linux-kernel - [PATCH 5.11 08/44] btrfs: avoid double put of block group when emptying cluster

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Date:   Mon,  8 Mar 2021 13:34:46 +0100
From:   gregkh@...uxfoundation.org
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>
Subject: [PATCH 5.11 08/44] btrfs: avoid double put of block group when emptying cluster

From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

From: Josef Bacik <josef@...icpanda.com>

commit 95c85fba1f64c3249c67f0078a29f8a125078189 upstream.

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@...r.kernel.org # 4.4+
Signed-off-by: Josef Bacik <josef@...icpanda.com>
Reviewed-by: David Sterba <dsterba@...e.com>
[ update changelog ]
Signed-off-by: David Sterba <dsterba@...e.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/btrfs/free-space-cache.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -2708,8 +2708,10 @@ static void __btrfs_return_cluster_to_fr
 	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;
@@ -2747,8 +2749,6 @@ static void __btrfs_return_cluster_to_fr
 				   entry->offset, &entry->offset_index, bitmap);
 	}
 	cluster->root = RB_ROOT;
-
-out:
 	spin_unlock(&cluster->lock);
 	btrfs_put_block_group(block_group);
 }