Adding upstream version 2.36.1.upstream/2.36.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 732 insertions, 0 deletions

diff --git a/libmount/src/lock.c b/libmount/src/lock.c
new file mode 100644
index 0000000..cc5340d
--- /dev/null
+++ b/libmount/src/lock.c
@@ -0,0 +1,732 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * This file is part of libmount from util-linux project.
+ *
+ * Copyright (C) 2009-2018 Karel Zak <kzak@redhat.com>
+ *
+ * libmount 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.
+ */
+
+/**
+ * SECTION: lock
+ * @title: Locking
+ * @short_description: locking methods for /etc/mtab or another libmount files
+ *
+ * The mtab lock is backwards compatible with the standard linux /etc/mtab
+ * locking.  Note, it's necessary to use the same locking schema in all
+ * applications that access the file.
+ */
+#include <sys/time.h>
+#include <time.h>
+#include <signal.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <sys/file.h>
+
+#include "strutils.h"
+#include "closestream.h"
+#include "pathnames.h"
+#include "mountP.h"
+#include "monotonic.h"
+
+/*
+ * lock handler
+ */
+struct libmnt_lock {
+	char	*lockfile;	/* path to lock file (e.g. /etc/mtab~) */
+	char	*linkfile;	/* path to link file (e.g. /etc/mtab~.<id>) */
+	int	lockfile_fd;	/* lock file descriptor */
+
+	unsigned int	locked :1,	/* do we own the lock? */
+			sigblock :1,	/* block signals when locked */
+			simplelock :1;	/* use flock rather than normal mtab lock */
+
+	sigset_t oldsigmask;
+};
+
+
+/**
+ * mnt_new_lock:
+ * @datafile: the file that should be covered by the lock
+ * @id: unique linkfile identifier or 0 (default is getpid())
+ *
+ * Returns: newly allocated lock handler or NULL on case of error.
+ */
+struct libmnt_lock *mnt_new_lock(const char *datafile, pid_t id)
+{
+	struct libmnt_lock *ml = NULL;
+	char *lo = NULL, *ln = NULL;
+	size_t losz;
+
+	if (!datafile)
+		return NULL;
+
+	/* for flock we use "foo.lock, for mtab "foo~"
+	 */
+	losz = strlen(datafile) + sizeof(".lock");
+	lo = malloc(losz);
+	if (!lo)
+		goto err;
+
+	/* default is mtab~ lock */
+	snprintf(lo, losz, "%s~", datafile);
+
+	if (asprintf(&ln, "%s~.%d", datafile, id ? : getpid()) == -1) {
+		ln = NULL;
+		goto err;
+	}
+	ml = calloc(1, sizeof(*ml) );
+	if (!ml)
+		goto err;
+
+	ml->lockfile_fd = -1;
+	ml->linkfile = ln;
+	ml->lockfile = lo;
+
+	DBG(LOCKS, ul_debugobj(ml, "alloc: default linkfile=%s, lockfile=%s", ln, lo));
+	return ml;
+err:
+	free(lo);
+	free(ln);
+	free(ml);
+	return NULL;
+}
+
+
+/**
+ * mnt_free_lock:
+ * @ml: struct libmnt_lock handler
+ *
+ * Deallocates mnt_lock.
+ */
+void mnt_free_lock(struct libmnt_lock *ml)
+{
+	if (!ml)
+		return;
+	DBG(LOCKS, ul_debugobj(ml, "free%s", ml->locked ? " !!! LOCKED !!!" : ""));
+	free(ml->lockfile);
+	free(ml->linkfile);
+	free(ml);
+}
+
+/**
+ * mnt_lock_block_signals:
+ * @ml: struct libmnt_lock handler
+ * @enable: TRUE/FALSE
+ *
+ * Block/unblock signals when the lock is locked, the signals are not blocked
+ * by default.
+ *
+ * Returns: <0 on error, 0 on success.
+ */
+int mnt_lock_block_signals(struct libmnt_lock *ml, int enable)
+{
+	if (!ml)
+		return -EINVAL;
+	DBG(LOCKS, ul_debugobj(ml, "signals: %s", enable ? "BLOCKED" : "UNBLOCKED"));
+	ml->sigblock = enable ? 1 : 0;
+	return 0;
+}
+
+/* don't export this to API
+ */
+int mnt_lock_use_simplelock(struct libmnt_lock *ml, int enable)
+{
+	size_t sz;
+
+	if (!ml)
+		return -EINVAL;
+
+	assert(ml->lockfile);
+
+	DBG(LOCKS, ul_debugobj(ml, "flock: %s", enable ? "ENABLED" : "DISABLED"));
+	ml->simplelock = enable ? 1 : 0;
+
+	sz = strlen(ml->lockfile);
+	assert(sz);
+
+	if (sz < 1)
+		return -EINVAL;
+
+	/* Change lock name:
+	 *
+	 *	flock:     "<name>.lock"
+	 *	mtab lock: "<name>~"
+	 */
+	if (ml->simplelock && endswith(ml->lockfile, "~"))
+		memcpy(ml->lockfile + sz - 1, ".lock", 6);
+
+	else if (!ml->simplelock && endswith(ml->lockfile, ".lock"))
+		 memcpy(ml->lockfile + sz - 5, "~", 2);
+
+	DBG(LOCKS, ul_debugobj(ml, "new lock filename: '%s'", ml->lockfile));
+	return 0;
+}
+
+/*
+ * Returns path to lockfile.
+ */
+static const char *mnt_lock_get_lockfile(struct libmnt_lock *ml)
+{
+	return ml ? ml->lockfile : NULL;
+}
+
+/*
+ * Note that the filename is generated by mnt_new_lock() and depends on
+ * getpid() or 'id' argument of the mnt_new_lock() function.
+ *
+ * Returns: unique (per process/thread) path to linkfile.
+ */
+static const char *mnt_lock_get_linkfile(struct libmnt_lock *ml)
+{
+	return ml ? ml->linkfile : NULL;
+}
+
+/*
+ * Simple flocking
+ */
+static void unlock_simplelock(struct libmnt_lock *ml)
+{
+	assert(ml);
+	assert(ml->simplelock);
+
+	if (ml->lockfile_fd >= 0) {
+		DBG(LOCKS, ul_debugobj(ml, "%s: unflocking",
+					mnt_lock_get_lockfile(ml)));
+		close(ml->lockfile_fd);
+	}
+}
+
+static int lock_simplelock(struct libmnt_lock *ml)
+{
+	const char *lfile;
+	int rc;
+	struct stat sb;
+	const mode_t lock_mask = S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH;
+
+	assert(ml);
+	assert(ml->simplelock);
+
+	lfile = mnt_lock_get_lockfile(ml);
+
+	DBG(LOCKS, ul_debugobj(ml, "%s: locking", lfile));
+
+	if (ml->sigblock) {
+		sigset_t sigs;
+		sigemptyset(&ml->oldsigmask);
+		sigfillset(&sigs);
+		sigprocmask(SIG_BLOCK, &sigs, &ml->oldsigmask);
+	}
+
+	ml->lockfile_fd = open(lfile, O_RDONLY|O_CREAT|O_CLOEXEC,
+				      S_IWUSR|S_IRUSR|S_IRGRP|S_IROTH);
+	if (ml->lockfile_fd < 0) {
+		rc = -errno;
+		goto err;
+	}
+
+	rc = fstat(ml->lockfile_fd, &sb);
+	if (rc < 0) {
+		rc = -errno;
+		goto err;
+	}
+
+	if ((sb.st_mode & lock_mask) != lock_mask) {
+		rc = fchmod(ml->lockfile_fd, lock_mask);
+		if (rc < 0) {
+			rc = -errno;
+			goto err;
+		}
+	}
+
+	while (flock(ml->lockfile_fd, LOCK_EX) < 0) {
+		int errsv;
+		if ((errno == EAGAIN) || (errno == EINTR))
+			continue;
+		errsv = errno;
+		close(ml->lockfile_fd);
+		ml->lockfile_fd = -1;
+		rc = -errsv;
+		goto err;
+	}
+	ml->locked = 1;
+	return 0;
+err:
+	if (ml->sigblock)
+		sigprocmask(SIG_SETMASK, &ml->oldsigmask, NULL);
+	return rc;
+}
+
+/*
+ * traditional mtab locking
+ */
+
+static void mnt_lockalrm_handler(int sig __attribute__((__unused__)))
+{
+	/* do nothing, say nothing, be nothing */
+}
+
+/*
+ * Waits for F_SETLKW, unfortunately we have to use SIGALRM here to interrupt
+ * fcntl() to avoid neverending waiting.
+ *
+ * Returns: 0 on success, 1 on timeout, -errno on error.
+ */
+static int mnt_wait_mtab_lock(struct libmnt_lock *ml, struct flock *fl, time_t maxtime)
+{
+	struct timeval now;
+	struct sigaction sa, osa;
+	int ret = 0;
+
+	gettime_monotonic(&now);
+	DBG(LOCKS, ul_debugobj(ml, "(%d) waiting for F_SETLKW (now=%lu, maxtime=%lu, diff=%lu)",
+				getpid(),
+				(unsigned long) now.tv_sec,
+				(unsigned long) maxtime,
+				(unsigned long) (maxtime - now.tv_sec)));
+
+	if (now.tv_sec >= maxtime)
+		return 1;		/* timeout */
+
+	/* setup ALARM handler -- we don't want to wait forever */
+	sa.sa_flags = 0;
+	sa.sa_handler = mnt_lockalrm_handler;
+	sigfillset (&sa.sa_mask);
+
+	sigaction(SIGALRM, &sa, &osa);
+
+
+	alarm(maxtime - now.tv_sec);
+	if (fcntl(ml->lockfile_fd, F_SETLKW, fl) == -1)
+		ret = errno == EINTR ? 1 : -errno;
+	alarm(0);
+
+	/* restore old sigaction */
+	sigaction(SIGALRM, &osa, NULL);
+
+	DBG(LOCKS, ul_debugobj(ml, "(%d) leaving mnt_wait_setlkw(), rc=%d",
+				getpid(), ret));
+	return ret;
+}
+
+/*
+ * Create the mtab lock file.
+ *
+ * The old code here used flock on a lock file /etc/mtab~ and deleted
+ * this lock file afterwards. However, as rgooch remarks, that has a
+ * race: a second mount may be waiting on the lock and proceed as
+ * soon as the lock file is deleted by the first mount, and immediately
+ * afterwards a third mount comes, creates a new /etc/mtab~, applies
+ * flock to that, and also proceeds, so that the second and third mount
+ * are now both scribbling in /etc/mtab.
+ *
+ * The new code uses a link() instead of a creat(), where we proceed
+ * only if it was us that created the lock, and hence we always have
+ * to delete the lock afterwards. Now the use of flock() is in principle
+ * superfluous, but avoids an arbitrary sleep().
+ *
+ * Where does the link point to? Obvious choices are mtab and mtab~~.
+ * HJLu points out that the latter leads to races. Right now we use
+ * mtab~.pid instead.
+ *
+ *
+ * The original mount locking code has used sleep(1) between attempts and
+ * maximal number of attempts has been 5.
+ *
+ * There was a very small number of attempts and extremely long waiting (1s)
+ * that is useless on machines with large number of mount processes.
+ *
+ * Now we wait for a few thousand microseconds between attempts and we have a global
+ * time limit (30s) rather than a limit for the number of attempts. The advantage
+ * is that this method also counts time which we spend in fcntl(F_SETLKW) and
+ * the number of attempts is not restricted.
+ * -- kzak@redhat.com [Mar-2007]
+ *
+ *
+ * This mtab locking code has been refactored and moved to libmount. The mtab
+ * locking is really not perfect (e.g. SIGALRM), but it's stable, reliable and
+ * backwardly compatible code.
+ *
+ * Don't forget that this code has to be compatible with 3rd party mounts
+ * (/sbin/mount.foo) and has to work with NFS.
+ * -- kzak@redhat.com [May-2009]
+ */
+
+/* maximum seconds between the first and the last attempt */
+#define MOUNTLOCK_MAXTIME		30
+
+/* sleep time (in microseconds, max=999999) between attempts */
+#define MOUNTLOCK_WAITTIME		5000
+
+static void unlock_mtab(struct libmnt_lock *ml)
+{
+	if (!ml)
+		return;
+
+	if (!ml->locked && ml->lockfile && ml->linkfile)
+	{
+		/* We (probably) have all the files, but we don't own the lock,
+		 * Really? Check it! Maybe ml->locked wasn't set properly
+		 * because the code was interrupted by a signal. Paranoia? Yes.
+		 *
+		 * We own the lock when linkfile == lockfile.
+		 */
+		struct stat lo, li;
+
+		if (!stat(ml->lockfile, &lo) && !stat(ml->linkfile, &li) &&
+		    lo.st_dev == li.st_dev && lo.st_ino == li.st_ino)
+			ml->locked = 1;
+	}
+
+	if (ml->linkfile)
+		unlink(ml->linkfile);
+	if (ml->lockfile_fd >= 0)
+		close(ml->lockfile_fd);
+	if (ml->locked && ml->lockfile) {
+		unlink(ml->lockfile);
+		DBG(LOCKS, ul_debugobj(ml, "unlink %s", ml->lockfile));
+	}
+}
+
+static int lock_mtab(struct libmnt_lock *ml)
+{
+	int i, rc = -1;
+	struct timespec waittime;
+	struct timeval maxtime;
+	const char *lockfile, *linkfile;
+
+	if (!ml)
+		return -EINVAL;
+	if (ml->locked)
+		return 0;
+
+	lockfile = mnt_lock_get_lockfile(ml);
+	if (!lockfile)
+		return -EINVAL;
+	linkfile = mnt_lock_get_linkfile(ml);
+	if (!linkfile)
+		return -EINVAL;
+
+	if (ml->sigblock) {
+		/*
+		 * Block all signals when locked, mnt_unlock_file() will
+		 * restore the old mask.
+		 */
+		sigset_t sigs;
+
+		sigemptyset(&ml->oldsigmask);
+		sigfillset(&sigs);
+		sigdelset(&sigs, SIGTRAP);
+		sigdelset(&sigs, SIGALRM);
+		sigprocmask(SIG_BLOCK, &sigs, &ml->oldsigmask);
+	}
+
+	i = open(linkfile, O_WRONLY|O_CREAT|O_CLOEXEC, S_IRUSR|S_IWUSR);
+	if (i < 0) {
+		/* linkfile does not exist (as a file) and we cannot create it.
+		 * Read-only or full filesystem? Too many files open in the system?
+		 */
+		if (errno > 0)
+			rc = -errno;
+		goto failed;
+	}
+	close(i);
+
+	gettime_monotonic(&maxtime);
+	maxtime.tv_sec += MOUNTLOCK_MAXTIME;
+
+	waittime.tv_sec = 0;
+	waittime.tv_nsec = (1000 * MOUNTLOCK_WAITTIME);
+
+	/* Repeat until it was us who made the link */
+	while (!ml->locked) {
+		struct timeval now;
+		struct flock flock;
+		int j;
+
+		j = link(linkfile, lockfile);
+		if (j == 0)
+			ml->locked = 1;
+
+		if (j < 0 && errno != EEXIST) {
+			if (errno > 0)
+				rc = -errno;
+			goto failed;
+		}
+		ml->lockfile_fd = open(lockfile, O_WRONLY|O_CLOEXEC);
+
+		if (ml->lockfile_fd < 0) {
+			/* Strange... Maybe the file was just deleted? */
+			int errsv = errno;
+			gettime_monotonic(&now);
+			if (errsv == ENOENT && now.tv_sec < maxtime.tv_sec) {
+				ml->locked = 0;
+				continue;
+			}
+			if (errsv > 0)
+				rc = -errsv;
+			goto failed;
+		}
+
+		flock.l_type = F_WRLCK;
+		flock.l_whence = SEEK_SET;
+		flock.l_start = 0;
+		flock.l_len = 0;
+
+		if (ml->locked) {
+			/* We made the link. Now claim the lock. */
+			if (fcntl (ml->lockfile_fd, F_SETLK, &flock) == -1) {
+				DBG(LOCKS, ul_debugobj(ml,
+					"%s: can't F_SETLK lockfile, errno=%d\n",
+					lockfile, errno));
+				/* proceed, since it was us who created the lockfile anyway */
+			}
+			break;
+		}
+
+		/* Someone else made the link. Wait. */
+		int err = mnt_wait_mtab_lock(ml, &flock, maxtime.tv_sec);
+
+		if (err == 1) {
+			DBG(LOCKS, ul_debugobj(ml,
+				"%s: can't create link: time out (perhaps "
+				"there is a stale lock file?)", lockfile));
+			rc = -ETIMEDOUT;
+			goto failed;
+
+		} else if (err < 0) {
+			rc = err;
+			goto failed;
+		}
+		nanosleep(&waittime, NULL);
+		close(ml->lockfile_fd);
+		ml->lockfile_fd = -1;
+	}
+	DBG(LOCKS, ul_debugobj(ml, "%s: (%d) successfully locked",
+					lockfile, getpid()));
+	unlink(linkfile);
+	return 0;
+
+failed:
+	mnt_unlock_file(ml);
+	return rc;
+}
+
+
+/**
+ * mnt_lock_file
+ * @ml: pointer to struct libmnt_lock instance
+ *
+ * Creates a lock file (e.g. /etc/mtab~). Note that this function may
+ * use alarm().
+ *
+ * Your application always has to call mnt_unlock_file() before exit.
+ *
+ * Traditional mtab locking scheme:
+ *
+ *   1. create linkfile (e.g. /etc/mtab~.$PID)
+ *   2. link linkfile --> lockfile (e.g. /etc/mtab~.$PID --> /etc/mtab~)
+ *   3. a) link() success: setups F_SETLK lock (see fcntl(2))
+ *      b) link() failed:  wait (max 30s) on F_SETLKW lock, goto 2.
+ *
+ * Note that when the lock is used by mnt_update_table() interface then libmount
+ * uses flock() for private library file /run/mount/utab. The fcntl(2) is used only
+ * for backwardly compatible stuff like /etc/mtab.
+ *
+ * Returns: 0 on success or negative number in case of error (-ETIMEOUT is case
+ * of stale lock file).
+ */
+int mnt_lock_file(struct libmnt_lock *ml)
+{
+	if (!ml)
+		return -EINVAL;
+
+	if (ml->simplelock)
+		return lock_simplelock(ml);
+
+	return lock_mtab(ml);
+}
+
+/**
+ * mnt_unlock_file:
+ * @ml: lock struct
+ *
+ * Unlocks the file. The function could be called independently of the
+ * lock status (for example from exit(3)).
+ */
+void mnt_unlock_file(struct libmnt_lock *ml)
+{
+	if (!ml)
+		return;
+
+	DBG(LOCKS, ul_debugobj(ml, "(%d) %s", getpid(),
+			ml->locked ? "unlocking" : "cleaning"));
+
+	if (ml->simplelock)
+		unlock_simplelock(ml);
+	else
+		unlock_mtab(ml);
+
+	ml->locked = 0;
+	ml->lockfile_fd = -1;
+
+	if (ml->sigblock) {
+		DBG(LOCKS, ul_debugobj(ml, "restoring sigmask"));
+		sigprocmask(SIG_SETMASK, &ml->oldsigmask, NULL);
+	}
+}
+
+#ifdef TEST_PROGRAM
+
+static struct libmnt_lock *lock;
+
+/*
+ * read number from @filename, increment the number and
+ * write the number back to the file
+ */
+static void increment_data(const char *filename, int verbose, int loopno)
+{
+	long num;
+	FILE *f;
+	char buf[256];
+
+	if (!(f = fopen(filename, "r" UL_CLOEXECSTR)))
+		err(EXIT_FAILURE, "%d: failed to open: %s", getpid(), filename);
+
+	if (!fgets(buf, sizeof(buf), f))
+		err(EXIT_FAILURE, "%d failed read: %s", getpid(), filename);
+
+	fclose(f);
+	num = atol(buf) + 1;
+
+	if (!(f = fopen(filename, "w" UL_CLOEXECSTR)))
+		err(EXIT_FAILURE, "%d: failed to open: %s", getpid(), filename);
+
+	fprintf(f, "%ld", num);
+
+	if (close_stream(f) != 0)
+		err(EXIT_FAILURE, "write failed: %s", filename);
+
+	if (verbose)
+		fprintf(stderr, "%d: %s: %ld --> %ld (loop=%d)\n", getpid(),
+				filename, num - 1, num, loopno);
+}
+
+static void clean_lock(void)
+{
+	if (!lock)
+		return;
+	mnt_unlock_file(lock);
+	mnt_free_lock(lock);
+}
+
+static void __attribute__((__noreturn__)) sig_handler(int sig)
+{
+	errx(EXIT_FAILURE, "\n%d: catch signal: %s\n", getpid(), strsignal(sig));
+}
+
+static int test_lock(struct libmnt_test *ts, int argc, char *argv[])
+{
+	time_t synctime = 0;
+	unsigned int usecs;
+	const char *datafile = NULL;
+	int verbose = 0, loops = 0, l, idx = 1;
+
+	if (argc < 3)
+		return -EINVAL;
+
+	if (strcmp(argv[idx], "--synctime") == 0) {
+		synctime = (time_t) atol(argv[idx + 1]);
+		idx += 2;
+	}
+	if (idx < argc && strcmp(argv[idx], "--verbose") == 0) {
+		verbose = 1;
+		idx++;
+	}
+
+	if (idx < argc)
+		datafile = argv[idx++];
+	if (idx < argc)
+		loops = atoi(argv[idx++]);
+
+	if (!datafile || !loops)
+		return -EINVAL;
+
+	if (verbose)
+		fprintf(stderr, "%d: start: synctime=%u, datafile=%s, loops=%d\n",
+			 getpid(), (int) synctime, datafile, loops);
+
+	atexit(clean_lock);
+
+	/* be paranoid and call exit() (=clean_lock()) for all signals */
+	{
+		int sig = 0;
+		struct sigaction sa;
+
+		sa.sa_handler = sig_handler;
+		sa.sa_flags = 0;
+		sigfillset(&sa.sa_mask);
+
+		while (sigismember(&sa.sa_mask, ++sig) != -1 && sig != SIGCHLD)
+			sigaction (sig, &sa, (struct sigaction *) 0);
+	}
+
+	/* start the test in exactly defined time */
+	if (synctime) {
+		struct timeval tv;
+
+		gettimeofday(&tv, NULL);
+		if (synctime && synctime - tv.tv_sec > 1) {
+			usecs = ((synctime - tv.tv_sec) * 1000000UL) -
+						(1000000UL - tv.tv_usec);
+			xusleep(usecs);
+		}
+	}
+
+	for (l = 0; l < loops; l++) {
+		lock = mnt_new_lock(datafile, 0);
+		if (!lock)
+			return -1;
+
+		if (mnt_lock_file(lock) != 0) {
+			fprintf(stderr, "%d: failed to lock %s file\n",
+					getpid(), datafile);
+			return -1;
+		}
+
+		increment_data(datafile, verbose, l);
+
+		mnt_unlock_file(lock);
+		mnt_free_lock(lock);
+		lock = NULL;
+
+		/* The mount command usually finishes after a mtab update. We
+		 * simulate this via short sleep -- it's also enough to make
+		 * concurrent processes happy.
+		 */
+		if (synctime)
+			xusleep(25000);
+	}
+
+	return 0;
+}
+
+/*
+ * Note that this test should be executed from a script that creates many
+ * parallel processes, otherwise this test does not make sense.
+ */
+int main(int argc, char *argv[])
+{
+	struct libmnt_test tss[] = {
+	{ "--lock", test_lock,  " [--synctime <time_t>] [--verbose] <datafile> <loops> "
+				"increment a number in datafile" },
+	{ NULL }
+	};
+
+	return mnt_run_test(tss, argc, argv);
+}
+
+#endif /* TEST_PROGRAM */