Add implementation of device/file locking for metadata.

To be used later.

lib/utils_device_locking.c

@@ -0,0 +1,338 @@
+/*
+ * Metadata on-disk locking for processes serialization
+ *
+ * Copyright (C) 2016-2017, Red Hat, Inc. All rights reserved.
+ * Copyright (C) 2016-2017, Ondrej Kozina. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <linux/limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/file.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+#ifdef HAVE_SYS_SYSMACROS_H
+# include <sys/sysmacros.h>     /* for major, minor */
+#endif
+#include <libgen.h>
+
+#include "internal.h"
+#include "utils_device_locking.h"
+
+#define same_inode(buf1, buf2) \
+	((buf1).st_ino == (buf2).st_ino && \
+	 (buf1).st_dev == (buf2).st_dev)
+
+#ifndef __GNUC__
+# define __typeof__ typeof
+#endif
+
+enum lock_type {
+	DEV_LOCK_READ = 0,
+	DEV_LOCK_WRITE
+};
+
+struct crypt_lock_handle {
+	dev_t devno;
+	int flock_fd;
+	enum lock_type type;
+	__typeof__( ((struct stat*)0)->st_mode) mode;
+};
+
+static int resource_by_devno(char *res, size_t res_size, dev_t devno, unsigned fullpath)
+{
+	int r;
+
+	if (fullpath)
+		r = snprintf(res, res_size, "%s/L_%d:%d", DEFAULT_LUKS2_LOCK_PATH, major(devno), minor(devno));
+	else
+		r = snprintf(res, res_size, "L_%d:%d", major(devno), minor(devno));
+
+	return (r < 0 || (size_t)r >= res_size) ? -EINVAL : 0;
+}
+
+static int open_lock_dir(struct crypt_device *cd, const char *dir, const char *base)
+{
+	int dirfd, lockdfd;
+
+	dirfd = open(dir, O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
+	if (dirfd < 0) {
+		log_dbg("Failed to open directory '%s': (%d: %s).", dir, errno, strerror(errno));
+		return -EINVAL;
+	}
+
+	lockdfd = openat(dirfd, base, O_RDONLY | O_NOFOLLOW | O_DIRECTORY | O_CLOEXEC);
+	if (lockdfd < 0) {
+		if (errno == ENOENT) {
+			log_std(cd, _("WARNING: Locking directory %s/%s is missing!\n"), dir, base);
+
+			/* success or failure w/ errno == EEXIST either way just try to open the 'base' directory again */
+			if (mkdirat(dirfd, base, DEFAULT_LUKS2_LOCK_DIR_PERMS) && errno != EEXIST)
+				log_dbg("Failed to create directory %s in %s (%d: %s).", base, dir, errno, strerror(errno));
+			else
+				lockdfd = openat(dirfd, base, O_RDONLY | O_NOFOLLOW | O_DIRECTORY | O_CLOEXEC);
+		} else
+			log_dbg("Failed to open directory %s/%s: (%d: %s)", dir, base, errno, strerror(errno));
+	}
+
+	close(dirfd);
+	return lockdfd >= 0 ? lockdfd : -EINVAL;
+}
+
+static int open_resource(struct crypt_device *cd, const char *res)
+{
+	int err, lockdir_fd, r;
+	char dir[] = DEFAULT_LUKS2_LOCK_PATH,
+	     base[] = DEFAULT_LUKS2_LOCK_PATH;
+
+	lockdir_fd = open_lock_dir(cd, dirname(dir), basename(base));
+	if (lockdir_fd < 0)
+		return -EINVAL;
+
+	log_dbg("Opening lock resource file %s/%s", DEFAULT_LUKS2_LOCK_PATH, res);
+	r = openat(lockdir_fd, res, O_CREAT | O_NOFOLLOW | O_RDWR | O_CLOEXEC, 0777);
+	err = errno;
+
+	close(lockdir_fd);
+
+	return r < 0 ? -err : r;
+}
+
+static int acquire_lock_handle(struct crypt_device *cd, const char *device_path, struct crypt_lock_handle *h)
+{
+	char res[PATH_MAX];
+	int dev_fd, fd;
+	struct stat st;
+
+	dev_fd = open(device_path, O_RDONLY | O_NONBLOCK | O_CLOEXEC);
+	if (dev_fd < 0)
+		return -EINVAL;
+
+	if (fstat(dev_fd, &st)) {
+		close(dev_fd);
+		return -EINVAL;
+	}
+
+	if (S_ISBLK(st.st_mode)) {
+		if (resource_by_devno(res, sizeof(res), st.st_rdev, 0)) {
+			close(dev_fd);
+			return -EINVAL;
+		}
+
+		fd = open_resource(cd, res);
+		close(dev_fd);
+		if (fd < 0)
+			return fd;
+
+		h->flock_fd = fd;
+		h->devno = st.st_rdev;
+	} else if (S_ISREG(st.st_mode)) {
+		// FIXME: workaround for nfsv4
+		fd = open(device_path, O_RDWR | O_NONBLOCK | O_CLOEXEC);
+		if (fd < 0)
+			h->flock_fd = dev_fd;
+		else {
+			h->flock_fd = fd;
+			close(dev_fd);
+		}
+	} else {
+		/* Wrong device type */
+		close(dev_fd);
+		return -EINVAL;
+	}
+
+	h->mode = st.st_mode;
+
+	return 0;
+}
+
+static void release_lock_handle(struct crypt_lock_handle *h)
+{
+	char res[PATH_MAX];
+	struct stat buf_a, buf_b;
+
+	if (S_ISBLK(h->mode) && /* was it block device */
+	    !flock(h->flock_fd, LOCK_EX | LOCK_NB) && /* lock to drop the file */
+	    !resource_by_devno(res, sizeof(res), h->devno, 1) && /* acquire lock resource name */
+	    !fstat(h->flock_fd, &buf_a) && /* read inode id refered by fd */
+	    !stat(res, &buf_b) && /* does path file stil exist? */
+	    same_inode(buf_a, buf_b)) /* is it same id as the one referenced by fd? */
+		if (unlink(res)) /* yes? unlink the file */
+			log_dbg("Failed to unlink resource file: %s", res);
+
+	if (close(h->flock_fd))
+		log_dbg("Failed to close resource fd (%d).", h->flock_fd);
+}
+
+int device_locked(struct crypt_lock_handle *h)
+{
+	return (h && (h->type == DEV_LOCK_READ || h->type == DEV_LOCK_WRITE));
+}
+
+int device_locked_readonly(struct crypt_lock_handle *h)
+{
+	return (h && h->type == DEV_LOCK_READ);
+}
+
+static int verify_lock_handle(const char *device_path, struct crypt_lock_handle *h)
+{
+	char res[PATH_MAX];
+	struct stat lck_st, res_st;
+
+	/* we locked a regular file, check during device_open() instead. No reason to check now */
+	if (S_ISREG(h->mode))
+		return 0;
+
+	if (resource_by_devno(res, sizeof(res), h->devno, 1))
+		return -EINVAL;
+
+	if (fstat(h->flock_fd, &lck_st))
+		return -EINVAL;
+
+	return (stat(res, &res_st) || !same_inode(lck_st, res_st)) ? -EAGAIN : 0;
+}
+
+struct crypt_lock_handle *device_read_lock_handle(struct crypt_device *cd, const char *device_path)
+{
+	int r;
+	struct crypt_lock_handle *h = malloc(sizeof(*h));
+
+	if (!h)
+		return NULL;
+
+	do {
+		r = acquire_lock_handle(cd, device_path, h);
+		if (r)
+			break;
+
+		log_dbg("Acquiring read lock for device %s.", device_path);
+
+		if (flock(h->flock_fd, LOCK_SH)) {
+			log_dbg("Shared flock failed with errno %d.", errno);
+			r = -EINVAL;
+			release_lock_handle(h);
+			break;
+		}
+
+		log_dbg("Verifying read lock handle for device %s.", device_path);
+
+		/*
+		 * check whether another libcryptsetup process removed resource file before this
+		 * one managed to flock() it. See release_lock_handle() for details
+		 */
+		r = verify_lock_handle(device_path, h);
+		if (r) {
+			flock(h->flock_fd, LOCK_UN);
+			release_lock_handle(h);
+			log_dbg("Read lock handle verification failed.");
+		}
+	} while (r == -EAGAIN);
+
+	if (r) {
+		free(h);
+		return NULL;
+	}
+
+	h->type = DEV_LOCK_READ;
+
+	return h;
+}
+
+struct crypt_lock_handle *device_write_lock_handle(struct crypt_device *cd, const char *device_path)
+{
+	int r;
+	struct crypt_lock_handle *h = malloc(sizeof(*h));
+
+	if (!h)
+		return NULL;
+
+	do {
+		r = acquire_lock_handle(cd, device_path, h);
+		if (r)
+			break;
+
+		log_dbg("Acquiring write lock for device %s.", device_path);
+
+		if (flock(h->flock_fd, LOCK_EX)) {
+			log_dbg("Exclusive flock failed with errno %d.", errno);
+			r = -EINVAL;
+			release_lock_handle(h);
+			break;
+		}
+
+		log_dbg("Verifying write lock handle for device %s.", device_path);
+
+		/*
+		 * check whether another libcryptsetup process removed resource file before this
+		 * one managed to flock() it. See release_lock_handle() for details
+		 */
+		r = verify_lock_handle(device_path, h);
+		if (r) {
+			flock(h->flock_fd, LOCK_UN);
+			release_lock_handle(h);
+			log_dbg("Write lock handle verification failed.");
+		}
+	} while (r == -EAGAIN);
+
+	if (r) {
+		free(h);
+		return NULL;
+	}
+
+	h->type = DEV_LOCK_WRITE;
+
+	return h;
+}
+
+void device_unlock_handle(struct crypt_lock_handle *h)
+{
+	if (flock(h->flock_fd, LOCK_UN))
+		log_dbg("flock on fd %d failed.", h->flock_fd);
+
+	release_lock_handle(h);
+
+	free(h);
+}
+
+int device_locked_verify(int dev_fd, struct crypt_lock_handle *h)
+{
+	char res[PATH_MAX];
+	struct stat dev_st, lck_st, st;
+
+	if (fstat(dev_fd, &dev_st) || fstat(h->flock_fd, &lck_st))
+		return 1;
+
+	/* if device handle is regular file the handle must match the lock handle */
+	if (S_ISREG(dev_st.st_mode)) {
+		log_dbg("Veryfing locked device handle (regular file)");
+		if (!same_inode(dev_st, lck_st))
+			return 1;
+	} else if (S_ISBLK(dev_st.st_mode)) {
+		log_dbg("Veryfing locked device handle (bdev)");
+		if (resource_by_devno(res, sizeof(res), dev_st.st_rdev, 1) ||
+		    stat(res, &st) ||
+		    !same_inode(lck_st, st))
+			return 1;
+	} else
+		return 1;
+
+	return 0;
+}