[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>

3 files changed, 63 insertions, 30 deletions

diff --git a/include/linux/dccp.h b/include/linux/dccp.h
index 7214031461d3..484e45c7c89a 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;
diff --git a/net/dccp/minisocks.c b/net/dccp/minisocks.c
index b1d5da61f6af..027d1814e1ab 100644
--- a/net/dccp/minisocks.c
+++ b/net/dccp/minisocks.c
@@ -117,11 +117,13 @@ struct sock *dccp_create_openreq_child(struct sock *sk,
                 struct dccp_sock *newdp = dccp_sk(newsk);
                 struct dccp_minisock *newdmsk = dccp_msk(newsk);
 
-                newdp->dccps_role          = DCCP_ROLE_SERVER;
-                newdp->dccps_hc_rx_ackvec  = NULL;
-                newdp->dccps_service_list  = NULL;
-                newdp->dccps_service       = dreq->dreq_service;
-                newicsk->icsk_rto          = DCCP_TIMEOUT_INIT;
+                newdp->dccps_role           = DCCP_ROLE_SERVER;
+                newdp->dccps_hc_rx_ackvec   = NULL;
+                newdp->dccps_service_list   = NULL;
+                newdp->dccps_service        = dreq->dreq_service;
+                newdp->dccps_timestamp_echo = dreq->dreq_timestamp_echo;
+                newdp->dccps_timestamp_time = dreq->dreq_timestamp_time;
+                newicsk->icsk_rto           = DCCP_TIMEOUT_INIT;
 
                 if (dccp_feat_clone(sk, newsk))
                         goto out_free;
@@ -303,9 +305,12 @@ EXPORT_SYMBOL_GPL(dccp_reqsk_send_ack);
 
 void dccp_reqsk_init(struct request_sock *req, struct sk_buff *skb)
 {
-        inet_rsk(req)->rmt_port = dccp_hdr(skb)->dccph_sport;
-        inet_rsk(req)->acked    = 0;
-        req->rcv_wnd            = sysctl_dccp_feat_sequence_window;
+        struct dccp_request_sock *dreq = dccp_rsk(req);
+
+        inet_rsk(req)->rmt_port   = dccp_hdr(skb)->dccph_sport;
+        inet_rsk(req)->acked      = 0;
+        req->rcv_wnd              = sysctl_dccp_feat_sequence_window;
+        dreq->dreq_timestamp_echo = 0;
 }
 
 EXPORT_SYMBOL_GPL(dccp_reqsk_init);
diff --git a/net/dccp/options.c b/net/dccp/options.c
index f496d4dc7efc..0c996d8c79a3 100644
--- a/net/dccp/options.c
+++ b/net/dccp/options.c
@@ -166,16 +166,27 @@ int dccp_parse_options(struct sock *sk, struct dccp_request_sock *dreq,
                 case DCCPO_TIMESTAMP:
                         if (len != 4)
                                 goto out_invalid_option;
-
+                        /*
+                         * RFC 4340 13.1: "The precise time corresponding to
+                         * Timestamp Value zero is not specified". We use
+                         * zero to indicate absence of a meaningful timestamp.
+                         */
                         opt_val = get_unaligned((__be32 *)value);
-                        opt_recv->dccpor_timestamp = ntohl(opt_val);
-
-                        /* FIXME: if dreq != NULL, don't store this on listening socket */
-                        dp->dccps_timestamp_echo = opt_recv->dccpor_timestamp;
-                        dp->dccps_timestamp_time = ktime_get_real();
+                        if (unlikely(opt_val == 0)) {
+                                DCCP_WARN("Timestamp with zero value\n");
+                                break;
+                        }
 
+                        if (dreq != NULL) {
+                                dreq->dreq_timestamp_echo = ntohl(opt_val);
+                                dreq->dreq_timestamp_time = dccp_timestamp();
+                        } else {
+                                opt_recv->dccpor_timestamp =
+                                        dp->dccps_timestamp_echo = ntohl(opt_val);
+                                dp->dccps_timestamp_time = dccp_timestamp();
+                        }
                         dccp_pr_debug("%s rx opt: TIMESTAMP=%u, ackno=%llu\n",
-                                      dccp_role(sk), opt_recv->dccpor_timestamp,
+                                      dccp_role(sk), ntohl(opt_val),
                                       (unsigned long long)
                                       DCCP_SKB_CB(skb)->dccpd_ack_seq);
                         break;
@@ -393,16 +404,24 @@ int dccp_insert_option_timestamp(struct sock *sk, struct sk_buff *skb)
 
 EXPORT_SYMBOL_GPL(dccp_insert_option_timestamp);
 
-static int dccp_insert_option_timestamp_echo(struct sock *sk,
+static int dccp_insert_option_timestamp_echo(struct dccp_sock *dp,
+                                             struct dccp_request_sock *dreq,
                                              struct sk_buff *skb)
 {
-        struct dccp_sock *dp = dccp_sk(sk);
         __be32 tstamp_echo;
-        int len, elapsed_time_len;
         unsigned char *to;
-        const suseconds_t delta = ktime_us_delta(ktime_get_real(),
-                                                 dp->dccps_timestamp_time);
-        u32 elapsed_time = delta / 10;
+        u32 elapsed_time, elapsed_time_len, len;
+
+        if (dreq != NULL) {
+                elapsed_time = dccp_timestamp() - dreq->dreq_timestamp_time;
+                tstamp_echo  = htonl(dreq->dreq_timestamp_echo);
+                dreq->dreq_timestamp_echo = 0;
+        } else {
+                elapsed_time = dccp_timestamp() - dp->dccps_timestamp_time;
+                tstamp_echo  = htonl(dp->dccps_timestamp_echo);
+                dp->dccps_timestamp_echo = 0;
+        }
+
         elapsed_time_len = dccp_elapsed_time_len(elapsed_time);
         len = 6 + elapsed_time_len;
 
@@ -415,7 +434,6 @@ static int dccp_insert_option_timestamp_echo(struct sock *sk,
         *to++ = DCCPO_TIMESTAMP_ECHO;
         *to++ = len;
 
-        tstamp_echo = htonl(dp->dccps_timestamp_echo);
         memcpy(to, &tstamp_echo, 4);
         to += 4;
 
@@ -427,8 +445,6 @@ static int dccp_insert_option_timestamp_echo(struct sock *sk,
                 memcpy(to, &var32, 4);
         }
 
-        dp->dccps_timestamp_echo = 0;
-        dp->dccps_timestamp_time = ktime_set(0, 0);
         return 0;
 }
 
@@ -537,10 +553,6 @@ int dccp_insert_options(struct sock *sk, struct sk_buff *skb)
                     dccp_ackvec_pending(dp->dccps_hc_rx_ackvec) &&
                     dccp_insert_option_ackvec(sk, skb))
                         return -1;
-
-                if (dp->dccps_timestamp_echo != 0 &&
-                    dccp_insert_option_timestamp_echo(sk, skb))
-                        return -1;
         }
 
         if (dp->dccps_hc_rx_insert_options) {
@@ -564,6 +576,10 @@ int dccp_insert_options(struct sock *sk, struct sk_buff *skb)
             dccp_insert_option_timestamp(sk, skb))
                 return -1;
 
+        if (dp->dccps_timestamp_echo != 0 &&
+            dccp_insert_option_timestamp_echo(dp, NULL, skb))
+                return -1;
+
         /* XXX: insert other options when appropriate */
 
         if (DCCP_SKB_CB(skb)->dccpd_opt_len != 0) {