kasan: detect invalid frees for large objects

Patch series "kasan: detect invalid frees".

KASAN detects double-frees, but does not detect invalid-frees (when a
pointer into a middle of heap object is passed to free).  We recently had
a very unpleasant case in crypto code which freed an inner object inside
of a heap allocation.  This left unnoticed during free, but totally
corrupted heap and later lead to a bunch of random crashes all over kernel
code.

Detect invalid frees.

This patch (of 5):

Detect frees of pointers into middle of large heap objects.

I dropped const from kasan_kfree_large() because it starts propagating
through a bunch of functions in kasan_report.c, slab/slub nearest_obj(),
all of their local variables, fixup_red_left(), etc.

Link: http://lkml.kernel.org/r/1b45b4fe1d20fc0de1329aab674c1dd973fee723.1514378558.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>

1 files changed, 5 insertions, 7 deletions

diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
index 8aaee42fcfab..ecb64fda79e6 100644
--- a/mm/kasan/kasan.c
+++ b/mm/kasan/kasan.c
@@ -511,8 +511,7 @@ bool kasan_slab_free(struct kmem_cache *cache, void *object)
 
 	shadow_byte = READ_ONCE(*(s8 *)kasan_mem_to_shadow(object));
 	if (shadow_byte < 0 || shadow_byte >= KASAN_SHADOW_SCALE_SIZE) {
-		kasan_report_double_free(cache, object,
-				__builtin_return_address(1));
+		kasan_report_invalid_free(object, __builtin_return_address(1));
 		return true;
 	}
 
@@ -602,12 +601,11 @@ void kasan_poison_kfree(void *ptr)
 		kasan_poison_slab_free(page->slab_cache, ptr);
 }
 
-void kasan_kfree_large(const void *ptr)
+void kasan_kfree_large(void *ptr)
 {
-	struct page *page = virt_to_page(ptr);
-
-	kasan_poison_shadow(ptr, PAGE_SIZE << compound_order(page),
-			KASAN_FREE_PAGE);
+	if (ptr != page_address(virt_to_head_page(ptr)))
+		kasan_report_invalid_free(ptr, __builtin_return_address(1));
+	/* The object will be poisoned by page_alloc. */
 }
 
 int kasan_module_alloc(void *addr, size_t size)