btrfs: add check to sysfs handler of label

Add a sanity check for the fs_info as we will dereference it, similar to
what the 'store features' handler does.

Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index 6a6bb60..3d14618 100644 (file)
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -377,6 +377,9 @@ static ssize_t btrfs_label_store(struct kobject *kobj,
        struct btrfs_fs_info *fs_info = to_fs_info(kobj);
        size_t p_len;
 
+       if (!fs_info)
+               return -EPERM;
+
        if (fs_info->sb->s_flags & MS_RDONLY)
                return -EROFS;