Re: KASAN: use-after-free Read in iowarrior_disconnect
From: Alan Stern
Date: Tue Aug 20 2019 - 10:24:03 EST
Oops, I replied to the wrong email message -- sorry. This was intended
to be about the problem with the yurex driver, not the iowarrior
On Tue, 20 Aug 2019, Alan Stern wrote:
> 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@xxxxxxxxxxxxxxxxxxxxxxxxx
> > >
> > #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
> (2) The control URB completes with an error.
> (3) The wait times out.
> (4) A disconnect occurs.
> Your patch doesn't handle cases (1) and (3). (And it doesn't get rid
> of the dev->waitq field, which is no longer used.)
> In fact, (1) is a little ambiguous. When the interrupt URB gets a
> command acknowledgment, there's no way (as far as I can tell) to know
> which command was acknowledged -- particularly if a prior command URB
> had to be cancelled because it timed out.
> And as it turns out, the driver neglects to kill the command URB in
> case (3). Furthermore, the driver doesn't have mutual exclusion for
> writes. So there's nothing to prevent the command URB from being
> submitted while it is still active (syzbot's new crash).
> I have to wonder if anybody's actually using this driver. It seems to
> be pretty broken. Maybe we should just mark it as such and forget
> about fixing it.
> Alan Stern