[PATCH net-next 06/11] mptcp: pm: drop TCP TS with ADD_ADDRv6 + port

[Matthieu Baerts (NGI0)]

With TCP-timestamps (padded) taking 12 bytes and ADD_ADDR IPv6 + port
taking 30 bytes, the 40-byte limit for the TCP options is reached. In
this case, it is then not possible to send the signal.

To be able to send this ADD_ADDR, the TCP timestamps option can now be
dropped. This is done, when needed by setting the *drop_ts parameter
from mptcp_established_options. This feature is controlled by a new
net.mptcp.add_addr_v6_port_drop_ts sysctl knob, enabled by default.

It is important to keep in mind that dropping the TCP timestamps option
for one packet of the connection could eventually disrupt some
middleboxes: even if it should be unlikely, they could drop the packet
or even block the connection. That's why this new feature can be
controlled by a sysctl knob.

Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/448
Reviewed-by: Mat Martineau <martineau@xxxxxxxxxx>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@xxxxxxxxxx>
---
 net/mptcp/options.c  |  8 ++++++--
 net/mptcp/pm.c       | 12 +++++++++++-
 net/mptcp/protocol.h |  2 +-
 3 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index ccb5ac0aa729..02336d1c1550 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -652,6 +652,7 @@ static u64 add_addr_generate_hmac(u64 key1, u64 key2,
 static bool mptcp_established_options_add_addr(struct sock *sk,
 					       struct sk_buff *skb, int *size,
 					       unsigned int remaining,
+					       bool *drop_ts,
 					       struct mptcp_out_options *opts)
 {
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
@@ -666,7 +667,7 @@ static bool mptcp_established_options_add_addr(struct sock *sk,
 	if (!mptcp_pm_should_add_signal(msk) ||
 	    (opts->suboptions & (OPTION_MPTCP_MPJ_ACK | OPTION_MPTCP_MPC_ACK)) ||
 	    !mptcp_pm_add_addr_signal(msk, skb, size, remaining, &addr, &echo,
-				      &drop_other_suboptions))
+				      &drop_other_suboptions, drop_ts))
 		return false;
 
 	/*
@@ -819,6 +820,7 @@ bool mptcp_established_options(struct sock *sk, struct sk_buff *skb,
 {
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
 	struct mptcp_sock *msk = mptcp_sk(subflow->conn);
+	bool add_addr_drop_ts = *drop_ts;
 	bool snd_data_fin;
 	bool ret = false;
 	int opt_size = 0;
@@ -869,10 +871,12 @@ bool mptcp_established_options(struct sock *sk, struct sk_buff *skb,
 
 	*size += opt_size;
 	remaining -= opt_size;
-	if (mptcp_established_options_add_addr(sk, skb, &opt_size, remaining, opts)) {
+	if (mptcp_established_options_add_addr(sk, skb, &opt_size, remaining,
+					       &add_addr_drop_ts, opts)) {
 		*size += opt_size;
 		remaining -= opt_size;
 		ret = true;
+		*drop_ts = add_addr_drop_ts;
 	} else if (mptcp_established_options_rm_addr(sk, &opt_size, remaining, opts)) {
 		*size += opt_size;
 		remaining -= opt_size;
diff --git a/net/mptcp/pm.c b/net/mptcp/pm.c
index 6a2cbe8616d3..b1b3f7482f7c 100644
--- a/net/mptcp/pm.c
+++ b/net/mptcp/pm.c
@@ -905,7 +905,7 @@ static int mptcp_add_addr_len(int family, bool echo, bool port)
 bool mptcp_pm_add_addr_signal(struct mptcp_sock *msk, const struct sk_buff *skb,
 			      int *size, int remaining,
 			      struct mptcp_addr_info *addr, bool *echo,
-			      bool *drop_other_suboptions)
+			      bool *drop_other_suboptions, bool *drop_ts)
 {
 	bool skip_add_addr = false;
 	bool ret = false;
@@ -949,6 +949,13 @@ bool mptcp_pm_add_addr_signal(struct mptcp_sock *msk, const struct sk_buff *skb,
 		if (!*drop_other_suboptions)
 			goto out_unlock;
 
+		if (*drop_ts && mptcp_add_addr_v6_port_drop_ts(net)) {
+			/* OK without TCP Timestamps? */
+			len -= TCPOLEN_TSTAMP_ALIGNED;
+			if (len <= remaining)
+				goto enough_space;
+		}
+
 		if (*echo) {
 			MPTCP_INC_STATS(net, MPTCP_MIB_ECHOADDTXDROP);
 		} else {
@@ -958,6 +965,9 @@ bool mptcp_pm_add_addr_signal(struct mptcp_sock *msk, const struct sk_buff *skb,
 		goto drop_signal_mark;
 	}
 
+	*drop_ts = false;
+
+enough_space:
 	ret = true;
 	*size = len;
 
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index f4276980d78a..50c3205cab46 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -1210,7 +1210,7 @@ static inline bool mptcp_pm_is_kernel(const struct mptcp_sock *msk)
 bool mptcp_pm_add_addr_signal(struct mptcp_sock *msk, const struct sk_buff *skb,
 			      int *size, int remaining,
 			      struct mptcp_addr_info *addr, bool *echo,
-			      bool *drop_other_suboptions);
+			      bool *drop_other_suboptions, bool *drop_ts);
 bool mptcp_pm_rm_addr_signal(struct mptcp_sock *msk, unsigned int remaining,
 			     struct mptcp_rm_list *rm_list, int *len);
 int mptcp_pm_get_local_id(struct mptcp_sock *msk, struct sock_common *skc);

-- 
2.53.0