[PATCH 1/2] kasan: add ability to detect double-kmem_cache_destroy()

[Marco Elver <elver@google.com>]

Because mm/slab_common.c is not instrumented with software KASAN modes,
it is not possible to detect use-after-free of the kmem_cache passed
into kmem_cache_destroy(). In particular, because of the s->refcount--
and subsequent early return if non-zero, KASAN would never be able to
see the double-free via kmem_cache_free(kmem_cache, s). To be able to
detect a double-kmem_cache_destroy(), check accessibility of the
kmem_cache, and in case of failure return early.

While KASAN_HW_TAGS is able to detect such bugs, by checking
accessibility and returning early we fail more gracefully and also
avoid corrupting reused objects (where tags mismatch).

A recent case of a double-kmem_cache_destroy() was detected by KFENCE:
https://lkml.kernel.org/r/0000000000003f654905c168b09d@google.com
, which was not detectable by software KASAN modes.

Signed-off-by: Marco Elver <elver@google.com>
---
 mm/slab_common.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index e5d080a93009..4bef4b6a2c76 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -491,7 +491,7 @@ void kmem_cache_destroy(struct kmem_cache *s)
 {
 	int err;
 
-	if (unlikely(!s))
+	if (unlikely(!s || !kasan_check_byte(s)))
 		return;
 
 	cpus_read_lock();
-- 
2.34.0.rc2.393.gf8c9666880-goog