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

["Kuan-Ying Lee (李冠穎)" <Kuan-Ying.Lee@mediatek.com>]

On Sat, 2023-01-28 at 23:37 +0100, Andrey Konovalov wrote:
> /On Sat, Jan 28, 2023 at 4:00 PM Kuan-Ying Lee
> <Kuan-Ying.Lee@mediatek.com> wrote:
> > 
> > From: Andrey Konovalov <andreyknvl@google.com>
> 
> Ah, I think you need to reset the commit author before sending, so
> that the patch gets recorded as authored by you.

Got it.
Will do in v4.

> > 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://urldefense.com/v3/__https://bugzilla.kernel.org/show_bug.cgi?id=216457__;!!CTRNKA9wMg0ARbw!mXW4Z05dX9YXnBYWxw-OOBYutqBM0JFoaApK61lFCSldptsVi0JEtWNSU9uaSnXbGq5oiKCBfyHLFFtEmY5uFgDl$ 
> >  
> > 
> > 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://urldefense.com/v3/__https://bugzilla.kernel.org/show_bug.cgi?id=216457__;!!CTRNKA9wMg0ARbw!mXW4Z05dX9YXnBYWxw-OOBYutqBM0JFoaApK61lFCSldptsVi0JEtWNSU9uaSnXbGq5oiKCBfyHLFFtEmY5uFgDl$ 
> >  
> > Co-developed-by: Andrey Konovalov <andreyknvl@gmail.com>
> > Signed-off-by: Kuan-Ying Lee <Kuan-Ying.Lee@mediatek.com>
> 
> Or change the Co-developed-by/Signed-off-by tags.
> 
> I don't mind either approach.
> 
> Thanks!