From: Anand Jain <anand.jain@oracle.com>
Date: Tue, 2 Apr 2019 18:07:38 +0800
Subject: btrfs: prop: fix zstd compression parameter validation
Git-commit: 50398fde997f6be8faebdb5f38e9c9c467370f51
Patch-mainline: v5.1-rc5
References: bsc#1182269

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>
Acked-by: Nikolay Borisov <nborisov@suse.com>
---
 fs/btrfs/props.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/btrfs/props.c
+++ b/fs/btrfs/props.c
@@ -407,7 +407,7 @@ static int prop_compression_apply(struct
 		type = BTRFS_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;
 	else
 		return -EINVAL;