Patch "mm: Fix NULL pointer dereference in madvise(MADV_WILLNEED) support" has been added to the 3.10-stable tree

This is a note to let you know that I've just added the patch titled

mm: Fix NULL pointer dereference in madvise(MADV_WILLNEED) support

to the 3.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mm-fix-null-pointer-dereference-in-madvise-madv_willneed-support.patch
and it can be found in the queue-3.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: "Kirill A. Shutemov" <[email protected]>
Date: Fri, 20 Dec 2013 15:10:03 +0200
Subject: mm: Fix NULL pointer dereference in madvise(MADV_WILLNEED) support

From: "Kirill A. Shutemov" <[email protected]>

commit ee53664bda169f519ce3c6a22d378f0b946c8178 upstream.

Sasha Levin found a NULL pointer dereference that is due to a missing page table lock, which in turn is due to the pmd entry in question being a transparent huge-table entry.

The code - introduced in commit 1998cc048901 ("mm: make madvise(MADV_WILLNEED) support swap file prefetch") - correctly checks for this situation using pmd_none_or_trans_huge_or_clear_bad(), but it turns out that that function doesn't work correctly.

pmd_none_or_trans_huge_or_clear_bad() expected that pmd_bad() would trigger if the transparent hugepage bit was set, but it doesn't do that if pmd_numa() is also set. Note that the NUMA bit only gets set on real NUMA machines, so people trying to reproduce this on most normal development systems would never actually trigger this.

Fix it by removing the very subtle (and subtly incorrect) expectation, and instead just checking pmd_trans_huge() explicitly.

[ Additionally remove the now stale test for pmd_trans_huge() inside the
pmd_bad() case - Linus ]

---
 include/asm-generic/pgtable.h |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

@@ -550,11 +550,10 @@ static inline int pmd_none_or_trans_huge
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 	barrier();
 #endif
-	if (pmd_none(pmdval))
+	if (pmd_none(pmdval) || pmd_trans_huge(pmdval))
 		return 1;
 	if (unlikely(pmd_bad(pmdval))) {
-		if (!pmd_trans_huge(pmdval))
-			pmd_clear_bad(pmd);
+		pmd_clear_bad(pmd);
 		return 1;
 	}
 	return 0;

Patches currently in stable-queue which might be from [email protected] are

queue-3.10/mm-fix-null-pointer-dereference-in-madvise-madv_willneed-support.patch