linux-kernel - Re: [PATCH] libceph: protect pending flags in ceph_con

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Date:   Wed, 2 Jan 2019 19:50:29 -0800
From:   Myungho Jung <mhjungk@...il.com>
To:     Ilya Dryomov <idryomov@...il.com>
Cc:     "Yan, Zheng" <zyan@...hat.com>, Sage Weil <sage@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Ceph Development <ceph-devel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] libceph: protect pending flags in ceph_con_keepalive()

On Wed, Jan 02, 2019 at 04:42:47PM +0100, Ilya Dryomov wrote:
> On Thu, Dec 27, 2018 at 8:08 PM Myungho Jung <mhjungk@...il.com> wrote:
> >
> > con_flag_test_and_set() sets CON_FLAG_KEEPALIVE_PENDING and
> > CON_FLAG_WRITE_PENDING flags without protection in ceph_con_keepalive().
> > It triggers WARN_ON() in clear_standby() if the flags are set after
> > con_fault() changes connection state to CON_STATE_STANDBY. Move
> > con_flag_test_and_set() to be called before releasing the lock and store
> > the condition to check after the critical section.
> >
> > Reported-by: syzbot+acdeb633f6211ccdf886@...kaller.appspotmail.com
> > Signed-off-by: Myungho Jung <mhjungk@...il.com>
> > ---
> >  net/ceph/messenger.c | 8 ++++++--
> >  1 file changed, 6 insertions(+), 2 deletions(-)
> >
> > diff --git a/net/ceph/messenger.c b/net/ceph/messenger.c
> > index 2f126eff275d..e15da22d4f37 100644
> > --- a/net/ceph/messenger.c
> > +++ b/net/ceph/messenger.c
> > @@ -3216,12 +3216,16 @@ void ceph_msg_revoke_incoming(struct ceph_msg *msg)
> >   */
> >  void ceph_con_keepalive(struct ceph_connection *con)
> >  {
> > +       bool pending;
> > +
> >         dout("con_keepalive %p\n", con);
> >         mutex_lock(&con->mutex);
> >         clear_standby(con);
> > +       pending = (con_flag_test_and_set(con,
> > +                                        CON_FLAG_KEEPALIVE_PENDING) == 0 &&
> > +                  con_flag_test_and_set(con, CON_FLAG_WRITE_PENDING) == 0);
> >         mutex_unlock(&con->mutex);
> > -       if (con_flag_test_and_set(con, CON_FLAG_KEEPALIVE_PENDING) == 0 &&
> > -           con_flag_test_and_set(con, CON_FLAG_WRITE_PENDING) == 0)
> > +       if (pending)
> >                 queue_con(con);
> >  }
> >  EXPORT_SYMBOL(ceph_con_keepalive);
> 
> Hi Myungho,
> 
> Were you able to reproduce?  If so, did you use the syzkaller output or
> something else?
> 
> Thanks,
> 
>                 Ilya
Hi Ilya,

I reproduced on vm using syzkaller utils and verified the fix by syzbot.

Thanks,
Myungho