[DCCP]: Handle timestamps on Request/Response exchange separately

In DCCP, timestamps can occur on packets anytime, CCID3 uses a timestamp(/echo) on the Request/Response
exchange. This patch addresses the following situation:
	* timestamps are recorded on the listening socket;
	* Responses are sent from dccp_request_sockets;
	* suppose two connections reach the listening socket with very small time in between:
	* the first timestamp value gets overwritten by the second connection request.

This is not really good, so this patch separates timestamps into
 * those which are received by the server during the initial handshake (on dccp_request_sock);
 * those which are received by the client or the client after connection establishment.

As before, a timestamp of 0 is regarded as indicating that no (meaningful) timestamp has been
received (in addition, a warning message is printed if hosts send 0-valued timestamps).

The timestamp-echoing now works as follows:
 * when a timestamp is present on the initial Request, it is placed into dreq, due to the
   call to dccp_parse_options in dccp_v{4,6}_conn_request;
 * when a timestamp is present on the Ack leading from RESPOND => OPEN, it is copied over
   from the request_sock into the child cocket in dccp_create_openreq_child;
 * timestamps received on an (established) dccp_sock are treated as before.

Since Elapsed Time is measured in hundredths of milliseconds (13.2), the new dccp_timestamp()
function is used, as it is expected that the time between receiving the timestamp and
sending the timestamp echo will be very small against the wrap-around time. As a byproduct,
this allows smaller timestamping-time fields.

Furthermore, inserting the Timestamp Echo option has been taken out of the block starting with
'!dccp_packet_without_ack()', since Timestamp Echo can be carried on any packet (5.8 and 13.3).

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 14 insertions, 2 deletions

diff --git a/include/linux/dccp.h b/include/linux/dccp.h
index 7214031461d..484e45c7c89 100644
--- a/include/linux/dccp.h
+++ b/include/linux/dccp.h
@@ -407,11 +407,23 @@ struct dccp_opt_pend {
 
 extern void dccp_minisock_init(struct dccp_minisock *dmsk);
 
+/**
+ * struct dccp_request_sock  -  represent DCCP-specific connection request
+ * @dreq_inet_rsk: structure inherited from
+ * @dreq_iss: initial sequence number sent on the Response (RFC 4340, 7.1)
+ * @dreq_isr: initial sequence number received on the Request
+ * @dreq_service: service code present on the Request (there is just one)
+ * The following two fields are analogous to the ones in dccp_sock:
+ * @dreq_timestamp_echo: last received timestamp to echo (13.1)
+ * @dreq_timestamp_echo: the time of receiving the last @dreq_timestamp_echo
+ */
 struct dccp_request_sock {
 	struct inet_request_sock dreq_inet_rsk;
 	__u64			 dreq_iss;
 	__u64			 dreq_isr;
 	__be32			 dreq_service;
+	__u32			 dreq_timestamp_echo;
+	__u32			 dreq_timestamp_time;
 };
 
 static inline struct dccp_request_sock *dccp_rsk(const struct request_sock *req)
@@ -477,8 +489,8 @@ struct dccp_ackvec;
  * @dccps_gar - greatest valid ack number received on a non-Sync; initialized to %dccps_iss
  * @dccps_service - first (passive sock) or unique (active sock) service code
  * @dccps_service_list - second .. last service code on passive socket
- * @dccps_timestamp_time - time of latest TIMESTAMP option
  * @dccps_timestamp_echo - latest timestamp received on a TIMESTAMP option
+ * @dccps_timestamp_time - time of receiving latest @dccps_timestamp_echo
  * @dccps_l_ack_ratio - feature-local Ack Ratio
  * @dccps_r_ack_ratio - feature-remote Ack Ratio
  * @dccps_pcslen - sender   partial checksum coverage (via sockopt)
@@ -514,8 +526,8 @@ struct dccp_sock {
 	__u64				dccps_gar;
 	__be32				dccps_service;
 	struct dccp_service_list	*dccps_service_list;
-	ktime_t				dccps_timestamp_time;
 	__u32				dccps_timestamp_echo;
+	__u32				dccps_timestamp_time;
 	__u16				dccps_l_ack_ratio;
 	__u16				dccps_r_ack_ratio;
 	__u16				dccps_pcslen;