1 files changed, 521 insertions, 0 deletions
diff --git a/lib/utils_device_locking.c b/lib/utils_device_locking.c
new file mode 100644
index 0000000..36e6496
--- /dev/null
+++ b/lib/utils_device_locking.c
@@ -0,0 +1,521 @@
+/*
+ * Metadata on-disk locking for processes serialization
+ *
+ * Copyright (C) 2016-2021 Red Hat, Inc. All rights reserved.
+ * Copyright (C) 2016-2021 Ondrej Kozina
+ *
+ * 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 <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 <assert.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)
+
+enum lock_type {
+	DEV_LOCK_READ = 0,
+	DEV_LOCK_WRITE
+};
+
+enum lock_mode {
+	DEV_LOCK_FILE = 0,
+	DEV_LOCK_BDEV,
+	DEV_LOCK_NAME
+};
+
+struct crypt_lock_handle {
+	unsigned refcnt;
+	int flock_fd;
+	enum lock_type type;
+	enum lock_mode mode;
+	union {
+	struct {
+		dev_t devno;
+	} bdev;
+	struct {
+		char *name;
+	} name;
+	} u;
+};
+
+static int resource_by_name(char *res, size_t res_size, const char *name, bool fullpath)
+{
+	int r;
+
+	if (fullpath)
+		r = snprintf(res, res_size, "%s/LN_%s", DEFAULT_LUKS2_LOCK_PATH, name);
+	else
+		r = snprintf(res, res_size, "LN_%s", name);
+
+	return (r < 0 || (size_t)r >= res_size) ? -EINVAL : 0;
+}
+
+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_CLOEXEC);
+	if (dirfd < 0) {
+		log_dbg(cd, "Failed to open directory %s: (%d: %s).", dir, errno, strerror(errno));
+		if (errno == ENOTDIR || errno == ENOENT)
+			log_err(cd, _("Locking aborted. The locking path %s/%s is unusable (not a directory or missing)."), dir, base);
+		return -EINVAL;
+	}
+
+	lockdfd = openat(dirfd, base, O_RDONLY | O_NOFOLLOW | O_DIRECTORY | O_CLOEXEC);
+	if (lockdfd < 0) {
+		if (errno == ENOENT) {
+			log_dbg(cd, _("Locking directory %s/%s will be created with default compiled-in permissions."), 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(cd, "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(cd, "Failed to open directory %s/%s: (%d: %s)", dir, base, errno, strerror(errno));
+			if (errno == ENOTDIR || errno == ELOOP)
+				log_err(cd, _("Locking aborted. The locking path %s/%s is unusable (%s is not a directory)."), dir, base, base);
+		}
+	}
+
+	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(cd, "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, struct device *device, struct crypt_lock_handle *h)
+{
+	char res[PATH_MAX];
+	int dev_fd, fd;
+	struct stat st;
+
+	dev_fd = open(device_path(device), 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->u.bdev.devno = st.st_rdev;
+		h->mode = DEV_LOCK_BDEV;
+	} else if (S_ISREG(st.st_mode)) {
+		// FIXME: workaround for nfsv4
+		fd = open(device_path(device), O_RDWR | O_NONBLOCK | O_CLOEXEC);
+		if (fd < 0)
+			h->flock_fd = dev_fd;
+		else {
+			h->flock_fd = fd;
+			close(dev_fd);
+		}
+		h->mode = DEV_LOCK_FILE;
+	} else {
+		/* Wrong device type */
+		close(dev_fd);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int acquire_lock_handle_by_name(struct crypt_device *cd, const char *name, struct crypt_lock_handle *h)
+{
+	char res[PATH_MAX];
+	int fd;
+
+	h->u.name.name = strdup(name);
+	if (!h->u.name.name)
+		return -ENOMEM;
+
+	if (resource_by_name(res, sizeof(res), name, false)) {
+		free(h->u.name.name);
+		return -EINVAL;
+	}
+
+	fd = open_resource(cd, res);
+	if (fd < 0) {
+		free(h->u.name.name);
+		return fd;
+	}
+
+	h->flock_fd = fd;
+	h->mode = DEV_LOCK_NAME;
+
+	return 0;
+}
+
+static void release_lock_handle(struct crypt_device *cd, struct crypt_lock_handle *h)
+{
+	char res[PATH_MAX];
+	struct stat buf_a, buf_b;
+
+	if ((h->mode == DEV_LOCK_NAME) && /* was it name lock */
+	    !flock(h->flock_fd, LOCK_EX | LOCK_NB) && /* lock to drop the file */
+	    !resource_by_name(res, sizeof(res), h->u.name.name, true) && /* acquire lock resource name */
+	    !fstat(h->flock_fd, &buf_a) && /* read inode id referred by fd */
+	    !stat(res, &buf_b) && /* does path file still exist? */
+	    same_inode(buf_a, buf_b)) { /* is it same id as the one referenced by fd? */
+		/* coverity[toctou] */
+		if (unlink(res)) /* yes? unlink the file */
+			log_dbg(cd, "Failed to unlink resource file: %s", res);
+	}
+
+	if ((h->mode == DEV_LOCK_BDEV) && /* was it block device */
+	    !flock(h->flock_fd, LOCK_EX | LOCK_NB) && /* lock to drop the file */
+	    !resource_by_devno(res, sizeof(res), h->u.bdev.devno, 1) && /* acquire lock resource name */
+	    !fstat(h->flock_fd, &buf_a) && /* read inode id referred by fd */
+	    !stat(res, &buf_b) && /* does path file still exist? */
+	    same_inode(buf_a, buf_b)) { /* is it same id as the one referenced by fd? */
+		/* coverity[toctou] */
+		if (unlink(res)) /* yes? unlink the file */
+			log_dbg(cd, "Failed to unlink resource file: %s", res);
+	}
+
+	if (h->mode == DEV_LOCK_NAME)
+		free(h->u.name.name);
+
+	if (close(h->flock_fd))
+		log_dbg(cd, "Failed to close lock 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 (h->mode == DEV_LOCK_FILE)
+		return 0;
+
+	if (h->mode == DEV_LOCK_NAME) {
+		if (resource_by_name(res, sizeof(res), h->u.name.name, true))
+			return -EINVAL;
+	} else if (h->mode == DEV_LOCK_BDEV) {
+		if (resource_by_devno(res, sizeof(res), h->u.bdev.devno, true))
+			return -EINVAL;
+	} else
+		return -EINVAL;
+
+	if (fstat(h->flock_fd, &lck_st))
+		return -EINVAL;
+
+	return (stat(res, &res_st) || !same_inode(lck_st, res_st)) ? -EAGAIN : 0;
+}
+
+static unsigned device_lock_inc(struct crypt_lock_handle *h)
+{
+	return ++h->refcnt;
+}
+
+static unsigned device_lock_dec(struct crypt_lock_handle *h)
+{
+	assert(h->refcnt);
+
+	return --h->refcnt;
+}
+
+static int acquire_and_verify(struct crypt_device *cd, struct device *device, const char *resource, int flock_op, struct crypt_lock_handle **lock)
+{
+	int r;
+	struct crypt_lock_handle *h;
+
+	if (device && resource)
+		return -EINVAL;
+
+	if (!(h = malloc(sizeof(*h))))
+		return -ENOMEM;
+
+	do {
+		r = device ? acquire_lock_handle(cd, device, h) : acquire_lock_handle_by_name(cd, resource, h);
+		if (r < 0)
+			break;
+
+		if (flock(h->flock_fd, flock_op)) {
+			log_dbg(cd, "Flock on fd %d failed with errno %d.", h->flock_fd, errno);
+			r = (errno == EWOULDBLOCK) ? -EBUSY : -EINVAL;
+			release_lock_handle(cd, h);
+			break;
+		}
+
+		log_dbg(cd, "Verifying lock handle for %s.", device ? device_path(device) : resource);
+
+		/*
+		 * 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(device), h);
+		if (r < 0) {
+			if (flock(h->flock_fd, LOCK_UN))
+				log_dbg(cd, "flock on fd %d failed.", h->flock_fd);
+			release_lock_handle(cd, h);
+			log_dbg(cd, "Lock handle verification failed.");
+		}
+	} while (r == -EAGAIN);
+
+	if (r < 0) {
+		free(h);
+		return r;
+	}
+
+	*lock = h;
+
+	return 0;
+}
+
+int device_read_lock_internal(struct crypt_device *cd, struct device *device)
+{
+	int r;
+	struct crypt_lock_handle *h;
+
+	if (!device)
+		return -EINVAL;
+
+	h = device_get_lock_handle(device);
+
+	if (device_locked(h)) {
+		device_lock_inc(h);
+		log_dbg(cd, "Device %s READ lock (or higher) already held.", device_path(device));
+		return 0;
+	}
+
+	log_dbg(cd, "Acquiring read lock for device %s.", device_path(device));
+
+	r = acquire_and_verify(cd, device, NULL, LOCK_SH, &h);
+	if (r < 0)
+		return r;
+
+	h->type = DEV_LOCK_READ;
+	h->refcnt = 1;
+	device_set_lock_handle(device, h);
+
+	log_dbg(cd, "Device %s READ lock taken.", device_path(device));
+
+	return 0;
+}
+
+int device_write_lock_internal(struct crypt_device *cd, struct device *device)
+{
+	int r;
+	struct crypt_lock_handle *h;
+
+	if (!device)
+		return -EINVAL;
+
+	h = device_get_lock_handle(device);
+
+	if (device_locked(h)) {
+		log_dbg(cd, "Device %s WRITE lock already held.", device_path(device));
+		return device_lock_inc(h);
+	}
+
+	log_dbg(cd, "Acquiring write lock for device %s.", device_path(device));
+
+	r = acquire_and_verify(cd, device, NULL, LOCK_EX, &h);
+	if (r < 0)
+		return r;
+
+	h->type = DEV_LOCK_WRITE;
+	h->refcnt = 1;
+	device_set_lock_handle(device, h);
+
+	log_dbg(cd, "Device %s WRITE lock taken.", device_path(device));
+
+	return 1;
+}
+
+int crypt_read_lock(struct crypt_device *cd, const char *resource, bool blocking, struct crypt_lock_handle **lock)
+{
+	int r;
+	struct crypt_lock_handle *h;
+
+	if (!resource)
+		return -EINVAL;
+
+	log_dbg(cd, "Acquiring %sblocking read lock for resource %s.", blocking ? "" : "non", resource);
+
+	r = acquire_and_verify(cd, NULL, resource, LOCK_SH | (blocking ? 0 : LOCK_NB), &h);
+	if (r < 0)
+		return r;
+
+	h->type = DEV_LOCK_READ;
+	h->refcnt = 1;
+
+	log_dbg(cd, "READ lock for resource %s taken.", resource);
+
+	*lock = h;
+
+	return 0;
+}
+
+int crypt_write_lock(struct crypt_device *cd, const char *resource, bool blocking, struct crypt_lock_handle **lock)
+{
+	int r;
+	struct crypt_lock_handle *h;
+
+	if (!resource)
+		return -EINVAL;
+
+	log_dbg(cd, "Acquiring %sblocking write lock for resource %s.", blocking ? "" : "non", resource);
+
+	r = acquire_and_verify(cd, NULL, resource, LOCK_EX | (blocking ? 0 : LOCK_NB), &h);
+	if (r < 0)
+		return r;
+
+	h->type = DEV_LOCK_WRITE;
+	h->refcnt = 1;
+
+	log_dbg(cd, "WRITE lock for resource %s taken.", resource);
+
+	*lock = h;
+
+	return 0;
+}
+
+static void unlock_internal(struct crypt_device *cd, struct crypt_lock_handle *h)
+{
+	if (flock(h->flock_fd, LOCK_UN))
+		log_dbg(cd, "flock on fd %d failed.", h->flock_fd);
+	release_lock_handle(cd, h);
+	free(h);
+}
+
+void crypt_unlock_internal(struct crypt_device *cd, struct crypt_lock_handle *h)
+{
+	if (!h)
+		return;
+
+	/* nested locks are illegal */
+	assert(!device_lock_dec(h));
+
+	log_dbg(cd, "Unlocking %s lock for resource %s.",
+		device_locked_readonly(h) ? "READ" : "WRITE", h->u.name.name);
+
+	unlock_internal(cd, h);
+}
+
+void device_unlock_internal(struct crypt_device *cd, struct device *device)
+{
+	bool readonly;
+	struct crypt_lock_handle *h = device_get_lock_handle(device);
+	unsigned u = device_lock_dec(h);
+
+	if (u)
+		return;
+
+	readonly = device_locked_readonly(h);
+
+	unlock_internal(cd, h);
+
+	log_dbg(cd, "Device %s %s lock released.", device_path(device),
+		readonly ? "READ" : "WRITE");
+
+	device_set_lock_handle(device, NULL);
+}
+
+int device_locked_verify(struct crypt_device *cd, 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(cd, "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(cd, "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;
+}