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Subject[PATCH 4/5] kasan: unify code between kasan_slab_free() and kasan_poison_kfree()
Date
Both of these functions deal with freeing of slab objects.
However, kasan_poison_kfree() mishandles SLAB_TYPESAFE_BY_RCU
(must also not poison such objects) and does not detect double-frees.

Unify code between these functions.
This solves both of the problems and allows to add more common code
(e.g. detection of invalid frees).

Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
Cc: kasan-dev@googlegroups.com
---
mm/kasan/kasan.c | 28 ++++++++++++----------------
1 file changed, 12 insertions(+), 16 deletions(-)

diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
index 77c103748728..578843fab5dc 100644
--- a/mm/kasan/kasan.c
+++ b/mm/kasan/kasan.c
@@ -489,21 +489,11 @@ void kasan_slab_alloc(struct kmem_cache *cache, void *object, gfp_t flags)
kasan_kmalloc(cache, object, cache->object_size, flags);
}

-static void kasan_poison_slab_free(struct kmem_cache *cache, void *object)
-{
- unsigned long size = cache->object_size;
- unsigned long rounded_up_size = round_up(size, KASAN_SHADOW_SCALE_SIZE);
-
- /* RCU slabs could be legally used after free within the RCU period */
- if (unlikely(cache->flags & SLAB_TYPESAFE_BY_RCU))
- return;
-
- kasan_poison_shadow(object, rounded_up_size, KASAN_KMALLOC_FREE);
-}
-
-bool kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip)
+static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
+ unsigned long ip, bool quarantine)
{
s8 shadow_byte;
+ unsigned long rounded_up_size;

/* RCU slabs could be legally used after free within the RCU period */
if (unlikely(cache->flags & SLAB_TYPESAFE_BY_RCU))
@@ -515,9 +505,10 @@ bool kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip)
return true;
}

- kasan_poison_slab_free(cache, object);
+ rounded_up_size = round_up(cache->object_size, KASAN_SHADOW_SCALE_SIZE);
+ kasan_poison_shadow(object, rounded_up_size, KASAN_KMALLOC_FREE);

- if (unlikely(!(cache->flags & SLAB_KASAN)))
+ if (!quarantine || unlikely(!(cache->flags & SLAB_KASAN)))
return false;

set_track(&get_alloc_info(cache, object)->free_track, GFP_NOWAIT);
@@ -525,6 +516,11 @@ bool kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip)
return true;
}

+bool kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip)
+{
+ return __kasan_slab_free(cache, object, ip, true);
+}
+
void kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
gfp_t flags)
{
@@ -602,7 +598,7 @@ void kasan_poison_kfree(void *ptr, unsigned long ip)
kasan_poison_shadow(ptr, PAGE_SIZE << compound_order(page),
KASAN_FREE_PAGE);
} else {
- kasan_poison_slab_free(page->slab_cache, ptr);
+ __kasan_slab_free(page->slab_cache, ptr, ip, false);
}
}

--
2.15.1.620.gb9897f4670-goog
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