd) {
        int cmd, type, r;

        assert(fd >= 0);

        if (ofd)
                cmd = (operation & LOCK_NB) ? F_OFD_SETLK : F_OFD_SETLKW;
        else
                cmd = (operation & LOCK_NB) ? F_SETLK : F_SETLKW;

        switch (operation & ~LOCK_NB) {
                case LOCK_EX:
                        type = F_WRLCK;
                        break;
                case LOCK_SH:
                        type = F_RDLCK;
                        break;
                case LOCK_UN:
                        type = F_UNLCK;
                        break;
                default:
                        assert_not_reached();
        }

        r = RET_NERRNO(fcntl(fd, cmd, &(struct flock) {
                .l_type = type,
                .l_whence = SEEK_SET,
                .l_start = 0,
                .l_len = 0,
        }));

        /* If we are doing non-blocking operations, treat EACCES/EAGAIN the same as per man page. But if
         * not, propagate EACCES back, as it will likely be due to an LSM denying the operation (for example
         * LXC with AppArmor when running on kernel < 6.2), and in some cases we want to gracefully
         * fallback (e.g.: PrivateNetwork=yes). As per documentation, it's only the non-blocking operation
         * F_SETLK that might return EACCES on some platforms (although the Linux implementation doesn't
         * seem to), as F_SETLKW and F_OFD_SETLKW block so this is not an issue, and F_OFD_SETLK is documented
         * to only return EAGAIN if the lock is already held. */
        if ((operation & LOCK_NB) && r == -EACCES)
                r = -EAGAIN;

        return r;
}

int posix_lock(int fd, int operation) {
        return fcntl_lock(fd, operation, /*ofd=*/ false);
}

int unposix_lock(int fd, int operation) {
        return fcntl_lock(fd, operation, /*ofd=*/ true);
}

void posix_unlockpp(int **fd) {
        assert(fd);

        if (!*fd || **fd < 0)
                return;

        (void) fcntl_lock(**fd, LOCK_UN, /*ofd=*/ false);
        *fd = NULL;
}

void unposix_unlockpp(int **fd) {
        assert(fd);

        if (!*fd || **fd < 0)
                return;

        (void) fcntl_lock(**fd, LOCK_UN, /*ofd=*/ true);
        *fd = NULL;
}

int lock_generic(int fd, LockType type, int operation) {
        assert(fd >= 0);

        switch (type) {
        case LOCK_NONE:
                return 0;
        case LOCK_BSD:
                return RET_NERRNO(flock(fd, operation));
        case LOCK_POSIX:
                return posix_lock(fd, operation);
        case LOCK_UNPOSIX:
                return unposix_lock(fd, operation);
        default:
                assert_not_reached();
        }
}

int lock_generic_with_timeout(int fd, LockType type, int operation, usec_t timeout) {
        _cleanup_(sigkill_waitp) pid_t pid = 0;
        int r;

        assert(fd >= 0);

        /* A version of lock_generic(), but with a timeout. We do this in a child process, since the kernel
         * APIs natively don't support a timeout. We set a SIGALRM timer that will kill the child after the
         * timeout is hit. Returns -ETIMEDOUT if the timeout is hit, and 0 on success.
         *
         * This only works for BSD and UNPOSIX locks, as only those are fd-bound, and hence can be acquired
         * from any process that has access to the fd. POSIX locks OTOH are process-bound, and hence if we'd
         * acquire them in a child process they'd remain unlocked in the parent. */

        if (type == LOCK_NONE)
                return 0;
        if (!IN_SET(type, LOCK_BSD, LOCK_UNPOSIX)) /* Not for POSIX locks, see above. */
                return -EOPNOTSUPP;

        /* First, try without forking anything off */
        r = lock_generic(fd, type, operation | (timeout == USEC_INFINITY ? 0 : LOCK_NB));
        if (r != -EAGAIN || timeout == 0 || FLAGS_SET(operation, LOCK_NB))
                return r;

        /* If that didn't work, try with a child */

        r = safe_fork("(sd-flock)", FORK_RESET_SIGNALS|FORK_DEATHSIG_SIGKILL, &pid);
        if (r < 0)
                return log_error_errno(r, "Failed to flock block device in child process: %m");
        if (r == 0) {
                struct sigevent sev = {
                        .sigev_notify = SIGEV_SIGNAL,
                        .sigev_signo = SIGALRM,
                };
                timer_t id;

                if (timer_create(CLOCK_MONOTONIC, &sev, &id) < 0) {
                        log_error_errno(errno, "Failed to allocate CLOCK_MONOTONIC timer: %m");
                        _exit(EXIT_FAILURE);
                }

                struct itimerspec its = {};
                timespec_store(&its.it_value, timeout);

                if (timer_settime(id, /* flags= */ 0, &its, NULL) < 0) {
                        log_error_errno(errno, "Failed to start CLOCK_MONOTONIC timer: %m");
                        _exit(EXIT_FAILURE);
                }

                if (lock_generic(fd, type, operation) < 0) {
                        log_error_errno(errno, "Unable to get an exclusive lock on the device: %m");
                        _exit(EXIT_FAILURE);
                }

                _exit(EXIT_SUCCESS);
        }

        siginfo_t status;
        r = wait_for_terminate(pid, &status);
        if (r < 0)
                return r;

        TAKE_PID(pid);

        switch (status.si_code) {

        case CLD_EXITED:
                if (status.si_status != EXIT_SUCCESS)
                        return -EPROTO;

                return 0;

        case CLD_KILLED:
                if (status.si_status == SIGALRM)
                        return -ETIMEDOUT;

                _fallthrough_;

        case CLD_DUMPED:
                return -EPROTO;

        default:
                assert_not_reached();
        }
}

1	/* SPDX-License-Identifier: LGPL-2.1-or-later */
2
3	#include <fcntl.h>
4	#include <signal.h>
5	#include <stdio.h>
6	#include <stdlib.h>
7	#include <string.h>
8	#include <sys/file.h>
9
10	#include "alloc-util.h"
11	#include "errno-util.h"
12	#include "fd-util.h"
13	#include "fs-util.h"
14	#include "lock-util.h"
15	#include "log.h"
16	#include "path-util.h"
17	#include "process-util.h"
18	#include "string-util.h"
19	#include "time-util.h"
20
21	int make_lock_file_at(int dir_fd, const char p, int operation, LockFile ret) {	242,832✔
22	_cleanup_close_ int fd = -EBADF, dfd = -EBADF;	242,832✔
23	_cleanup_free_ char *t = NULL;	242,832✔
24
25	assert(dir_fd >= 0 \|\| dir_fd == AT_FDCWD);	242,832✔
26	assert(p);	242,832✔
27	assert(IN_SET(operation & ~LOCK_NB, LOCK_EX, LOCK_SH));	242,832✔
28	assert(ret);	242,832✔
29
30	if (isempty(p))	485,664✔
31	return -EINVAL;
32
33	/* We use UNPOSIX locks as they have nice semantics, and are mostly compatible with NFS. */
34
35	dfd = fd_reopen(dir_fd, O_CLOEXEC\|O_PATH\|O_DIRECTORY);	242,832✔
36	if (dfd < 0)	242,832✔
37	return dfd;
38
39	t = strdup(p);	242,832✔
40	if (!t)	242,832✔
41	return -ENOMEM;
42
43	fd = xopenat_lock_full(dfd,	242,832✔
44	p,
45	O_CREAT\|O_RDWR\|O_NOFOLLOW\|O_CLOEXEC\|O_NOCTTY,
46	/* xopen_flags = */ 0,
47	0600,
48	LOCK_UNPOSIX,
49	operation);
50	if (fd < 0)	242,832✔
51	return fd == -EAGAIN ? -EBUSY : fd;	3✔
52
53	*ret = (LockFile) {	242,829✔
54	.dir_fd = TAKE_FD(dfd),	242,829✔
55	.path = TAKE_PTR(t),	242,829✔
56	.fd = TAKE_FD(fd),	242,829✔
57	.operation = operation,
58	};
59
60	return 0;	242,829✔
61	}
62
63	int make_lock_file_for(const char p, int operation, LockFile ret) {	629✔
64	_cleanup_free_ char fn = NULL, dn = NULL, *t = NULL;	629✔
65	int r;	629✔
66
67	assert(p);	629✔
68	assert(ret);	629✔
69
70	r = path_extract_filename(p, &fn);	629✔
71	if (r < 0)	629✔
72	return r;
73
74	r = path_extract_directory(p, &dn);	629✔
75	if (r < 0)	629✔
76	return r;
77
78	t = strjoin(dn, "/.#", fn, ".lck");	629✔
79	if (!t)	629✔
80	return -ENOMEM;
81
82	return make_lock_file(t, operation, ret);	629✔
83	}
84
85	void release_lock_file(LockFile *f) {	485,011✔
86	if (!f)	485,011✔
87	return;
88
89	if (f->path) {	485,011✔
90
91	/* If we are the exclusive owner we can safely delete
92	* the lock file itself. If we are not the exclusive
93	* owner, we can try becoming it. */
94
95	if (f->fd >= 0 &&	242,414✔
96	(f->operation & ~LOCK_NB) == LOCK_SH &&	242,882✔
97	unposix_lock(f->fd, LOCK_EX\|LOCK_NB) >= 0)	468✔
98	f->operation = LOCK_EX\|LOCK_NB;	467✔
99
100	if ((f->operation & ~LOCK_NB) == LOCK_EX)	242,414✔
101	(void) unlinkat(f->dir_fd, f->path, 0);	242,413✔
102
103	f->path = mfree(f->path);	242,414✔
104	}
105
106	f->dir_fd = safe_close(f->dir_fd);	485,011✔
107	f->fd = safe_close(f->fd);	485,011✔
108	f->operation = 0;	485,011✔
109	}
110
111	static int fcntl_lock(int fd, int operation, bool ofd) {	261,833✔
112	int cmd, type, r;	261,833✔
113
114	assert(fd >= 0);	261,833✔
115
116	if (ofd)	261,833✔
117	cmd = (operation & LOCK_NB) ? F_OFD_SETLK : F_OFD_SETLKW;	261,424✔
118	else
119	cmd = (operation & LOCK_NB) ? F_SETLK : F_SETLKW;	409✔
120
121	switch (operation & ~LOCK_NB) {	261,833✔
122	case LOCK_EX:
123	type = F_WRLCK;
124	break;
125	case LOCK_SH:	504✔
126	type = F_RDLCK;	504✔
127	break;	504✔
128	case LOCK_UN:	204✔
129	type = F_UNLCK;	204✔
130	break;	204✔
UNCOV 131	default:	×
UNCOV 132	assert_not_reached();	×
133	}
134
135	r = RET_NERRNO(fcntl(fd, cmd, &(struct flock) {	261,833✔
136	.l_type = type,
137	.l_whence = SEEK_SET,
138	.l_start = 0,
139	.l_len = 0,
140	}));
141
142	/* If we are doing non-blocking operations, treat EACCES/EAGAIN the same as per man page. But if
143	* not, propagate EACCES back, as it will likely be due to an LSM denying the operation (for example
144	* LXC with AppArmor when running on kernel < 6.2), and in some cases we want to gracefully
145	* fallback (e.g.: PrivateNetwork=yes). As per documentation, it's only the non-blocking operation
146	* F_SETLK that might return EACCES on some platforms (although the Linux implementation doesn't
147	* seem to), as F_SETLKW and F_OFD_SETLKW block so this is not an issue, and F_OFD_SETLK is documented
148	* to only return EAGAIN if the lock is already held. */
149	if ((operation & LOCK_NB) && r == -EACCES)	261,833✔
UNCOV 150	r = -EAGAIN;	×
151
152	return r;	261,833✔
153	}
154
155	int posix_lock(int fd, int operation) {	261✔
156	return fcntl_lock(fd, operation, /ofd=/ false);	261✔
157	}
158
159	int unposix_lock(int fd, int operation) {	261,424✔
160	return fcntl_lock(fd, operation, /ofd=/ true);	261,424✔
161	}
162
163	void posix_unlockpp(int **fd) {	148✔
164	assert(fd);	148✔
165
166	if (!fd \|\| *fd < 0)	148✔
167	return;
168
169	(void) fcntl_lock(*fd, LOCK_UN, /ofd=*/ false);	148✔
170	*fd = NULL;	148✔
171	}
172
UNCOV 173	void unposix_unlockpp(int **fd) {	×
UNCOV 174	assert(fd);	×
175
176	if (!fd \|\| *fd < 0)	×
177	return;
178
UNCOV 179	(void) fcntl_lock(*fd, LOCK_UN, /ofd=*/ true);	×
UNCOV 180	*fd = NULL;	×
181	}
182
183	int lock_generic(int fd, LockType type, int operation) {	298,143✔
184	assert(fd >= 0);	298,143✔
185
186	switch (type) {	298,143✔
187	case LOCK_NONE:
188	return 0;
189	case LOCK_BSD:	3,021✔
190	return RET_NERRNO(flock(fd, operation));	3,021✔
191	case LOCK_POSIX:	1✔
192	return posix_lock(fd, operation);	1✔
193	case LOCK_UNPOSIX:	260,675✔
194	return unposix_lock(fd, operation);	260,675✔
UNCOV 195	default:	×
UNCOV 196	assert_not_reached();	×
197	}
198	}
199
200	int lock_generic_with_timeout(int fd, LockType type, int operation, usec_t timeout) {	475✔
201	_cleanup_(sigkill_waitp) pid_t pid = 0;	475✔
202	int r;	475✔
203
204	assert(fd >= 0);	475✔
205
206	/* A version of lock_generic(), but with a timeout. We do this in a child process, since the kernel
207	* APIs natively don't support a timeout. We set a SIGALRM timer that will kill the child after the
208	* timeout is hit. Returns -ETIMEDOUT if the timeout is hit, and 0 on success.
209	*
210	* This only works for BSD and UNPOSIX locks, as only those are fd-bound, and hence can be acquired
211	* from any process that has access to the fd. POSIX locks OTOH are process-bound, and hence if we'd
212	* acquire them in a child process they'd remain unlocked in the parent. */
213
214	if (type == LOCK_NONE)	475✔
215	return 0;
216	if (!IN_SET(type, LOCK_BSD, LOCK_UNPOSIX)) /* Not for POSIX locks, see above. */	475✔
217	return -EOPNOTSUPP;
218
219	/* First, try without forking anything off */
220	r = lock_generic(fd, type, operation \| (timeout == USEC_INFINITY ? 0 : LOCK_NB));	950✔
221	if (r != -EAGAIN \|\| timeout == 0 \|\| FLAGS_SET(operation, LOCK_NB))	475✔
222	return r;
223
224	/* If that didn't work, try with a child */
225
226	r = safe_fork("(sd-flock)", FORK_RESET_SIGNALS\|FORK_DEATHSIG_SIGKILL, &pid);	464✔
227	if (r < 0)	926✔
UNCOV 228	return log_error_errno(r, "Failed to flock block device in child process: %m");	×
229	if (r == 0) {	926✔
230	struct sigevent sev = {	462✔
231	.sigev_notify = SIGEV_SIGNAL,
232	.sigev_signo = SIGALRM,
233	};
234	timer_t id;	462✔
235
236	if (timer_create(CLOCK_MONOTONIC, &sev, &id) < 0) {	462✔
UNCOV 237	log_error_errno(errno, "Failed to allocate CLOCK_MONOTONIC timer: %m");	×
UNCOV 238	_exit(EXIT_FAILURE);	×
239	}
240
241	struct itimerspec its = {};	462✔
242	timespec_store(&its.it_value, timeout);	462✔
243
244	if (timer_settime(id, /* flags= */ 0, &its, NULL) < 0) {	462✔
UNCOV 245	log_error_errno(errno, "Failed to start CLOCK_MONOTONIC timer: %m");	×
UNCOV 246	_exit(EXIT_FAILURE);	×
247	}
248
249	if (lock_generic(fd, type, operation) < 0) {	462✔
UNCOV 250	log_error_errno(errno, "Unable to get an exclusive lock on the device: %m");	×
UNCOV 251	_exit(EXIT_FAILURE);	×
252	}
253
254	_exit(EXIT_SUCCESS);	462✔
255	}
256
257	siginfo_t status;	464✔
258	r = wait_for_terminate(pid, &status);	464✔
259	if (r < 0)	464✔
260	return r;
261
262	TAKE_PID(pid);	464✔
263
264	switch (status.si_code) {	464✔
265
266	case CLD_EXITED:	462✔
267	if (status.si_status != EXIT_SUCCESS)	462✔
UNCOV 268	return -EPROTO;	×
269
270	return 0;
271
272	case CLD_KILLED:	2✔
273	if (status.si_status == SIGALRM)	2✔
274	return -ETIMEDOUT;	2✔
275
276	_fallthrough_;
277
278	case CLD_DUMPED:
279	return -EPROTO;
280
UNCOV 281	default:	×
UNCOV 282	assert_not_reached();	×
283	}
284	}

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