mptcp: Close remaining subflows when falling back in mptcp_verif_dss_…

…csum

Since commit b079a18 ("mptcp: Remove cnt_subflows") subflows can
actually be in non-fully established and we will still send an MP_FAIL.

Thus, there can be multiple subflows and we need to make sure that the
other ones are getting closed in that case.

Otherwise, we will hit the case where we have a TCP-subflow hanging
around (potentially calling tcp_write_err()) when the meta is already
closed and we will get a warning like:
[  213.983095] ------------[ cut here ]------------
[  213.984532] Meta already closed i_rcv 0 i_snd 0 send_i 1 flags 0x2000301
[  213.986591] WARNING: CPU: 3 PID: 0 at /mnt/tmp/builder/builder_env/mptcp/net/mptcp/mptcp_ctrl.c:626 mptcp_sock_def_error_report+0xe0/0xf0
[...]

Fixes: b079a18 ("mptcp: Remove cnt_subflows")
Signed-off-by: Christoph Paasch <[email protected]>
Signed-off-by: Matthieu Baerts <[email protected]>

net/mptcp/mptcp_input.c

@@ -387,6 +387,8 @@ static int mptcp_verif_dss_csum(struct sock *sk)
 				kfree_skb(tmp);
 			}
 
+			mptcp_sub_force_close_all(tp->mpcb, sk);
+
 			ans = 0;
 		}
 	}