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

[Jakub Kicinski]

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.

> 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@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Florian Westphal <fw@xxxxxxxxx>