[PATCH v3] kasan: infer allocation size by scanning metadata

[Andrey Konovalov]

/On Sat, Jan 28, 2023 at 4:00 PM Kuan-Ying Lee
<Kuan-Ying.Lee at mediatek.com> wrote:
>
> From: Andrey Konovalov <andreyknvl at google.com>

Ah, I think you need to reset the commit author before sending, so
that the patch gets recorded as authored by you.

> Make KASAN scan metadata to infer the requested allocation size instead of
> printing cache->object_size.
>
> This patch fixes confusing slab-out-of-bounds reports as reported in:
>
> https://bugzilla.kernel.org/show_bug.cgi?id=216457
>
> As an example of the confusing behavior, the report below hints that the
> allocation size was 192, while the kernel actually called kmalloc(184):
>
> ==================================================================
> BUG: KASAN: slab-out-of-bounds in _find_next_bit+0x143/0x160 lib/find_bit.c:109
> Read of size 8 at addr ffff8880175766b8 by task kworker/1:1/26
> ...
> The buggy address belongs to the object at ffff888017576600
>  which belongs to the cache kmalloc-192 of size 192
> The buggy address is located 184 bytes inside of
>  192-byte region [ffff888017576600, ffff8880175766c0)
> ...
> Memory state around the buggy address:
>  ffff888017576580: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>  ffff888017576600: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> >ffff888017576680: 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc
>                                         ^
>  ffff888017576700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  ffff888017576780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ==================================================================
>
> With this patch, the report shows:
>
> ==================================================================
> ...
> The buggy address belongs to the object at ffff888017576600
>  which belongs to the cache kmalloc-192 of size 192
> The buggy address is located 0 bytes to the right of
>  allocated 184-byte region [ffff888017576600, ffff8880175766b8)
> ...
> ==================================================================
>
> Also report slab use-after-free bugs as "slab-use-after-free" and print
> "freed" instead of "allocated" in the report when describing the accessed
> memory region.
>
> Also improve the metadata-related comment in kasan_find_first_bad_addr
> and use addr_has_metadata across KASAN code instead of open-coding
> KASAN_SHADOW_START checks.
>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=216457
> Co-developed-by: Andrey Konovalov <andreyknvl at gmail.com>
> Signed-off-by: Kuan-Ying Lee <Kuan-Ying.Lee at mediatek.com>

Or change the Co-developed-by/Signed-off-by tags.

I don't mind either approach.

Thanks!