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SubjectRe: [PATCH v3 1/2] kasan: detect negative size in memory operation function
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On 11/4/19 5:05 AM, Walter Wu wrote:

>
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 6814d6d6a023..4ff67e2fd2db 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -99,10 +99,14 @@ bool __kasan_check_write(const volatile void *p, unsigned int size)
> }
> EXPORT_SYMBOL(__kasan_check_write);
>
> +extern bool report_enabled(void);
> +
> #undef memset
> void *memset(void *addr, int c, size_t len)
> {
> - check_memory_region((unsigned long)addr, len, true, _RET_IP_);
> + if (report_enabled() &&
> + !check_memory_region((unsigned long)addr, len, true, _RET_IP_))
> + return NULL;
>
> return __memset(addr, c, len);
> }
> @@ -110,8 +114,10 @@ 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 (report_enabled() &&
> + (!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 +125,10 @@ 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 (report_enabled() &&

report_enabled() checks seems to be useless.

> + (!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)) {

if (unlikely(addr + size < addr)) {

> + 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.
> + */

Completely fail to understand 2) and 3). 2) talks something about *NOT* producing new bug
type, but at the same time you code actually does that.
3) says something about user-space which have nothing to do with kasan.

> + if ((long)info->access_size < 0)

if (info->access_addr + info->access_size < info->access_addr)

> + 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/report.c b/mm/kasan/report.c
> index 621782100eaa..c79e28814e8f 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;
> 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)) {

if (unlikely(addr + size < addr)) {

> + 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)

if (info->access_addr + info->access_size < info->access_addr)

> + return "heap-out-of-bounds";
> +
> #ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY
> struct kasan_alloc_meta *alloc_meta;
> struct kmem_cache *cache;
>

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