[NETFILTER] ctnetlink: allow userspace to change TCP state

This patch adds the ability of changing the state a TCP connection. I know
that this must be used with care but it's required to provide a complete
conntrack creation via conntrack_netlink. So I'll document this aspect on
the upcoming docs.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Harald Welte <laforge@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 26 insertions, 0 deletions

diff --git a/include/linux/netfilter_ipv4/ip_conntrack_protocol.h b/include/linux/netfilter_ipv4/ip_conntrack_protocol.h
index b6b99be8632a..2c76b879e3dc 100644
--- a/include/linux/netfilter_ipv4/ip_conntrack_protocol.h
+++ b/include/linux/netfilter_ipv4/ip_conntrack_protocol.h
@@ -52,6 +52,9 @@ struct ip_conntrack_protocol
         int (*to_nfattr)(struct sk_buff *skb, struct nfattr *nfa,
                          const struct ip_conntrack *ct);
 
+        /* convert nfnetlink attributes to protoinfo */
+        int (*from_nfattr)(struct nfattr *tb[], struct ip_conntrack *ct);
+
         int (*tuple_to_nfattr)(struct sk_buff *skb,
                                const struct ip_conntrack_tuple *t);
         int (*nfattr_to_tuple)(struct nfattr *tb[],
diff --git a/net/ipv4/netfilter/ip_conntrack_proto_tcp.c b/net/ipv4/netfilter/ip_conntrack_proto_tcp.c
index 75e27e65c28f..d6701cafbcc2 100644
--- a/net/ipv4/netfilter/ip_conntrack_proto_tcp.c
+++ b/net/ipv4/netfilter/ip_conntrack_proto_tcp.c
@@ -356,6 +356,28 @@ nfattr_failure:
         read_unlock_bh(&tcp_lock);
         return -1;
 }
+
+static int nfattr_to_tcp(struct nfattr *cda[], struct ip_conntrack *ct)
+{
+        struct nfattr *attr = cda[CTA_PROTOINFO_TCP-1];
+        struct nfattr *tb[CTA_PROTOINFO_TCP_MAX];
+
+        if (nfattr_parse_nested(tb, CTA_PROTOINFO_TCP_MAX, attr) < 0)
+                goto nfattr_failure;
+
+        if (!tb[CTA_PROTOINFO_TCP_STATE-1])
+                return -EINVAL;
+
+        write_lock_bh(&tcp_lock);
+        ct->proto.tcp.state = 
+                *(u_int8_t *)NFA_DATA(tb[CTA_PROTOINFO_TCP_STATE-1]);
+        write_unlock_bh(&tcp_lock);
+
+        return 0;
+
+nfattr_failure:
+        return -1;
+}
 #endif
 
 static unsigned int get_conntrack_index(const struct tcphdr *tcph)
@@ -1127,6 +1149,7 @@ struct ip_conntrack_protocol ip_conntrack_protocol_tcp =
 #if defined(CONFIG_IP_NF_CONNTRACK_NETLINK) || \
     defined(CONFIG_IP_NF_CONNTRACK_NETLINK_MODULE)
         .to_nfattr              = tcp_to_nfattr,
+        .from_nfattr            = nfattr_to_tcp,
         .tuple_to_nfattr        = ip_ct_port_tuple_to_nfattr,
         .nfattr_to_tuple        = ip_ct_port_nfattr_to_tuple,
 #endif