ipv4: new ip_no_pmtu_disc mode to always discard incoming frag needed msgs

This new mode discards all incoming fragmentation-needed notifications
as I guess was originally intended with this knob. To not break backward
compatibility too much, I only added a special case for mode 2 in the
receiving path.

Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index f76d177..d71afa8 100644 (file)
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -15,12 +15,18 @@ ip_default_ttl - INTEGER
        forwarded) IP packets. Should be between 1 and 255 inclusive.
        Default: 64 (as recommended by RFC1700)
 
-ip_no_pmtu_disc - BOOLEAN
-       Disable Path MTU Discovery. If enabled and a
+ip_no_pmtu_disc - INTEGER
+       Disable Path MTU Discovery. If enabled in mode 1 and a
        fragmentation-required ICMP is received, the PMTU to this
        destination will be set to min_pmtu (see below). You will need
        to raise min_pmtu to the smallest interface MTU on your system
        manually if you want to avoid locally generated fragments.
+
+       In mode 2 incoming Path MTU Discovery messages will be
+       discarded. Outgoing frames are handled the same as in mode 1,
+       implicitly setting IP_PMTUDISC_DONT on every created socket.
+
+       Possible values: 0-2
        Default: FALSE
 
 min_pmtu - INTEGER

diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index 1a4ee84..fb3c563 100644 (file)
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -705,7 +705,9 @@ static void icmp_unreach(struct sk_buff *skb)
                case ICMP_PORT_UNREACH:
                        break;
                case ICMP_FRAG_NEEDED:
-                       if (net->ipv4.sysctl_ip_no_pmtu_disc) {
+                       if (net->ipv4.sysctl_ip_no_pmtu_disc == 2) {
+                               goto out;
+                       } else if (net->ipv4.sysctl_ip_no_pmtu_disc) {
                                LIMIT_NETDEBUG(KERN_INFO pr_fmt("%pI4: fragmentation needed and DF set\n"),
                                               &iph->daddr);
                        } else {