Allow disabling TCP timestamp options per route

Implement querying and acting upon the no timestamp bit in the feature
field.

Signed-off-by: Gilad Ben-Yossef <gilad@codefidence.com>
Sigend-off-by: Ori Finkelman <ori@comsleep.com>
Sigend-off-by: Yony Amit <yony@comsleep.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/rtnetlink.h

@@ -378,7 +378,7 @@ enum
 
 #define RTAX_FEATURE_ECN	0x00000001
 #define RTAX_FEATURE_NO_SACK	0x00000002
-#define RTAX_FEATURE_TIMESTAMP	0x00000004
+#define RTAX_FEATURE_NO_TSTAMP	0x00000004
 #define RTAX_FEATURE_ALLFRAG	0x00000008
 
 struct rta_session

net/ipv4/tcp_input.c

@@ -3755,7 +3755,8 @@ void tcp_parse_options(struct sk_buff *skb, struct tcp_options_received *opt_rx,
 			case TCPOPT_TIMESTAMP:
 				if ((opsize == TCPOLEN_TIMESTAMP) &&
 				    ((estab && opt_rx->tstamp_ok) ||
-				     (!estab && sysctl_tcp_timestamps))) {
+				     (!estab && sysctl_tcp_timestamps &&
+				      !dst_feature(dst, RTAX_FEATURE_NO_TSTAMP)))) {
 					opt_rx->saw_tstamp = 1;
 					opt_rx->rcv_tsval = get_unaligned_be32(ptr);
 					opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4);

net/ipv4/tcp_output.c

@@ -488,7 +488,9 @@ static unsigned tcp_syn_options(struct sock *sk, struct sk_buff *skb,
 	opts->mss = tcp_advertise_mss(sk);
 	size += TCPOLEN_MSS_ALIGNED;
 
-	if (likely(sysctl_tcp_timestamps && *md5 == NULL)) {
+	if (likely(sysctl_tcp_timestamps &&
+		   !dst_feature(dst, RTAX_FEATURE_NO_TSTAMP) &&
+		   *md5 == NULL)) {
 		opts->options |= OPTION_TS;
 		opts->tsval = TCP_SKB_CB(skb)->when;
 		opts->tsecr = tp->rx_opt.ts_recent;
@@ -2317,7 +2319,9 @@ static void tcp_connect_init(struct sock *sk)
 	 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
 	 */
 	tp->tcp_header_len = sizeof(struct tcphdr) +
-		(sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0);
+		(sysctl_tcp_timestamps &&
+		(!dst_feature(dst, RTAX_FEATURE_NO_TSTAMP) ?
+		  TCPOLEN_TSTAMP_ALIGNED : 0));
 
 #ifdef CONFIG_TCP_MD5SIG
 	if (tp->af_specific->md5_lookup(sk, sk) != NULL)