[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>

1 files changed, 13 insertions, 0 deletions

diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 4cfdad4e8356..5a5b7d4ad31c 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -567,6 +567,19 @@ static int ip6_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *))
         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;