kernel/net/mptcp/protocol.h, branch linux-rolling-lts

mptcp: fix receive space timestamp initialization

2026-02-26T22:59:20Z

[ Upstream commit 70274765fef555af92a1532d5bd5450c691fca9d ] MPTCP initialize the receive buffer stamp in mptcp_rcv_space_init(), using the provided subflow stamp. Such helper is invoked in several places; for passive sockets, space init happened at clone time. In such scenario, MPTCP ends-up accesses the subflow stamp before its initialization, leading to quite randomic timing for the first receive buffer auto-tune event, as the timestamp for newly created subflow is not refreshed there. Fix the issue moving the stamp initialization out of the mentioned helper, at the data transfer start, and always using a fresh timestamp. Fixes: 013e3179dbd2 ("mptcp: fix rcv space initialization") Reviewed-by: Mat Martineau Signed-off-by: Paolo Abeni Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20260203-net-next-mptcp-misc-feat-6-20-v1-2-31ec8bfc56d1@kernel.org Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin

mptcp: ensure context reset on disconnect()

2026-01-11T14:26:19Z

[ Upstream commit 86730ac255b0497a272704de9a1df559f5d6602e ] After the blamed commit below, if the MPC subflow is already in TCP_CLOSE status or has fallback to TCP at mptcp_disconnect() time, mptcp_do_fastclose() skips setting the `send_fastclose flag` and the later __mptcp_close_ssk() does not reset anymore the related subflow context. Any later connection will be created with both the `request_mptcp` flag and the msk-level fallback status off (it is unconditionally cleared at MPTCP disconnect time), leading to a warning in subflow_data_ready(): WARNING: CPU: 26 PID: 8996 at net/mptcp/subflow.c:1519 subflow_data_ready (net/mptcp/subflow.c:1519 (discriminator 13)) Modules linked in: CPU: 26 UID: 0 PID: 8996 Comm: syz.22.39 Not tainted 6.18.0-rc7-05427-g11fc074f6c36 #1 PREEMPT(voluntary) Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 RIP: 0010:subflow_data_ready (net/mptcp/subflow.c:1519 (discriminator 13)) Code: 90 0f 0b 90 90 e9 04 fe ff ff e8 b7 1e f5 fe 89 ee bf 07 00 00 00 e8 db 19 f5 fe 83 fd 07 0f 84 35 ff ff ff e8 9d 1e f5 fe 90 <0f> 0b 90 e9 27 ff ff ff e8 8f 1e f5 fe 4c 89 e7 48 89 de e8 14 09 RSP: 0018:ffffc9002646fb30 EFLAGS: 00010293 RAX: 0000000000000000 RBX: ffff88813b218000 RCX: ffffffff825c8435 RDX: ffff8881300b3580 RSI: ffffffff825c8443 RDI: 0000000000000005 RBP: 000000000000000b R08: ffffffff825c8435 R09: 000000000000000b R10: 0000000000000005 R11: 0000000000000007 R12: ffff888131ac0000 R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 FS: 00007f88330af6c0(0000) GS:ffff888a93dd2000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f88330aefe8 CR3: 000000010ff59000 CR4: 0000000000350ef0 Call Trace: tcp_data_ready (net/ipv4/tcp_input.c:5356) tcp_data_queue (net/ipv4/tcp_input.c:5445) tcp_rcv_state_process (net/ipv4/tcp_input.c:7165) tcp_v4_do_rcv (net/ipv4/tcp_ipv4.c:1955) __release_sock (include/net/sock.h:1158 (discriminator 6) net/core/sock.c:3180 (discriminator 6)) release_sock (net/core/sock.c:3737) mptcp_sendmsg (net/mptcp/protocol.c:1763 net/mptcp/protocol.c:1857) inet_sendmsg (net/ipv4/af_inet.c:853 (discriminator 7)) __sys_sendto (net/socket.c:727 (discriminator 15) net/socket.c:742 (discriminator 15) net/socket.c:2244 (discriminator 15)) __x64_sys_sendto (net/socket.c:2247) do_syscall_64 (arch/x86/entry/syscall_64.c:63 (discriminator 1) arch/x86/entry/syscall_64.c:94 (discriminator 1)) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130) RIP: 0033:0x7f883326702d Address the issue setting an explicit `fastclosing` flag at fastclose time, and checking such flag after mptcp_do_fastclose(). Fixes: ae155060247b ("mptcp: fix duplicate reset on fastclose") Cc: stable@vger.kernel.org Signed-off-by: Paolo Abeni Reviewed-by: Matthieu Baerts (NGI0) Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20251212-net-mptcp-subflow_data_ready-warn-v1-2-d1f9fd1c36c8@kernel.org Signed-off-by: Paolo Abeni [ Adjust context ] Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

mptcp: fallback earlier on simult connection

2026-01-08T09:17:09Z

commit 71154bbe49423128c1c8577b6576de1ed6836830 upstream. Syzkaller reports a simult-connect race leading to inconsistent fallback status: WARNING: CPU: 3 PID: 33 at net/mptcp/subflow.c:1515 subflow_data_ready+0x40b/0x7c0 net/mptcp/subflow.c:1515 Modules linked in: CPU: 3 UID: 0 PID: 33 Comm: ksoftirqd/3 Not tainted syzkaller #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014 RIP: 0010:subflow_data_ready+0x40b/0x7c0 net/mptcp/subflow.c:1515 Code: 89 ee e8 78 61 3c f6 40 84 ed 75 21 e8 8e 66 3c f6 44 89 fe bf 07 00 00 00 e8 c1 61 3c f6 41 83 ff 07 74 09 e8 76 66 3c f6 90 <0f> 0b 90 e8 6d 66 3c f6 48 89 df e8 e5 ad ff ff 31 ff 89 c5 89 c6 RSP: 0018:ffffc900006cf338 EFLAGS: 00010246 RAX: 0000000000000000 RBX: ffff888031acd100 RCX: ffffffff8b7f2abf RDX: ffff88801e6ea440 RSI: ffffffff8b7f2aca RDI: 0000000000000005 RBP: 0000000000000000 R08: 0000000000000005 R09: 0000000000000007 R10: 0000000000000004 R11: 0000000000002c10 R12: ffff88802ba69900 R13: 1ffff920000d9e67 R14: ffff888046f81800 R15: 0000000000000004 FS: 0000000000000000(0000) GS:ffff8880d69bc000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000560fc0ca1670 CR3: 0000000032c3a000 CR4: 0000000000352ef0 Call Trace: tcp_data_queue+0x13b0/0x4f90 net/ipv4/tcp_input.c:5197 tcp_rcv_state_process+0xfdf/0x4ec0 net/ipv4/tcp_input.c:6922 tcp_v6_do_rcv+0x492/0x1740 net/ipv6/tcp_ipv6.c:1672 tcp_v6_rcv+0x2976/0x41e0 net/ipv6/tcp_ipv6.c:1918 ip6_protocol_deliver_rcu+0x188/0x1520 net/ipv6/ip6_input.c:438 ip6_input_finish+0x1e4/0x4b0 net/ipv6/ip6_input.c:489 NF_HOOK include/linux/netfilter.h:318 [inline] NF_HOOK include/linux/netfilter.h:312 [inline] ip6_input+0x105/0x2f0 net/ipv6/ip6_input.c:500 dst_input include/net/dst.h:471 [inline] ip6_rcv_finish net/ipv6/ip6_input.c:79 [inline] NF_HOOK include/linux/netfilter.h:318 [inline] NF_HOOK include/linux/netfilter.h:312 [inline] ipv6_rcv+0x264/0x650 net/ipv6/ip6_input.c:311 __netif_receive_skb_one_core+0x12d/0x1e0 net/core/dev.c:5979 __netif_receive_skb+0x1d/0x160 net/core/dev.c:6092 process_backlog+0x442/0x15e0 net/core/dev.c:6444 __napi_poll.constprop.0+0xba/0x550 net/core/dev.c:7494 napi_poll net/core/dev.c:7557 [inline] net_rx_action+0xa9f/0xfe0 net/core/dev.c:7684 handle_softirqs+0x216/0x8e0 kernel/softirq.c:579 run_ksoftirqd kernel/softirq.c:968 [inline] run_ksoftirqd+0x3a/0x60 kernel/softirq.c:960 smpboot_thread_fn+0x3f7/0xae0 kernel/smpboot.c:160 kthread+0x3c2/0x780 kernel/kthread.c:463 ret_from_fork+0x5d7/0x6f0 arch/x86/kernel/process.c:148 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 The TCP subflow can process the simult-connect syn-ack packet after transitioning to TCP_FIN1 state, bypassing the MPTCP fallback check, as the sk_state_change() callback is not invoked for * -> FIN_WAIT1 transitions. That will move the msk socket to an inconsistent status and the next incoming data will hit the reported splat. Close the race moving the simult-fallback check at the earliest possible stage - that is at syn-ack generation time. About the fixes tags: [2] was supposed to also fix this issue introduced by [3]. [1] is required as a dependence: it was not explicitly marked as a fix, but it is one and it has already been backported before [3]. In other words, this commit should be backported up to [3], including [2] and [1] if that's not already there. Fixes: 23e89e8ee7be ("tcp: Don't drop SYN+ACK for simultaneous connect().") [1] Fixes: 4fd19a307016 ("mptcp: fix inconsistent state on fastopen race") [2] Fixes: 1e777f39b4d7 ("mptcp: add MSG_FASTOPEN sendmsg flag support") [3] Cc: stable@vger.kernel.org Reported-by: syzbot+0ff6b771b4f7a5bce83b@syzkaller.appspotmail.com Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/586 Signed-off-by: Paolo Abeni Reviewed-by: Matthieu Baerts (NGI0) Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20251212-net-mptcp-subflow_data_ready-warn-v1-1-d1f9fd1c36c8@kernel.org Signed-off-by: Paolo Abeni Signed-off-by: Greg Kroah-Hartman

mptcp: decouple mptcp fastclose from tcp close

2025-11-20T04:07:15Z

With the current fastclose implementation, the mptcp_do_fastclose() helper is in charge of two distinct actions: send the fastclose reset and cleanup the subflows. Formally decouple the two steps, ensuring that mptcp explicitly closes all the subflows after the mentioned helper. This will make the upcoming fix simpler, and allows dropping the 2nd argument from mptcp_destroy_common(). The Fixes tag is then the same as in the next commit to help with the backports. Fixes: d21f83485518 ("mptcp: use fastclose on more edge scenarios") Cc: stable@vger.kernel.org Signed-off-by: Paolo Abeni Reviewed-by: Geliang Tang Reviewed-by: Matthieu Baerts (NGI0) Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20251118-net-mptcp-misc-fixes-6-18-rc6-v1-5-806d3781c95f@kernel.org Signed-off-by: Jakub Kicinski

mptcp: avoid unneeded subflow-level drops

2025-11-20T04:07:14Z

The rcv window is shared among all the subflows. Currently, MPTCP sync the TCP-level rcv window with the MPTCP one at tcp_transmit_skb() time. The above means that incoming data may sporadically observe outdated TCP-level rcv window and being wrongly dropped by TCP. Address the issue checking for the edge condition before queuing the data at TCP level, and eventually syncing the rcv window as needed. Note that the issue is actually present from the very first MPTCP implementation, but backports older than the blamed commit below will range from impossible to useless. Before: $ nstat -n; sleep 1; nstat -z TcpExtBeyondWindow TcpExtBeyondWindow 14 0.0 After: $ nstat -n; sleep 1; nstat -z TcpExtBeyondWindow TcpExtBeyondWindow 0 0.0 Fixes: fa3fe2b15031 ("mptcp: track window announced to peer") Cc: stable@vger.kernel.org Signed-off-by: Paolo Abeni Reviewed-by: Matthieu Baerts (NGI0) Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20251118-net-mptcp-misc-fixes-6-18-rc6-v1-2-806d3781c95f@kernel.org Signed-off-by: Jakub Kicinski

mptcp: drop bogus optimization in __mptcp_check_push()

2025-10-30T00:44:28Z

Accessing the transmit queue without owning the msk socket lock is inherently racy, hence __mptcp_check_push() could actually quit early even when there is pending data. That in turn could cause unexpected tx lock and timeout. Dropping the early check avoids the race, implicitly relaying on later tests under the relevant lock. With such change, all the other mptcp_send_head() call sites are now under the msk socket lock and we can additionally drop the now unneeded annotation on the transmit head pointer accesses. Fixes: 6e628cd3a8f7 ("mptcp: use mptcp release_cb for delayed tasks") Cc: stable@vger.kernel.org Signed-off-by: Paolo Abeni Reviewed-by: Geliang Tang Tested-by: Geliang Tang Reviewed-by: Mat Martineau Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20251028-net-mptcp-send-timeout-v1-1-38ffff5a9ec8@kernel.org Signed-off-by: Jakub Kicinski

mptcp: rcvbuf auto-tuning improvement

2025-09-30T01:23:35Z

Apply to the MPTCP auto-tuning the same improvements introduced for the TCP protocol by the merge commit 2da35e4b4df9 ("Merge branch 'tcp-receive-side-improvements'"). The main difference is that TCP subflow and the main MPTCP socket need to account separately for OoO: MPTCP does not care for TCP-level OoO and vice versa, as a consequence do not reflect MPTCP-level rcvbuf increase due to OoO packets at the subflow level. This refeactor additionally allow dropping the msk receive buffer update at receive time, as the latter only intended to cope with subflow receive buffer increase due to OoO packets. Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/487 Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/559 Reviewed-by: Geliang Tang Tested-by: Geliang Tang Signed-off-by: Paolo Abeni Reviewed-by: Matthieu Baerts (NGI0) Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20250927-net-next-mptcp-rcv-path-imp-v1-3-5da266aa9c1a@kernel.org Signed-off-by: Jakub Kicinski

mptcp: pm: in-kernel: add laminar endpoints

2025-09-27T00:44:05Z

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: reduce pernet struct size

2025-09-27T00:44:05Z

All the 'unsigned int' variables from the 'pm_nl_pernet' structure are bounded to MPTCP_PM_ADDR_MAX, currently set to 8. The endpoint ID is also bounded by the protocol to 8-bit. MPTCP_PM_ADDR_MAX, if extended later, will never over 8-bit. So no need to use 'unsigned int' variables, 'u8' is enough. Note that the exposed counters in MPTCP_INFO are already limited to 8-bit, same for pm->extra_subflows, and others. So it seems even better to limit them to 8-bit. Reviewed-by: Mat Martineau Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20250925-net-next-mptcp-c-flag-laminar-v1-13-ad126cc47c6b@kernel.org Signed-off-by: Jakub Kicinski

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

2025-09-27T00:44:05Z

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