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

Andy Shevchenko
2022-04-11T14:55:52Z

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.

> 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