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Commit 47adccce authored by Dmitry Vyukov's avatar Dmitry Vyukov Committed by Linus Torvalds
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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: default avatarDmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>a
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d321599c

include/linux/kasan.h

+2 −2
Original line number Diff line number Diff line
@@ -56,7 +56,7 @@ void kasan_poison_object_data(struct kmem_cache *cache, void *object); 
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(const void *ptr);

void kasan_kfree_large(void *ptr);

void kasan_poison_kfree(void *ptr);

void kasan_kmalloc(struct kmem_cache *s, const void *object, size_t size,

		  gfp_t flags);
@@ -108,7 +108,7 @@ static inline void kasan_init_slab_obj(struct kmem_cache *cache, 
				const void *object) {}



static inline void kasan_kmalloc_large(void *ptr, size_t size, gfp_t flags) {}

static inline void kasan_kfree_large(const void *ptr) {}

static inline void kasan_kfree_large(void *ptr) {}

static inline void kasan_poison_kfree(void *ptr) {}

static inline void kasan_kmalloc(struct kmem_cache *s, const void *object,

				size_t size, gfp_t flags) {}

lib/test_kasan.c

+33 −0
Original line number Diff line number Diff line
@@ -94,6 +94,37 @@ static noinline void __init kmalloc_pagealloc_oob_right(void) 
	ptr[size] = 0;

	kfree(ptr);

}



static noinline void __init kmalloc_pagealloc_uaf(void)

{

	char *ptr;

	size_t size = KMALLOC_MAX_CACHE_SIZE + 10;



	pr_info("kmalloc pagealloc allocation: use-after-free\n");

	ptr = kmalloc(size, GFP_KERNEL);

	if (!ptr) {

		pr_err("Allocation failed\n");

		return;

	}



	kfree(ptr);

	ptr[0] = 0;

}



static noinline void __init kmalloc_pagealloc_invalid_free(void)

{

	char *ptr;

	size_t size = KMALLOC_MAX_CACHE_SIZE + 10;



	pr_info("kmalloc pagealloc allocation: invalid-free\n");

	ptr = kmalloc(size, GFP_KERNEL);

	if (!ptr) {

		pr_err("Allocation failed\n");

		return;

	}



	kfree(ptr + 1);

}

#endif



static noinline void __init kmalloc_large_oob_right(void)
@@ -505,6 +536,8 @@ static int __init kmalloc_tests_init(void) 
	kmalloc_node_oob_right();

#ifdef CONFIG_SLUB

	kmalloc_pagealloc_oob_right();

	kmalloc_pagealloc_uaf();

	kmalloc_pagealloc_invalid_free();

#endif

	kmalloc_large_oob_right();

	kmalloc_oob_krealloc_more();

mm/kasan/kasan.c

+5 −7
Original line number Diff line number Diff line
@@ -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)

mm/kasan/kasan.h

+1 −2
Original line number Diff line number Diff line
@@ -107,8 +107,7 @@ static inline const void *kasan_shadow_to_mem(const void *shadow_addr) 


void kasan_report(unsigned long addr, size_t size,

		bool is_write, unsigned long ip);

void kasan_report_double_free(struct kmem_cache *cache, void *object,

					void *ip);

void kasan_report_invalid_free(void *object, void *ip);



#if defined(CONFIG_SLAB) || defined(CONFIG_SLUB)

void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache);

mm/kasan/report.c

+1 −2
Original line number Diff line number Diff line
@@ -326,8 +326,7 @@ static void print_shadow_for_address(const void *addr) 
	}

}



void kasan_report_double_free(struct kmem_cache *cache, void *object,

				void *ip)

void kasan_report_invalid_free(void *object, void *ip)

{

	unsigned long flags;