linux-kernel - Re: [PATCH] i2c: i801: Fix memory corruption in i801_isr_byte

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Message-ID: <20200323093733.GA26299@kadam>
Date:   Mon, 23 Mar 2020 12:37:33 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Jean Delvare <jdelvare@...e.de>
Cc:     Daniel Kurtz <djkurtz@...omium.org>, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        syzbot <syzbot+ed71512d469895b5b34e@...kaller.appspotmail.com>
Subject: Re: [PATCH] i2c: i801: Fix memory corruption in i801_isr_byte_done()

On Sun, Mar 22, 2020 at 11:11:06PM +0100, Jean Delvare wrote:
> Definitely not correct. The first byte of the block data array MUST be
> the size of the block read. Even if the code above does not do the
> right thing, removing the line will not help.
> 

Yeah.  I misread the code.

> Is it possible that kasan got this wrong due to the convoluted logic?
> It's late and I'll check again tomorrow morning but the code looks OK
> to me.

KASan doesn't work like that.  It works at runtime and doesn't care
about the logic.

https://syzkaller.appspot.com/bug?id=426fc8b1c1b63fb0af524d839dfcf452f2d858e2

At the bottom of the report it shows that we're in a field of f9
poisoned data so it's not priv->len which is wrong.  (My patch was way
off).

mm/kasan/kasan.h:#define KASAN_VMALLOC_INVALID   0xF9  /* unallocated space in vmapped page */

The logic looks okay to me too.  So possibly this was a race condition
or even memory corruption in an unrelated part of the kernel.

regards,
dan carpenter