[PATCH 4.14 48/69] btrfs: prop: fix vanished compression property after failed set

[Greg Kroah-Hartman]

From: Anand Jain <anand.j...@oracle.com>

commit 272e5326c7837697882ce3162029ba893059b616 upstream.

The compression property resets to NULL, instead of the old value if we
fail to set the new compression parameter.

  $ btrfs prop get /btrfs compression
    compression=lzo
  $ btrfs prop set /btrfs compression zli
    ERROR: failed to set compression for /btrfs: Invalid argument
  $ btrfs prop get /btrfs compression

This is because the compression property ->validate() is successful for
'zli' as the strncmp() used the length passed from the userspace.

Fix it by using the expected string length in strncmp().

Fixes: 63541927c8d1 ("Btrfs: add support for inode properties")
Fixes: 5c1aab1dd544 ("btrfs: Add zstd support")
CC: sta...@vger.kernel.org # 4.14+
Reviewed-by: Nikolay Borisov <nbori...@suse.com>
Signed-off-by: Anand Jain <anand.j...@oracle.com>
Reviewed-by: David Sterba <dste...@suse.com>
Signed-off-by: David Sterba <dste...@suse.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 fs/btrfs/props.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/fs/btrfs/props.c
+++ b/fs/btrfs/props.c
@@ -386,11 +386,11 @@ int btrfs_subvol_inherit_props(struct bt
 
 static int prop_compression_validate(const char *value, size_t len)
 {
-       if (!strncmp("lzo", value, len))
+       if (!strncmp("lzo", value, 3))
                return 0;
-       else if (!strncmp("zlib", value, len))
+       else if (!strncmp("zlib", value, 4))
                return 0;
-       else if (!strncmp("zstd", value, len))
+       else if (!strncmp("zstd", value, 4))
                return 0;
 
        return -EINVAL;