From 77552735ba84a410447af7e3375625eb4cfd577b Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Mon, 7 Apr 2014 15:37:50 -0700 Subject: [PATCH] mm: try_to_unmap_cluster() should lock_page() before mlocking commit 57e68e9cd65b4b8eb4045a1e0d0746458502554c upstream. A BUG_ON(!PageLocked) was triggered in mlock_vma_page() by Sasha Levin fuzzing with trinity. The call site try_to_unmap_cluster() does not lock the pages other than its check_page parameter (which is already locked). The BUG_ON in mlock_vma_page() is not documented and its purpose is somewhat unclear, but apparently it serializes against page migration, which could otherwise fail to transfer the PG_mlocked flag. This would not be fatal, as the page would be eventually encountered again, but NR_MLOCK accounting would become distorted nevertheless. This patch adds a comment to the BUG_ON in mlock_vma_page() and munlock_vma_page() to that effect. The call site try_to_unmap_cluster() is fixed so that for page != check_page, trylock_page() is attempted (to avoid possible deadlocks as we already have check_page locked) and mlock_vma_page() is performed only upon success. If the page lock cannot be obtained, the page is left without PG_mlocked, which is again not a problem in the whole unevictable memory design. Fixes CVE-2014-3122 Upstream-Status: Backport Signed-off-by: Vlastimil Babka Signed-off-by: Bob Liu Reported-by: Sasha Levin Cc: Wanpeng Li Cc: Michel Lespinasse Cc: KOSAKI Motohiro Acked-by: Rik van Riel Cc: David Rientjes Cc: Mel Gorman Cc: Hugh Dickins Cc: Joonsoo Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman Signed-off-by: Sona Sarmadi --- mm/mlock.c | 2 ++ mm/rmap.c | 14 ++++++++++++-- 2 files changed, 14 insertions(+), 2 deletions(-) diff --git a/mm/mlock.c b/mm/mlock.c index 79b7cf7..713e462 100644 --- a/mm/mlock.c +++ b/mm/mlock.c @@ -76,6 +76,7 @@ void clear_page_mlock(struct page *page) */ void mlock_vma_page(struct page *page) { + /* Serialize with page migration */ BUG_ON(!PageLocked(page)); if (!TestSetPageMlocked(page)) { @@ -106,6 +107,7 @@ unsigned int munlock_vma_page(struct page *page) { unsigned int page_mask = 0; + /* For try_to_munlock() and to serialize with page migration */ BUG_ON(!PageLocked(page)); if (TestClearPageMlocked(page)) { diff --git a/mm/rmap.c b/mm/rmap.c index 3f60774..fbf0040 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1390,9 +1390,19 @@ static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount, BUG_ON(!page || PageAnon(page)); if (locked_vma) { - mlock_vma_page(page); /* no-op if already mlocked */ - if (page == check_page) + if (page == check_page) { + /* we know we have check_page locked */ + mlock_vma_page(page); ret = SWAP_MLOCK; + } else if (trylock_page(page)) { + /* + * If we can lock the page, perform mlock. + * Otherwise leave the page alone, it will be + * eventually encountered again later. + */ + mlock_vma_page(page); + unlock_page(page); + } continue; /* don't unmap */ } -- 1.9.1