Merge branch 'mptcp-pm-nl-announce-deny-join-id0-flag'

Matthieu Baerts says:

====================
mptcp: pm: nl: announce deny-join-id0 flag

During the connection establishment, a peer can tell the other one that
it cannot establish new subflows to the initial IP address and port by
setting the 'C' flag [1]. Doing so makes sense when the sender is behind
a strict NAT, operating behind a legacy Layer 4 load balancer, or using
anycast IP address for example.

When this 'C' flag is set, the path-managers must then not try to
establish new subflows to the other peer's initial IP address and port.
The in-kernel PM has access to this info, but the userspace PM didn't,
not letting the userspace daemon able to respect the RFC8684.

Here are a few fixes related to this 'C' flag (aka 'deny-join-id0'):

- Patch 1: add remote_deny_join_id0 info on passive connections. A fix
  for v5.14.

- Patch 2: let the userspace PM daemon know about the deny_join_id0
  attribute, so when set, it can avoid creating new subflows to the
  initial IP address and port. A fix for v5.19.

- Patch 3: a validation for the previous commit.

- Patch 4: record the deny_join_id0 info when TFO is used. A fix for
  v6.2.

- Patch 5: not related to deny-join-id0, but it fixes errors messages in
  the sockopt selftests, not to create confusions. A fix for v6.5.
====================

Link: https://patch.msgid.link/20250912-net-mptcp-pm-uspace-deny_join_id0-v1-0-40171884ade8@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

2 files changed, 4 insertions, 2 deletions

diff --git a/include/uapi/linux/mptcp.h b/include/uapi/linux/mptcp.h
index 67d015df8893..5fd5b4cf75ca 100644
--- a/include/uapi/linux/mptcp.h
+++ b/include/uapi/linux/mptcp.h
@@ -31,6 +31,8 @@
 #define MPTCP_INFO_FLAG_FALLBACK		_BITUL(0)
 #define MPTCP_INFO_FLAG_REMOTE_KEY_RECEIVED	_BITUL(1)
 
+#define MPTCP_PM_EV_FLAG_DENY_JOIN_ID0		_BITUL(0)
+
 #define MPTCP_PM_ADDR_FLAG_SIGNAL                      (1 << 0)
 #define MPTCP_PM_ADDR_FLAG_SUBFLOW                     (1 << 1)
 #define MPTCP_PM_ADDR_FLAG_BACKUP                      (1 << 2)
diff --git a/include/uapi/linux/mptcp_pm.h b/include/uapi/linux/mptcp_pm.h
index 6ac84b2f636c..7359d34da446 100644
--- a/include/uapi/linux/mptcp_pm.h
+++ b/include/uapi/linux/mptcp_pm.h
@@ -16,10 +16,10 @@
  *   good time to allocate memory and send ADD_ADDR if needed. Depending on the
  *   traffic-patterns it can take a long time until the MPTCP_EVENT_ESTABLISHED
  *   is sent. Attributes: token, family, saddr4 | saddr6, daddr4 | daddr6,
- *   sport, dport, server-side.
+ *   sport, dport, server-side, [flags].
  * @MPTCP_EVENT_ESTABLISHED: A MPTCP connection is established (can start new
  *   subflows). Attributes: token, family, saddr4 | saddr6, daddr4 | daddr6,
- *   sport, dport, server-side.
+ *   sport, dport, server-side, [flags].
  * @MPTCP_EVENT_CLOSED: A MPTCP connection has stopped. Attribute: token.
  * @MPTCP_EVENT_ANNOUNCED: A new address has been announced by the peer.
  *   Attributes: token, rem_id, family, daddr4 | daddr6 [, dport].