[PATCH] btrfs: avoid use-after-free when return the error code

[void0red]

free_extent_map(em) will free em->map_lookup, so it is
wrong to use it when return.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=216721
Signed-off-by: void0red <void0red@xxxxxxxxx>
Reported-by: eriri <1527030098@xxxxxx>
---
 fs/btrfs/volumes.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 635f45f1a2ef..dba087ad40ea 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -7241,8 +7241,9 @@ static int read_one_chunk(struct btrfs_key *key, struct extent_buffer *leaf,
 			map->stripes[i].dev = handle_missing_device(fs_info,
 								    devid, uuid);
 			if (IS_ERR(map->stripes[i].dev)) {
+				ret = PTR_ERR(map->stripes[i].dev);
 				free_extent_map(em);
-				return PTR_ERR(map->stripes[i].dev);
+				return ret;
 			}
 		}
 
-- 
2.34.1