linux-kernel - Re: [PATCH] kasan: fix the missing underflow in memmove and memcpy with CONFIG_KASAN

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Date:   Tue, 8 Oct 2019 14:11:23 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Qian Cai <cai@....pw>
Cc:     Walter Wu <walter-zh.wu@...iatek.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Linux-MM <linux-mm@...ck.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-mediatek@...ts.infradead.org,
        wsd_upstream <wsd_upstream@...iatek.com>
Subject: Re: [PATCH] kasan: fix the missing underflow in memmove and memcpy
 with CONFIG_KASAN_GENERIC=y

On Tue, Oct 8, 2019 at 1:42 PM Qian Cai <cai@....pw> wrote:
> > On Oct 8, 2019, at 7:02 AM, Walter Wu <walter-zh.wu@...iatek.com> wrote:
> > I don't know very well in UBSAN, but I try to build ubsan kernel and
> > test a negative number in memset and kmalloc_memmove_invalid_size(), it
> > look like no check.
>
> It sounds like more important to figure out why the UBSAN is not working in this case rather than duplicating functionality elsewhere.

Detecting out-of-bounds accesses is the direct KASAN responsibility.
Even more direct than for KUBSAN. We are not even adding
functionality, it's just a plain bug in KASAN code, it tricks itself
into thinking that access size is 0.
Maybe it's already detected by KUBSAN too?