btrfs: fix potential oops in device_list_add

alloc_fs_devices() can return ERR_PTR(-ENOMEM), so dereferencing its
result before the check for IS_ERR() is a bad idea.

Fixes: d1a63002829a4 ("btrfs: add members to fs_devices to track fsid changes")
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 3e4f8f8..1556192 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -957,11 +957,11 @@ static noinline struct btrfs_device *device_list_add(const char *path,
                else
                        fs_devices = alloc_fs_devices(disk_super->fsid, NULL);
 
-               fs_devices->fsid_change = fsid_change_in_progress;
-
                if (IS_ERR(fs_devices))
                        return ERR_CAST(fs_devices);
 
+               fs_devices->fsid_change = fsid_change_in_progress;
+
                mutex_lock(&fs_devices->device_list_mutex);
                list_add(&fs_devices->fs_list, &fs_uuids);