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

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Date:   Sat, 25 Apr 2020 14:12:42 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Oliver Neukum <oneukum@...e.com>
cc:     Pete Zaitcev <zaitcev@...hat.com>, Hillf Danton <hdanton@...a.com>,
        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>
Subject: Re: KASAN: use-after-free Read in usblp_bulk_read

On Sat, 25 Apr 2020, Oliver Neukum wrote:

> Am Donnerstag, den 23.04.2020, 12:29 -0400 schrieb Alan Stern:
> > On Thu, 23 Apr 2020, Oliver Neukum wrote:
> 
> > The only suspicious thing I see is that usblp_resume() calls 
> > handle_bidir() without first acquiring any mutex.  But resume shouldn't 
> > race with disconnect.
> 
> Right.
> 
> > The only other place where read URBs get submitted is under
> > usblp_read(), which does acquire the mutex
> 
> Right.
> 
> >  and checks for disconnection
> > while holding it.
> 
> Where? It should, but I do not see where it does so.

usblp_read() calls usblp_rwait_and_lock(), which calls usblp_rtest(), 
which returns -ENODEV if usblp->present is clear.

Alan Stern