On top of standard net branch, no previous patch required. === commit 46bfc78a6b91251fd55140b27f382259fc3333a2 Author: Jan Engelhardt <jengelh@xxxxxxxxxxxxxxx> Date: Wed Jan 23 16:35:00 2008 +0100 [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> diff --git a/net/netfilter/xt_TCPMSS.c b/net/netfilter/xt_TCPMSS.c index 60e3767..d2b3a27 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 +147,30 @@ tcpmss_mangle_packet(struct sk_buff *skb, return TCPOLEN_MSS; } +static u_int32_t tcpmss_reverse_mtu4(const struct iphdr *iph) +{ + struct flowi fl = {.nl_u = {.ip4_u = { + .daddr = iph->saddr, + .tos = RT_TOS(iph->tos), + .scope = RT_SCOPE_UNIVERSE, + }}}; + 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, @@ -146,8 +180,8 @@ tcpmss_tg4(struct sk_buff *skb, const struct net_device *in, __be16 newlen; int ret; - ret = tcpmss_mangle_packet(skb, targinfo, iph->ihl * 4, - sizeof(*iph) + sizeof(struct tcphdr)); + ret = tcpmss_mangle_packet(skb, targinfo, tcpmss_reverse_mtu4(iph), + iph->ihl * 4, sizeof(*iph) + sizeof(struct tcphdr)); if (ret < 0) return NF_DROP; if (ret > 0) { @@ -160,6 +194,31 @@ 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 = {.nl_u = {.ip6_u = { + .daddr = iph->saddr, + .flowlabel = ((iph->flow_lbl[0] << 16) | + (iph->flow_lbl[1] << 8) | iph->flow_lbl[2]) & + 0x00FFFFFF, + }}}; + 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, @@ -174,8 +233,8 @@ 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, - sizeof(*ipv6h) + sizeof(struct tcphdr)); + ret = tcpmss_mangle_packet(skb, targinfo, tcpmss_reverse_mtu6(ipv6h), + tcphoff, sizeof(*ipv6h) + sizeof(struct tcphdr)); if (ret < 0) return NF_DROP; if (ret > 0) { - To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html