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

Andrey Ryabinin
2019-11-21T12:27:17Z

On 11/12/19 9:53 AM, Walter Wu wrote:

> 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;
>

I realized that we are going a wrong direction here. Entirely skipping mem*() operation on any
poisoned shadow value might only make things worse. Some bugs just don't have any serious consequences,
but skipping the mem*() ops entirely might introduce such consequences, which wouldn't happen otherwise.

So let's keep this code as this, no need to check the result of check_memory_region().