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

[Mat Martineau <mathew.j.martineau@linux.intel.com>]

On Mon, 6 Dec 2021, Matthieu Baerts wrote:

> Hi Florian,
>
> (without netdev and syzbot ML)
>
> On 05/12/2021 20:27, 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:
>>
>> 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.
>
> Good catch!
> Indeed, it doesn't make sense to support TCP_ULP.
>
>> Reported-by: syzbot+1fd9b69cde42967d1add@syzkaller.appspotmail.com
>> Signed-off-by: Florian Westphal <fw@strlen.de>
>
> I guess we need a Fixes tag here:
>
> Fixes: d9e4c1291810 ("mptcp: only admit explicitly supported sockopt")
>

Thanks Florian.

Matthieu, could you apply this to the export branch with your suggested 
Fixes tag?

Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>

--
Mat Martineau
Intel