Re: [PATCH] driver: usb: nullify dangling pointer in cdc_ncm_free

From: Dongliang Mu <mudongliangabcd@gmail.com>
To: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Dongliang Mu <dzm91@hust.edu.cn>,
	Oliver Neukum <oliver@neukum.org>,
	"David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	syzbot+eabbf2aaa999cc507108@syzkaller.appspotmail.com,
	USB <linux-usb@vger.kernel.org>, netdev <netdev@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] driver: usb: nullify dangling pointer in cdc_ncm_free
Date: Thu, 14 Apr 2022 21:59:41 +0800	[thread overview]
Message-ID: <CAD-N9QU2A58QKs9JkYmbH2hdLZOU6Qeqk1WG0Ftv1i9nYjq0tw@mail.gmail.com> (raw)
In-Reply-To: <CAHp75Vc4hGOJ8gr9R5WqgZ1QkC-uEeQ7WXAqO0YjynDx9jOvnw@mail.gmail.com>

On Mon, Apr 11, 2022 at 10:55 PM Andy Shevchenko
<andy.shevchenko@gmail.com> wrote:
>
> On Sun, Apr 10, 2022 at 5:14 AM Dongliang Mu <dzm91@hust.edu.cn> wrote:
> >
> > From: Dongliang Mu <mudongliangabcd@gmail.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.

OK, no problem.

>
> > 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.

Sure. I will revise them in the v2 patch.

>
> ...
>
> The code seems fine.
>
> --
> With Best Regards,
> Andy Shevchenko