to be used in combination with tcp option set support to mimic
iptables TCPMSS --clamp-mss-to-pmtu.
Signed-off-by: Florian Westphal <f...@strlen.de>
---
include/uapi/linux/netfilter/nf_tables.h | 2 +
net/netfilter/nft_rt.c | 65 ++++++++++++++++++++++++++++++++
2 files changed, 67 insertions(+)
diff --git a/include/uapi/linux/netfilter/nf_tables.h
b/include/uapi/linux/netfilter/nf_tables.h
index 40fd199f7531..b49da72efa68 100644
--- 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 c7383d8f88d0..69ed601d6fc6 100644
--- a/net/netfilter/nft_rt.c
+++ b/net/netfilter/nft_rt.c
@@ -23,6 +23,41 @@ 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 dst_entry *dst;
+ 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)
+ 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 +92,9 @@ 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 +132,9 @@ 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 +159,29 @@ static int nft_rt_get_dump(struct sk_buff *skb,
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 +189,7 @@ 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 = {
--
2.13.0
--
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