Fix a bug introduced with r182851 splitting tcp_mss() into

tcp_mss() and tcp_mss_update() so that tcp_mtudisc() could
re-use the same code.

Move the TSO logic back to tcp_mss() and out of tcp_mss_update().
We tried to avoid that initially but if were are called from
tcp_output() with EMSGSIZE, we cleared the TSO flag on the tcpcb
there, called into tcp_mtudisc() and tcp_mss_update() which
then would reenable TSO on the tcpcb based on TSO capabilities
of the interface as learnt in tcp_maxmtu/6().
So if TSO was enabled on the (possibly new) outgoing interface
it was turned back on, which lead to an endless loop between
tcp_output() and tcp_mtudisc() until we overflew the stack.

Reported by:	kmacy
MFC after:	2 months (along with r182851)

1 files changed, 10 insertions, 9 deletions

diff --git a/sys/netinet/tcp_input.c b/sys/netinet/tcp_input.c
index 9dd7b8c..a1e72e8 100644
--- a/sys/netinet/tcp_input.c
+++ b/sys/netinet/tcp_input.c
@@ -2812,7 +2812,8 @@ tcp_xmit_timer(struct tcpcb *tp, int rtt)
  * segment. Outgoing SYN/ACK MSS settings are handled in tcp_mssopt().
  */
 void
-tcp_mss_update(struct tcpcb *tp, int offer, struct hc_metrics_lite *metricptr)
+tcp_mss_update(struct tcpcb *tp, int offer,
+    struct hc_metrics_lite *metricptr, int *mtuflags)
 {
 	INIT_VNET_INET(tp->t_inpcb->inp_vnet);
 	int mss;
@@ -2820,7 +2821,6 @@ tcp_mss_update(struct tcpcb *tp, int offer, struct hc_metrics_lite *metricptr)
 	struct inpcb *inp = tp->t_inpcb;
 	struct hc_metrics_lite metrics;
 	int origoffer = offer;
-	int mtuflags = 0;
 #ifdef INET6
 	int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
 	size_t min_protoh = isipv6 ?
@@ -2835,12 +2835,12 @@ tcp_mss_update(struct tcpcb *tp, int offer, struct hc_metrics_lite *metricptr)
 	/* Initialize. */
 #ifdef INET6
 	if (isipv6) {
-		maxmtu = tcp_maxmtu6(&inp->inp_inc, &mtuflags);
+		maxmtu = tcp_maxmtu6(&inp->inp_inc, mtuflags);
 		tp->t_maxopd = tp->t_maxseg = V_tcp_v6mssdflt;
 	} else
 #endif
 	{
-		maxmtu = tcp_maxmtu(&inp->inp_inc, &mtuflags);
+		maxmtu = tcp_maxmtu(&inp->inp_inc, mtuflags);
 		tp->t_maxopd = tp->t_maxseg = V_tcp_mssdflt;
 	}
 
@@ -2858,10 +2858,6 @@ tcp_mss_update(struct tcpcb *tp, int offer, struct hc_metrics_lite *metricptr)
 		return;
 	}
 
-	/* Check the interface for TSO capabilities. */
-	if (mtuflags & CSUM_TSO)
-		tp->t_flags |= TF_TSO;
-
 	/* What have we got? */
 	switch (offer) {
 		case 0:
@@ -2980,12 +2976,13 @@ tcp_mss(struct tcpcb *tp, int offer)
 	struct inpcb *inp;
 	struct socket *so;
 	struct hc_metrics_lite metrics;
+	int mtuflags = 0;
 #ifdef INET6
 	int isipv6;
 #endif
 	KASSERT(tp != NULL, ("%s: tp == NULL", __func__));
 	
-	tcp_mss_update(tp, offer, &metrics);
+	tcp_mss_update(tp, offer, &metrics, &mtuflags);
 
 	mss = tp->t_maxseg;
 	inp = tp->t_inpcb;
@@ -3098,6 +3095,10 @@ tcp_mss(struct tcpcb *tp, int offer)
 		tp->snd_cwnd = mss * V_ss_fltsz_local;
 	else
 		tp->snd_cwnd = mss * V_ss_fltsz;
+
+	/* Check the interface for TSO capabilities. */
+	if (mtuflags & CSUM_TSO)
+		tp->t_flags |= TF_TSO;
 }
 
 /*