kernel/linux.git/net/mptcp/protocol.c, branch v6.12.93

mptcp: do not drop partial packets

2026-06-09T10:26:04+00:00

[ Upstream commit 50c2d91c5dfa0e465826ec1f8dbad9cdc254bd85 ] When a packet arrives with map_seq < ack_seq < end_seq, the beginning of the packet has already been acknowledged but the end contains new data. Currently the entire packet is dropped as "old data," forcing the sender to retransmit. Instead, skip the already-acked bytes by adjusting the skb offset and enqueue only the new portion. Update bytes_received and ack_seq to reflect the new data consumed. A previous attempt at this fix has been sent by Paolo Abeni [1], but had issues [2]: it also added a zero-window check and changed rcv_wnd_sent initialization, which caused test regressions. This version addresses only the partial packet handling without modifying receive window accounting. Fixes: ab174ad8ef76 ("mptcp: move ooo skbs into msk out of order queue.") Cc: stable@vger.kernel.org Link: https://lore.kernel.org/c9b426a4e163aa3c4fe8b80c79f1a610f47ae7d8.1763075056.git.pabeni@redhat.com [1] Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/600 [2] Signed-off-by: Shardul Bankar [pabeni@redhat.com: update map] Signed-off-by: Paolo Abeni Reviewed-by: Matthieu Baerts (NGI0) Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20260515-net-mptcp-misc-fixes-7-1-rc4-v2-1-701e96419f2f@kernel.org Signed-off-by: Paolo Abeni Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

mptcp: handle first subflow closing consistently

2026-06-09T10:26:03+00:00

[ Upstream commit 0eeb372deebce6c25b9afc09e35d6c75a744299a ] Currently, as soon as the PM closes a subflow, the msk stops accepting data from it, even if the TCP socket could be still formally open in the incoming direction, with the notable exception of the first subflow. The root cause of such behavior is that code currently piggy back two separate semantic on the subflow->disposable bit: the subflow context must be released and that the subflow must stop accepting incoming data. The first subflow is never disposed, so it also never stop accepting incoming data. Use a separate bit to mark the latter status and set such bit in __mptcp_close_ssk() for all subflows. Beyond making per subflow behaviour more consistent this will also simplify the next patch. Signed-off-by: Paolo Abeni Reviewed-by: Mat Martineau Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20251121-net-next-mptcp-memcg-backlog-imp-v1-11-1f34b6c1e0b1@kernel.org Signed-off-by: Jakub Kicinski Stable-dep-of: 50c2d91c5dfa ("mptcp: do not drop partial packets") Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

mptcp: introduce the mptcp_init_skb helper

2026-06-09T10:26:03+00:00

[ Upstream commit 9a0afe0db46720ce1a009c7dac168aa0584bd732 ] Factor out all the skb initialization step in a new helper and use it. Note that this change moves the MPTCP CB initialization earlier: we can do such step as soon as the skb leaves the subflow socket receive queues. Reviewed-by: Matthieu Baerts (NGI0) Signed-off-by: Paolo Abeni Reviewed-by: Geliang Tang Tested-by: Geliang Tang Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20250927-net-next-mptcp-rcv-path-imp-v1-4-5da266aa9c1a@kernel.org Signed-off-by: Jakub Kicinski Stable-dep-of: 50c2d91c5dfa ("mptcp: do not drop partial packets") Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

mptcp: reset rcv wnd on disconnect

2026-06-09T10:26:03+00:00

[ Upstream commit 0981f90e1a05773a4c29c6e720f5ea1e3c8f1876 ] If the MPTCP socket fallback to TCP before the MP handshake completion, the IASN remain 0, and the rcv_wnd_sent field is not explicitly initialized, just incremented over time with the data transfer. At disconnect time such value is not cleared. If the next connection falls back to TCP before the MP handshake completion, the data transfer will keep incrementing the receive window end sequence starting from the last value used in the previous connection: the announced window will be unrelated from the actual receiver buffer size and likely too big. Address the issue zeroing the field at disconnect time. Fixes: b29fcfb54cd7 ("mptcp: full disconnect implementation") 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/20260515-net-mptcp-misc-fixes-7-1-rc4-v2-4-701e96419f2f@kernel.org Signed-off-by: Paolo Abeni Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

mptcp: cleanup fallback dummy mapping generation

2026-06-09T10:26:03+00:00

[ Upstream commit 2834f8edd74d5dda368087a654c0e52b141e9893 ] MPTCP currently access ack_seq outside the msk socket log scope to generate the dummy mapping for fallback socket. Soon we are going to introduce backlog usage and even for fallback socket the ack_seq value will be significantly off outside of the msk socket lock scope. Avoid relying on ack_seq for dummy mapping generation, using instead the subflow sequence number. Note that in case of disconnect() and (re)connect() we must ensure that any previous state is re-set. 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/20251121-net-next-mptcp-memcg-backlog-imp-v1-6-1f34b6c1e0b1@kernel.org Signed-off-by: Jakub Kicinski Stable-dep-of: 0981f90e1a05 ("mptcp: reset rcv wnd on disconnect") Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

mptcp: sync the msk->sndbuf at accept() time

2026-06-01T15:46:13+00:00

commit fcf04b14334641f4b0b8647824480935e9416d52 upstream. On passive MPTCP connections, the msk sndbuf is not updated correctly. The root cause is an order issue in the accept path: - tcp_check_req() -> subflow_syn_recv_sock() -> mptcp_sk_clone_init() calls __mptcp_propagate_sndbuf() to copy the ssk sndbuf into msk - Later, tcp_child_process() -> tcp_init_transfer() -> tcp_sndbuf_expand() grows the ssk sndbuf. So __mptcp_propagate_sndbuf() runs before the ssk sndbuf has been expanded and the msk ends up with a much smaller sndbuf than the subflow: MPTCP: msk->sndbuf:20480, msk->first->sndbuf:2626560 Fix this by moving the __mptcp_propagate_sndbuf() call from mptcp_sk_clone_init() -- the ssk sndbuf is not yet finalized there -- to __mptcp_propagate_sndbuf() at accept() time, when the ssk sndbuf has been fully expanded by tcp_sndbuf_expand(). Fixes: 8005184fd1ca ("mptcp: refactor sndbuf auto-tuning") Cc: stable@vger.kernel.org Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/602 Signed-off-by: Gang Yan Acked-by: Paolo Abeni Reviewed-by: Matthieu Baerts (NGI0) Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20260420-net-mptcp-sync-sndbuf-accept-v1-1-e3523e3aeb44@kernel.org Signed-off-by: Paolo Abeni [ No conflicts, but move __mptcp_propagate_sndbuf() above the for-loop (mptcp_for_each_subflow()) present in this version, which will modify 'subflow' used by __mptcp_propagate_sndbuf() in this new patch. ] Signed-off-by: Matthieu Baerts (NGI0) Signed-off-by: Sasha Levin

mptcp: drop __mptcp_fastopen_gen_msk_ackseq()

2026-05-23T11:05:01+00:00

[ Upstream commit f03afb3aeb9d81f6c5ab728a61a040012923e3b3 ] When we will move the whole RX path under the msk socket lock, updating the already queued skb for passive fastopen socket at 3rd ack time will be extremely painful and race prone The map_seq for already enqueued skbs is used only to allow correct coalescing with later data; preventing collapsing to the first skb of a fastopen connect we can completely remove the __mptcp_fastopen_gen_msk_ackseq() helper. Before dropping this helper, a new item had to be added to the mptcp_skb_cb structure. Because this item will be frequently tested in the fast path -- almost on every packet -- and because there is free space there, a single byte is used instead of a bitfield. This micro optimisation slightly reduces the number of CPU operations to do the associated check. Signed-off-by: Paolo Abeni Reviewed-by: Matthieu Baerts (NGI0) Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20250218-net-next-mptcp-rx-path-refactor-v1-2-4a47d90d7998@kernel.org Signed-off-by: Jakub Kicinski Stable-dep-of: 6254a16d6f0c ("mptcp: fix rx timestamp corruption on fastopen") Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

mptcp: fastclose msk when linger time is 0

2026-05-14T13:29:26+00:00

commit f14d6e9c3678a067f304abba561e0c5446c7e845 upstream. The SO_LINGER socket option has been supported for a while with MPTCP sockets [1], but it didn't cause the equivalent of a TCP reset as expected when enabled and its time was set to 0. This was causing some behavioural differences with TCP where some connections were not promptly stopped as expected. To fix that, an extra condition is checked at close() time before sending an MP_FASTCLOSE, the MPTCP equivalent of a TCP reset. Note that backporting up to [1] will be difficult as more changes are needed to be able to send MP_FASTCLOSE. It seems better to stop at [2], which was supposed to already imitate TCP. Validated with MPTCP packetdrill tests [3]. Fixes: 268b12387460 ("mptcp: setsockopt: support SO_LINGER") [1] Fixes: d21f83485518 ("mptcp: use fastclose on more edge scenarios") [2] Cc: stable@vger.kernel.org Reported-by: Lance Tuller Closes: https://github.com/lance0/xfr/pull/67 Link: https://github.com/multipath-tcp/packetdrill/pull/196 [3] Reviewed-by: Mat Martineau Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20260427-net-mptcp-misc-fixes-7-1-rc2-v1-3-7432b7f279fa@kernel.org Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman

mptcp: fix slab-use-after-free in __inet_lookup_established

2026-04-18T08:41:55+00:00

commit 9b55b253907e7431210483519c5ad711a37dafa1 upstream. The ehash table lookups are lockless and rely on SLAB_TYPESAFE_BY_RCU to guarantee socket memory stability during RCU read-side critical sections. Both tcp_prot and tcpv6_prot have their slab caches created with this flag via proto_register(). However, MPTCP's mptcp_subflow_init() copies tcpv6_prot into tcpv6_prot_override during inet_init() (fs_initcall, level 5), before inet6_init() (module_init/device_initcall, level 6) has called proto_register(&tcpv6_prot). At that point, tcpv6_prot.slab is still NULL, so tcpv6_prot_override.slab remains NULL permanently. This causes MPTCP v6 subflow child sockets to be allocated via kmalloc (falling into kmalloc-4k) instead of the TCPv6 slab cache. The kmalloc-4k cache lacks SLAB_TYPESAFE_BY_RCU, so when these sockets are freed without SOCK_RCU_FREE (which is cleared for child sockets by design), the memory can be immediately reused. Concurrent ehash lookups under rcu_read_lock can then access freed memory, triggering a slab-use-after-free in __inet_lookup_established. Fix this by splitting the IPv6-specific initialization out of mptcp_subflow_init() into a new mptcp_subflow_v6_init(), called from mptcp_proto_v6_init() before protocol registration. This ensures tcpv6_prot_override.slab correctly inherits the SLAB_TYPESAFE_BY_RCU slab cache. Fixes: b19bc2945b40 ("mptcp: implement delegated actions") Cc: stable@vger.kernel.org Signed-off-by: Jiayuan Chen Reviewed-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20260406031512.189159-1-jiayuan.chen@linux.dev Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman

mptcp: fix receive space timestamp initialization

2026-03-04T12:20:08+00:00

[ 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