kasan: detect invalid frees for large mempool objects

Detect frees of pointers into middle of mempool objects.

I did a one-off test, but it turned out to be very tricky, so I reverted
it.  First, mempool does not call kasan_poison_kfree() unless allocation
function fails.  I stubbed an allocation function to fail on second and
subsequent allocations.  But then mempool stopped to call
kasan_poison_kfree() at all, because it does it only when allocation
function is mempool_kmalloc().  We could support this special failing
test allocation function in mempool, but it also can't live with kasan
tests, because these are in a module.

Link: http://lkml.kernel.org/r/bf7a7d035d7a5ed62d2dd0e3d2e8a4fcdf456aa7.1514378558.git.dvyukov@google.com
Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>a
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/kasan.h

@@ -57,7 +57,7 @@ void kasan_init_slab_obj(struct kmem_cache *cache, const void *object);
 
 void kasan_kmalloc_large(const void *ptr, size_t size, gfp_t flags);
 void kasan_kfree_large(void *ptr, unsigned long ip);
-void kasan_poison_kfree(void *ptr);
+void kasan_poison_kfree(void *ptr, unsigned long ip);
 void kasan_kmalloc(struct kmem_cache *s, const void *object, size_t size,
 		  gfp_t flags);
 void kasan_krealloc(const void *object, size_t new_size, gfp_t flags);
@@ -109,7 +109,7 @@ static inline void kasan_init_slab_obj(struct kmem_cache *cache,
 
 static inline void kasan_kmalloc_large(void *ptr, size_t size, gfp_t flags) {}
 static inline void kasan_kfree_large(void *ptr, unsigned long ip) {}
-static inline void kasan_poison_kfree(void *ptr) {}
+static inline void kasan_poison_kfree(void *ptr, unsigned long ip) {}
 static inline void kasan_kmalloc(struct kmem_cache *s, const void *object,
 				size_t size, gfp_t flags) {}
 static inline void kasan_krealloc(const void *object, size_t new_size,

mm/kasan/kasan.c

@@ -588,17 +588,22 @@ void kasan_krealloc(const void *object, size_t size, gfp_t flags)
 		kasan_kmalloc(page->slab_cache, object, size, flags);
 }
 
-void kasan_poison_kfree(void *ptr)
+void kasan_poison_kfree(void *ptr, unsigned long ip)
 {
 	struct page *page;
 
 	page = virt_to_head_page(ptr);
 
-	if (unlikely(!PageSlab(page)))
+	if (unlikely(!PageSlab(page))) {
+		if (ptr != page_address(page)) {
+			kasan_report_invalid_free(ptr, ip);
+			return;
+		}
 		kasan_poison_shadow(ptr, PAGE_SIZE << compound_order(page),
 				KASAN_FREE_PAGE);
-	else
+	} else {
 		kasan_poison_slab_free(page->slab_cache, ptr);
+	}
 }
 
 void kasan_kfree_large(void *ptr, unsigned long ip)

mm/mempool.c

@@ -103,10 +103,10 @@ static inline void poison_element(mempool_t *pool, void *element)
 }
 #endif /* CONFIG_DEBUG_SLAB || CONFIG_SLUB_DEBUG_ON */
 
-static void kasan_poison_element(mempool_t *pool, void *element)
+static __always_inline void kasan_poison_element(mempool_t *pool, void *element)
 {
 	if (pool->alloc == mempool_alloc_slab || pool->alloc == mempool_kmalloc)
-		kasan_poison_kfree(element);
+		kasan_poison_kfree(element, _RET_IP_);
 	if (pool->alloc == mempool_alloc_pages)
 		kasan_free_pages(element, (unsigned long)pool->pool_data);
 }
@@ -119,7 +119,7 @@ static void kasan_unpoison_element(mempool_t *pool, void *element, gfp_t flags)
 		kasan_alloc_pages(element, (unsigned long)pool->pool_data);
 }
 
-static void add_element(mempool_t *pool, void *element)
+static __always_inline void add_element(mempool_t *pool, void *element)
 {
 	BUG_ON(pool->curr_nr >= pool->min_nr);
 	poison_element(pool, element);