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

[Dmitry Vyukov <dvyukov@google.com>]

On Mon, Oct 14, 2019 at 12:36 PM Walter Wu <walter-zh.wu@mediatek.com> wrote:
>
> KASAN missed detecting size is negative numbers in memset(), memcpy(),
> and memmove(), it will cause out-of-bounds bug, so needs to be detected
> by KASAN.
>
> If size is negative numbers, then it has three reasons to be
> defined as heap-out-of-bounds bug type.
> 1) 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.
> 2) If KASAN has new bug type and user-space passes negative size,
>    then there are duplicate reports. So don't produce new bug type
>    in order to prevent duplicate reports by some systems (e.g. syzbot)
>    to report the same bug twice.
> 3) When size is negative numbers, it may be passed from user-space.
>    So we always print heap-out-of-bounds in order to prevent that
>    kernel-space and user-space have the same bug but have duplicate
>    reports.
>
> KASAN report:
>
>  BUG: KASAN: heap-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>

> ---
>  mm/kasan/common.c         | 13 ++++++++-----
>  mm/kasan/generic.c        |  5 +++++
>  mm/kasan/generic_report.c | 18 ++++++++++++++++++
>  mm/kasan/tags.c           |  5 +++++
>  mm/kasan/tags_report.c    | 18 ++++++++++++++++++
>  5 files changed, 54 insertions(+), 5 deletions(-)
>
> 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..52a92c7db697 100644
> --- a/mm/kasan/generic_report.c
> +++ b/mm/kasan/generic_report.c
> @@ -107,6 +107,24 @@ 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 negative numbers, then it has three reasons
> +        * to be defined as heap-out-of-bounds bug type.
> +        * 1) 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.
> +        * 2) If KASAN has new bug type and user-space passes negative size,
> +        *    then there are duplicate reports. So don't produce new bug type
> +        *    in order to prevent duplicate reports by some systems
> +        *    (e.g. syzbot) to report the same bug twice.
> +        * 3) When size is negative numbers, it may be passed from user-space.
> +        *    So we always print heap-out-of-bounds in order to prevent that
> +        *    kernel-space and user-space have the same bug but have duplicate
> +        *    reports.
> +        */
> +       if ((long)info->access_size < 0)
> +               return "heap-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..f7ae474aef3a 100644
> --- a/mm/kasan/tags_report.c
> +++ b/mm/kasan/tags_report.c
> @@ -36,6 +36,24 @@
>
>  const char *get_bug_type(struct kasan_access_info *info)
>  {
> +       /*
> +        * If access_size is negative numbers, then it has three reasons
> +        * to be defined as heap-out-of-bounds bug type.
> +        * 1) 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.
> +        * 2) If KASAN has new bug type and user-space passes negative size,
> +        *    then there are duplicate reports. So don't produce new bug type
> +        *    in order to prevent duplicate reports by some systems
> +        *    (e.g. syzbot) to report the same bug twice.
> +        * 3) When size is negative numbers, it may be passed from user-space.
> +        *    So we always print heap-out-of-bounds in order to prevent that
> +        *    kernel-space and user-space have the same bug but have duplicate
> +        *    reports.
> +        */
> +       if ((long)info->access_size < 0)
> +               return "heap-out-of-bounds";
> +
>  #ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY
>         struct kasan_alloc_meta *alloc_meta;
>         struct kmem_cache *cache;
> --
> 2.18.0
>
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