The patch titled
Subject: khugepaged: fix null-pointer dereference due to race
has been added to the -mm tree. Its filename is
khugepaged-fix-null-pointer-dereference-due-to-race.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/khugepaged-fix-null-pointer-dereference-due-to-race.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/khugepaged-fix-null-pointer-dereference-due-to-race.patch
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------------------------------------------------------
From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Subject: 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.
Link: http://lkml.kernel.org/r/20200722121439.44328-1-kirill.shutemov@xxxxxxxxxxxxxxx
Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS")
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Reported-by: syzbot+ed318e8b790ca72c5ad0@xxxxxxxxxxxxxxxxxxxxxxxxx
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
Acked-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/khugepaged.c | 3 +++
1 file changed, 3 insertions(+)
--- a/mm/khugepaged.c~khugepaged-fix-null-pointer-dereference-due-to-race
+++ a/mm/khugepaged.c
@@ -958,6 +958,9 @@ static int hugepage_vma_revalidate(struc
return SCAN_ADDRESS_RANGE;
if (!hugepage_vma_check(vma, vma->vm_flags))
return SCAN_VMA_CHECK;
+ /* Anon VMA expected */
+ if (!vma->anon_vma || vma->vm_ops)
+ return SCAN_VMA_CHECK;
return 0;
}
_
Patches currently in -mm which might be from kirill.shutemov@xxxxxxxxxxxxxxx are
mm-close-race-between-munmap-and-expand_upwards-downwards.patch
khugepaged-fix-null-pointer-dereference-due-to-race.patch
