[PATCH 3.10 34/40] mm: rmap: fix use-after-free in __put_anon_vma

Greg Kroah-Hartman
2014-06-09T22:46:57Z

From: Andrey Ryabinin <a.ryabinin@samsung.com>

commit 624483f3ea82598ab0f62f1bdb9177f531ab1892 upstream.

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 fixes it by freeing the child anon_vma before freeing
anon_vma->root.

Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
mm/rmap.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1675,10 +1675,9 @@ void __put_anon_vma(struct anon_vma *ano
{
struct anon_vma *root = anon_vma->root;

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

#ifdef CONFIG_MIGRATION