[ 34/40] mm/huge_memory.c: fix potential NULL pointer dereference

From: Greg Kroah-Hartman
Date: Tue Sep 24 2013 - 20:14:23 EST

3.4-stable review patch. If anyone has any objections, please let me know.


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.

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
@@ -1894,6 +1894,8 @@ 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)

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