[PATCH net 0/7] mptcp: fix endpoints with 'signal' and 'subflow' flags

[PATCH net 0/7] mptcp: fix endpoints with 'signal' and 'subflow' flags

[Matthieu Baerts (NGI0)]

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.

Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
Matthieu Baerts (NGI0) (7):
      mptcp: fully established after ADD_ADDR echo on MPJ
      mptcp: pm: deny endp with signal + subflow + port
      mptcp: pm: reduce indentation blocks
      mptcp: pm: don't try to create sf if alloc failed
      mptcp: pm: do not ignore 'subflow' if 'signal' flag is also set
      selftests: mptcp: join: ability to invert ADD_ADDR check
      selftests: mptcp: join: test both signal & subflow

 net/mptcp/options.c                             |  3 +-
 net/mptcp/pm_netlink.c                          | 47 +++++++++++++--------
 tools/testing/selftests/net/mptcp/mptcp_join.sh | 55 ++++++++++++++++++-------
 3 files changed, 73 insertions(+), 32 deletions(-)
---
base-commit: 0bf50cead4c4710d9f704778c32ab8af47ddf070
change-id: 20240731-upstream-net-20240731-mptcp-endp-subflow-signal-181d640cf5e8

Best regards,
-- 
Matthieu Baerts (NGI0) <matttbe@kernel.org>

[PATCH net 1/7] mptcp: fully established after ADD_ADDR echo on MPJ

[Matthieu Baerts (NGI0)]

Before this patch, receiving an ADD_ADDR echo on the just connected
MP_JOIN subflow -- initiator side, after the MP_JOIN 3WHS -- was
resulting in an MP_RESET. That's because only ACKs with a DSS or
ADD_ADDRs without the echo bit were allowed.

Not allowing the ADD_ADDR echo after an MP_CAPABLE 3WHS makes sense, as
we are not supposed to send an ADD_ADDR before because it requires to be
in full established mode first. For the MP_JOIN 3WHS, that's different:
the ADD_ADDR can be sent on a previous subflow, and the ADD_ADDR echo
can be received on the recently created one. The other peer will already
be in fully established, so it is allowed to send that.

We can then relax the conditions here to accept the ADD_ADDR echo for
MPJ subflows.

Fixes: 67b12f792d5e ("mptcp: full fully established support after ADD_ADDR")
Cc: stable@vger.kernel.org
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/options.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index 8a68382a4fe9..ac2f1a54cc43 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -958,7 +958,8 @@ static bool check_fully_established(struct mptcp_sock *msk, struct sock *ssk,
 
 	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.
 		 */

-- 
2.45.2

[PATCH net 2/7] mptcp: pm: deny endp with signal + subflow + port

[Matthieu Baerts (NGI0)]

As mentioned in the 'Fixes' commit, the port flag is only supported by
the 'signal' flag, and not by the 'subflow' one. Then if both the
'signal' and 'subflow' flags are set, the problem is the same: the
feature cannot work with the 'subflow' flag.

Technically, if both the 'signal' and 'subflow' flags are set, it will
be possible to create the listening socket, but not to establish a
subflow using this source port. So better to explicitly deny it, not to
create some confusions because the expected behaviour is not possible.

Fixes: 09f12c3ab7a5 ("mptcp: allow to use port and non-signal in set_flags")
Cc: stable@vger.kernel.org
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/pm_netlink.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index 37954a0b087d..c921d07e5940 100644
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -1328,8 +1328,8 @@ int mptcp_pm_nl_add_addr_doit(struct sk_buff *skb, struct genl_info *info)
 	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;
 	}
 

-- 
2.45.2

[PATCH net 3/7] mptcp: pm: reduce indentation blocks

[Matthieu Baerts (NGI0)]

That will simplify the following commits.

No functional changes intended.

Suggested-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/pm_netlink.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index c921d07e5940..780f4cca165c 100644
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -567,16 +567,19 @@ static void mptcp_pm_create_subflow_or_signal_addr(struct mptcp_sock *msk)
 		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);
-			}
-		}
+		if (!local)
+			goto subflow;
+
+		if (!mptcp_pm_alloc_anno_list(msk, &local->addr))
+			goto subflow;
+
+		__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);
 	}
 
+subflow:
 	/* check if should create a new subflow */
 	while (msk->pm.local_addr_used < local_addr_max &&
 	       msk->pm.subflows < subflows_max) {

-- 
2.45.2

[PATCH net 4/7] mptcp: pm: don't try to create sf if alloc failed

[Matthieu Baerts (NGI0)]

It sounds better to avoid wasting cycles and / or put extreme memory
pressure on the system by trying to create new subflows if it was not
possible to add a new item in the announce list.

While at it, a warning is now printed if the entry was already in the
list as it should not happen with the in-kernel path-manager. With this
PM, mptcp_pm_alloc_anno_list() should only fail in case of memory
pressure.

Fixes: b6c08380860b ("mptcp: remove addr and subflow in PM netlink")
Cc: stable@vger.kernel.org
Suggested-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/pm_netlink.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index 780f4cca165c..2be7af377cda 100644
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -348,7 +348,7 @@ bool mptcp_pm_alloc_anno_list(struct mptcp_sock *msk,
 	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,
@@ -555,8 +555,6 @@ static void mptcp_pm_create_subflow_or_signal_addr(struct mptcp_sock *msk)
 
 	/* 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
@@ -567,11 +565,15 @@ static void mptcp_pm_create_subflow_or_signal_addr(struct mptcp_sock *msk)
 		if (msk->pm.addr_signal & BIT(MPTCP_ADD_ADDR_SIGNAL))
 			return;
 
+		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))
-			goto subflow;
+			return;
 
 		__clear_bit(local->addr.id, msk->pm.id_avail_bitmap);
 		msk->pm.add_addr_signaled++;

-- 
2.45.2

[PATCH net 5/7] mptcp: pm: do not ignore 'subflow' if 'signal' flag is also set

[Matthieu Baerts (NGI0)]

Up to the 'Fixes' commit, having an endpoint with both the 'signal' and
'subflow' flags, resulted in the creation of a subflow and an address
announcement using the address linked to this endpoint. After this
commit, only the address announcement was done, ignoring the 'subflow'
flag.

That's because the same bitmap is used for the two flags. It is OK to
keep this single bitmap, the already selected local endpoint simply have
to be re-used, but not via select_local_address() not to look at the
just modified bitmap.

Note that it is unusual to set the two flags together: creating a new
subflow using a new local address will implicitly advertise it to the
other peer. So in theory, no need to advertise it explicitly as well.
Maybe there are use-cases -- the subflow might not reach the other peer
that way, we can ask the other peer to try initiating the new subflow
without delay -- or very likely the user is confused, and put both flags
"just to be sure at least the right one is set". Still, if it is
allowed, the kernel should do what has been asked: using this endpoint
to announce the address and to create a new subflow from it.

An alternative is to forbid the use of the two flags together, but
that's probably too late, there are maybe use-cases, and it was working
before. This patch will avoid people complaining subflows are not
created using the endpoint they added with the 'subflow' and 'signal'
flag.

Note that with the current patch, the subflow might not be created in
some corner cases, e.g. if the 'subflows' limit was reached when sending
the ADD_ADDR, but changed later on. It is probably not worth splitting
id_avail_bitmap per target ('signal', 'subflow'), which will add another
large field to the msk "just" to track (again) endpoints. Anyway,
currently when the limits are changed, the kernel doesn't check if new
subflows can be created or removed, because we would need to keep track
of the received ADD_ADDR, and more. It sounds OK to assume that the
limits should be properly configured before establishing new
connections.

Fixes: 86e39e04482b ("mptcp: keep track of local endpoint still available for each msk")
Cc: stable@vger.kernel.org
Suggested-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/pm_netlink.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index 2be7af377cda..4cae2aa7be5c 100644
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -512,8 +512,8 @@ __lookup_addr(struct pm_nl_pernet *pernet, const struct mptcp_addr_info *info)
 
 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;
@@ -579,6 +579,9 @@ static void mptcp_pm_create_subflow_or_signal_addr(struct mptcp_sock *msk)
 		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:
@@ -589,9 +592,14 @@ static void mptcp_pm_create_subflow_or_signal_addr(struct mptcp_sock *msk)
 		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);
 

-- 
2.45.2

[PATCH net 6/7] selftests: mptcp: join: ability to invert ADD_ADDR check

[Matthieu Baerts (NGI0)]

In the following commit, the client will initiate the ADD_ADDR, instead
of the server. We need to way to verify the ADD_ADDR have been correctly
sent.

Note: the default expected counters for when the port number is given
are never changed by the caller, no need to accept them as parameter
then.

The 'Fixes' tag here below is the same as the one from the previous
commit: this patch here is not fixing anything wrong in the selftests,
but it validates the previous fix for an issue introduced by this commit
ID.

Fixes: 86e39e04482b ("mptcp: keep track of local endpoint still available for each msk")
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 tools/testing/selftests/net/mptcp/mptcp_join.sh | 40 ++++++++++++++++---------
 1 file changed, 26 insertions(+), 14 deletions(-)

diff --git a/tools/testing/selftests/net/mptcp/mptcp_join.sh b/tools/testing/selftests/net/mptcp/mptcp_join.sh
index 4df48f1f14ab..52a25ac43d10 100755
--- a/tools/testing/selftests/net/mptcp/mptcp_join.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_join.sh
@@ -1415,18 +1415,28 @@ chk_add_nr()
 	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
@@ -1438,7 +1448,7 @@ chk_add_nr()
 	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
@@ -1449,7 +1459,7 @@ chk_add_nr()
 
 	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
@@ -1459,7 +1469,7 @@ chk_add_nr()
 		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
@@ -1470,7 +1480,7 @@ chk_add_nr()
 		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
@@ -1481,7 +1491,7 @@ chk_add_nr()
 		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
@@ -1492,7 +1502,7 @@ chk_add_nr()
 		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
@@ -1503,7 +1513,7 @@ chk_add_nr()
 		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
@@ -1513,6 +1523,8 @@ chk_add_nr()
 			print_ok
 		fi
 	fi
+
+	print_info "$extra_msg"
 }
 
 chk_add_tx_nr()

-- 
2.45.2

[PATCH net 7/7] selftests: mptcp: join: test both signal & subflow

[Matthieu Baerts (NGI0)]

It should be quite uncommon to set both the subflow and the signal
flags: the initiator of the connection is typically the one creating new
subflows, not the other peer, then no need to announce additional local
addresses, and use it to create subflows.

But some people might be confused about the flags, and set both "just to
be sure at least the right one is set". To verify the previous fix, and
avoid future regressions, this specific case is now validated: the
client announces a new address, and initiates a new subflow from the
same address.

While working on this, another bug has been noticed, where the client
reset the new subflow because an ADD_ADDR echo got received as the 3rd
ACK: this new test also explicitly checks that no RST have been sent by
the client and server.

The 'Fixes' tag here below is the same as the one from the previous
commit: this patch here is not fixing anything wrong in the selftests,
but it validates the previous fix for an issue introduced by this commit
ID.

Fixes: 86e39e04482b ("mptcp: keep track of local endpoint still available for each msk")
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 tools/testing/selftests/net/mptcp/mptcp_join.sh | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/tools/testing/selftests/net/mptcp/mptcp_join.sh b/tools/testing/selftests/net/mptcp/mptcp_join.sh
index 52a25ac43d10..9ea6d698e9d3 100755
--- a/tools/testing/selftests/net/mptcp/mptcp_join.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_join.sh
@@ -1989,6 +1989,21 @@ signal_address_tests()
 		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
 	if reset "multiple subflows and signal"; then
 		pm_nl_set_limits $ns1 0 3

-- 
2.45.2

Re: [PATCH net 0/7] mptcp: fix endpoints with 'signal' and 'subflow' flags

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Wed, 31 Jul 2024 13:05:52 +0200 you wrote:
> 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.
> 
> [...]

Here is the summary with links:
  - [net,1/7] mptcp: fully established after ADD_ADDR echo on MPJ
    https://git.kernel.org/netdev/net/c/d67c5649c154
  - [net,2/7] mptcp: pm: deny endp with signal + subflow + port
    https://git.kernel.org/netdev/net/c/8af1f11865f2
  - [net,3/7] mptcp: pm: reduce indentation blocks
    https://git.kernel.org/netdev/net/c/c95eb32ced82
  - [net,4/7] mptcp: pm: don't try to create sf if alloc failed
    https://git.kernel.org/netdev/net/c/cd7c957f936f
  - [net,5/7] mptcp: pm: do not ignore 'subflow' if 'signal' flag is also set
    https://git.kernel.org/netdev/net/c/85df533a787b
  - [net,6/7] selftests: mptcp: join: ability to invert ADD_ADDR check
    https://git.kernel.org/netdev/net/c/bec1f3b119eb
  - [net,7/7] selftests: mptcp: join: test both signal & subflow
    https://git.kernel.org/netdev/net/c/4d2868b5d191

You are awesome, thank you!
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