Date:   Fri, 19 Nov 2021 15:22:18 +0100
Message-Id: <20211119142219.1519617-1-elver@google.com>
Mime-Version: 1.0
Subject: [PATCH 1/2] kasan: add ability to detect double-kmem_cache_destroy()
From:   Marco Elver <elver@google.com>
To:     elver@google.com, Andrew Morton <akpm@linux-foundation.org>
Cc:     Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        Alexander Potapenko <glider@google.com>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Vlastimil Babka <vbabka@suse.cz>, kasan-dev@googlegroups.com,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

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