In the Linux kernel, the following vulnerability has been resolved:

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().

References

• https://nvd.nist.gov/vuln/detail/CVE-2024-50217
• https://git.kernel.org/stable/c/47a83f8df39545f3f552bb6a1b6d9c30e37621dd
• https://git.kernel.org/stable/c/aec8e6bf839101784f3ef037dcdb9432c3f32343