In the Linux kernel 5.0.21, mounting a crafted btrfs filesystem image, performing some operations, and then making a syncfs system call can lead to a use-after-free in __mutex_lock in kernel/locking/mutex.c. This is related to mutex_can_spin_on_owner in kernel/locking/mutex.c, __btrfs_qgroup_free_meta in fs/btrfs/qgroup.c, and btrfs_insert_delayed_items in fs/btrfs/delayed-inode.c.

References

• https://nvd.nist.gov/vuln/detail/CVE-2019-19813
• https://github.com/bobfuzzer/CVE/tree/master/CVE-2019-19813
• https://lists.debian.org/debian-lts-announce/2020/09/msg00025.html
• https://lists.debian.org/debian-lts-announce/2021/03/msg00010.html
• https://security.netapp.com/advisory/ntap-20200103-0001/
• https://usn.ubuntu.com/4414-1/