netfilter: rt: add support to fetch path mss

to be used in combination with tcp option set support to mimic
iptables TCPMSS --clamp-mss-to-pmtu.

v2: Eric Dumazet points out dst must be initialized.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/include/uapi/linux/netfilter/nf_tables.h b/include/uapi/linux/netfilter/nf_tables.h
index 40fd199f7531ac236b49639d4f9a7ad41875d04e..b49da72efa68c6f34c3fb1a0acdd9747a9a45f38 100644 (file)
--- a/include/uapi/linux/netfilter/nf_tables.h
+++ b/include/uapi/linux/netfilter/nf_tables.h
@@ -811,11 +811,13 @@ enum nft_meta_keys {
  * @NFT_RT_CLASSID: realm value of packet's route (skb->dst->tclassid)
  * @NFT_RT_NEXTHOP4: routing nexthop for IPv4
  * @NFT_RT_NEXTHOP6: routing nexthop for IPv6
+ * @NFT_RT_TCPMSS: fetch current path tcp mss
  */
 enum nft_rt_keys {
        NFT_RT_CLASSID,
        NFT_RT_NEXTHOP4,
        NFT_RT_NEXTHOP6,
+       NFT_RT_TCPMSS,
 };
 
 /**

diff --git a/net/netfilter/nft_rt.c b/net/netfilter/nft_rt.c
index c7383d8f88d0b2fa90b9bc9d94df20e6198dd2de..e142e65d3176123a41b343296afbd3a320813ea6 100644 (file)
--- a/net/netfilter/nft_rt.c
+++ b/net/netfilter/nft_rt.c
@@ -23,6 +23,42 @@ struct nft_rt {
        enum nft_registers      dreg:8;
 };
 
+static u16 get_tcpmss(const struct nft_pktinfo *pkt, const struct dst_entry *skbdst)
+{
+       u32 minlen = sizeof(struct ipv6hdr), mtu = dst_mtu(skbdst);
+       const struct sk_buff *skb = pkt->skb;
+       const struct nf_afinfo *ai;
+       struct flowi fl;
+
+       memset(&fl, 0, sizeof(fl));
+
+       switch (nft_pf(pkt)) {
+       case NFPROTO_IPV4:
+               fl.u.ip4.daddr = ip_hdr(skb)->saddr;
+               minlen = sizeof(struct iphdr);
+               break;
+       case NFPROTO_IPV6:
+               fl.u.ip6.daddr = ipv6_hdr(skb)->saddr;
+               break;
+       }
+
+       ai = nf_get_afinfo(nft_pf(pkt));
+       if (ai) {
+               struct dst_entry *dst = NULL;
+
+               ai->route(nft_net(pkt), &dst, &fl, false);
+               if (dst) {
+                       mtu = min(mtu, dst_mtu(dst));
+                       dst_release(dst);
+               }
+       }
+
+       if (mtu <= minlen || mtu > 0xffff)
+               return TCP_MSS_DEFAULT;
+
+       return mtu - minlen;
+}
+
 static void nft_rt_get_eval(const struct nft_expr *expr,
                            struct nft_regs *regs,
                            const struct nft_pktinfo *pkt)
@@ -57,6 +93,9 @@ static void nft_rt_get_eval(const struct nft_expr *expr,
                                         &ipv6_hdr(skb)->daddr),
                       sizeof(struct in6_addr));
                break;
+       case NFT_RT_TCPMSS:
+               nft_reg_store16(dest, get_tcpmss(pkt, dst));
+               break;
        default:
                WARN_ON(1);
                goto err;
@@ -94,6 +133,9 @@ static int nft_rt_get_init(const struct nft_ctx *ctx,
        case NFT_RT_NEXTHOP6:
                len = sizeof(struct in6_addr);
                break;
+       case NFT_RT_TCPMSS:
+               len = sizeof(u16);
+               break;
        default:
                return -EOPNOTSUPP;
        }
@@ -118,6 +160,29 @@ nla_put_failure:
        return -1;
 }
 
+static int nft_rt_validate(const struct nft_ctx *ctx, const struct nft_expr *expr,
+                          const struct nft_data **data)
+{
+       const struct nft_rt *priv = nft_expr_priv(expr);
+       unsigned int hooks;
+
+       switch (priv->key) {
+       case NFT_RT_NEXTHOP4:
+       case NFT_RT_NEXTHOP6:
+       case NFT_RT_CLASSID:
+               return 0;
+       case NFT_RT_TCPMSS:
+               hooks = (1 << NF_INET_FORWARD) |
+                       (1 << NF_INET_LOCAL_OUT) |
+                       (1 << NF_INET_POST_ROUTING);
+               break;
+       default:
+               return -EINVAL;
+       }
+
+       return nft_chain_validate_hooks(ctx->chain, hooks);
+}
+
 static struct nft_expr_type nft_rt_type;
 static const struct nft_expr_ops nft_rt_get_ops = {
        .type           = &nft_rt_type,
@@ -125,6 +190,7 @@ static const struct nft_expr_ops nft_rt_get_ops = {
        .eval           = nft_rt_get_eval,
        .init           = nft_rt_get_init,
        .dump           = nft_rt_get_dump,
+       .validate       = nft_rt_validate,
 };
 
 static struct nft_expr_type nft_rt_type __read_mostly = {