ip_tunnel: don't force DF when MTU is locked

[ Upstream commit 16f7eb2b77b55da816c4e207f3f9440a8cafc00a ]

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@queasysnail.net>
Reviewed-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/ipv4/ip_tunnel_core.c b/net/ipv4/ip_tunnel_core.c
index dbda0565781cfe8ae1486994b3fe0795d736f71e..4916d1857b75a1f83011cf339baca990714da8b9 100644 (file)
--- a/net/ipv4/ip_tunnel_core.c
+++ b/net/ipv4/ip_tunnel_core.c
@@ -71,7 +71,7 @@ int 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;