[PATCH] kasan: separate double free case from invalid free

[Andrey Konovalov]

On Wed, Jun 15, 2022 at 8:22 AM 'Kuan-Ying Lee' via kasan-dev
<kasan-dev at googlegroups.com> wrote:
>
> Currently, KASAN describes all invalid-free/double-free bugs as
> "double-free or invalid-free". This is ambiguous.
>
> KASAN should report "double-free" when a double-free is a more
> likely cause (the address points to the start of an object) and
> report "invalid-free" otherwise [1].
>
> [1] https://bugzilla.kernel.org/show_bug.cgi?id=212193
>
> Signed-off-by: Kuan-Ying Lee <Kuan-Ying.Lee at mediatek.com>
> ---
>  mm/kasan/common.c |  8 ++++----
>  mm/kasan/kasan.h  |  3 ++-
>  mm/kasan/report.c | 12 ++++++++----
>  3 files changed, 14 insertions(+), 9 deletions(-)
>
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index c40c0e7b3b5f..707c3a527fcb 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -343,7 +343,7 @@ static inline bool ____kasan_slab_free(struct kmem_cache *cache, void *object,
>
>         if (unlikely(nearest_obj(cache, virt_to_slab(object), object) !=
>             object)) {
> -               kasan_report_invalid_free(tagged_object, ip);
> +               kasan_report_invalid_free(tagged_object, ip, KASAN_REPORT_INVALID_FREE);
>                 return true;
>         }
>
> @@ -352,7 +352,7 @@ static inline bool ____kasan_slab_free(struct kmem_cache *cache, void *object,
>                 return false;
>
>         if (!kasan_byte_accessible(tagged_object)) {
> -               kasan_report_invalid_free(tagged_object, ip);
> +               kasan_report_invalid_free(tagged_object, ip, KASAN_REPORT_DOUBLE_FREE);
>                 return true;
>         }
>
> @@ -377,12 +377,12 @@ bool __kasan_slab_free(struct kmem_cache *cache, void *object,
>  static inline bool ____kasan_kfree_large(void *ptr, unsigned long ip)
>  {
>         if (ptr != page_address(virt_to_head_page(ptr))) {
> -               kasan_report_invalid_free(ptr, ip);
> +               kasan_report_invalid_free(ptr, ip, KASAN_REPORT_INVALID_FREE);
>                 return true;
>         }
>
>         if (!kasan_byte_accessible(ptr)) {
> -               kasan_report_invalid_free(ptr, ip);
> +               kasan_report_invalid_free(ptr, ip, KASAN_REPORT_DOUBLE_FREE);
>                 return true;
>         }
>
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index 610d60d6e5b8..01c03e45acd4 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -125,6 +125,7 @@ static inline bool kasan_sync_fault_possible(void)
>  enum kasan_report_type {
>         KASAN_REPORT_ACCESS,
>         KASAN_REPORT_INVALID_FREE,
> +       KASAN_REPORT_DOUBLE_FREE,
>  };
>
>  struct kasan_report_info {
> @@ -277,7 +278,7 @@ static inline void kasan_print_address_stack_frame(const void *addr) { }
>
>  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);
> +void kasan_report_invalid_free(void *object, unsigned long ip, enum kasan_report_type type);
>
>  struct page *kasan_addr_to_page(const void *addr);
>  struct slab *kasan_addr_to_slab(const void *addr);
> diff --git a/mm/kasan/report.c b/mm/kasan/report.c
> index b341a191651d..fe3f606b3a98 100644
> --- a/mm/kasan/report.c
> +++ b/mm/kasan/report.c
> @@ -176,8 +176,12 @@ static void end_report(unsigned long *flags, void *addr)
>  static void print_error_description(struct kasan_report_info *info)
>  {
>         if (info->type == KASAN_REPORT_INVALID_FREE) {
> -               pr_err("BUG: KASAN: double-free or invalid-free in %pS\n",
> -                      (void *)info->ip);
> +               pr_err("BUG: KASAN: invalid-free in %pS\n", (void *)info->ip);
> +               return;
> +       }
> +
> +       if (info->type == KASAN_REPORT_DOUBLE_FREE) {
> +               pr_err("BUG: KASAN: double-free in %pS\n", (void *)info->ip);
>                 return;
>         }
>
> @@ -433,7 +437,7 @@ static void print_report(struct kasan_report_info *info)
>         }
>  }
>
> -void kasan_report_invalid_free(void *ptr, unsigned long ip)
> +void kasan_report_invalid_free(void *ptr, unsigned long ip, enum kasan_report_type type)
>  {
>         unsigned long flags;
>         struct kasan_report_info info;
> @@ -448,7 +452,7 @@ void kasan_report_invalid_free(void *ptr, unsigned long ip)
>
>         start_report(&flags, true);
>
> -       info.type = KASAN_REPORT_INVALID_FREE;
> +       info.type = type;
>         info.access_addr = ptr;
>         info.first_bad_addr = kasan_reset_tag(ptr);
>         info.access_size = 0;
> --
> 2.18.0

Reviewed-by: Andrey Konovalov <andreyknvl at gmail.com>

Thanks for the patch!