diff options context: 1 2 3 4 5 6 7 8 9 10 15 20 25 30 35 40 space: include ignore mode: unified ssdiff stat only

author 2016-10-13 13:07:36 -0700 committer 2016-10-18 14:13:29 -0700 commit 19be0eaffa3ac7d8eb6784ad9bdbc7d67ed8e619 (patch) tree 9ed601a5726b067beb3e29414c469f88c499a63b parent 6b25e21fa6f26d0f0d45f161d169029411c84286 (diff) download linux-19be0eaffa3ac7d8eb6784ad9bdbc7d67ed8e619.tar.gz



mm: remove gup_flags FOLL_WRITE games from __get_user_pages()

This is an ancient bug that was actually attempted to be fixed once (badly) by me eleven years ago in commit 4ceb5db9757a ("Fix get_user_pages() race for write access") but that was then undone due to problems on s390 by commit f33ea7f404e5 ("fix get_user_pages bug"). In the meantime, the s390 situation has long been fixed, and we can now fix it by checking the pte_dirty() bit properly (and do it better). The s390 dirty bit was implemented in abf09bed3cce ("s390/mm: implement software dirty bits") which made it into v3.9. Earlier kernels will have to look at the page state itself. Also, the VM has become more scalable, and what used a purely theoretical race back then has become easier to trigger. To fix it, we introduce a new internal FOLL_COW flag to mark the "yes, we already did a COW" rather than play racy games with FOLL_WRITE that is very fundamental, and then use the pte dirty flag to validate that the FOLL_COW flag is still valid. Reported-and-tested-by: Phil "not Paul" Oester <kernel@linuxace.com> Acked-by: Hugh Dickins <hughd@google.com> Reviewed-by: Michal Hocko <mhocko@suse.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Kees Cook <keescook@chromium.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Willy Tarreau <w@1wt.eu> Cc: Nick Piggin <npiggin@gmail.com> Cc: Greg Thelen <gthelen@google.com> Cc: stable@vger.kernel.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 13 insertions, 2 deletions