act_nat: fix the wrong checksum when addr isn't in old_addr/mask

fix the wrong checksum when addr isn't in old_addr/mask

For TCP and UDP packets, when addr isn't in old_addr/mask we don't do SNAT or
DNAT, and we should not update layer 4 checksum.

Signed-off-by: Changli Gao <xiaosuo@gmail.com>
----
 net/sched/act_nat.c |    4 ++++
 1 file changed, 4 insertions(+)
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 0 deletions

diff --git a/net/sched/act_nat.c b/net/sched/act_nat.c
index d885ba311564..570949417f38 100644
--- a/net/sched/act_nat.c
+++ b/net/sched/act_nat.c
@@ -159,6 +159,9 @@ static int tcf_nat(struct sk_buff *skb, struct tc_action *a,
                         iph->daddr = new_addr;
 
                 csum_replace4(&iph->check, addr, new_addr);
+        } else if ((iph->frag_off & htons(IP_OFFSET)) ||
+                   iph->protocol != IPPROTO_ICMP) {
+                goto out;
         }
 
         ihl = iph->ihl * 4;
@@ -247,6 +250,7 @@ static int tcf_nat(struct sk_buff *skb, struct tc_action *a,
                 break;
         }
 
+out:
         return action;
 
 drop: