linux-kernel - Re: KASAN: use-after-free Read in usblp_bulk

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Date:   Wed, 6 May 2020 11:47:32 -0500
From:   Pete Zaitcev <zaitcev@...hat.com>
To:     Oliver Neukum <oneukum@...e.com>
Cc:     Alan Stern <stern@...land.harvard.edu>,
        syzbot <syzbot+be5b5f86a162a6c281e6@...kaller.appspotmail.com>,
        andreyknvl@...gle.com, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        syzkaller-bugs@...glegroups.com, zaitcev@...hat.com
Subject: Re: KASAN: use-after-free Read in usblp_bulk_read

On Wed, 06 May 2020 11:14:42 +0200
Oliver Neukum <oneukum@...e.com> wrote:

> Very well. We are not going to find it without exceptional luck. Yet
> there may be a real issue, too. We simply do not know. How about the
> attached patch?

>  	usblp_unlink_urbs(usblp);
>  	mutex_unlock(&usblp->mut);
> +	usb_poison_anchored_urbs(&usblp->urbs);
>  
>  	if (!usblp->used)
>  		usblp_cleanup(usblp);

This can't be right. Our URBs are freed by the callback, and this
technique is not compatible with poisoning, at least with how the
usb/core.c implements it. The usb_poison_urb() waits for URB
to complete, and if the callback frees it, it's a problem.

-- Pete