A flaw was found in the Linux kernels implementation of the BTRFS file system. A local attacker with the ability to mount a file system can create a use-after-free after the file system has been unmounted. This may lead to memory corruption or possibly privilege escalation.
Created kernel tracking bugs for this issue:
Affects: fedora-all [bug 1781895]
As the btrfs module will be auto-loaded when required, its use can be disabled by preventing the module from loading with the following instructions:
# echo "install btrfs /bin/true" >> /etc/modprobe.d/disable-btrfs.conf
The system will need to be restarted if the BTRFS modules are loaded. In most circumstances, the CIFS kernel modules will be unable to be unloaded while any network interfaces are active and the protocol is in use.
If the system requires this module to work correctly (as a filesytem required to run), this mitigation may not be suitable.
If you need further assistance, see KCS article https://access.redhat.com/solutions/41278 or contact Red Hat Global Support Services.
This flaw is rated as moderate, the attacker would need to have physical access or permission to mount/write to a filesystem to abuse this. If they can write to a block device they can already do other evil things, like make a setuid binary etc.
This was fixed for Fedora with the 5.5.18 stable kernel updates.