linux-kernel - Re: [PATCH] driver: usb: nullify dangling pointer in cdc_ncm

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Date:   Mon, 11 Apr 2022 17:51:15 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Dongliang Mu <dzm91@...t.edu.cn>
Cc:     Oliver Neukum <oliver@...kum.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Dongliang Mu <mudongliangabcd@...il.com>,
        syzbot+eabbf2aaa999cc507108@...kaller.appspotmail.com,
        USB <linux-usb@...r.kernel.org>, netdev <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] driver: usb: nullify dangling pointer in cdc_ncm_free

On Sun, Apr 10, 2022 at 5:14 AM Dongliang Mu <dzm91@...t.edu.cn> wrote:
>
> From: Dongliang Mu <mudongliangabcd@...il.com>
>
> cdc_ncm_bind calls cdc_ncm_bind_common and sets dev->data[0]
> with ctx. However, in the unbind function - cdc_ncm_unbind,
> it calls cdc_ncm_free and frees ctx, leaving dev->data[0] as
> a dangling pointer. The following ioctl operation will trigger
> the UAF in the function cdc_ncm_set_dgram_size.

First of all, please use the standard form of referring to the func()
as in this sentence.

> Fix this by setting dev->data[0] as zero.
>
> ==================================================================
> BUG: KASAN: use-after-free in cdc_ncm_set_dgram_size+0xc91/0xde0
> Read of size 8 at addr ffff8880755210b0 by task dhcpcd/3174
>

Please, avoid SO noisy commit messages. Find the core part of the
traceback(s) which should be rarely more than 5-10 lines.

...

The code seems fine.

-- 
With Best Regards,
Andy Shevchenko