[ Cc += Nick & Aneesh & Paul ] Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> writes: > On Sun, Apr 14, 2019 at 10:19 PM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: >> >> Can we please have the page refcount overflow fixes out on the list >> for review, even if it is after the fact? > > They were actually on a list for review long before the fact, but it > was the security mailing list. The issue actually got discussed back > in January along with early versions of the patches, but then we > dropped the ball because it just wasn't on anybody's radar and it got > resurrected late March. Willy wrote a rather bigger patch-series, and > review of that is what then resulted in those commits. So they may > look recent, but that's just because the original patches got > seriously edited down and rewritten. > > That said, powerpc and s390 should at least look at maybe adding a > check for the page ref in their gup paths too. Powerpc has the special > gup_hugepte() case Which uses page_cache_add_speculative(), which handles the case of the refcount being zero but not overflow. So that looks like it needs fixing. We also have follow_huge_pd() that should use try_get_page(). And we have a few uses of bare get_page() in KVM code which might be subject to the same attack. cheers
