From 48b1de4c110a7afa4b85862f6c75af817db26fad Mon Sep 17 00:00:00 2001 From: Patrick McHardy Date: Tue, 27 Aug 2013 08:50:14 +0200 Subject: netfilter: add SYNPROXY core/target Add a SYNPROXY for netfilter. The code is split into two parts, the synproxy core with common functions and an address family specific target. The SYNPROXY receives the connection request from the client, responds with a SYN/ACK containing a SYN cookie and announcing a zero window and checks whether the final ACK from the client contains a valid cookie. It then establishes a connection to the original destination and, if successful, sends a window update to the client with the window size announced by the server. Support for timestamps, SACK, window scaling and MSS options can be statically configured as target parameters if the features of the server are known. If timestamps are used, the timestamp value sent back to the client in the SYN/ACK will be different from the real timestamp of the server. In order to now break PAWS, the timestamps are translated in the direction server->client. Signed-off-by: Patrick McHardy Tested-by: Martin Topholm Signed-off-by: Jesper Dangaard Brouer Signed-off-by: Pablo Neira Ayuso --- net/netfilter/nf_conntrack_proto_tcp.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) (limited to 'net/netfilter/nf_conntrack_proto_tcp.c') diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c index 984a8d1..44d1ea3 100644 --- a/net/netfilter/nf_conntrack_proto_tcp.c +++ b/net/netfilter/nf_conntrack_proto_tcp.c @@ -28,6 +28,7 @@ #include #include #include +#include #include #include #include @@ -946,6 +947,21 @@ static int tcp_packet(struct nf_conn *ct, "state %s ", tcp_conntrack_names[old_state]); return NF_ACCEPT; case TCP_CONNTRACK_MAX: + /* Special case for SYN proxy: when the SYN to the server or + * the SYN/ACK from the server is lost, the client may transmit + * a keep-alive packet while in SYN_SENT state. This needs to + * be associated with the original conntrack entry in order to + * generate a new SYN with the correct sequence number. + */ + if (nfct_synproxy(ct) && old_state == TCP_CONNTRACK_SYN_SENT && + index == TCP_ACK_SET && dir == IP_CT_DIR_ORIGINAL && + ct->proto.tcp.last_dir == IP_CT_DIR_ORIGINAL && + ct->proto.tcp.seen[dir].td_end - 1 == ntohl(th->seq)) { + pr_debug("nf_ct_tcp: SYN proxy client keep alive\n"); + spin_unlock_bh(&ct->lock); + return NF_ACCEPT; + } + /* Invalid packet */ pr_debug("nf_ct_tcp: Invalid dir=%i index=%u ostate=%u\n", dir, get_conntrack_index(th), old_state); -- cgit v1.1