diff options
| author | Phil Oester <kernel@linuxace.com> | 2013-06-04 05:09:27 +0000 |
|---|---|---|
| committer | Pablo Neira Ayuso <pablo@netfilter.org> | 2013-06-05 13:59:22 +0200 |
| commit | 409b545ac10d9548929557a75ad86540f59a2c83 (patch) | |
| tree | 2d6be092933a6540dce90a36c10548859f09cc9e | |
| parent | 37bc4f8dfa72fb43b84381abca39cfdbbc8ff2df (diff) | |
netfilter: xt_TCPMSS: Fix violation of RFC879 in absence of MSS option
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@linuxace.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
| -rw-r--r-- | net/netfilter/xt_TCPMSS.c | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/net/netfilter/xt_TCPMSS.c b/net/netfilter/xt_TCPMSS.c index a75240f0d42..afaebc76693 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)); |