btrfs: avoid double put of block group when emptying cluster

It's wrong calling btrfs_put_block_group in
__btrfs_return_cluster_to_free_space if the block group passed is
different than the block group the cluster represents. As this means the
cluster doesn't have a reference to the passed block group. This results
in double put and a use-after-free bug.

Fix this by simply bailing if the block group we passed in does not
match the block group on the cluster.

Fixes: fa9c0d795f7b ("Btrfs: rework allocation clustering")
CC: stable@vger.kernel.org # 4.4+
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ update changelog ]
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index abcf951..711a6a7 100644 (file)
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -2801,8 +2801,10 @@ static void __btrfs_return_cluster_to_free_space(
        struct rb_node *node;
 
        spin_lock(&cluster->lock);
-       if (cluster->block_group != block_group)
-               goto out;
+       if (cluster->block_group != block_group) {
+               spin_unlock(&cluster->lock);
+               return;
+       }
 
        cluster->block_group = NULL;
        cluster->window_start = 0;
@@ -2840,8 +2842,6 @@ static void __btrfs_return_cluster_to_free_space(
                                   entry->offset, &entry->offset_index, bitmap);
        }
        cluster->root = RB_ROOT;
-
-out:
        spin_unlock(&cluster->lock);
        btrfs_put_block_group(block_group);
 }