Merge branch 'mptcp-fix-endpoints-with-signal-and-subflow-flags'

Matthieu Baerts says:

====================
mptcp: fix endpoints with 'signal' and 'subflow' flags

When looking at improving the user experience around the MPTCP endpoints
setup, I noticed that setting an endpoint with both the 'signal' and the
'subflow' flags -- as it has been done in the past by users according to
bug reports we got -- was resulting on only announcing the endpoint, but
not using it to create subflows: the 'subflow' flag was then ignored.

My initial thought was to modify IPRoute2 to warn the user when the two
flags were set, but it doesn't sound normal to ignore one of them. I
then looked at modifying the kernel not to allow having the two flags
set, but when discussing about that with Mat, we thought it was maybe
not ideal to do that, as there might be use-cases, we might break some
configs. Then I saw it was working before v5.17. So instead, I fixed the
support on the kernel side (patch 5) using Paolo's suggestion. This also
includes a fix on the options side (patch 1: for v5.11+), an explicit
deny of some options combinations (patch 2: for v5.18+), and some
refactoring (patches 3 and 4) to ease the inclusion of the patch 5.

While at it, I added a new selftest (patch 7) to validate this case --
including a modification of the chk_add_nr helper to inverse the sides
were the counters are checked (patch 6) -- and allowed ADD_ADDR echo
just after the MP_JOIN 3WHS.

The selftests modification have the same Fixes tag as the previous
commit, but no 'Cc: Stable': if the backport can work, that's good --
but it still need to be verified by running the selftests -- if not, no
need to worry, many CIs will use the selftests from the last stable
version to validate previous stable releases.
====================

Link: https://patch.msgid.link/20240731-u[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

net/mptcp/options.c

···
 
 	if (subflow->remote_key_valid &&
 	    (((mp_opt->suboptions & OPTION_MPTCP_DSS) && mp_opt->use_ack) ||
-	     ((mp_opt->suboptions & OPTION_MPTCP_ADD_ADDR) && !mp_opt->echo))) {
+	     ((mp_opt->suboptions & OPTION_MPTCP_ADD_ADDR) &&
+	      (!mp_opt->echo || subflow->mp_join)))) {
 		/* subflows are fully established as soon as we get any
 		 * additional ack, including ADD_ADDR.
 		 */

net/mptcp/pm_netlink.c

···
 	add_entry = mptcp_lookup_anno_list_by_saddr(msk, addr);
 
 	if (add_entry) {
-		if (mptcp_pm_is_kernel(msk))
+		if (WARN_ON_ONCE(mptcp_pm_is_kernel(msk)))
 			return false;
 
 		sk_reset_timer(sk, &add_entry->add_timer,
···
 
 static void mptcp_pm_create_subflow_or_signal_addr(struct mptcp_sock *msk)
 {
+	struct mptcp_pm_addr_entry *local, *signal_and_subflow = NULL;
 	struct sock *sk = (struct sock *)msk;
-	struct mptcp_pm_addr_entry *local;
 	unsigned int add_addr_signal_max;
 	unsigned int local_addr_max;
 	struct pm_nl_pernet *pernet;
···
 
 	/* check first for announce */
 	if (msk->pm.add_addr_signaled < add_addr_signal_max) {
-		local = select_signal_address(pernet, msk);
-
 		/* due to racing events on both ends we can reach here while
 		 * previous add address is still running: if we invoke now
 		 * mptcp_pm_announce_addr(), that will fail and the
···
 		if (msk->pm.addr_signal & BIT(MPTCP_ADD_ADDR_SIGNAL))
 			return;
 
-		if (local) {
-			if (mptcp_pm_alloc_anno_list(msk, &local->addr)) {
-				__clear_bit(local->addr.id, msk->pm.id_avail_bitmap);
-				msk->pm.add_addr_signaled++;
-				mptcp_pm_announce_addr(msk, &local->addr, false);
-				mptcp_pm_nl_addr_send_ack(msk);
-			}
-		}
+		local = select_signal_address(pernet, msk);
+		if (!local)
+			goto subflow;
+
+		/* If the alloc fails, we are on memory pressure, not worth
+		 * continuing, and trying to create subflows.
+		 */
+		if (!mptcp_pm_alloc_anno_list(msk, &local->addr))
+			return;
+
+		__clear_bit(local->addr.id, msk->pm.id_avail_bitmap);
+		msk->pm.add_addr_signaled++;
+		mptcp_pm_announce_addr(msk, &local->addr, false);
+		mptcp_pm_nl_addr_send_ack(msk);
+
+		if (local->flags & MPTCP_PM_ADDR_FLAG_SUBFLOW)
+			signal_and_subflow = local;
 	}
 
+subflow:
 	/* check if should create a new subflow */
 	while (msk->pm.local_addr_used < local_addr_max &&
 	       msk->pm.subflows < subflows_max) {
···
 		bool fullmesh;
 		int i, nr;
 
-		local = select_local_address(pernet, msk);
-		if (!local)
-			break;
+		if (signal_and_subflow) {
+			local = signal_and_subflow;
+			signal_and_subflow = NULL;
+		} else {
+			local = select_local_address(pernet, msk);
+			if (!local)
+				break;
+		}
 
 		fullmesh = !!(local->flags & MPTCP_PM_ADDR_FLAG_FULLMESH);
 
···
 	if (ret < 0)
 		return ret;
 
-	if (addr.addr.port && !(addr.flags & MPTCP_PM_ADDR_FLAG_SIGNAL)) {
-		GENL_SET_ERR_MSG(info, "flags must have signal when using port");
+	if (addr.addr.port && !address_use_port(&addr)) {
+		GENL_SET_ERR_MSG(info, "flags must have signal and not subflow when using port");
 		return -EINVAL;
 	}
 

tools/testing/selftests/net/mptcp/mptcp_join.sh

···
 	local add_nr=$1
 	local echo_nr=$2
 	local port_nr=${3:-0}
-	local syn_nr=${4:-$port_nr}
-	local syn_ack_nr=${5:-$port_nr}
-	local ack_nr=${6:-$port_nr}
-	local mis_syn_nr=${7:-0}
-	local mis_ack_nr=${8:-0}
+	local ns_invert=${4:-""}
+	local syn_nr=$port_nr
+	local syn_ack_nr=$port_nr
+	local ack_nr=$port_nr
+	local mis_syn_nr=0
+	local mis_ack_nr=0
+	local ns_tx=$ns1
+	local ns_rx=$ns2
+	local extra_msg=""
 	local count
 	local timeout
 
-	timeout=$(ip netns exec $ns1 sysctl -n net.mptcp.add_addr_timeout)
+	if [[ $ns_invert = "invert" ]]; then
+		ns_tx=$ns2
+		ns_rx=$ns1
+		extra_msg="invert"
+	fi
+
+	timeout=$(ip netns exec ${ns_tx} sysctl -n net.mptcp.add_addr_timeout)
 
 	print_check "add"
-	count=$(mptcp_lib_get_counter ${ns2} "MPTcpExtAddAddr")
+	count=$(mptcp_lib_get_counter ${ns_rx} "MPTcpExtAddAddr")
 	if [ -z "$count" ]; then
 		print_skip
 	# if the test configured a short timeout tolerate greater then expected
···
 	fi
 
 	print_check "echo"
-	count=$(mptcp_lib_get_counter ${ns1} "MPTcpExtEchoAdd")
+	count=$(mptcp_lib_get_counter ${ns_tx} "MPTcpExtEchoAdd")
 	if [ -z "$count" ]; then
 		print_skip
 	elif [ "$count" != "$echo_nr" ]; then
···
 
 	if [ $port_nr -gt 0 ]; then
 		print_check "pt"
-		count=$(mptcp_lib_get_counter ${ns2} "MPTcpExtPortAdd")
+		count=$(mptcp_lib_get_counter ${ns_rx} "MPTcpExtPortAdd")
 		if [ -z "$count" ]; then
 			print_skip
 		elif [ "$count" != "$port_nr" ]; then
···
 		fi
 
 		print_check "syn"
-		count=$(mptcp_lib_get_counter ${ns1} "MPTcpExtMPJoinPortSynRx")
+		count=$(mptcp_lib_get_counter ${ns_tx} "MPTcpExtMPJoinPortSynRx")
 		if [ -z "$count" ]; then
 			print_skip
 		elif [ "$count" != "$syn_nr" ]; then
···
 		fi
 
 		print_check "synack"
-		count=$(mptcp_lib_get_counter ${ns2} "MPTcpExtMPJoinPortSynAckRx")
+		count=$(mptcp_lib_get_counter ${ns_rx} "MPTcpExtMPJoinPortSynAckRx")
 		if [ -z "$count" ]; then
 			print_skip
 		elif [ "$count" != "$syn_ack_nr" ]; then
···
 		fi
 
 		print_check "ack"
-		count=$(mptcp_lib_get_counter ${ns1} "MPTcpExtMPJoinPortAckRx")
+		count=$(mptcp_lib_get_counter ${ns_tx} "MPTcpExtMPJoinPortAckRx")
 		if [ -z "$count" ]; then
 			print_skip
 		elif [ "$count" != "$ack_nr" ]; then
···
 		fi
 
 		print_check "syn"
-		count=$(mptcp_lib_get_counter ${ns1} "MPTcpExtMismatchPortSynRx")
+		count=$(mptcp_lib_get_counter ${ns_tx} "MPTcpExtMismatchPortSynRx")
 		if [ -z "$count" ]; then
 			print_skip
 		elif [ "$count" != "$mis_syn_nr" ]; then
···
 		fi
 
 		print_check "ack"
-		count=$(mptcp_lib_get_counter ${ns1} "MPTcpExtMismatchPortAckRx")
+		count=$(mptcp_lib_get_counter ${ns_tx} "MPTcpExtMismatchPortAckRx")
 		if [ -z "$count" ]; then
 			print_skip
 		elif [ "$count" != "$mis_ack_nr" ]; then
···
 			print_ok
 		fi
 	fi
+
+	print_info "$extra_msg"
 }
 
 chk_add_tx_nr()
···
 		run_tests $ns1 $ns2 10.0.1.1
 		chk_join_nr 2 2 2
 		chk_add_nr 1 1
+	fi
+
+	# uncommon: subflow and signal flags on the same endpoint
+	# or because the user wrongly picked both, but still expects the client
+	# to create additional subflows
+	if reset "subflow and signal together"; then
+		pm_nl_set_limits $ns1 0 2
+		pm_nl_set_limits $ns2 0 2
+		pm_nl_add_endpoint $ns2 10.0.3.2 flags signal,subflow
+		run_tests $ns1 $ns2 10.0.1.1
+		chk_join_nr 1 1 1
+		chk_add_nr 1 1 0 invert  # only initiated by ns2
+		chk_add_nr 0 0 0         # none initiated by ns1
+		chk_rst_nr 0 0 invert    # no RST sent by the client
+		chk_rst_nr 0 0           # no RST sent by the server
 	fi
 
 	# accept and use add_addr with additional subflows