From 45ef0891cccdf45b8d1469eddff299b1812e1c1d Mon Sep 17 00:00:00 2001 From: "Matthieu Baerts (NGI0)" Date: Mon, 9 Sep 2024 18:49:48 +0200 Subject: [PATCH] mptcp: fallback to TCP after SYN+MPC drops Some middleboxes might be nasty with MPTCP, and decide to drop packets with MPTCP options, instead of just dropping the MPTCP options (or letting them pass...). In this case, it sounds better to fallback to "plain" TCP, and try again. Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/477 Signed-off-by: Matthieu Baerts (NGI0) --- include/net/mptcp.h | 4 ++++ net/ipv4/tcp_timer.c | 1 + net/mptcp/ctrl.c | 20 ++++++++++++++++++++ net/mptcp/mib.c | 1 + net/mptcp/mib.h | 1 + 5 files changed, 27 insertions(+) diff --git a/include/net/mptcp.h b/include/net/mptcp.h index 0bc4ab03f4878..814b5f2e3ed5e 100644 --- a/include/net/mptcp.h +++ b/include/net/mptcp.h @@ -223,6 +223,8 @@ static inline __be32 mptcp_reset_option(const struct sk_buff *skb) return htonl(0u); } + +void mptcp_active_detect_blackhole(struct sock *sk, bool expired); #else static inline void mptcp_init(void) @@ -307,6 +309,8 @@ static inline struct request_sock *mptcp_subflow_reqsk_alloc(const struct reques } static inline __be32 mptcp_reset_option(const struct sk_buff *skb) { return htonl(0u); } + +static inline void mptcp_active_detect_blackhole(struct sock *sk, bool expired) { } #endif /* CONFIG_MPTCP */ #if IS_ENABLED(CONFIG_MPTCP_IPV6) diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c index 86169127e4d1f..79064580c8c0d 100644 --- a/net/ipv4/tcp_timer.c +++ b/net/ipv4/tcp_timer.c @@ -282,6 +282,7 @@ static int tcp_write_timeout(struct sock *sk) expired = retransmits_timed_out(sk, retry_until, READ_ONCE(icsk->icsk_user_timeout)); tcp_fastopen_active_detect_blackhole(sk, expired); + mptcp_active_detect_blackhole(sk, expired); if (BPF_SOCK_OPS_TEST_FLAG(tp, BPF_SOCK_OPS_RTO_CB_FLAG)) tcp_call_bpf_3arg(sk, BPF_SOCK_OPS_RTO_CB, diff --git a/net/mptcp/ctrl.c b/net/mptcp/ctrl.c index 99382c317ebb6..0b23e3c5e8ff4 100644 --- a/net/mptcp/ctrl.c +++ b/net/mptcp/ctrl.c @@ -12,6 +12,7 @@ #include #include "protocol.h" +#include "mib.h" #define MPTCP_SYSCTL_PATH "net/mptcp" @@ -277,6 +278,25 @@ static void mptcp_pernet_del_table(struct mptcp_pernet *pernet) {} #endif /* CONFIG_SYSCTL */ +/* Check the number of retransmissions, and fallback to TCP if needed */ +void mptcp_active_detect_blackhole(struct sock *ssk, bool expired) +{ + struct mptcp_subflow_context *subflow; + u32 timeouts; + + if (!sk_is_mptcp(ssk)) + return; + + timeouts = inet_csk(ssk)->icsk_retransmits; + subflow = mptcp_subflow_ctx(ssk); + + if (subflow->request_mptcp && ssk->sk_state == TCP_SYN_SENT && + (timeouts == 2 || (timeouts < 2 && expired))) { + MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_MPCAPABLEACTIVEDROP); + mptcp_subflow_early_fallback(mptcp_sk(subflow->conn), subflow); + } +} + static int __net_init mptcp_net_init(struct net *net) { struct mptcp_pernet *pernet = mptcp_get_pernet(net); diff --git a/net/mptcp/mib.c b/net/mptcp/mib.c index ec0d461cb921e..d70a3e2bfad62 100644 --- a/net/mptcp/mib.c +++ b/net/mptcp/mib.c @@ -15,6 +15,7 @@ static const struct snmp_mib mptcp_snmp_list[] = { SNMP_MIB_ITEM("MPCapableACKRX", MPTCP_MIB_MPCAPABLEPASSIVEACK), SNMP_MIB_ITEM("MPCapableFallbackACK", MPTCP_MIB_MPCAPABLEPASSIVEFALLBACK), SNMP_MIB_ITEM("MPCapableFallbackSYNACK", MPTCP_MIB_MPCAPABLEACTIVEFALLBACK), + SNMP_MIB_ITEM("MPCapableSYNTXDrop", MPTCP_MIB_MPCAPABLEACTIVEDROP), SNMP_MIB_ITEM("MPFallbackTokenInit", MPTCP_MIB_TOKENFALLBACKINIT), SNMP_MIB_ITEM("MPTCPRetrans", MPTCP_MIB_RETRANSSEGS), SNMP_MIB_ITEM("MPJoinNoTokenFound", MPTCP_MIB_JOINNOTOKEN), diff --git a/net/mptcp/mib.h b/net/mptcp/mib.h index d68136f93dac5..062775700b632 100644 --- a/net/mptcp/mib.h +++ b/net/mptcp/mib.h @@ -10,6 +10,7 @@ enum linux_mptcp_mib_field { MPTCP_MIB_MPCAPABLEPASSIVEACK, /* Received third ACK with MP_CAPABLE */ MPTCP_MIB_MPCAPABLEPASSIVEFALLBACK,/* Server-side fallback during 3-way handshake */ MPTCP_MIB_MPCAPABLEACTIVEFALLBACK, /* Client-side fallback during 3-way handshake */ + MPTCP_MIB_MPCAPABLEACTIVEDROP, /* Client-side fallback due to a MPC drop */ MPTCP_MIB_TOKENFALLBACKINIT, /* Could not init/allocate token */ MPTCP_MIB_RETRANSSEGS, /* Segments retransmitted at the MPTCP-level */ MPTCP_MIB_JOINNOTOKEN, /* Received MP_JOIN but the token was not found */