netdev - [PATCH net] ip_tunnel: don't force DF when MTU is locked

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Message-Id: <218932a71a1f19b07dc6f92daaf9baed9e532cfe.1542382139.git.sd@queasysnail.net>
Date:   Fri, 16 Nov 2018 16:58:19 +0100
From:   Sabrina Dubroca <sd@...asysnail.net>
To:     netdev@...r.kernel.org
Cc:     sbrivio@...hat.com, Sabrina Dubroca <sd@...asysnail.net>
Subject: [PATCH net] ip_tunnel: don't force DF when MTU is locked

The various types of tunnels running over IPv4 can ask to set the DF
bit to do PMTU discovery. However, PMTU discovery is subject to the
threshold set by the net.ipv4.route.min_pmtu sysctl, and is also
disabled on routes with "mtu lock". In those cases, we shouldn't set
the DF bit.

This patch makes setting the DF bit conditional on the route's MTU
locking state.

This issue seems to be older than git history.

Signed-off-by: Sabrina Dubroca <sd@...asysnail.net>
Reviewed-by: Stefano Brivio <sbrivio@...hat.com>
---
 net/ipv4/ip_tunnel_core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/ip_tunnel_core.c b/net/ipv4/ip_tunnel_core.c
index f45b96d715f0..c857ec6b9784 100644
--- a/net/ipv4/ip_tunnel_core.c
+++ b/net/ipv4/ip_tunnel_core.c
@@ -80,7 +80,7 @@ void iptunnel_xmit(struct sock *sk, struct rtable *rt, struct sk_buff *skb,
 
 	iph->version	=	4;
 	iph->ihl	=	sizeof(struct iphdr) >> 2;
-	iph->frag_off	=	df;
+	iph->frag_off	=	ip_mtu_locked(&rt->dst) ? 0 : df;
 	iph->protocol	=	proto;
 	iph->tos	=	tos;
 	iph->daddr	=	dst;
-- 
2.19.1