kernel/linux.git/include/uapi/linux/mptcp.h, branch v6.18.21

mptcp: pm: ignore unknown endpoint flags

2026-01-02T11:57:12+00:00

commit 0ace3297a7301911e52d8195cb1006414897c859 upstream. Before this patch, the kernel was saving any flags set by the userspace, even unknown ones. This doesn't cause critical issues because the kernel is only looking at specific ones. But on the other hand, endpoints dumps could tell the userspace some recent flags seem to be supported on older kernel versions. Instead, ignore all unknown flags when parsing them. By doing that, the userspace can continue to set unsupported flags, but it has a way to verify what is supported by the kernel. Note that it sounds better to continue accepting unsupported flags not to change the behaviour, but also that eases things on the userspace side by adding "optional" endpoint types only supported by newer kernel versions without having to deal with the different kernel versions. A note for the backports: there will be conflicts in mptcp.h on older versions not having the mentioned flags, the new line should still be added last, and the '5' needs to be adapted to have the same value as the last entry. Fixes: 01cacb00b35c ("mptcp: add netlink-based PM") Cc: stable@vger.kernel.org Reviewed-by: Mat Martineau Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20251205-net-mptcp-misc-fixes-6-19-rc1-v1-1-9e4781a6c1b8@kernel.org Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman

mptcp: pm: in-kernel: add laminar endpoints

2025-09-27T00:44:05+00:00

Currently, upon the reception of an ADD_ADDR (and when the fullmesh flag is not used), the in-kernel PM will create new subflows using the local address the routing configuration will pick. It would be easier to pick local addresses from a selected list of endpoints, and use it only once, than relying on routing rules. Use case: both the client (C) and the server (S) have two addresses (a and b). The client establishes the connection between C(a) and S(a). Once established, the server announces its additional address S(b). Once received, the client connects to it using its second address C(b). Compared to a situation without the 'laminar' endpoint for C(b), the client didn't use this address C(b) to establish a subflow to the server's primary address S(a). So at the end, we have: C S C(a) --- S(a) C(b) --- S(b) In case of a 3rd address on each side (C(c) and S(c)), upon the reception of an ADD_ADDR with S(c), the client should not pick C(b) because it has already been used. C(c) should then be used. Note that this situation is currently possible if C doesn't add any endpoint, but configure the routing in order to pick C(b) for the route to S(b), and pick C(c) for the route to S(c). That doesn't sound very practical because it means knowing in advance the IP addresses that will be used and announced by the server. 'laminar', like the idea of laminar flows: the different subflows don't mix with each other on an endpoint, unlike the "turbulent" way traffic is mixed by 'fullmesh'. In the code, the new endpoint type is added. Similar to the other subflow types, an MPTCP_INFO counter is added. While at it, hole are now commented in struct mptcp_info, to remember next time that these holes can no longer be used. Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/503 Reviewed-by: Mat Martineau Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20250925-net-next-mptcp-c-flag-laminar-v1-15-ad126cc47c6b@kernel.org Signed-off-by: Jakub Kicinski

mptcp: pm: in-kernel: rename 'local_addr_max' to 'endp_subflow_max'

2025-09-27T00:44:05+00:00

A few variables linked to the in-kernel Path-Manager are confusing, and it would help current and future developers, to clarify them. One of them is 'local_addr_max', which in fact represents the maximum number of 'subflow' endpoints that can be used to create new subflows, and not the number of local addresses that have been used to create subflows. While at it, add an additional name for the corresponding variable in MPTCP INFO: mptcpi_endp_subflow_max. Not to break the current uAPI, the new name is added as a 'define' pointing to the former name. This will then also help userspace devs. Also move the variable and function next to the other 'endp_X_max' ones. No functional changes intended. Reviewed-by: Geliang Tang Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20250925-net-next-mptcp-c-flag-laminar-v1-9-ad126cc47c6b@kernel.org Signed-off-by: Jakub Kicinski

mptcp: pm: in-kernel: rename 'add_addr_accept_max' to 'limit_add_addr_accepted'

2025-09-27T00:44:04+00:00

A few variables linked to the in-kernel Path-Manager are confusing, and it would help current and future developers, to clarify them. One of them is 'add_addr_accept_max', which in fact represents the limit of ADD_ADDR that can be accepted: the limit set via 'ip mptcp limit add_addr_accepted X' for example. It is not linked to the maximum number of accepted ADD_ADDR. While at it, add an additional name for the corresponding variable in MPTCP INFO: mptcpi_limit_add_addr_accepted. Not to break the current uAPI, the new name is added as a 'define' pointing to the former name. This will then also help userspace devs. No functional changes intended. Reviewed-by: Geliang Tang Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20250925-net-next-mptcp-c-flag-laminar-v1-8-ad126cc47c6b@kernel.org Signed-off-by: Jakub Kicinski

mptcp: pm: in-kernel: rename 'add_addr_signal_max' to 'endp_signal_max'

2025-09-27T00:44:04+00:00

A few variables linked to the in-kernel Path-Manager are confusing, and it would help current and future developers, to clarify them. One of them is 'add_addr_signal_max', which in fact represents the maximum number of 'signal' endpoints that can be used to announced addresses, and not the number of ADD_ADDR that can be signalled. While at it, add an additional name for the corresponding variable in MPTCP INFO: mptcpi_endp_signal_max. Not to break the current uAPI, the new name is added as a 'define' pointing to the former name. This will then also help userspace devs. No functional changes intended. Reviewed-by: Geliang Tang Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20250925-net-next-mptcp-c-flag-laminar-v1-7-ad126cc47c6b@kernel.org Signed-off-by: Jakub Kicinski

mptcp: pm: in-kernel: rename 'subflows_max' to 'limit_extra_subflows'

2025-09-27T00:44:04+00:00

A few variables linked to the in-kernel Path-Manager are confusing, and it would help current and future developers, to clarify them. One of them is 'subflows_max', which in fact represents the limit of extra subflows: the limit set via 'ip mptcp limit subflows X' for example. It is not linked to the maximum number of created / possible subflows. While at it, add an additional name for the corresponding variable in MPTCP INFO: mptcpi_limit_extra_subflows. Not to break the current uAPI, the new name is added as a 'define' pointing to the former name. This will then also help userspace devs. No functional changes intended. Reviewed-by: Geliang Tang Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20250925-net-next-mptcp-c-flag-laminar-v1-6-ad126cc47c6b@kernel.org Signed-off-by: Jakub Kicinski

mptcp: pm: rename 'subflows' to 'extra_subflows'

2025-09-27T00:44:04+00:00

A few variables linked to the Path-Managers are confusing, and it would help current and future developers, to clarify them. One of them is 'subflows', which in fact represents the number of extra subflows: all the additional subflows created after the initial one, and not the total number of subflows. While at it, add an additional name for the corresponding variable in MPTCP INFO: mptcpi_extra_subflows. Not to break the current uAPI, the new name is added as a 'define' pointing to the former name. This will then also help userspace devs. No functional changes intended. Reviewed-by: Geliang Tang Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20250925-net-next-mptcp-c-flag-laminar-v1-5-ad126cc47c6b@kernel.org Signed-off-by: Jakub Kicinski

mptcp: use _BITUL() instead of (1 << x)

2025-09-22T18:51:25+00:00

Simply to use the proper way to declare bits, and to align with all other flags declared in this file. No functional changes intended. Reviewed-by: Geliang Tang Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20250919-net-next-mptcp-server-side-flag-v1-5-a97a5d561a8b@kernel.org Signed-off-by: Jakub Kicinski

mptcp: pm: netlink: announce server-side flag

2025-09-22T18:51:24+00:00

Now that the 'flags' attribute is used, it seems interesting to add one flag for 'server-side', a boolean value. This is duplicating the info from the dedicated 'server-side' attribute, but it will be deprecated in the next commit, and removed in a few versions. Reviewed-by: Geliang Tang Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20250919-net-next-mptcp-server-side-flag-v1-2-a97a5d561a8b@kernel.org Signed-off-by: Jakub Kicinski

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

2025-09-16T01:12:05+00:00

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. The RFC8684 [1] is strict about that: (...) therefore the receiver MUST NOT try to open any additional subflows toward this address and port. So it is important to tell the userspace about that as it is responsible for the respect of this flag. When a new connection is created and established, the Netlink events now contain the existing but not currently used 'flags' attribute. When MPTCP_PM_EV_FLAG_DENY_JOIN_ID0 is set, it means no other subflows to the initial IP address and port -- info that are also part of the event -- can be established. Link: https://datatracker.ietf.org/doc/html/rfc8684#section-3.1-20.6 [1] Fixes: 702c2f646d42 ("mptcp: netlink: allow userspace-driven subflow establishment") Reported-by: Marek Majkowski Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/532 Reviewed-by: Mat Martineau Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20250912-net-mptcp-pm-uspace-deny_join_id0-v1-2-40171884ade8@kernel.org Signed-off-by: Jakub Kicinski