A race condition was found in the way Linux kernel's memory subsystem handled breakage of the read only private mappings COW (copy-on-write mapping) situation on write access.
This is new privilege escalation issue, similar to Dirty COW (CVE-2016-5195), but it's limited to shmem only.
The user can corrupt only shared memory (shmem / tmpfs), so this issue could be considered less severe, than CVE-2016-5195.

An unprivileged local user could use this flaw to gain write access to otherwise read only memory mappings and thus increase their privileges on the system.

Fixes: 9ae0f87d009c ("mm/shmem: unconditionally set pte dirty in mfill_atomic_install_pte").
that is part of upstream Linux since v5.16.