Linux'x New Core MM Tree Ready With Numerous Fixes For "Nasty Long-Standing Bugs"

New to the Linux 7.4 kernel cycle is the Core MM tree as the route for herding some of the core memory management Linux kernel patches to the mainline kernel rather than it all going through Andrew Morton's "MM" tree. As the second pull request from this new kernel tree, a number of fixes were sent out today to address "nasty long-standing bugs" within the kernel. David Hildenbrand of Arm who is helping oversee this new Core MM initiative explained of these post-RC1 fixes: "Here is a bigger set of MM fixes that we didn't manage to have ready for -rc1. All fixes are stable-worthy; the majority fixes nasty long-standing bugs instead of being purely hotfixes. We have some more of these kinds of stable-worthy fixes in the pipeline, but we'll focus on the really urgent fixes as we get closer to the release. (leaving urgent MM fixes lurking for various weeks is not good, but having too many changes close to the release is also not good, it's tricky ...) Most issues were reported by Anthropic. Others were found while reworking proposed fixes, and of course some of the fixes were just reported and fixed on the mailing list." So this round, credit goes to Anthropic. As for the material affected with this week's Core MM pull request: "Core memory management fixes for 7.4-rc2 This includes fixes to: - THP (Transparent Huge Pages) - GUP (Get User Pages) - KSM (Kernel Samepage Merging) - USERFAULTFD - SHARED MEMORY (shmem/tmpfs/memfd) - HUGETLB - Core MM, PAGE CACHE and MEMORY RECLAIM The main changes are: - Prevent information leaks through memfd pinning, and out-of bounds writes in GUP. - Fix data loss in shmem, THP collapse, KSM and memfd pinning. - Fix corruption and reference-counting errors with huge PMD/PUD mappings, and incorrect TLB flushing and unmapping. - Fix various use-after-free bugs, deadlocks and unkillable loops, with a a focus on shmem swap handling. - Fix execution-seal enforcement for memfd (incl. hugetlb). Other changes fix accounting, quota and userfaultfd (un)registration handling." Multiple information leaks, data loss, corruption, and UAF bugs in this pull request. The pull is pending on the Linux kernel mailing list.