linux-kernel - [PATCH] btrfs: fix memory leak of fs_devices in degraded seed device path

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Message-ID: <20251210132807.3263207-1-kartikey406@gmail.com>
Date: Wed, 10 Dec 2025 18:58:07 +0530
From: Deepanshu Kartikey <kartikey406@...il.com>
To: clm@...com,
	dsterba@...e.com,
	miaox@...fujitsu.com
Cc: linux-btrfs@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Deepanshu Kartikey <kartikey406@...il.com>,
	syzbot+eadd98df8bceb15d7fed@...kaller.appspotmail.com
Subject: [PATCH] btrfs: fix memory leak of fs_devices in degraded seed device path

In open_seed_devices(), when find_fsid() fails and we're in DEGRADED
mode, a new fs_devices is allocated via alloc_fs_devices() but is never
added to the seed_list before returning. This contrasts with the normal
path where fs_devices is properly added via list_add().

If any error occurs later in read_one_dev() or btrfs_read_chunk_tree(),
the cleanup code iterates seed_list to free seed devices, but this
orphaned fs_devices is never found and never freed, causing a memory
leak. Any devices allocated via add_missing_dev() and attached to this
fs_devices are also leaked.

Fix this by adding the newly allocated fs_devices to seed_list in the
degraded path, consistent with the normal path.

Fixes: 5f37583569442 ("Btrfs: move the missing device to its own fs device list")
Reported-by: syzbot+eadd98df8bceb15d7fed@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=eadd98df8bceb15d7fed
Tested-by: syzbot+eadd98df8bceb15d7fed@...kaller.appspotmail.com
Signed-off-by: Deepanshu Kartikey <kartikey406@...il.com>
---
 fs/btrfs/volumes.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index ae1742a35e76..13c514684cfb 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -7128,6 +7128,7 @@ static struct btrfs_fs_devices *open_seed_devices(struct btrfs_fs_info *fs_info,

 		fs_devices->seeding = true;
 		fs_devices->opened = 1;
+		list_add(&fs_devices->seed_list, &fs_info->fs_devices->seed_list);
 		return fs_devices;
 	}

-- 
2.43.0