[PATCH] rmap: validate pointer in anon_vma_clone

[Leon Ma]

If memory allocation failed in first loop, root will be NULL and
will lead to kernel panic.

Signed-off-by: Leon Ma <xindong.ma@xxxxxxxxx>
---
 mm/rmap.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index 9c3e773..6e53aed 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -246,8 +246,10 @@ int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src)
 
 		avc = anon_vma_chain_alloc(GFP_NOWAIT | __GFP_NOWARN);
 		if (unlikely(!avc)) {
-			unlock_anon_vma_root(root);
-			root = NULL;
+			if (!root) {
+				unlock_anon_vma_root(root);
+				root = NULL;
+			}
 			avc = anon_vma_chain_alloc(GFP_KERNEL);
 			if (!avc)
 				goto enomem_failure;
-- 
1.7.9.5

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