[PATCH] mm: rmap: fix use-after-free in __put_anon_vma

Andrey Ryabinin
2014-06-06T11:36:22Z

While working address sanitizer for kernel I've discovered use-after-free
bug in __put_anon_vma.
For the last anon_vma, anon_vma->root freed before child anon_vma.
Later in anon_vma_free(anon_vma) we are referencing to already freed anon_vma->root
to check rwsem.
This patch puts freeing of child anon_vma before freeing of anon_vma->root.

Cc: stable@vger.kernel.org # v3.0+
Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com>
---
mm/rmap.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index 9c3e773..161bffc7 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1564,10 +1564,11 @@ void __put_anon_vma(struct anon_vma *anon_vma)
{
struct anon_vma *root = anon_vma->root;

- if (root != anon_vma && atomic_dec_and_test(&root->refcount))
+ if (root != anon_vma && atomic_dec_and_test(&root->refcount)) {
+ anon_vma_free(anon_vma);
anon_vma_free(root);
-
- anon_vma_free(anon_vma);
+ } else
+ anon_vma_free(anon_vma);
}

static struct anon_vma *rmap_walk_anon_lock(struct page *page,
--
1.8.5.5