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mptcp: fallback to TCP after SYN+MPC drops

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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 after 2
retransmissions, and try again.

Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/477
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20240909-net-next-mptcp-fallback-x-mpc-v1-2-da7ebb4cd2a3@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Matthieu Baerts (NGI0) 2024-09-09 22:09:22 +02:00 committed by Jakub Kicinski
parent 65b02260a0
commit 6982826fe5
5 changed files with 27 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
include/net/mptcp.h
View File

@ -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)

1
net/ipv4/tcp_timer.c
View File

@ -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,

20
net/mptcp/ctrl.c
View File

@ -12,6 +12,7 @@
#include <net/netns/generic.h>
#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);

1
net/mptcp/mib.c
View File

@ -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),

1
net/mptcp/mib.h
View File

@ -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 */