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

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Date:   Wed, 2 Jan 2019 16:42:47 +0100
From:   Ilya Dryomov <idryomov@...il.com>
To:     Myungho Jung <mhjungk@...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 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