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

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Date:   Mon, 29 Jun 2020 16:22:55 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     syzkaller <syzkaller@...glegroups.com>,
        Hillf Danton <hdanton@...a.com>,
        syzbot <syzbot+a929647172775e335941@...kaller.appspotmail.com>,
        chuck.lever@...cle.com, Doug Ledford <dledford@...hat.com>,
        Leon Romanovsky <leon@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        RDMA mailing list <linux-rdma@...r.kernel.org>,
        parav@...lanox.com, Markus Elfring <Markus.Elfring@....de>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: KASAN: use-after-free Read in addr_handler (2)

On Mon, Jun 29, 2020 at 07:27:40PM +0200, Dmitry Vyukov wrote:
> On Mon, Jun 29, 2020 at 4:42 PM Dmitry Vyukov <dvyukov@...gle.com> wrote:
> >
> > On Sun, Jun 28, 2020 at 12:25 AM Jason Gunthorpe <jgg@...pe.ca> wrote:
> > >
> > > On Sat, Jun 27, 2020 at 09:02:05PM +0800, Hillf Danton wrote:
> > > > > So, to hit this syzkaller one of these must have happened:
> > > > >  1) rdma_addr_cancel() didn't work and the process_one_work() is still
> > > > >     runnable/running
> > > >
> > > > What syzbot reported indicates that the kworker did survive not only
> > > > canceling work but the handler_mutex, despite it's a sync cancel that
> > > > waits for the work to complete.
> > >
> > > The syzbot report doesn't confirm that the cancel work was actaully
> > > called.
> > >
> > > The most likely situation is that it was skipped because of the state
> > > mangling the patch fixes..
> > >
> > > > >  2) The state changed away from RDMA_CM_ADDR_QUERY without doing
> > > > >     rdma_addr_cancel()
> > > >
> > > > The cancel does cover the query state in the reported case, and have
> > > > difficult time working out what's in the patch below preventing the
> > > > work from going across the line the sync cancel draws. That's the
> > > > question we can revisit once there is a reproducer available.
> > >
> > > rdma-cm never seems to get reproducers from syzkaller
> >
> > +syzkaller mailing list
> >
> > Hi Jason,
> >
> > Wonder if there is some systematic issue. Let me double check.
> 
> By scanning bugs at:
> https://syzkaller.appspot.com/upstream
> https://syzkaller.appspot.com/upstream/fixed
> 
> I found a significant number of bugs that I would qualify as "rdma-cm"
> and that have reproducers. Here is an incomplete list (I did not get
> to the end):
> 
> https://syzkaller.appspot.com/bug?id=b8febdb3c7c8c1f1b606fb903cee66b21b2fd02f
> https://syzkaller.appspot.com/bug?id=d5222b3e1659e0aea19df562c79f216515740daa
> https://syzkaller.appspot.com/bug?id=c600e111223ce0a20e5f2fb4e9a4ebdff54d7fa6
> https://syzkaller.appspot.com/bug?id=a9796acbdecc1b2ba927578917755899c63c48af
> https://syzkaller.appspot.com/bug?id=95f89b8fb9fdc42e28ad586e657fea074e4e719b
> https://syzkaller.appspot.com/bug?id=8dc0bcd9dd6ec915ba10b3354740eb420884acaa
> https://syzkaller.appspot.com/bug?id=805ad726feb6910e35088ae7bbe61f4125e573b7
> https://syzkaller.appspot.com/bug?id=56b60fb3340c5995373fe5b8eae9e8722a012fc4
> https://syzkaller.appspot.com/bug?id=38d36d1b26b4299bf964d50af4d79688d39ab960
> https://syzkaller.appspot.com/bug?id=25e00dd59f31783f233185cb60064b0ab645310f
> https://syzkaller.appspot.com/bug?id=2f38d7e5312fdd0acc979c5e26ef2ef8f3370996
> 
> Do you mean some specific subset of bugs by "rdma-cm"? If yes, what is
> that subset?

The race condition bugs never seem to get reproducers, I checked a few
of the above and these are much more deterministic things.

I think the recurrance rate for the races is probably too low?

Jason