[PATCH] tcp: reinitialize MTU probing when setting MSS in a TCP repair

[PATCH] tcp: reinitialize MTU probing when setting MSS in a TCP repair

[Douglas Caetano dos Santos]

From: Douglas Caetano dos Santos <douglascs@taghos.com.br>

MTU probing initialization occurred only at connect() and at SYN or
SYN-ACK reception, but the former sets MSS to either the default or the
user set value (through TCP_MAXSEG sockopt) and the latter never happens
with repaired sockets.

The result was that, with MTU probing enabled and unless TCP_MAXSEG
sockopt was used before connect(), probing would be stuck at
tcp_base_mss value until tcp_probe_interval seconds have passed.

Signed-off-by: Douglas Caetano dos Santos <douglascs@taghos.com.br>
---
I'm not sure if there are any side effects doing this, so comments are welcome
as always.

Also, I changed the function's argument from struct tcp_sock to struct sock
because I couldn't find any inverse of tcp_sk() funciton and thought that using
"&tp->inet_conn.icsk_inet.sk" or "(struct sock *)tp" would be worse.

 net/ipv4/tcp.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 842b575f8fdd..d782637e595e 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2378,9 +2378,10 @@ static int tcp_repair_set_window(struct tcp_sock *tp, char __user *optbuf, int l
 	return 0;
 }
 
-static int tcp_repair_options_est(struct tcp_sock *tp,
+static int tcp_repair_options_est(struct sock *sk,
 		struct tcp_repair_opt __user *optbuf, unsigned int len)
 {
+	struct tcp_sock *tp = tcp_sk(sk);
 	struct tcp_repair_opt opt;
 
 	while (len >= sizeof(opt)) {
@@ -2393,6 +2394,7 @@ static int tcp_repair_options_est(struct tcp_sock *tp,
 		switch (opt.opt_code) {
 		case TCPOPT_MSS:
 			tp->rx_opt.mss_clamp = opt.opt_val;
+			tcp_mtup_init(sk);
 			break;
 		case TCPOPT_WINDOW:
 			{
@@ -2552,7 +2554,7 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
 		if (!tp->repair)
 			err = -EINVAL;
 		else if (sk->sk_state == TCP_ESTABLISHED)
-			err = tcp_repair_options_est(tp,
+			err = tcp_repair_options_est(sk,
 					(struct tcp_repair_opt __user *)optval,
 					optlen);
 		else
-- 
2.12.2

Re: [PATCH] tcp: reinitialize MTU probing when setting MSS in a TCP repair

[David Miller]

From: Douglas Caetano dos Santos <douglascs@taghos.com.br>
Date: Fri, 26 May 2017 14:28:00 -0300

> From: Douglas Caetano dos Santos <douglascs@taghos.com.br>
> 
> MTU probing initialization occurred only at connect() and at SYN or
> SYN-ACK reception, but the former sets MSS to either the default or the
> user set value (through TCP_MAXSEG sockopt) and the latter never happens
> with repaired sockets.
> 
> The result was that, with MTU probing enabled and unless TCP_MAXSEG
> sockopt was used before connect(), probing would be stuck at
> tcp_base_mss value until tcp_probe_interval seconds have passed.
> 
> Signed-off-by: Douglas Caetano dos Santos <douglascs@taghos.com.br>

This seems fine to me, as long as you call tcp_mtup_init() after setting
the mss_clamp, whichy you are, everything should be alright.

Applied, thanks.