Hi Shubham,

On 03/02/25 18:07, Shubham Pushpkar wrote:

From: Zhihao Cheng chengzhihao1@huawei.com

commit aec8e6bf839101784f3ef037dcdb9432c3f32343 ("btrfs: fix use-after-free of block device file in __btrfs_free_extra_devids()")

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 (cherry picked from commit aec8e6bf839101784f3ef037dcdb9432c3f32343) Signed-off-by: Shubham Pushpkar spushpka@cisco.com

---

fs/btrfs/volumes.c | 1 + 1 file changed, 1 insertion(+)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index b9a0b26d08e1..ab2412542ce5 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -1176,6 +1176,7 @@ static void btrfs_close_one_device(struct btrfs_device *device) if (device->bdev) { fs_devices->open_devices--; device->bdev = NULL;

• device->bdev_file = NULL;
  

Looks bad.

"bdev_file" is not a member of struct btrfs_device in 6.6.y. It is added only in commit: 9ae061cf2a46 ("btrfs: port device access to file") which is not in 6.6.y

Hint: This has CC:stable and Fixes tag and a clean cherry-pick so there should be a reason why this didn't get into stable easily.(reason in this case in build failure)

Thanks, Harshit

} clear_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state); btrfs_destroy_dev_zone_info(device);