[PATCH] mm/huge_memory: Fix to make vma_adjust_trans_huge() use find_vma() correctly

[Jeongjun Park <aha310510@gmail.com>]

vma_adjust_trans_huge() uses find_vma() to get the VMA, but find_vma() uses
the returned pointer without any verification, even though it may return NULL.
In this case, NULL pointer dereference may occur, so to prevent this,
vma_adjust_trans_huge() should be fix to verify the return value of find_vma().

Cc: <stable@vger.kernel.org>
Fixes: 685405020b9f ("mm/khugepaged: stop using vma linked list")
Signed-off-by: Jeongjun Park <aha310510@gmail.com>
---
 mm/huge_memory.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 5734d5d5060f..db55b8abae2e 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2941,9 +2941,12 @@ void vma_adjust_trans_huge(struct vm_area_struct *vma,
 	 */
 	if (adjust_next > 0) {
 		struct vm_area_struct *next = find_vma(vma->vm_mm, vma->vm_end);
-		unsigned long nstart = next->vm_start;
-		nstart += adjust_next;
-		split_huge_pmd_if_needed(next, nstart);
+
+		if (likely(next)) {
+			unsigned long nstart = next->vm_start;
+			nstart += adjust_next;
+			split_huge_pmd_if_needed(next, nstart);
+		}
 	}
 }
 
--