diff options
authorKirill A. Shutemov <>2020-07-24 07:15:34 +0300
committerLinus Torvalds <>2020-07-24 22:42:41 +0300
commit594cced14ad3903166c8b091ff96adac7552f0b3 (patch)
parentdbda8feadfa46b3d8dd7a2304f84ccbc036effe9 (diff)
khugepaged: fix null-pointer dereference due to race
khugepaged has to drop mmap lock several times while collapsing a page. The situation can change while the lock is dropped and we need to re-validate that the VMA is still in place and the PMD is still subject for collapse. But we miss one corner case: while collapsing an anonymous pages the VMA could be replaced with file VMA. If the file VMA doesn't have any private pages we get NULL pointer dereference: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] anon_vma_lock_write include/linux/rmap.h:120 [inline] collapse_huge_page mm/khugepaged.c:1110 [inline] khugepaged_scan_pmd mm/khugepaged.c:1349 [inline] khugepaged_scan_mm_slot mm/khugepaged.c:2110 [inline] khugepaged_do_scan mm/khugepaged.c:2193 [inline] khugepaged+0x3bba/0x5a10 mm/khugepaged.c:2238 The fix is to make sure that the VMA is anonymous in hugepage_vma_revalidate(). The helper is only used for collapsing anonymous pages. Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS") Reported-by: Signed-off-by: Kirill A. Shutemov <> Signed-off-by: Andrew Morton <> Reviewed-by: David Hildenbrand <> Acked-by: Yang Shi <> Cc: <> Link: Signed-off-by: Linus Torvalds <>
1 files changed, 3 insertions, 0 deletions
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index b043c40a21d4..700f5160f3e4 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -958,6 +958,9 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
if (!hugepage_vma_check(vma, vma->vm_flags))
+ /* Anon VMA expected */
+ if (!vma->anon_vma || vma->vm_ops)
+ return SCAN_VMA_CHECK;
return 0;