[PATCH 06/14] netfilter: synproxy: fix erroneous tcp mss option

[Pablo Neira Ayuso]

From: Fernando Fernandez Mancera <ffmanc...@riseup.net>

Now synproxy sends the mss value set by the user on client syn-ack packet
instead of the mss value that client announced.

Fixes: 48b1de4c110a ("netfilter: add SYNPROXY core/target")
Signed-off-by: Fernando Fernandez Mancera <ffmanc...@riseup.net>
Signed-off-by: Pablo Neira Ayuso <pa...@netfilter.org>
---
 include/net/netfilter/nf_conntrack_synproxy.h | 1 +
 net/ipv4/netfilter/ipt_SYNPROXY.c             | 2 ++
 net/ipv6/netfilter/ip6t_SYNPROXY.c            | 2 ++
 net/netfilter/nf_synproxy_core.c              | 4 ++--
 net/netfilter/nft_synproxy.c                  | 2 ++
 5 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/include/net/netfilter/nf_conntrack_synproxy.h 
b/include/net/netfilter/nf_conntrack_synproxy.h
index 8f00125b06f4..44513b93bd55 100644
--- a/include/net/netfilter/nf_conntrack_synproxy.h
+++ b/include/net/netfilter/nf_conntrack_synproxy.h
@@ -68,6 +68,7 @@ struct synproxy_options {
        u8                              options;
        u8                              wscale;
        u16                             mss;
+       u16                             mss_encode;
        u32                             tsval;
        u32                             tsecr;
 };
diff --git a/net/ipv4/netfilter/ipt_SYNPROXY.c 
b/net/ipv4/netfilter/ipt_SYNPROXY.c
index 8e7f84ec783d..0e70f3f65f6f 100644
--- a/net/ipv4/netfilter/ipt_SYNPROXY.c
+++ b/net/ipv4/netfilter/ipt_SYNPROXY.c
@@ -36,6 +36,8 @@ synproxy_tg4(struct sk_buff *skb, const struct 
xt_action_param *par)
                        opts.options |= XT_SYNPROXY_OPT_ECN;
 
                opts.options &= info->options;
+               opts.mss_encode = opts.mss;
+               opts.mss = info->mss;
                if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
                        synproxy_init_timestamp_cookie(info, &opts);
                else
diff --git a/net/ipv6/netfilter/ip6t_SYNPROXY.c 
b/net/ipv6/netfilter/ip6t_SYNPROXY.c
index e77ea1ed5edd..5cdb4a69d277 100644
--- a/net/ipv6/netfilter/ip6t_SYNPROXY.c
+++ b/net/ipv6/netfilter/ip6t_SYNPROXY.c
@@ -36,6 +36,8 @@ synproxy_tg6(struct sk_buff *skb, const struct 
xt_action_param *par)
                        opts.options |= XT_SYNPROXY_OPT_ECN;
 
                opts.options &= info->options;
+               opts.mss_encode = opts.mss;
+               opts.mss = info->mss;
                if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
                        synproxy_init_timestamp_cookie(info, &opts);
                else
diff --git a/net/netfilter/nf_synproxy_core.c b/net/netfilter/nf_synproxy_core.c
index b101f187eda8..09718e5a9e41 100644
--- a/net/netfilter/nf_synproxy_core.c
+++ b/net/netfilter/nf_synproxy_core.c
@@ -470,7 +470,7 @@ synproxy_send_client_synack(struct net *net,
        struct iphdr *iph, *niph;
        struct tcphdr *nth;
        unsigned int tcp_hdr_size;
-       u16 mss = opts->mss;
+       u16 mss = opts->mss_encode;
 
        iph = ip_hdr(skb);
 
@@ -884,7 +884,7 @@ synproxy_send_client_synack_ipv6(struct net *net,
        struct ipv6hdr *iph, *niph;
        struct tcphdr *nth;
        unsigned int tcp_hdr_size;
-       u16 mss = opts->mss;
+       u16 mss = opts->mss_encode;
 
        iph = ipv6_hdr(skb);
 
diff --git a/net/netfilter/nft_synproxy.c b/net/netfilter/nft_synproxy.c
index 80060ade8a5b..928e661d1517 100644
--- a/net/netfilter/nft_synproxy.c
+++ b/net/netfilter/nft_synproxy.c
@@ -31,6 +31,8 @@ static void nft_synproxy_tcp_options(struct synproxy_options 
*opts,
                opts->options |= NF_SYNPROXY_OPT_ECN;
 
        opts->options &= priv->info.options;
+       opts->mss_encode = opts->mss;
+       opts->mss = info->mss;
        if (opts->options & NF_SYNPROXY_OPT_TIMESTAMP)
                synproxy_init_timestamp_cookie(info, opts);
        else
-- 
2.11.0