netdev - Re: [PATCH mptcp] mptcp: remove tcp ulp setsockopt support

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Date:   Mon, 6 Dec 2021 07:55:15 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Florian Westphal <fw@...len.de>
Cc:     <mptcp@...ts.linux.dev>, syzkaller-bugs@...glegroups.com,
        <netdev@...r.kernel.org>, linux-kernel@...r.kernel.org,
        syzbot+1fd9b69cde42967d1add@...kaller.appspotmail.com
Subject: Re: [PATCH mptcp] mptcp: remove tcp ulp setsockopt support

On Mon, 6 Dec 2021 07:53:26 -0800 Jakub Kicinski wrote:
> On Sun,  5 Dec 2021 20:27:00 +0100 Florian Westphal wrote:
> > TCP_ULP setsockopt cannot be used for mptcp because its already
> > used internally to plumb subflow (tcp) sockets to the mptcp layer.
> > 
> > syzbot managed to trigger a crash for mptcp connections that are
> > in fallback mode:  
> 
> Fallback mode meaning ops are NULL? I'm slightly confused by this
> report.

Ah, it's the socket not the ops.

> > KASAN: null-ptr-deref in range [0x0000000000000020-0x0000000000000027]
> > CPU: 1 PID: 1083 Comm: syz-executor.3 Not tainted 5.16.0-rc2-syzkaller #0
> > RIP: 0010:tls_build_proto net/tls/tls_main.c:776 [inline]
> > [..]
> >  __tcp_set_ulp net/ipv4/tcp_ulp.c:139 [inline]
> >  tcp_set_ulp+0x428/0x4c0 net/ipv4/tcp_ulp.c:160
> >  do_tcp_setsockopt+0x455/0x37c0 net/ipv4/tcp.c:3391
> >  mptcp_setsockopt+0x1b47/0x2400 net/mptcp/sockopt.c:638
> > 
> > Remove support for TCP_ULP setsockopt.
> > 
> > Reported-by: syzbot+1fd9b69cde42967d1add@...kaller.appspotmail.com
> > Signed-off-by: Florian Westphal <fw@...len.de>