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Subject[PATCH 1/3] Support arbitrary initial TCP timestamps
Date
Introduce the ability to send arbitrary initial tcp timestamps that are not
tied directly to jiffies. The basic conecpt is every tcp_request_sock and
tcp_sock now has a ts_off offset that represents the difference between
tcp_time_stamp and the timestamp we send and expect to
receive.

This has the advantage of not divulging system information (uptime)
depending on the policy chosen for the initial timestamps.

A policy where ts_off is always set to zero should produce no change in
behavior. The policy implemented is not intended for real use, but just as
a simple example. A realistic example would probably be similar to the tcp
init sequence generator.

Signed-off-by: Glenn Griffin <ggriffin.kernel@gmail.com>
---
include/linux/tcp.h | 6 ++++++
include/net/tcp.h | 2 +-
net/ipv4/tcp_input.c | 12 ++++++------
net/ipv4/tcp_ipv4.c | 2 +-
net/ipv4/tcp_minisocks.c | 5 +++--
net/ipv4/tcp_output.c | 8 +++++---
net/ipv6/tcp_ipv6.c | 2 +-
7 files changed, 23 insertions(+), 14 deletions(-)
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 08027f1..68387dc 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -232,6 +232,7 @@ struct tcp_request_sock {
#endif
u32 rcv_isn;
u32 snt_isn;
+ u32 ts_off;
};

static inline struct tcp_request_sock *tcp_rsk(const struct request_sock *req)
@@ -311,6 +312,11 @@ struct tcp_sock {
struct tcp_options_received rx_opt;

/*
+ * offset of transmitted tcp timestamp from jiffies
+ */
+ u32 ts_off;
+
+/*
* Slow start and congestion control (see also Nagle, and Karn & Partridge)
*/
u32 snd_ssthresh; /* Slow start size threshold */
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 7de4ea3..c935de7 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -395,7 +395,7 @@ extern int tcp_recvmsg(struct kiocb *iocb, struct sock *sk,

extern void tcp_parse_options(struct sk_buff *skb,
struct tcp_options_received *opt_rx,
- int estab);
+ int estab, u32 tsecr_off);

/*
* TCP v4 functions exported for the inet6 API
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 19c449f..95fa8dc 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3264,7 +3264,7 @@ uninteresting_ack:
* the fast version below fails.
*/
void tcp_parse_options(struct sk_buff *skb, struct tcp_options_received *opt_rx,
- int estab)
+ int estab, u32 tsecr_off)
{
unsigned char *ptr;
struct tcphdr *th = tcp_hdr(skb);
@@ -3322,7 +3322,7 @@ void tcp_parse_options(struct sk_buff *skb, struct tcp_options_received *opt_rx,
(!estab && sysctl_tcp_timestamps))) {
opt_rx->saw_tstamp = 1;
opt_rx->rcv_tsval = ntohl(get_unaligned((__be32 *)ptr));
- opt_rx->rcv_tsecr = ntohl(get_unaligned((__be32 *)(ptr+4)));
+ opt_rx->rcv_tsecr = ntohl(get_unaligned((__be32 *)(ptr+4))) - tsecr_off;
}
break;
case TCPOPT_SACK_PERM:
@@ -3374,11 +3374,11 @@ static int tcp_fast_parse_options(struct sk_buff *skb, struct tcphdr *th,
++ptr;
tp->rx_opt.rcv_tsval = ntohl(*ptr);
++ptr;
- tp->rx_opt.rcv_tsecr = ntohl(*ptr);
+ tp->rx_opt.rcv_tsecr = ntohl(*ptr) - tp->ts_off;
return 1;
}
}
- tcp_parse_options(skb, &tp->rx_opt, 1);
+ tcp_parse_options(skb, &tp->rx_opt, 1, tp->ts_off);
return 1;
}

@@ -4615,7 +4615,7 @@ int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
++ptr;
tp->rx_opt.rcv_tsval = ntohl(*ptr);
++ptr;
- tp->rx_opt.rcv_tsecr = ntohl(*ptr);
+ tp->rx_opt.rcv_tsecr = ntohl(*ptr) - tp->ts_off;

/* If PAWS failed, check it more carefully in slow path */
if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
@@ -4824,7 +4824,7 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
struct inet_connection_sock *icsk = inet_csk(sk);
int saved_clamp = tp->rx_opt.mss_clamp;

- tcp_parse_options(skb, &tp->rx_opt, 0);
+ tcp_parse_options(skb, &tp->rx_opt, 0, tp->ts_off);

if (th->ack) {
/* rfc793:
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 63414ea..267eda9 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1295,7 +1295,7 @@ int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
tmp_opt.mss_clamp = 536;
tmp_opt.user_mss = tcp_sk(sk)->rx_opt.user_mss;

- tcp_parse_options(skb, &tmp_opt, 0);
+ tcp_parse_options(skb, &tmp_opt, 0, 0);

if (want_cookie) {
tcp_clear_options(&tmp_opt);
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index b61b768..648f84e 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -102,7 +102,7 @@ tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb,

tmp_opt.saw_tstamp = 0;
if (th->doff > (sizeof(*th) >> 2) && tcptw->tw_ts_recent_stamp) {
- tcp_parse_options(skb, &tmp_opt, 0);
+ tcp_parse_options(skb, &tmp_opt, 0, 0);

if (tmp_opt.saw_tstamp) {
tmp_opt.ts_recent = tcptw->tw_ts_recent;
@@ -442,6 +442,7 @@ struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req,
inet_csk_reset_keepalive_timer(newsk,
keepalive_time_when(newtp));

+ newtp->ts_off = treq->ts_off;
newtp->rx_opt.tstamp_ok = ireq->tstamp_ok;
if ((newtp->rx_opt.sack_ok = ireq->sack_ok) != 0) {
if (sysctl_tcp_fack)
@@ -502,7 +503,7 @@ struct sock *tcp_check_req(struct sock *sk,struct sk_buff *skb,

tmp_opt.saw_tstamp = 0;
if (th->doff > (sizeof(struct tcphdr)>>2)) {
- tcp_parse_options(skb, &tmp_opt, 0);
+ tcp_parse_options(skb, &tmp_opt, 0, tcp_rsk(req)->ts_off);

if (tmp_opt.saw_tstamp) {
tmp_opt.ts_recent = req->ts_recent;
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index ed750f9..81f1383 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -583,7 +583,7 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
(sysctl_flags & SYSCTL_FLAG_SACK),
(sysctl_flags & SYSCTL_FLAG_WSCALE),
tp->rx_opt.rcv_wscale,
- tcb->when,
+ tcb->when + tp->ts_off,
tp->rx_opt.ts_recent,

#ifdef CONFIG_TCP_MD5SIG
@@ -592,7 +592,7 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
NULL);
} else {
tcp_build_and_update_options((__be32 *)(th + 1),
- tp, tcb->when,
+ tp, tcb->when + tp->ts_off,
#ifdef CONFIG_TCP_MD5SIG
md5 ? &md5_hash_location :
#endif
@@ -2227,9 +2227,10 @@ struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
th->window = htons(min(req->rcv_wnd, 65535U));

TCP_SKB_CB(skb)->when = tcp_time_stamp;
+ tcp_rsk(req)->ts_off = 1000 - TCP_SKB_CB(skb)->when;
tcp_syn_build_options((__be32 *)(th + 1), dst_metric(dst, RTAX_ADVMSS), ireq->tstamp_ok,
ireq->sack_ok, ireq->wscale_ok, ireq->rcv_wscale,
- TCP_SKB_CB(skb)->when,
+ TCP_SKB_CB(skb)->when + tcp_rsk(req)->ts_off,
req->ts_recent,
(
#ifdef CONFIG_TCP_MD5SIG
@@ -2335,6 +2336,7 @@ int tcp_connect(struct sock *sk)

/* Send it off. */
TCP_SKB_CB(buff)->when = tcp_time_stamp;
+ tp->ts_off = 2000 - TCP_SKB_CB(buff)->when;
tp->retrans_stamp = TCP_SKB_CB(buff)->when;
skb_header_release(buff);
__tcp_add_write_queue_tail(sk, buff);
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 12750f2..896ebd0 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1264,7 +1264,7 @@ static int tcp_v6_conn_request(struct sock *sk, struct sk_buff *skb)
tmp_opt.mss_clamp = IPV6_MIN_MTU - sizeof(struct tcphdr) - sizeof(struct ipv6hdr);
tmp_opt.user_mss = tp->rx_opt.user_mss;

- tcp_parse_options(skb, &tmp_opt, 0);
+ tcp_parse_options(skb, &tmp_opt, 0, 0);

tmp_opt.tstamp_ok = tmp_opt.saw_tstamp;
tcp_openreq_init(req, &tmp_opt, skb);
--
1.5.4


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