The patch below does not apply to the v6.1-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

Thanks, Sasha

------------------ original commit in Linus's tree ------------------

From aec8e6bf839101784f3ef037dcdb9432c3f32343 Mon Sep 17 00:00:00 2001 From: Zhihao Cheng chengzhihao1@huawei.com Date: Mon, 21 Oct 2024 22:02:15 +0800 Subject: [PATCH] btrfs: fix use-after-free of block device file in __btrfs_free_extra_devids() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit

Mounting btrfs from two images (which have the same one fsid and two different dev_uuids) in certain executing order may trigger an UAF for variable 'device->bdev_file' in __btrfs_free_extra_devids(). And following are the details:

1. Attach image_1 to loop0, attach image_2 to loop1, and scan btrfs devices by ioctl(BTRFS_IOC_SCAN_DEV):

/ btrfs_device_1 → loop0 fs_device \ btrfs_device_2 → loop1 2. mount /dev/loop0 /mnt btrfs_open_devices btrfs_device_1->bdev_file = btrfs_get_bdev_and_sb(loop0) btrfs_device_2->bdev_file = btrfs_get_bdev_and_sb(loop1) btrfs_fill_super open_ctree fail: btrfs_close_devices // -ENOMEM btrfs_close_bdev(btrfs_device_1) fput(btrfs_device_1->bdev_file) // btrfs_device_1->bdev_file is freed btrfs_close_bdev(btrfs_device_2) fput(btrfs_device_2->bdev_file)

3. mount /dev/loop1 /mnt btrfs_open_devices btrfs_get_bdev_and_sb(&bdev_file) // EIO, btrfs_device_1->bdev_file is not assigned, // which points to a freed memory area btrfs_device_2->bdev_file = btrfs_get_bdev_and_sb(loop1) btrfs_fill_super open_ctree btrfs_free_extra_devids if (btrfs_device_1->bdev_file) fput(btrfs_device_1->bdev_file) // UAF !

Fix it by setting 'device->bdev_file' as 'NULL' after closing the btrfs_device in btrfs_close_one_device().

Fixes: 142388194191 ("btrfs: do not background blkdev_put()") CC: stable@vger.kernel.org # 4.19+ Link: https://bugzilla.kernel.org/show_bug.cgi?id=219408 Signed-off-by: Zhihao Cheng chengzhihao1@huawei.com Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com --- fs/btrfs/volumes.c | 1 + 1 file changed, 1 insertion(+)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 8f340ad1d9384..eb51b609190fb 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -1105,6 +1105,7 @@ static void btrfs_close_one_device(struct btrfs_device *device) if (device->bdev) { fs_devices->open_devices--; device->bdev = NULL; + device->bdev_file = NULL; } clear_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state); btrfs_destroy_dev_zone_info(device);