Re: [PATCH] kasan: fix the missing underflow in memmove and memcpy with CONFIG_KASAN_GENERIC=y

[Walter Wu]

On Fri, 2019-10-04 at 11:54 +0200, Dmitry Vyukov wrote:
> > > "out-of-bounds" is the _least_ frequent KASAN bug type. So saying
> > > "out-of-bounds" has downsides of both approaches and won't prevent
> > > duplicate reports by syzbot...
> > >
> > maybe i should add your comment into the comment in get_bug_type?
> 
> Yes, that's exactly what I meant above:
> 
> "I would change get_bug_type() to return "slab-out-of-bounds" (as the
> most common OOB) in such case (with a comment)."
> 
>  ;)


The patchset help to produce KASAN report when size is negative size in
memory operation function. It is helpful for programmer to solve the
undefined behavior issue. Patch 1 based on Dmitry's suggestion and
review, patch 2 is a test in order to verify the patch 1.

[1]https://bugzilla.kernel.org/show_bug.cgi?id=199341
[2]https://lore.kernel.org/linux-arm-kernel/20190927034338.15813-1-walter-zh.wu@xxxxxxxxxxxx/

Walter Wu (2):
kasan: detect invalid size in memory operation function
kasan: add test for invalid size in memmove

lib/test_kasan.c          | 18 ++++++++++++++++++
mm/kasan/common.c         | 13 ++++++++-----
mm/kasan/generic.c        |  5 +++++
mm/kasan/generic_report.c | 10 ++++++++++
mm/kasan/tags.c           |  5 +++++
mm/kasan/tags_report.c    | 10 ++++++++++
6 files changed, 56 insertions(+), 5 deletions(-)




commit 0bc50c759a425fa0aafb7ef623aa1598b3542c67
Author: Walter Wu <walter-zh.wu@xxxxxxxxxxxx>
Date:   Fri Oct 4 18:38:31 2019 +0800

    kasan: detect invalid size in memory operation function
    
    It is an undefined behavior to pass a negative value to
memset()/memcpy()/memmove()
    , so need to be detected by KASAN.
    
    If size is negative value, then it will be larger than ULONG_MAX/2,
    so that we will qualify as out-of-bounds issue.
    
    KASAN report:
    
     BUG: KASAN: out-of-bounds in kmalloc_memmove_invalid_size+0x70/0xa0
     Read of size 18446744073709551608 at addr ffffff8069660904 by task
cat/72
    
     CPU: 2 PID: 72 Comm: cat Not tainted
5.4.0-rc1-next-20191004ajb-00001-gdb8af2f372b2-dirty #1
     Hardware name: linux,dummy-virt (DT)
     Call trace:
      dump_backtrace+0x0/0x288
      show_stack+0x14/0x20
      dump_stack+0x10c/0x164
      print_address_description.isra.9+0x68/0x378
      __kasan_report+0x164/0x1a0
      kasan_report+0xc/0x18
      check_memory_region+0x174/0x1d0
      memmove+0x34/0x88
      kmalloc_memmove_invalid_size+0x70/0xa0
    
    [1] https://bugzilla.kernel.org/show_bug.cgi?id=199341
    
    Signed-off-by: Walter Wu <walter-zh.wu@xxxxxxxxxxxx>
    Reported -by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
    Suggested-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 6814d6d6a023..6ef0abd27f06 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -102,7 +102,8 @@ EXPORT_SYMBOL(__kasan_check_write);
 #undef memset
 void *memset(void *addr, int c, size_t len)
 {
-	check_memory_region((unsigned long)addr, len, true, _RET_IP_);
+	if (!check_memory_region((unsigned long)addr, len, true, _RET_IP_))
+		return NULL;
 
 	return __memset(addr, c, len);
 }
@@ -110,8 +111,9 @@ void *memset(void *addr, int c, size_t len)
 #undef memmove
 void *memmove(void *dest, const void *src, size_t len)
 {
-	check_memory_region((unsigned long)src, len, false, _RET_IP_);
-	check_memory_region((unsigned long)dest, len, true, _RET_IP_);
+	if (!check_memory_region((unsigned long)src, len, false, _RET_IP_) ||
+	!check_memory_region((unsigned long)dest, len, true, _RET_IP_))
+		return NULL;
 
 	return __memmove(dest, src, len);
 }
@@ -119,8 +121,9 @@ void *memmove(void *dest, const void *src, size_t
len)
 #undef memcpy
 void *memcpy(void *dest, const void *src, size_t len)
 {
-	check_memory_region((unsigned long)src, len, false, _RET_IP_);
-	check_memory_region((unsigned long)dest, len, true, _RET_IP_);
+	if (!check_memory_region((unsigned long)src, len, false, _RET_IP_) ||
+	!check_memory_region((unsigned long)dest, len, true, _RET_IP_))
+		return NULL;
 
 	return __memcpy(dest, src, len);
 }
diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
index 616f9dd82d12..02148a317d27 100644
--- a/mm/kasan/generic.c
+++ b/mm/kasan/generic.c
@@ -173,6 +173,11 @@ static __always_inline bool
check_memory_region_inline(unsigned long addr,
 	if (unlikely(size == 0))
 		return true;
 
+	if (unlikely((long)size < 0)) {
+		kasan_report(addr, size, write, ret_ip);
+		return false;
+	}
+
 	if (unlikely((void *)addr <
 		kasan_shadow_to_mem((void *)KASAN_SHADOW_START))) {
 		kasan_report(addr, size, write, ret_ip);
diff --git a/mm/kasan/generic_report.c b/mm/kasan/generic_report.c
index 36c645939bc9..23951a453681 100644
--- a/mm/kasan/generic_report.c
+++ b/mm/kasan/generic_report.c
@@ -107,6 +107,16 @@ static const char *get_wild_bug_type(struct
kasan_access_info *info)
 
 const char *get_bug_type(struct kasan_access_info *info)
 {
+	/*
+	 * if access_size < 0, then it will be larger than ULONG_MAX/2,
+	 * so that this can qualify as out-of-bounds.
+	 * out-of-bounds is the _least_ frequent KASAN bug type. So saying
+	 * out-of-bounds has downsides of both approaches and won't prevent
+	 * duplicate reports by syzbot.
+	 */
+	if ((long)info->access_size < 0)
+		return "out-of-bounds";
+
 	if (addr_has_shadow(info->access_addr))
 		return get_shadow_bug_type(info);
 	return get_wild_bug_type(info);
diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
index 0e987c9ca052..b829535a3ad7 100644
--- a/mm/kasan/tags.c
+++ b/mm/kasan/tags.c
@@ -86,6 +86,11 @@ bool check_memory_region(unsigned long addr, size_t
size, bool write,
 	if (unlikely(size == 0))
 		return true;
 
+	if (unlikely((long)size < 0)) {
+		kasan_report(addr, size, write, ret_ip);
+		return false;
+	}
+
 	tag = get_tag((const void *)addr);
 
 	/*
diff --git a/mm/kasan/tags_report.c b/mm/kasan/tags_report.c
index 969ae08f59d7..19b9e364b397 100644
--- a/mm/kasan/tags_report.c
+++ b/mm/kasan/tags_report.c
@@ -36,6 +36,16 @@
 
 const char *get_bug_type(struct kasan_access_info *info)
 {
+	/*
+	 * if access_size < 0, then it will be larger than ULONG_MAX/2,
+	 * so that this can qualify as out-of-bounds.
+	 * out-of-bounds is the _least_ frequent KASAN bug type. So saying
+	 * out-of-bounds has downsides of both approaches and won't prevent
+	 * duplicate reports by syzbot.
+	 */
+	if ((long)info->access_size < 0)
+		return "out-of-bounds";
+
 #ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY
 	struct kasan_alloc_meta *alloc_meta;
 	struct kmem_cache *cache;



commit fb5cf7bd16e939d1feef229af0211a8616c9ea03
Author: Walter Wu <walter-zh.wu@xxxxxxxxxxxx>
Date:   Fri Oct 4 18:32:03 2019 +0800

    kasan: add test for invalid size in memmove
    
    Test size is negative vaule in memmove in order to verify
    if it correctly produce KASAN report.
    
    Signed-off-by: Walter Wu <walter-zh.wu@xxxxxxxxxxxx>

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index 49cc4d570a40..06942cf585cc 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -283,6 +283,23 @@ static noinline void __init
kmalloc_oob_in_memset(void)
 	kfree(ptr);
 }
 
+static noinline void __init kmalloc_memmove_invalid_size(void)
+{
+	char *ptr;
+	size_t size = 64;
+
+	pr_info("invalid size in memmove\n");
+	ptr = kmalloc(size, GFP_KERNEL);
+	if (!ptr) {
+		pr_err("Allocation failed\n");
+		return;
+	}
+
+	memset((char *)ptr, 0, 64);
+	memmove((char *)ptr, (char *)ptr + 4, -2);
+	kfree(ptr);
+}
+
 static noinline void __init kmalloc_uaf(void)
 {
 	char *ptr;
@@ -773,6 +790,7 @@ static int __init kmalloc_tests_init(void)
 	kmalloc_oob_memset_4();
 	kmalloc_oob_memset_8();
 	kmalloc_oob_memset_16();
+	kmalloc_memmove_invalid_size();
 	kmalloc_uaf();
 	kmalloc_uaf_memset();
 	kmalloc_uaf2();