btrfs: fix extent map use-after-free when handling missing device in read_one_chunk

Store the error code before freeing the extent_map. Though it's
reference counted structure, in that function it's the first and last
allocation so this would lead to a potential use-after-free.

The error can happen eg. when chunk is stored on a missing device and
the degraded mount option is missing.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=216721
Reported-by: eriri <1527030098@qq.com>
Fixes: adfb69af7d8c ("btrfs: add_missing_dev() should return the actual error")
CC: stable@vger.kernel.org # 4.9+
Signed-off-by: void0red <void0red@gmail.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index acab20f2863d5f60dce95c146eb880fe1aee92fe..aa25fa335d3ed16d9133a4ce4c535830f994248c 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -6976,8 +6976,9 @@ 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;
                        }
                }