On Tue, 29 Nov 2022 14:35:16 -0500 Peter Xu <peterx@xxxxxxxxxx> wrote: > Based on latest mm-unstable (9ed079378408). > > This can be seen as a follow-up series to Mike's recent hugetlb vma lock > series for pmd unsharing, but majorly covering safe use of huge_pte_offset. We're at -rc7 (a -rc8 appears probable this time) and I'm looking to settle down and stabilize things... > > ... > > huge_pte_offset() is always called with mmap lock held with either read or > write. It was assumed to be safe but it's actually not. One race > condition can easily trigger by: (1) firstly trigger pmd share on a memory > range, (2) do huge_pte_offset() on the range, then at the meantime, (3) > another thread unshare the pmd range, and the pgtable page is prone to lost > if the other shared process wants to free it completely (by either munmap > or exit mm). That sounds like a hard-to-hit memory leak, but what we have here is a user-triggerable use-after-free and an oops. Ugh. Could people please prioritize the review and testing of this patchset?
