Use After Free Affecting kernel-modules package, versions *

Note: Versions mentioned in the description apply only to the upstream kernel-modules package and not the kernel-modules package as distributed by RHEL. See How to fix? for RHEL:8 relevant fixed versions and status.

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

mm/khugepaged: invoke MMU notifiers in shmem/file collapse paths

Any codepath that zaps page table entries must invoke MMU notifiers to ensure that secondary MMUs (like KVM) don't keep accessing pages which aren't mapped anymore. Secondary MMUs don't hold their own references to pages that are mirrored over, so failing to notify them can lead to page use-after-free.

I'm marking this as addressing an issue introduced in commit f3f0e1d2150b ("khugepaged: add support of collapse for tmpfs/shmem pages"), but most of the security impact of this only came in commit 27e1f8273113 ("khugepaged: enable collapse pmd for pte-mapped THP"), which actually omitted flushes for the removal of present PTEs, not just for the removal of empty page tables.

• https://access.redhat.com/security/cve/CVE-2022-48991
• https://git.kernel.org/stable/c/1a3f8c6cd29d9078cc81b29d39d0e9ae1d6a03c3
• https://git.kernel.org/stable/c/275c626c131cfe141beeb6c575e31fa53d32da19
• https://git.kernel.org/stable/c/5450535901d89a5dcca5fbbc59a24fe89caeb465
• https://git.kernel.org/stable/c/5ffc2a75534d9d74d49760f983f8eb675fa63d69
• https://git.kernel.org/stable/c/7f445ca2e0e59c7971d0b7b853465e50844ab596
• https://git.kernel.org/stable/c/c23105673228c349739e958fa33955ed8faddcaf
• https://git.kernel.org/stable/c/f268f6cf875f3220afc77bdd0bf1bb136eb54db9
• https://git.kernel.org/stable/c/ff2a1a6f869650aec99e9d070b5ab625bfbc5bc3