linux-kernel - Re: [PATCH] usb: gadget: use after free in dev

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Date:   Thu, 30 Dec 2021 10:15:02 +0800
From:   Hangyu Hua <hbh25y@...il.com>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     balbi@...nel.org, gregkh@...uxfoundation.org, axboe@...nel.dk,
        dan.carpenter@...cle.com, jj251510319013@...il.com,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: gadget: use after free in dev_config

Thank for your suggesions. I will break this up into two separate 
patches later. And i think it's necessary to clear up dev->config and
dev->hs_config and dev->dev. For example, dev->hs_config is used in
ep0_read() which may lead a UAF.

Thanks.

On 2021/12/30 上午5:11, Alan Stern wrote:
> On Tue, Dec 28, 2021 at 05:21:26PM +0800, Hangyu Hua wrote:
>> There are two bugs:
> 
> You should break this up into two separate patches, one for each bug.
> 
>> dev->buf does not need to be released if it already exists before
>> executing dev_config.
> 
> That's right.  The call to dev_config should fail without changing any
> of the stored values.
> 
>> dev->config and dev->hs_config and dev->dev need to be cleaned if
>> dev_config fails to avoid UAF.
> 
> Do they really need to be cleared?  I think if dev_config fails then
> those pointers never get used, so it doesn't matter what they contain.
> 
> Of course, clearing them doesn't hurt, but it would be best to clear
> all of them in the "fail:" part of the routine.  And then you would
> want to change the pathway where usb_gadget_probe_driver fails, to make
> it go to "fail:" also.
> 
> Alan Stern
>