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

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Date:   Tue, 20 Aug 2019 16:38:36 +0200
From:   Oliver Neukum <oneukum@...e.com>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     keescook@...omium.org, gustavo@...eddedor.com,
        andreyknvl@...gle.com, syzkaller-bugs@...glegroups.com,
        gregkh@...uxfoundation.org,
        syzbot <syzbot+cfe6d93e0abab9a0de05@...kaller.appspotmail.com>,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: KASAN: use-after-free Read in iowarrior_disconnect

Am Dienstag, den 20.08.2019, 10:18 -0400 schrieb Alan Stern:
> On Mon, 19 Aug 2019, Oliver Neukum wrote:
> 
> > Am Montag, den 19.08.2019, 07:48 -0700 schrieb syzbot:
> > > Hello,
> > > 
> > > syzbot found the following crash on:
> > > 
> > > HEAD commit:    d0847550 usb-fuzzer: main usb gadget fuzzer driver
> > > git tree:       https://github.com/google/kasan.git usb-fuzzer
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=139be302600000
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=dbc9c80cc095da19
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=cfe6d93e0abab9a0de05
> > > compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> > > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12fe6b02600000
> > > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1548189c600000
> > > 
> > > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > > Reported-by: syzbot+cfe6d93e0abab9a0de05@...kaller.appspotmail.com
> > > 
> > 
> > #syz test: https://github.com/google/kasan.git d0847550
> 
> There's no need for us to work at cross purposes on this.  We can go 
> with your approach.
> 
> However, the code is more complicated than your patch accounts for.  
> The wait can finish in several different ways:
> 
> (1)	The control URB succeeds and the interrupt URB gets an 
> 	acknowledgment.
> 
> (2)	The control URB completes with an error.
> 
> (3)	The wait times out.
> 
> (4)	A disconnect occurs.

I absolutely agree. There is something quite wrong in this driver.
Unfortunately this is likely exploitable by a malicious gadget,
so just ignoring this is a bad option. I will need to go through the
logic. Or do you want to have a shot at it?

The patch was really only for testing. I wanted to know whether
I was hitting this very issue. This driver will need more surgery.

	Regards
		Oliver