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

[Dmitry Vyukov]

On Mon, 4 Jul 2022 at 01:15, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> On Wed, 15 Jun 2022 14:22:18 +0800 Kuan-Ying Lee <Kuan-Ying.Lee@xxxxxxxxxxxx> 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
> >
> > ...
>
> Could we please have some review of this?


Looks reasonable to me.
Looking through git log it seems the only reason to combine them was
laziness/didn't seem important enough.

Reviewed-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>

I will update syzkaller parsing of bug messages to not produce
duplicates for existing double-frees.
Not sure if anything needs to be done for other kernel testing systems.


> > 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
> >