From 8346242a7e32c4c93316684ad8f45473932586b9 Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" Date: Thu, 9 Mar 2017 16:17:20 -0800 Subject: [PATCH] rmap: fix NULL-pointer dereference on THP munlocking The following test case triggers NULL-pointer derefernce in try_to_unmap_one(): #include #include #include #include int main(int argc, char *argv[]) { int fd; system("mount -t tmpfs -o huge=always none /mnt"); fd = open("/mnt/test", O_CREAT | O_RDWR); ftruncate(fd, 2UL << 20); mmap(NULL, 2UL << 20, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_FIXED | MAP_LOCKED, fd, 0); mmap(NULL, 2UL << 20, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_LOCKED, fd, 0); munlockall(); return 0; } Apparently, there's a case when we call try_to_unmap() on huge PMDs: it's TTU_MUNLOCK. Let's handle this case correctly. Fixes: c7ab0d2fdc84 ("mm: convert try_to_unmap_one() to use page_vma_mapped_walk()") Link: http://lkml.kernel.org/r/20170302151159.30592-1-kirill.shutemov@linux.intel.com Signed-off-by: Kirill A. Shutemov Cc: Andrea Arcangeli Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/rmap.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) diff --git a/mm/rmap.c b/mm/rmap.c index 2da487d6cea8..250635dc47b7 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1316,12 +1316,6 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma, } while (page_vma_mapped_walk(&pvmw)) { - subpage = page - page_to_pfn(page) + pte_pfn(*pvmw.pte); - address = pvmw.address; - - /* Unexpected PMD-mapped THP? */ - VM_BUG_ON_PAGE(!pvmw.pte, page); - /* * If the page is mlock()d, we cannot swap it out. * If it's recently referenced (perhaps page_referenced @@ -1345,6 +1339,13 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma, continue; } + /* Unexpected PMD-mapped THP? */ + VM_BUG_ON_PAGE(!pvmw.pte, page); + + subpage = page - page_to_pfn(page) + pte_pfn(*pvmw.pte); + address = pvmw.address; + + if (!(flags & TTU_IGNORE_ACCESS)) { if (ptep_clear_flush_young_notify(vma, address, pvmw.pte)) { -- 2.30.2