From: Phil Oester <kernel@xxxxxxxxxxxx> The clamp-mss-to-pmtu option of the xt_TCPMSS target can cause issues connecting to websites if there was no MSS option present in the original SYN packet from the client. In these cases, it may add a MSS higher than the default specified in RFC879. Fix this by never setting a value > 536 if no MSS option was specified by the client. This closes netfilter's bugzilla #662. Signed-off-by: Phil Oester <kernel@xxxxxxxxxxxx> Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx> --- net/netfilter/xt_TCPMSS.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/net/netfilter/xt_TCPMSS.c b/net/netfilter/xt_TCPMSS.c index a75240f..afaebc7 100644 --- a/net/netfilter/xt_TCPMSS.c +++ b/net/netfilter/xt_TCPMSS.c @@ -125,6 +125,12 @@ 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. + */ + newmss = min(newmss, (u16)536); + opt = (u_int8_t *)tcph + sizeof(struct tcphdr); memmove(opt + TCPOLEN_MSS, opt, tcplen - sizeof(struct tcphdr)); -- 1.7.10.4 -- 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
