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[NETFILTER]: xt_TCPMSS: consider reverse route's MTU in clamp-to-pmtu

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The TCPMSS target in Xtables should consider the MTU of the reverse
route on forwarded packets as part of the path MTU.

Point in case: IN=ppp0, OUT=eth0. MSS set to 1460 in spite of MTU of
ppp0 being 1392.

Signed-off-by: Jan Engelhardt <jengelh@computergmbh.de>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jan Engelhardt 2008-01-31 04:06:10 -08:00 committed by David S. Miller
parent df200969b1
commit 37c08387fc
1 changed files with 59 additions and 3 deletions
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62
net/netfilter/xt_TCPMSS.c
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@ -13,7 +13,10 @@
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/tcp.h>
#include <net/dst.h>
#include <net/flow.h>
#include <net/ipv6.h>
#include <net/route.h>
#include <net/tcp.h>
#include <linux/netfilter_ipv4/ip_tables.h>
@ -41,6 +44,7 @@ optlen(const u_int8_t *opt, unsigned int offset)
static int
tcpmss_mangle_packet(struct sk_buff *skb,
const struct xt_tcpmss_info *info,
unsigned int in_mtu,
unsigned int tcphoff,
unsigned int minlen)
{
@ -76,7 +80,13 @@ tcpmss_mangle_packet(struct sk_buff *skb,
dst_mtu(skb->dst));
return -1;
}
newmss = dst_mtu(skb->dst) - minlen;
if (in_mtu <= minlen) {
if (net_ratelimit())
printk(KERN_ERR "xt_TCPMSS: unknown or "
"invalid path-MTU (%u)\n", in_mtu);
return -1;
}
newmss = min(dst_mtu(skb->dst), in_mtu) - minlen;
} else
newmss = info->mss;
@ -137,6 +147,28 @@ tcpmss_mangle_packet(struct sk_buff *skb,
return TCPOLEN_MSS;
}
static u_int32_t tcpmss_reverse_mtu4(const struct iphdr *iph)
{
struct flowi fl = {
.fl4_dst = iph->saddr,
};
const struct nf_afinfo *ai;
struct rtable *rt = NULL;
u_int32_t mtu = ~0U;
rcu_read_lock();
ai = nf_get_afinfo(AF_INET);
if (ai != NULL)
ai->route((struct dst_entry **)&rt, &fl);
rcu_read_unlock();
if (rt != NULL) {
mtu = dst_mtu(&rt->u.dst);
dst_release(&rt->u.dst);
}
return mtu;
}
static unsigned int
tcpmss_tg4(struct sk_buff *skb, const struct net_device *in,
const struct net_device *out, unsigned int hooknum,
@ -146,7 +178,8 @@ tcpmss_tg4(struct sk_buff *skb, const struct net_device *in,
__be16 newlen;
int ret;
ret = tcpmss_mangle_packet(skb, targinfo, iph->ihl * 4,
ret = tcpmss_mangle_packet(skb, targinfo, tcpmss_reverse_mtu4(iph),
iph->ihl * 4,
sizeof(*iph) + sizeof(struct tcphdr));
if (ret < 0)
return NF_DROP;
@ -160,6 +193,28 @@ tcpmss_tg4(struct sk_buff *skb, const struct net_device *in,
}
#if defined(CONFIG_IP6_NF_IPTABLES) || defined(CONFIG_IP6_NF_IPTABLES_MODULE)
static u_int32_t tcpmss_reverse_mtu6(const struct ipv6hdr *iph)
{
struct flowi fl = {
.fl6_dst = iph->saddr,
};
const struct nf_afinfo *ai;
struct rtable *rt = NULL;
u_int32_t mtu = ~0U;
rcu_read_lock();
ai = nf_get_afinfo(AF_INET6);
if (ai != NULL)
ai->route((struct dst_entry **)&rt, &fl);
rcu_read_unlock();
if (rt != NULL) {
mtu = dst_mtu(&rt->u.dst);
dst_release(&rt->u.dst);
}
return mtu;
}
static unsigned int
tcpmss_tg6(struct sk_buff *skb, const struct net_device *in,
const struct net_device *out, unsigned int hooknum,
@ -174,7 +229,8 @@ tcpmss_tg6(struct sk_buff *skb, const struct net_device *in,
tcphoff = ipv6_skip_exthdr(skb, sizeof(*ipv6h), &nexthdr);
if (tcphoff < 0)
return NF_DROP;
ret = tcpmss_mangle_packet(skb, targinfo, tcphoff,
ret = tcpmss_mangle_packet(skb, targinfo, tcpmss_reverse_mtu6(ipv6h),
tcphoff,
sizeof(*ipv6h) + sizeof(struct tcphdr));
if (ret < 0)
return NF_DROP;