netfilter: xt_TCPMSS: Refactor the codes to decrease one condition check and more readable

The origin codes perform two condition checks with dst_mtu(skb_dst(skb))
and in_mtu. And the last statement is "min(dst_mtu(skb_dst(skb)),
in_mtu) - minlen". It may let reader think about how about the result.
Would it be negative.

Now assign the result of min(dst_mtu(skb_dst(skb)), in_mtu) to a new
variable, then only perform one condition check, and it is more readable.

Signed-off-by: Gao Feng <fgao@ikuai8.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 4 insertions, 8 deletions

diff --git a/net/netfilter/xt_TCPMSS.c b/net/netfilter/xt_TCPMSS.c
index e118397254af..872db2d0e2a9 100644
--- a/net/netfilter/xt_TCPMSS.c
+++ b/net/netfilter/xt_TCPMSS.c
@@ -110,18 +110,14 @@ tcpmss_mangle_packet(struct sk_buff *skb,
         if (info->mss == XT_TCPMSS_CLAMP_PMTU) {
                 struct net *net = par->net;
                 unsigned int in_mtu = tcpmss_reverse_mtu(net, skb, family);
+                unsigned int min_mtu = min(dst_mtu(skb_dst(skb)), in_mtu);
 
-                if (dst_mtu(skb_dst(skb)) <= minlen) {
+                if (min_mtu <= minlen) {
                         net_err_ratelimited("unknown or invalid path-MTU (%u)\n",
-                                            dst_mtu(skb_dst(skb)));
+                                            min_mtu);
                         return -1;
                 }
-                if (in_mtu <= minlen) {
-                        net_err_ratelimited("unknown or invalid path-MTU (%u)\n",
-                                            in_mtu);
-                        return -1;
-                }
-                newmss = min(dst_mtu(skb_dst(skb)), in_mtu) - minlen;
+                newmss = min_mtu - minlen;
         } else
                 newmss = info->mss;