Re: [PATCH v4 1/2] kasan: detect negative size in memory operation function

Walter Wu
2019-11-20T08:35:07Z

On Tue, 2019-11-12 at 14:53 +0800, Walter Wu wrote:
> KASAN missed detecting size is a negative number in memset(), memcpy(),
> and memmove(), it will cause out-of-bounds bug. So needs to be detected
> by KASAN.
>
> If size is a negative number, then it has a reason to be defined as
> out-of-bounds bug type.
> Casting negative numbers to size_t would indeed turn up as
> a large size_t and its value will be larger than ULONG_MAX/2,
> so that this can qualify as out-of-bounds.
>
> KASAN report is shown below:
>
> 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@mediatek.com>
> Reported-by: Dmitry Vyukov <dvyukov@google.com>
> Suggested-by: Dmitry Vyukov <dvyukov@google.com>
> Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
> Cc: Alexander Potapenko <glider@google.com>
> Reported-by: kernel test robot <lkp@intel.com>
> ---
> include/linux/kasan.h | 2 +-
> mm/kasan/common.c | 25 ++++++++++++++++++-------
> mm/kasan/generic.c | 9 +++++----
> mm/kasan/generic_report.c | 11 +++++++++++
> mm/kasan/kasan.h | 2 +-
> mm/kasan/report.c | 5 +----
> mm/kasan/tags.c | 9 +++++----
> mm/kasan/tags_report.c | 11 +++++++++++
> 8 files changed, 53 insertions(+), 21 deletions(-)
>
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index cc8a03cc9674..2ef6b8fc63ef 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -180,7 +180,7 @@ void kasan_init_tags(void);
>
> void *kasan_reset_tag(const void *addr);
>
> -void kasan_report(unsigned long addr, size_t size,
> +bool kasan_report(unsigned long addr, size_t size,
> bool is_write, unsigned long ip);
>
> #else /* CONFIG_KASAN_SW_TAGS */
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 6814d6d6a023..4bfce0af881f 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);
> }
> @@ -627,12 +630,20 @@ void kasan_free_shadow(const struct vm_struct *vm)
> }
>
> extern void __kasan_report(unsigned long addr, size_t size, bool is_write, unsigned long ip);
> +extern bool report_enabled(void);
>
> -void kasan_report(unsigned long addr, size_t size, bool is_write, unsigned long ip)
> +bool kasan_report(unsigned long addr, size_t size, bool is_write, unsigned long ip)
> {
> - unsigned long flags = user_access_save();
> + unsigned long flags;
> +
> + if (likely(!report_enabled()))
> + return false;
> +
> + flags = user_access_save();
> __kasan_report(addr, size, is_write, ip);
> user_access_restore(flags);
> +
> + return true;
> }
>
> #ifdef CONFIG_MEMORY_HOTPLUG
> diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
> index 616f9dd82d12..56ff8885fe2e 100644
> --- a/mm/kasan/generic.c
> +++ b/mm/kasan/generic.c
> @@ -173,17 +173,18 @@ static __always_inline bool check_memory_region_inline(unsigned long addr,
> if (unlikely(size == 0))
> return true;
>
> + if (unlikely(addr + size < addr))
> + return !kasan_report(addr, size, write, ret_ip);
> +
> if (unlikely((void *)addr <
> kasan_shadow_to_mem((void *)KASAN_SHADOW_START))) {
> - kasan_report(addr, size, write, ret_ip);
> - return false;
> + return !kasan_report(addr, size, write, ret_ip);
> }
>
> if (likely(!memory_is_poisoned(addr, size)))
> return true;
>
> - kasan_report(addr, size, write, ret_ip);
> - return false;
> + return !kasan_report(addr, size, write, ret_ip);
> }
>
> bool check_memory_region(unsigned long addr, size_t size, bool write,
> diff --git a/mm/kasan/generic_report.c b/mm/kasan/generic_report.c
> index 36c645939bc9..c82bc3f52c9a 100644
> --- a/mm/kasan/generic_report.c
> +++ b/mm/kasan/generic_report.c
> @@ -107,6 +107,17 @@ 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 is a negative number, then it has reason to be
> + * defined as out-of-bounds bug type.
> + *
> + * Casting negative numbers to size_t would indeed turn up as
> + * a large size_t and its value will be larger than ULONG_MAX/2,
> + * so that this can qualify as out-of-bounds.
> + */
> + if (info->access_addr + info->access_size < info->access_addr)
> + 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/kasan.h b/mm/kasan/kasan.h
> index 35cff6bbb716..afada2ce14bf 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -152,7 +152,7 @@ bool check_memory_region(unsigned long addr, size_t size, bool write,
> void *find_first_bad_addr(void *addr, size_t size);
> const char *get_bug_type(struct kasan_access_info *info);
>
> -void kasan_report(unsigned long addr, size_t size,
> +bool kasan_report(unsigned long addr, size_t size,
> bool is_write, unsigned long ip);
> void kasan_report_invalid_free(void *object, unsigned long ip);
>
> diff --git a/mm/kasan/report.c b/mm/kasan/report.c
> index 621782100eaa..c94f8e9c78d4 100644
> --- a/mm/kasan/report.c
> +++ b/mm/kasan/report.c
> @@ -446,7 +446,7 @@ static void print_shadow_for_address(const void *addr)
> }
> }
>
> -static bool report_enabled(void)
> +bool report_enabled(void)
> {
> if (current->kasan_depth)
> return false;
> @@ -478,9 +478,6 @@ void __kasan_report(unsigned long addr, size_t size, bool is_write, unsigned lon
> void *untagged_addr;
> unsigned long flags;
>
> - if (likely(!report_enabled()))
> - return;
> -
> disable_trace_on_warning();
>
> tagged_addr = (void *)addr;
> diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
> index 0e987c9ca052..25b7734e7013 100644
> --- a/mm/kasan/tags.c
> +++ b/mm/kasan/tags.c
> @@ -86,6 +86,9 @@ bool check_memory_region(unsigned long addr, size_t size, bool write,
> if (unlikely(size == 0))
> return true;
>
> + if (unlikely(addr + size < addr))
> + return !kasan_report(addr, size, write, ret_ip);
> +
> tag = get_tag((const void *)addr);
>
> /*
> @@ -111,15 +114,13 @@ bool check_memory_region(unsigned long addr, size_t size, bool write,
> untagged_addr = reset_tag((const void *)addr);
> if (unlikely(untagged_addr <
> kasan_shadow_to_mem((void *)KASAN_SHADOW_START))) {
> - kasan_report(addr, size, write, ret_ip);
> - return false;
> + return !kasan_report(addr, size, write, ret_ip);
> }
> shadow_first = kasan_mem_to_shadow(untagged_addr);
> shadow_last = kasan_mem_to_shadow(untagged_addr + size - 1);
> for (shadow = shadow_first; shadow <= shadow_last; shadow++) {
> if (*shadow != tag) {
> - kasan_report(addr, size, write, ret_ip);
> - return false;
> + return !kasan_report(addr, size, write, ret_ip);
> }
> }
>
> diff --git a/mm/kasan/tags_report.c b/mm/kasan/tags_report.c
> index 969ae08f59d7..1d412760551a 100644
> --- a/mm/kasan/tags_report.c
> +++ b/mm/kasan/tags_report.c
> @@ -36,6 +36,17 @@
>
> const char *get_bug_type(struct kasan_access_info *info)
> {
> + /*
> + * If access_size is a negative number, then it has reason to be
> + * defined as out-of-bounds bug type.
> + *
> + * Casting negative numbers to size_t would indeed turn up as
> + * a large size_t and its value will be larger than ULONG_MAX/2,
> + * so that this can qualify as out-of-bounds.
> + */
> + if (info->access_addr + info->access_size < info->access_addr)
> + return "out-of-bounds";
> +
> #ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY
> struct kasan_alloc_meta *alloc_meta;
> struct kmem_cache *cache;

Hi Andrey,

Would you have any concerns?
Thanks.

Walter