From: Sasha Levin <sashal@kernel.org>
To: stable@vger.kernel.org
Cc: Hongling Zeng <zenghongling@kylinos.cn>,
	Johannes Thumshirn <johannes.thumshirn@wdc.com>,
	David Sterba <dsterba@suse.com>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 6.6.y] btrfs: take commit root semaphore when iterating in mark_block_group_to_copy()
Date: Tue, 22 Sep 2026 11:32:01 -0400
Message-ID: <20260922153201.2820708-1-sashal@kernel.org>
In-Reply-To: <2026092246-stagnant-delete-08e7@gregkh>
References: <2026092246-stagnant-delete-08e7@gregkh>
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MIME-Version: 1.0
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From: Hongling Zeng <zenghongling@kylinos.cn>

[ Upstream commit 0594e3423f4ba3137c734371169491f9a98e9af4 ]

mark_block_group_to_copy() iterates over the commit root with
skip_locking=true. A concurrent transaction commit can swap and free
the commit root during iteration, causing use-after-free when
accessing extent buffers.

Fix it by using path->need_commit_sem to protect the commit root search.

Fixes: 78ce9fc269af ("btrfs: zoned: mark block groups to copy for device-replace")
CC: stable@vger.kernel.org
Assisted-by: Codex:gpt-5.5
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Hongling Zeng <zenghongling@kylinos.cn>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
[ changed path->need_commit_sem assignment from true to 1 to match the older unsigned bitfield representation. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/btrfs/dev-replace.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
index f77ef719a3b11..4f97a9222b74e 100644
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -506,6 +506,7 @@ static int mark_block_group_to_copy(struct btrfs_fs_info *fs_info,
 	path->reada = READA_FORWARD;
 	path->search_commit_root = 1;
 	path->skip_locking = 1;
+	path->need_commit_sem = 1;
 
 	key.objectid = src_dev->devid;
 	key.type = BTRFS_DEV_EXTENT_KEY;
-- 
2.53.0