Patch "mm/huge_memory.c: fix potential NULL pointer dereference" has been added to the 3.0-stable tree

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

    mm/huge_memory.c: fix potential NULL pointer dereference

to the 3.0-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-huge_memory.c-fix-potential-null-pointer-dereference.patch
and it can be found in the queue-3.0 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From a8f531ebc33052642b4bd7b812eedf397108ce64 Mon Sep 17 00:00:00 2001
From: Libin <huawei.libin@xxxxxxxxxx>
Date: Wed, 11 Sep 2013 14:20:38 -0700
Subject: mm/huge_memory.c: fix potential NULL pointer dereference

From: Libin <huawei.libin@xxxxxxxxxx>

commit a8f531ebc33052642b4bd7b812eedf397108ce64 upstream.

In collapse_huge_page() there is a race window between releasing the
mmap_sem read lock and taking the mmap_sem write lock, so find_vma() may
return NULL.  So check the return value to avoid NULL pointer dereference.

collapse_huge_page
	khugepaged_alloc_page
		up_read(&mm->mmap_sem)
	down_write(&mm->mmap_sem)
	vma = find_vma(mm, address)

Signed-off-by: Libin <huawei.libin@xxxxxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Reviewed-by: Wanpeng Li <liwanp@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Michal Hocko <mhocko@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 mm/huge_memory.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1838,6 +1838,8 @@ static void collapse_huge_page(struct mm
 		goto out;
 
 	vma = find_vma(mm, address);
+	if (!vma)
+		goto out;
 	hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
 	hend = vma->vm_end & HPAGE_PMD_MASK;
 	if (address < hstart || address + HPAGE_PMD_SIZE > hend)


Patches currently in stable-queue which might be from huawei.libin@xxxxxxxxxx are

queue-3.0/mm-huge_memory.c-fix-potential-null-pointer-dereference.patch
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