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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>
This commit is contained in:
Florian Westphal 2017-08-08 15:48:04 +02:00 committed by Pablo Neira Ayuso
parent 99d1712bc4
commit 6b5dc98e8f
2 changed files with 68 additions and 0 deletions
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2
include/uapi/linux/netfilter/nf_tables.h
View File

@ -811,11 +811,13 @@ enum nft_meta_keys {
* @NFT_RT_CLASSID: realm value of packet's route (skb->dst->tclassid) * @NFT_RT_CLASSID: realm value of packet's route (skb->dst->tclassid)
* @NFT_RT_NEXTHOP4: routing nexthop for IPv4 * @NFT_RT_NEXTHOP4: routing nexthop for IPv4
* @NFT_RT_NEXTHOP6: routing nexthop for IPv6 * @NFT_RT_NEXTHOP6: routing nexthop for IPv6
* @NFT_RT_TCPMSS: fetch current path tcp mss
*/ */
enum nft_rt_keys { enum nft_rt_keys {
NFT_RT_CLASSID, NFT_RT_CLASSID,
NFT_RT_NEXTHOP4, NFT_RT_NEXTHOP4,
NFT_RT_NEXTHOP6, NFT_RT_NEXTHOP6,
NFT_RT_TCPMSS,
}; };
/** /**

66
net/netfilter/nft_rt.c
View File

@ -23,6 +23,42 @@ struct nft_rt {
enum nft_registers dreg:8; 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, static void nft_rt_get_eval(const struct nft_expr *expr,
struct nft_regs *regs, struct nft_regs *regs,
const struct nft_pktinfo *pkt) const struct nft_pktinfo *pkt)
@ -57,6 +93,9 @@ static void nft_rt_get_eval(const struct nft_expr *expr,
&ipv6_hdr(skb)->daddr), &ipv6_hdr(skb)->daddr),
sizeof(struct in6_addr)); sizeof(struct in6_addr));
break; break;
case NFT_RT_TCPMSS:
nft_reg_store16(dest, get_tcpmss(pkt, dst));
break;
default: default:
WARN_ON(1); WARN_ON(1);
goto err; goto err;
@ -94,6 +133,9 @@ static int nft_rt_get_init(const struct nft_ctx *ctx,
case NFT_RT_NEXTHOP6: case NFT_RT_NEXTHOP6:
len = sizeof(struct in6_addr); len = sizeof(struct in6_addr);
break; break;
case NFT_RT_TCPMSS:
len = sizeof(u16);
break;
default: default:
return -EOPNOTSUPP; return -EOPNOTSUPP;
} }
@ -118,6 +160,29 @@ static int nft_rt_get_dump(struct sk_buff *skb,
return -1; 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 struct nft_expr_type nft_rt_type;
static const struct nft_expr_ops nft_rt_get_ops = { static const struct nft_expr_ops nft_rt_get_ops = {
.type = &nft_rt_type, .type = &nft_rt_type,
@ -125,6 +190,7 @@ static const struct nft_expr_ops nft_rt_get_ops = {
.eval = nft_rt_get_eval, .eval = nft_rt_get_eval,
.init = nft_rt_get_init, .init = nft_rt_get_init,
.dump = nft_rt_get_dump, .dump = nft_rt_get_dump,
.validate = nft_rt_validate,
}; };
static struct nft_expr_type nft_rt_type __read_mostly = { static struct nft_expr_type nft_rt_type __read_mostly = {