An issue was found in Overlayfs in the Linux kernel were it replace vma->vm_file in their mmap handlers. On error the original value is not restored, and the reference is put for the file to which vm_file points. On upstream kernels this is not an issue, as no callers dereference vm_file following after call_mmap() returns an error. However, the aufs patchs change mmap_region() to replace the fput() using a local variable with vma_fput(), which will fput() vm_file, leading to a refcount underflow. This can lead to an invalid address access and a DoS problem. Reference: https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/eoan/commit/?id=270d16ae48a4dbf1c7e25e94cc3e38b4bea37635 https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1850994
Created kernel tracking bugs for this issue: Affects: fedora-all [bug 1832271]
Mitigation: Mitigation for this issue is either not available or the currently available options don't meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.
The use case of compiling a third party AUFS (filesystem) to allow this flaw to be triggered, means that this flaw is not able to be triggered for most users of overlayfs in Red Hat Enterprise Linux.