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Subject[PATCH 5.0 076/117] btrfs: prop: fix vanished compression property after failed set
From: Anand Jain <>

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
$ 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: # 4.14+
Reviewed-by: Nikolay Borisov <>
Signed-off-by: Anand Jain <>
Reviewed-by: David Sterba <>
Signed-off-by: David Sterba <>
Signed-off-by: Greg Kroah-Hartman <>

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

--- a/fs/btrfs/props.c
+++ b/fs/btrfs/props.c
@@ -366,11 +366,11 @@ 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;

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