kernel/linux.git/net/mptcp/protocol.c, branch v6.18.35

mptcp: reset rcv wnd on disconnect

2026-06-09T10:28:51+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

2026-06-09T10:28:51+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: do not drop partial packets

2026-06-09T10:28:51+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: borrow forward memory from subflow

2026-06-09T10:28:51+00:00

[ Upstream commit 9db5b3cec4ec1c0cd3239689f5c8653d691a1754 ] In the MPTCP receive path, we release the subflow allocated fwd memory just to allocate it again shortly after for the msk. That could increases the failures chances, especially when we will add backlog processing, with other actions could consume the just released memory before the msk socket has a chance to do the rcv allocation. Replace the skb_orphan() call with an open-coded variant that explicitly borrows, the fwd memory from the subflow socket instead of releasing it. The borrowed memory does not have PAGE_SIZE granularity; rounding to the page size will make the fwd allocated memory higher than what is strictly required and could make the incoming subflow fwd mem consistently negative. Instead, keep track of the accumulated frag and borrow the full page at subflow close time. This allow removing the last drop in the TCP to MPTCP transition and the associated, now unused, MIB. 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-v1-12-1f34b6c1e0b1@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: handle first subflow closing consistently

2026-06-09T10:28:50+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: fastclose msk when linger time is 0

2026-05-14T13:30:22+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: sync the msk->sndbuf at accept() time

2026-05-14T13:30:11+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: fix slab-use-after-free in __inet_lookup_established

2026-04-18T08:44:57+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 soft lockup in mptcp_recvmsg()

2026-04-11T12:26:24+00:00

[ Upstream commit 5dd8025a49c268ab6b94d978532af3ad341132a7 ] syzbot reported a soft lockup in mptcp_recvmsg() [0]. When receiving data with MSG_PEEK | MSG_WAITALL flags, the skb is not removed from the sk_receive_queue. This causes sk_wait_data() to always find available data and never perform actual waiting, leading to a soft lockup. Fix this by adding a 'last' parameter to track the last peeked skb. This allows sk_wait_data() to make informed waiting decisions and prevent infinite loops when MSG_PEEK is used. [0]: watchdog: BUG: soft lockup - CPU#2 stuck for 156s! [server:1963] Modules linked in: CPU: 2 UID: 0 PID: 1963 Comm: server Not tainted 6.19.0-rc8 #61 PREEMPT(none) Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014 RIP: 0010:sk_wait_data+0x15/0x190 Code: 80 00 00 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 41 56 41 55 41 54 49 89 f4 55 48 89 d5 53 48 89 fb <48> 83 ec 30 65 48 8b 05 17 a4 6b 01 48 89 44 24 28 31 c0 65 48 8b RSP: 0018:ffffc90000603ca0 EFLAGS: 00000246 RAX: 0000000000000000 RBX: ffff888102bf0800 RCX: 0000000000000001 RDX: 0000000000000000 RSI: ffffc90000603d18 RDI: ffff888102bf0800 RBP: 0000000000000000 R08: 0000000000000002 R09: 0000000000000101 R10: 0000000000000000 R11: 0000000000000075 R12: ffffc90000603d18 R13: ffff888102bf0800 R14: ffff888102bf0800 R15: 0000000000000000 FS: 00007f6e38b8c4c0(0000) GS:ffff8881b877e000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000055aa7bff1680 CR3: 0000000105cbe000 CR4: 00000000000006f0 Call Trace: mptcp_recvmsg+0x547/0x8c0 net/mptcp/protocol.c:2329 inet_recvmsg+0x11f/0x130 net/ipv4/af_inet.c:891 sock_recvmsg+0x94/0xc0 net/socket.c:1100 __sys_recvfrom+0xb2/0x130 net/socket.c:2256 __x64_sys_recvfrom+0x1f/0x30 net/socket.c:2267 do_syscall_64+0x59/0x2d0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x76/0x7e arch/x86/entry/entry_64.S:131 RIP: 0033:0x7f6e386a4a1d Code: 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 8d 05 f1 de 2c 00 41 89 ca 8b 00 85 c0 75 20 45 31 c9 45 31 c0 b8 2d 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 6b f3 c3 66 0f 1f 84 00 00 00 00 00 41 56 41 RSP: 002b:00007ffc3c4bb078 EFLAGS: 00000246 ORIG_RAX: 000000000000002d RAX: ffffffffffffffda RBX: 000000000000861e RCX: 00007f6e386a4a1d RDX: 00000000000003ff RSI: 00007ffc3c4bb150 RDI: 0000000000000004 RBP: 00007ffc3c4bb570 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000103 R11: 0000000000000246 R12: 00005605dbc00be0 R13: 00007ffc3c4bb650 R14: 0000000000000000 R15: 0000000000000000 Fixes: 8e04ce45a8db ("mptcp: fix MSG_PEEK stream corruption") Signed-off-by: Li Xiasong Reviewed-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20260330120335.659027-1-lixiasong1@huawei.com Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin

mptcp: add eat_recv_skb helper

2026-04-11T12:26:24+00:00

[ Upstream commit 436510df0cafb1bc36f12e92e0e76599be28d8f4 ] This patch extracts the free skb related code in __mptcp_recvmsg_mskq() into a new helper mptcp_eat_recv_skb(). This new helper will be used in the next patch. Signed-off-by: Geliang Tang Reviewed-by: Mat Martineau Signed-off-by: Matthieu Baerts (NGI0) Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20260130-net-next-mptcp-splice-v2-1-31332ba70d7f@kernel.org Signed-off-by: Jakub Kicinski Stable-dep-of: 5dd8025a49c2 ("mptcp: fix soft lockup in mptcp_recvmsg()") Signed-off-by: Sasha Levin