[PATCH 3.11 119/138] net: ipv6: send pkttoobig immediately if orig frag size > mtu

From: Luis Henriques
Date: Tue Jun 03 2014 - 07:47:55 EST -stable review patch. If anyone has any objections, please let me know.


From: Florian Westphal <fw@xxxxxxxxx>

commit 418a31561d594a2b636c1e2fa94ecd9e1245abb1 upstream.

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

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@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
net/ipv6/ip6_output.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index d18c00a36fde..fe0bc8e0e866 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -348,12 +348,16 @@ static inline int ip6_forward_finish(struct sk_buff *skb)

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;


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