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netfilter: xt_TCPMSS: Fix IPv6 default MSS too

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As a followup to commit 409b545a ("netfilter: xt_TCPMSS: Fix violation
of RFC879 in absence of MSS option"), John Heffner points out that IPv6
has a higher MTU than IPv4, and thus a higher minimum MSS. Update TCPMSS
target to account for this, and update RFC comment.

While at it, point to more recent reference RFC1122 instead of RFC879.

Signed-off-by: Phil Oester <kernel@linuxace.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Phil Oester 2013-06-12 10:44:51 +02:00 committed by Pablo Neira Ayuso
parent ed82c43732
commit 70d19f805f
1 changed files with 14 additions and 7 deletions
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21
net/netfilter/xt_TCPMSS.c
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@ -45,11 +45,12 @@ optlen(const u_int8_t *opt, unsigned int offset)
static int
tcpmss_mangle_packet(struct sk_buff *skb,
const struct xt_tcpmss_info *info,
const struct xt_action_param *par,
unsigned int in_mtu,
unsigned int tcphoff,
unsigned int minlen)
{
const struct xt_tcpmss_info *info = par->targinfo;
struct tcphdr *tcph;
unsigned int tcplen, i;
__be16 oldval;
@ -125,11 +126,17 @@ tcpmss_mangle_packet(struct sk_buff *skb,
skb_put(skb, TCPOLEN_MSS);
/* RFC 879 states that the default MSS is 536 without specific
* knowledge that the destination host is prepared to accept larger.
* Since no MSS was provided, we MUST NOT set a value > 536.
/*
* IPv4: RFC 1122 states "If an MSS option is not received at
* connection setup, TCP MUST assume a default send MSS of 536".
* IPv6: RFC 2460 states IPv6 has a minimum MTU of 1280 and a minimum
* length IPv6 header of 60, ergo the default MSS value is 1220
* Since no MSS was provided, we must use the default values
*/
newmss = min(newmss, (u16)536);
if (par->family == NFPROTO_IPV4)
newmss = min(newmss, (u16)536);
else
newmss = min(newmss, (u16)1220);
opt = (u_int8_t *)tcph + sizeof(struct tcphdr);
memmove(opt + TCPOLEN_MSS, opt, tcplen - sizeof(struct tcphdr));
@ -188,7 +195,7 @@ tcpmss_tg4(struct sk_buff *skb, const struct xt_action_param *par)
__be16 newlen;
int ret;
ret = tcpmss_mangle_packet(skb, par->targinfo,
ret = tcpmss_mangle_packet(skb, par,
tcpmss_reverse_mtu(skb, PF_INET),
iph->ihl * 4,
sizeof(*iph) + sizeof(struct tcphdr));
@ -217,7 +224,7 @@ tcpmss_tg6(struct sk_buff *skb, const struct xt_action_param *par)
tcphoff = ipv6_skip_exthdr(skb, sizeof(*ipv6h), &nexthdr, &frag_off);
if (tcphoff < 0)
return NF_DROP;
ret = tcpmss_mangle_packet(skb, par->targinfo,
ret = tcpmss_mangle_packet(skb, par,
tcpmss_reverse_mtu(skb, PF_INET6),
tcphoff,
sizeof(*ipv6h) + sizeof(struct tcphdr));