btrfs: prop: fix zstd compression parameter validation

commit 50398fde997f6be8faebdb5f38e9c9c467370f51 upstream.

We let pass zstd compression parameter even if it is not fully valid.
For example:

  $ btrfs prop set /btrfs compression zst
  $ btrfs prop get /btrfs compression
     compression=zst

zlib and lzo are fine.

Fix it by checking the correct prefix length.

Fixes: 5c1aab1dd544 ("btrfs: Add zstd support")
CC: stable@vger.kernel.org # 4.14+
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/btrfs/props.c b/fs/btrfs/props.c
index cbabc6f2b3221b44a9b05988106348b6cc14c1f9..3eee2f7e1dd2cbe985ee5f5eeff7c755f4538b58 100644 (file)
--- a/fs/btrfs/props.c
+++ b/fs/btrfs/props.c
@@ -416,7 +416,7 @@ static int prop_compression_apply(struct inode *inode,
                btrfs_set_fs_incompat(fs_info, COMPRESS_LZO);
        } else if (!strncmp("zlib", value, 4)) {
                type = BTRFS_COMPRESS_ZLIB;
-       } else if (!strncmp("zstd", value, len)) {
+       } else if (!strncmp("zstd", value, 4)) {
                type = BTRFS_COMPRESS_ZSTD;
                btrfs_set_fs_incompat(fs_info, COMPRESS_ZSTD);
        } else {