[IPV6]: MTU discovery check in ip6_fragment()
Adds a check in ip6_fragment() mirroring ip_fragment() for packets
that we can't fragment, and sends an ICMP Packet Too Big message
in response.
Signed-off-by: John Heffner <jheffner@psc.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 4cfdad4..5a5b7d4 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -567,6 +567,19 @@
nexthdr = *prevhdr;
mtu = dst_mtu(&rt->u.dst);
+
+ /* We must not fragment if the socket is set to force MTU discovery
+ * or if the skb it not generated by a local socket. (This last
+ * check should be redundant, but it's free.)
+ */
+ if (!np || np->pmtudisc >= IPV6_PMTUDISC_DO) {
+ skb->dev = skb->dst->dev;
+ icmpv6_send(skb, ICMPV6_PKT_TOOBIG, 0, mtu, skb->dev);
+ IP6_INC_STATS(ip6_dst_idev(skb->dst), IPSTATS_MIB_FRAGFAILS);
+ kfree_skb(skb);
+ return -EMSGSIZE;
+ }
+
if (np && np->frag_size < mtu) {
if (np->frag_size)
mtu = np->frag_size;