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Subject[PATCH 5/5] kasan: detect invalid frees
Date
Detect frees of pointers into middle of heap objects.

Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
Cc: kasan-dev@googlegroups.com
---
lib/test_kasan.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
mm/kasan/kasan.c | 6 ++++++
2 files changed, 56 insertions(+)

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index e9c5d765be66..a808d81b409d 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -523,6 +523,54 @@ static noinline void __init kasan_alloca_oob_right(void)
*(volatile char *)p;
}

+static noinline void __init kmem_cache_double_free(void)
+{
+ char *p;
+ size_t size = 200;
+ struct kmem_cache *cache;
+
+ cache = kmem_cache_create("test_cache", size, 0, 0, NULL);
+ if (!cache) {
+ pr_err("Cache allocation failed\n");
+ return;
+ }
+ pr_info("double-free on heap object\n");
+ p = kmem_cache_alloc(cache, GFP_KERNEL);
+ if (!p) {
+ pr_err("Allocation failed\n");
+ kmem_cache_destroy(cache);
+ return;
+ }
+
+ kmem_cache_free(cache, p);
+ kmem_cache_free(cache, p);
+ kmem_cache_destroy(cache);
+}
+
+static noinline void __init kmem_cache_invalid_free(void)
+{
+ char *p;
+ size_t size = 200;
+ struct kmem_cache *cache;
+
+ cache = kmem_cache_create("test_cache", size, 0, SLAB_TYPESAFE_BY_RCU,
+ NULL);
+ if (!cache) {
+ pr_err("Cache allocation failed\n");
+ return;
+ }
+ pr_info("invalid-free of heap object\n");
+ p = kmem_cache_alloc(cache, GFP_KERNEL);
+ if (!p) {
+ pr_err("Allocation failed\n");
+ kmem_cache_destroy(cache);
+ return;
+ }
+
+ kmem_cache_free(cache, p + 1);
+ kmem_cache_destroy(cache);
+}
+
static int __init kmalloc_tests_init(void)
{
/*
@@ -560,6 +608,8 @@ static int __init kmalloc_tests_init(void)
ksize_unpoisons_memory();
copy_user_test();
use_after_scope_test();
+ kmem_cache_double_free();
+ kmem_cache_invalid_free();

kasan_restore_multi_shot(multishot);

diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
index 578843fab5dc..3fb497d4fbf8 100644
--- a/mm/kasan/kasan.c
+++ b/mm/kasan/kasan.c
@@ -495,6 +495,12 @@ static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
s8 shadow_byte;
unsigned long rounded_up_size;

+ if (unlikely(nearest_obj(cache, virt_to_head_page(object), object) !=
+ object)) {
+ kasan_report_invalid_free(object, ip);
+ return true;
+ }
+
/* RCU slabs could be legally used after free within the RCU period */
if (unlikely(cache->flags & SLAB_TYPESAFE_BY_RCU))
return false;
--
2.15.1.620.gb9897f4670-goog
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