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Subject[PATCH 91/93] mm/huge_memory.c: fix potential NULL pointer dereference
Date
3.8.13.10 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Libin <huawei.libin@huawei.com>

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@huawei.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
mm/huge_memory.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 9459edd..e9308d3 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2327,6 +2327,8 @@ static void collapse_huge_page(struct mm_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)
--
1.8.1.2


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