mptcp: do not inherit inet proto ops

We need to initialise the struct ourselves, else we expose tcp-specific
callbacks such as tcp_splice_read which will then trigger splat because
the socket is an mptcp one:

BUG: KASAN: slab-out-of-bounds in tcp_mstamp_refresh+0x80/0xa0 net/ipv4/tcp_output.c:57
Write of size 8 at addr ffff888116aa21d0 by task syz-executor.0/5478

CPU: 1 PID: 5478 Comm: syz-executor.0 Not tainted 5.5.0-rc6 #3
Call Trace:
 tcp_mstamp_refresh+0x80/0xa0 net/ipv4/tcp_output.c:57
 tcp_rcv_space_adjust+0x72/0x7f0 net/ipv4/tcp_input.c:612
 tcp_read_sock+0x622/0x990 net/ipv4/tcp.c:1674
 tcp_splice_read+0x20b/0xb40 net/ipv4/tcp.c:791
 do_splice+0x1259/0x1560 fs/splice.c:1205

To prevent build error with ipv6, add the recv/sendmsg function
declaration to ipv6.h.  The functions are already accessible "thanks"
to retpoline related work, but they are currently only made visible
by socket.c specific INDIRECT_CALLABLE macros.
Reported-by: Christoph Paasch <cpaasch@apple.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/ipv6.h

@@ -1113,6 +1113,9 @@ int inet6_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg);
 
 int inet6_hash_connect(struct inet_timewait_death_row *death_row,
 			      struct sock *sk);
+int inet6_sendmsg(struct socket *sock, struct msghdr *msg, size_t size);
+int inet6_recvmsg(struct socket *sock, struct msghdr *msg, size_t size,
+		  int flags);
 
 /*
  * reassembly.c

net/mptcp/protocol.c

@@ -1163,7 +1163,31 @@ static int mptcp_shutdown(struct socket *sock, int how)
 	return ret;
 }
 
-static struct proto_ops mptcp_stream_ops;
+static const struct proto_ops mptcp_stream_ops = {
+	.family		   = PF_INET,
+	.owner		   = THIS_MODULE,
+	.release	   = inet_release,
+	.bind		   = mptcp_bind,
+	.connect	   = mptcp_stream_connect,
+	.socketpair	   = sock_no_socketpair,
+	.accept		   = mptcp_stream_accept,
+	.getname	   = mptcp_v4_getname,
+	.poll		   = mptcp_poll,
+	.ioctl		   = inet_ioctl,
+	.gettstamp	   = sock_gettstamp,
+	.listen		   = mptcp_listen,
+	.shutdown	   = mptcp_shutdown,
+	.setsockopt	   = sock_common_setsockopt,
+	.getsockopt	   = sock_common_getsockopt,
+	.sendmsg	   = inet_sendmsg,
+	.recvmsg	   = inet_recvmsg,
+	.mmap		   = sock_no_mmap,
+	.sendpage	   = inet_sendpage,
+#ifdef CONFIG_COMPAT
+	.compat_setsockopt = compat_sock_common_setsockopt,
+	.compat_getsockopt = compat_sock_common_getsockopt,
+#endif
+};
 
 static struct inet_protosw mptcp_protosw = {
 	.type		= SOCK_STREAM,
@@ -1176,14 +1200,6 @@ static struct inet_protosw mptcp_protosw = {
 void mptcp_proto_init(void)
 {
 	mptcp_prot.h.hashinfo = tcp_prot.h.hashinfo;
-	mptcp_stream_ops = inet_stream_ops;
-	mptcp_stream_ops.bind = mptcp_bind;
-	mptcp_stream_ops.connect = mptcp_stream_connect;
-	mptcp_stream_ops.poll = mptcp_poll;
-	mptcp_stream_ops.accept = mptcp_stream_accept;
-	mptcp_stream_ops.getname = mptcp_v4_getname;
-	mptcp_stream_ops.listen = mptcp_listen;
-	mptcp_stream_ops.shutdown = mptcp_shutdown;
 
 	mptcp_subflow_init();
 
@@ -1194,7 +1210,32 @@ void mptcp_proto_init(void)
 }
 
 #if IS_ENABLED(CONFIG_MPTCP_IPV6)
-static struct proto_ops mptcp_v6_stream_ops;
+static const struct proto_ops mptcp_v6_stream_ops = {
+	.family		   = PF_INET6,
+	.owner		   = THIS_MODULE,
+	.release	   = inet6_release,
+	.bind		   = mptcp_bind,
+	.connect	   = mptcp_stream_connect,
+	.socketpair	   = sock_no_socketpair,
+	.accept		   = mptcp_stream_accept,
+	.getname	   = mptcp_v6_getname,
+	.poll		   = mptcp_poll,
+	.ioctl		   = inet6_ioctl,
+	.gettstamp	   = sock_gettstamp,
+	.listen		   = mptcp_listen,
+	.shutdown	   = mptcp_shutdown,
+	.setsockopt	   = sock_common_setsockopt,
+	.getsockopt	   = sock_common_getsockopt,
+	.sendmsg	   = inet6_sendmsg,
+	.recvmsg	   = inet6_recvmsg,
+	.mmap		   = sock_no_mmap,
+	.sendpage	   = inet_sendpage,
+#ifdef CONFIG_COMPAT
+	.compat_setsockopt = compat_sock_common_setsockopt,
+	.compat_getsockopt = compat_sock_common_getsockopt,
+#endif
+};
+
 static struct proto mptcp_v6_prot;
 
 static void mptcp_v6_destroy(struct sock *sk)
@@ -1226,15 +1267,6 @@ int mptcp_proto_v6_init(void)
 	if (err)
 		return err;
 
-	mptcp_v6_stream_ops = inet6_stream_ops;
-	mptcp_v6_stream_ops.bind = mptcp_bind;
-	mptcp_v6_stream_ops.connect = mptcp_stream_connect;
-	mptcp_v6_stream_ops.poll = mptcp_poll;
-	mptcp_v6_stream_ops.accept = mptcp_stream_accept;
-	mptcp_v6_stream_ops.getname = mptcp_v6_getname;
-	mptcp_v6_stream_ops.listen = mptcp_listen;
-	mptcp_v6_stream_ops.shutdown = mptcp_shutdown;
-
 	err = inet6_register_protosw(&mptcp_v6_protosw);
 	if (err)
 		proto_unregister(&mptcp_v6_prot);