[NETFILTER]: xt_TCPMSS: consider reverse route's MTU in clamp-to-pmtu
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@xxxxxxxxxxxxxxx>
Signed-off-by: Patrick McHardy <kaber@xxxxxxxxx>
---
commit 09a855c601cbbf240e7f127705dea74317658c45
tree ee82dc3cf0ff1e97e3bfa126678b4625d3a6d7b1
parent 5925cf9534dffe7165056399a6911609bd1fb44b
author Jan Engelhardt <jengelh@xxxxxxxxxxxxxxx> Tue, 29 Jan 2008 16:22:03 +0100
committer Patrick McHardy <kaber@xxxxxxxxx> Wed, 30 Jan 2008 15:04:18 +0100
net/netfilter/xt_TCPMSS.c | 62 +++++++++++++++++++++++++++++++++++++++++++--
1 files changed, 59 insertions(+), 3 deletions(-)
diff --git a/net/netfilter/xt_TCPMSS.c b/net/netfilter/xt_TCPMSS.c
index 60e3767..217e2b6 100644
--- a/net/netfilter/xt_TCPMSS.c
+++ b/net/netfilter/xt_TCPMSS.c
@@ -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;
-
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