net: ipv6: send pkttoobig immediately if orig frag size > mtu

[ Upstream commit 418a31561d594a2b636c1e2fa94ecd9e1245abb1 ]

If conntrack defragments incoming ipv6 frags it stores largest original
frag size in ip6cb and sets ->local_df.

We must thus first test the largest original frag size vs. mtu, and not
vice versa.

Without this patch PKTTOOBIG is still generated in ip6_fragment() later
in the stack, but

1) IPSTATS_MIB_INTOOBIGERRORS won't increment
2) packet did (needlessly) traverse netfilter postrouting hook.

Fixes: fe6cc55f3a9 ("net: ip, ipv6: handle gso skbs in forwarding path")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 3702d17..264a984 100644 (file)
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -344,12 +344,16 @@ static unsigned int ip6_dst_mtu_forward(const struct dst_entry *dst)
 
 static bool ip6_pkt_too_big(const struct sk_buff *skb, unsigned int mtu)
 {
-       if (skb->len <= mtu || skb->local_df)
+       if (skb->len <= mtu)
                return false;
 
+       /* ipv6 conntrack defrag sets max_frag_size + local_df */
        if (IP6CB(skb)->frag_max_size && IP6CB(skb)->frag_max_size > mtu)
                return true;
 
+       if (skb->local_df)
+               return false;
+
        if (skb_is_gso(skb) && skb_gso_network_seglen(skb) <= mtu)
                return false;