On 25.01.21 г. 23:42 ч., Josef Bacik wrote:
In __btrfs_return_cluster_to_free_space we will bail doing the cleanup of the cluster if the block group we passed in doesn't match the block group on the cluster. However we drop a reference to block_group, as the cluster holds a reference to the block group while it's attached to the cluster. If cluster->block_group != block_group however then this is an extra put, which means we'll go negative and free this block group down the line, leading to a UAF.
Was this found by code inspection or did you hit in production. Also why in btrfs_remove_free_space_cache just before __btrfs_return_cluster_to_free_space there is:
WARN_ON(cluster->block_group != block_group);
IMO this patch should also remove the WARN_ON if it's a valid condition to have the passed bg be different than the one in the cluster. Also that WARN_ON is likely racy since it's done outside of cluster->lock.
Fix this by simply bailing if the block group we passed in does not match the block group on the cluster.
CC: stable@vger.kernel.org Fixes: fa9c0d795f7b ("Btrfs: rework allocation clustering") Signed-off-by: Josef Bacik josef@toxicpanda.com
fs/btrfs/free-space-cache.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c index 0d6dcb5ff963..8be36cc6cbd8 100644 --- a/fs/btrfs/free-space-cache.c +++ b/fs/btrfs/free-space-cache.c @@ -2711,8 +2711,10 @@ 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; @@ -2750,8 +2752,6 @@ 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); }