mirror of
https://github.com/morgan9e/systemd
synced 2026-04-15 00:47:10 +09:00
4f18ff2e29
We use symbols provided by unistd.h without including it. E.g. open(), close(), read(), write(), access(), symlink(), unlink(), rmdir(), fsync(), syncfs(), lseek(), ftruncate(), fchown(), dup2(), pipe2(), getuid(), getgid(), gettid(), getppid(), pipe2(), execv(), _exit(), environ, STDIN_FILENO, STDOUT_FILENO, STDERR_FILENO, F_OK, and their friends and variants, so on. Currently, unistd.h is indirectly included mainly in the following two paths: - through missing_syscall.h, which is planned to covert to .c file. - through signal.h -> bits/sigstksz.h, which is new since glibc-2.34. Note, signal.h is included by sd-eevent.h. So, many source files indirectly include unistd.h if newer glibc is used. Currently, our baseline on glibc is 2.31. We need to support glibc older than 2.34, but unfortunately, we do not have any CI environments with such old glibc. CIFuzz uses glibc-2.31, but it builds only fuzzers, and many files are even not compiled.
286 lines
8.7 KiB
C
286 lines
8.7 KiB
C
/* SPDX-License-Identifier: LGPL-2.1-or-later */
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#include <fcntl.h>
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#include <signal.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/file.h>
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#include <unistd.h>
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#include "alloc-util.h"
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#include "errno-util.h"
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#include "fd-util.h"
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#include "fs-util.h"
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#include "lock-util.h"
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#include "log.h"
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#include "path-util.h"
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#include "process-util.h"
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#include "string-util.h"
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#include "time-util.h"
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int make_lock_file_at(int dir_fd, const char *p, int operation, LockFile *ret) {
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_cleanup_close_ int fd = -EBADF, dfd = -EBADF;
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_cleanup_free_ char *t = NULL;
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assert(dir_fd >= 0 || dir_fd == AT_FDCWD);
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assert(p);
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assert(IN_SET(operation & ~LOCK_NB, LOCK_EX, LOCK_SH));
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assert(ret);
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if (isempty(p))
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return -EINVAL;
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/* We use UNPOSIX locks as they have nice semantics, and are mostly compatible with NFS. */
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dfd = fd_reopen(dir_fd, O_CLOEXEC|O_PATH|O_DIRECTORY);
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if (dfd < 0)
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return dfd;
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t = strdup(p);
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if (!t)
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return -ENOMEM;
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fd = xopenat_lock_full(dfd,
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p,
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O_CREAT|O_RDWR|O_NOFOLLOW|O_CLOEXEC|O_NOCTTY,
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/* xopen_flags = */ 0,
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0600,
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LOCK_UNPOSIX,
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operation);
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if (fd < 0)
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return fd == -EAGAIN ? -EBUSY : fd;
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*ret = (LockFile) {
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.dir_fd = TAKE_FD(dfd),
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.path = TAKE_PTR(t),
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.fd = TAKE_FD(fd),
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.operation = operation,
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};
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return 0;
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}
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int make_lock_file_for(const char *p, int operation, LockFile *ret) {
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_cleanup_free_ char *fn = NULL, *dn = NULL, *t = NULL;
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int r;
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assert(p);
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assert(ret);
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r = path_extract_filename(p, &fn);
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if (r < 0)
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return r;
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r = path_extract_directory(p, &dn);
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if (r < 0)
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return r;
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t = strjoin(dn, "/.#", fn, ".lck");
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if (!t)
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return -ENOMEM;
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return make_lock_file(t, operation, ret);
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}
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void release_lock_file(LockFile *f) {
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if (!f)
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return;
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if (f->path) {
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/* If we are the exclusive owner we can safely delete
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* the lock file itself. If we are not the exclusive
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* owner, we can try becoming it. */
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if (f->fd >= 0 &&
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(f->operation & ~LOCK_NB) == LOCK_SH &&
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unposix_lock(f->fd, LOCK_EX|LOCK_NB) >= 0)
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f->operation = LOCK_EX|LOCK_NB;
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if ((f->operation & ~LOCK_NB) == LOCK_EX)
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(void) unlinkat(f->dir_fd, f->path, 0);
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f->path = mfree(f->path);
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}
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f->dir_fd = safe_close(f->dir_fd);
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f->fd = safe_close(f->fd);
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f->operation = 0;
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}
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static int fcntl_lock(int fd, int operation, bool ofd) {
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int cmd, type, r;
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assert(fd >= 0);
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if (ofd)
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cmd = (operation & LOCK_NB) ? F_OFD_SETLK : F_OFD_SETLKW;
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else
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cmd = (operation & LOCK_NB) ? F_SETLK : F_SETLKW;
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switch (operation & ~LOCK_NB) {
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case LOCK_EX:
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type = F_WRLCK;
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break;
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case LOCK_SH:
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type = F_RDLCK;
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break;
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case LOCK_UN:
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type = F_UNLCK;
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break;
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default:
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assert_not_reached();
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}
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r = RET_NERRNO(fcntl(fd, cmd, &(struct flock) {
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.l_type = type,
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.l_whence = SEEK_SET,
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.l_start = 0,
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.l_len = 0,
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}));
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/* If we are doing non-blocking operations, treat EACCES/EAGAIN the same as per man page. But if
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* not, propagate EACCES back, as it will likely be due to an LSM denying the operation (for example
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* LXC with AppArmor when running on kernel < 6.2), and in some cases we want to gracefully
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* fallback (e.g.: PrivateNetwork=yes). As per documentation, it's only the non-blocking operation
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* F_SETLK that might return EACCES on some platforms (although the Linux implementation doesn't
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* seem to), as F_SETLKW and F_OFD_SETLKW block so this is not an issue, and F_OFD_SETLK is documented
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* to only return EAGAIN if the lock is already held. */
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if ((operation & LOCK_NB) && r == -EACCES)
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r = -EAGAIN;
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return r;
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}
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int posix_lock(int fd, int operation) {
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return fcntl_lock(fd, operation, /*ofd=*/ false);
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}
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int unposix_lock(int fd, int operation) {
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return fcntl_lock(fd, operation, /*ofd=*/ true);
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}
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void posix_unlockpp(int **fd) {
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assert(fd);
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if (!*fd || **fd < 0)
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return;
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(void) fcntl_lock(**fd, LOCK_UN, /*ofd=*/ false);
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*fd = NULL;
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}
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void unposix_unlockpp(int **fd) {
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assert(fd);
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if (!*fd || **fd < 0)
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return;
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(void) fcntl_lock(**fd, LOCK_UN, /*ofd=*/ true);
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*fd = NULL;
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}
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int lock_generic(int fd, LockType type, int operation) {
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assert(fd >= 0);
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switch (type) {
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case LOCK_NONE:
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return 0;
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case LOCK_BSD:
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return RET_NERRNO(flock(fd, operation));
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case LOCK_POSIX:
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return posix_lock(fd, operation);
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case LOCK_UNPOSIX:
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return unposix_lock(fd, operation);
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default:
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assert_not_reached();
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}
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}
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int lock_generic_with_timeout(int fd, LockType type, int operation, usec_t timeout) {
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_cleanup_(sigkill_waitp) pid_t pid = 0;
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int r;
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assert(fd >= 0);
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/* A version of lock_generic(), but with a timeout. We do this in a child process, since the kernel
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* APIs natively don't support a timeout. We set a SIGALRM timer that will kill the child after the
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* timeout is hit. Returns -ETIMEDOUT if the timeout is hit, and 0 on success.
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*
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* This only works for BSD and UNPOSIX locks, as only those are fd-bound, and hence can be acquired
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* from any process that has access to the fd. POSIX locks OTOH are process-bound, and hence if we'd
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* acquire them in a child process they'd remain unlocked in the parent. */
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if (type == LOCK_NONE)
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return 0;
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if (!IN_SET(type, LOCK_BSD, LOCK_UNPOSIX)) /* Not for POSIX locks, see above. */
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return -EOPNOTSUPP;
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/* First, try without forking anything off */
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r = lock_generic(fd, type, operation | (timeout == USEC_INFINITY ? 0 : LOCK_NB));
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if (r != -EAGAIN || timeout == 0 || FLAGS_SET(operation, LOCK_NB))
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return r;
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/* If that didn't work, try with a child */
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r = safe_fork("(sd-flock)", FORK_RESET_SIGNALS|FORK_DEATHSIG_SIGKILL, &pid);
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if (r < 0)
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return log_error_errno(r, "Failed to flock block device in child process: %m");
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if (r == 0) {
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struct sigevent sev = {
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.sigev_notify = SIGEV_SIGNAL,
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.sigev_signo = SIGALRM,
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};
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timer_t id;
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if (timer_create(CLOCK_MONOTONIC, &sev, &id) < 0) {
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log_error_errno(errno, "Failed to allocate CLOCK_MONOTONIC timer: %m");
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_exit(EXIT_FAILURE);
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}
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struct itimerspec its = {};
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timespec_store(&its.it_value, timeout);
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if (timer_settime(id, /* flags= */ 0, &its, NULL) < 0) {
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log_error_errno(errno, "Failed to start CLOCK_MONOTONIC timer: %m");
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_exit(EXIT_FAILURE);
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}
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if (lock_generic(fd, type, operation) < 0) {
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log_error_errno(errno, "Unable to get an exclusive lock on the device: %m");
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_exit(EXIT_FAILURE);
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}
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_exit(EXIT_SUCCESS);
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}
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siginfo_t status;
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r = wait_for_terminate(pid, &status);
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if (r < 0)
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return r;
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TAKE_PID(pid);
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switch (status.si_code) {
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case CLD_EXITED:
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if (status.si_status != EXIT_SUCCESS)
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return -EPROTO;
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return 0;
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case CLD_KILLED:
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if (status.si_status == SIGALRM)
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return -ETIMEDOUT;
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_fallthrough_;
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case CLD_DUMPED:
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return -EPROTO;
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default:
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assert_not_reached();
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}
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}
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