netfilter: xt_TCPMSS: Get mtu only if clamp-mss-to-pmtu is specified

This patch refactors the code to skip tcpmss_reverse_mtu if no
clamp-mss-to-pmtu is specified.

Signed-off-by: Gao feng <gaofeng@cn.fujitsu.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/netfilter/xt_TCPMSS.c b/net/netfilter/xt_TCPMSS.c
index cd24290..62776de 100644 (file)
--- a/net/netfilter/xt_TCPMSS.c
+++ b/net/netfilter/xt_TCPMSS.c
@@ -43,10 +43,41 @@ optlen(const u_int8_t *opt, unsigned int offset)
                return opt[offset+1];
 }
 
+static u_int32_t tcpmss_reverse_mtu(const struct sk_buff *skb,
+                                   unsigned int family)
+{
+       struct flowi fl;
+       const struct nf_afinfo *ai;
+       struct rtable *rt = NULL;
+       u_int32_t mtu     = ~0U;
+
+       if (family == PF_INET) {
+               struct flowi4 *fl4 = &fl.u.ip4;
+               memset(fl4, 0, sizeof(*fl4));
+               fl4->daddr = ip_hdr(skb)->saddr;
+       } else {
+               struct flowi6 *fl6 = &fl.u.ip6;
+
+               memset(fl6, 0, sizeof(*fl6));
+               fl6->daddr = ipv6_hdr(skb)->saddr;
+       }
+       rcu_read_lock();
+       ai = nf_get_afinfo(family);
+       if (ai != NULL)
+               ai->route(&init_net, (struct dst_entry **)&rt, &fl, false);
+       rcu_read_unlock();
+
+       if (rt != NULL) {
+               mtu = dst_mtu(&rt->dst);
+               dst_release(&rt->dst);
+       }
+       return mtu;
+}
+
 static int
 tcpmss_mangle_packet(struct sk_buff *skb,
                     const struct xt_action_param *par,
-                    unsigned int in_mtu,
+                    unsigned int family,
                     unsigned int tcphoff,
                     unsigned int minlen)
 {
@@ -76,6 +107,8 @@ tcpmss_mangle_packet(struct sk_buff *skb,
                return -1;
 
        if (info->mss == XT_TCPMSS_CLAMP_PMTU) {
+               unsigned int in_mtu = tcpmss_reverse_mtu(skb, family);
+
                if (dst_mtu(skb_dst(skb)) <= minlen) {
                        net_err_ratelimited("unknown or invalid path-MTU (%u)\n",
                                            dst_mtu(skb_dst(skb)));
@@ -165,37 +198,6 @@ tcpmss_mangle_packet(struct sk_buff *skb,
        return TCPOLEN_MSS;
 }
 
-static u_int32_t tcpmss_reverse_mtu(const struct sk_buff *skb,
-                                   unsigned int family)
-{
-       struct flowi fl;
-       const struct nf_afinfo *ai;
-       struct rtable *rt = NULL;
-       u_int32_t mtu     = ~0U;
-
-       if (family == PF_INET) {
-               struct flowi4 *fl4 = &fl.u.ip4;
-               memset(fl4, 0, sizeof(*fl4));
-               fl4->daddr = ip_hdr(skb)->saddr;
-       } else {
-               struct flowi6 *fl6 = &fl.u.ip6;
-
-               memset(fl6, 0, sizeof(*fl6));
-               fl6->daddr = ipv6_hdr(skb)->saddr;
-       }
-       rcu_read_lock();
-       ai = nf_get_afinfo(family);
-       if (ai != NULL)
-               ai->route(&init_net, (struct dst_entry **)&rt, &fl, false);
-       rcu_read_unlock();
-
-       if (rt != NULL) {
-               mtu = dst_mtu(&rt->dst);
-               dst_release(&rt->dst);
-       }
-       return mtu;
-}
-
 static unsigned int
 tcpmss_tg4(struct sk_buff *skb, const struct xt_action_param *par)
 {
@@ -204,7 +206,7 @@ tcpmss_tg4(struct sk_buff *skb, const struct xt_action_param *par)
        int ret;
 
        ret = tcpmss_mangle_packet(skb, par,
-                                  tcpmss_reverse_mtu(skb, PF_INET),
+                                  PF_INET,
                                   iph->ihl * 4,
                                   sizeof(*iph) + sizeof(struct tcphdr));
        if (ret < 0)
@@ -233,7 +235,7 @@ tcpmss_tg6(struct sk_buff *skb, const struct xt_action_param *par)
        if (tcphoff < 0)
                return NF_DROP;
        ret = tcpmss_mangle_packet(skb, par,
-                                  tcpmss_reverse_mtu(skb, PF_INET6),
+                                  PF_INET6,
                                   tcphoff,
                                   sizeof(*ipv6h) + sizeof(struct tcphdr));
        if (ret < 0)