2 files changed, 19 insertions, 4 deletions
diff --git a/src/shared/btrfs-util.c b/src/shared/btrfs-util.c
index 254483c31a..b34ac8b15a 100644
--- a/src/shared/btrfs-util.c
+++ b/src/shared/btrfs-util.c
@@ -228,14 +228,18 @@ int btrfs_subvol_remove(const char *path) {
         return 0;
 }
 
-int btrfs_subvol_set_read_only(const char *path, bool b) {
-        _cleanup_close_ int fd = -1;
+int btrfs_subvol_set_read_only_fd(int fd, bool b) {
         uint64_t flags, nflags;
+        struct stat st;
 
-        fd = open(path, O_RDONLY|O_NOCTTY|O_CLOEXEC);
-        if (fd < 0)
+        assert(fd >= 0);
+
+        if (fstat(fd, &st) < 0)
                 return -errno;
 
+        if (!S_ISDIR(st.st_mode) || st.st_ino != 256)
+                return -EINVAL;
+
         if (ioctl(fd, BTRFS_IOC_SUBVOL_GETFLAGS, &flags) < 0)
                 return -errno;
 
@@ -253,6 +257,16 @@ int btrfs_subvol_set_read_only(const char *path, bool b) {
         return 0;
 }
 
+int btrfs_subvol_set_read_only(const char *path, bool b) {
+        _cleanup_close_ int fd = -1;
+
+        fd = open(path, O_RDONLY|O_NOCTTY|O_CLOEXEC|O_DIRECTORY);
+        if (fd < 0)
+                return -errno;
+
+        return btrfs_subvol_set_read_only_fd(fd, b);
+}
+
 int btrfs_subvol_get_read_only_fd(int fd) {
         uint64_t flags;
 
diff --git a/src/shared/btrfs-util.h b/src/shared/btrfs-util.h
index 28946c60c9..d5249d1bf1 100644
--- a/src/shared/btrfs-util.h
+++ b/src/shared/btrfs-util.h
@@ -48,6 +48,7 @@ int btrfs_subvol_make_label(const char *path);
 int btrfs_subvol_remove(const char *path);
 int btrfs_subvol_snapshot(const char *old_path, const char *new_path, bool read_only, bool fallback_copy);
 
+int btrfs_subvol_set_read_only_fd(int fd, bool b);
 int btrfs_subvol_set_read_only(const char *path, bool b);
 int btrfs_subvol_get_read_only_fd(int fd);
 int btrfs_subvol_get_id_fd(int fd, uint64_t *ret);