[PATCH net-next v3 1/2] tcp: randomize tcp timestamp offsets for each connection

[PATCH net-next v3 1/2] tcp: randomize tcp timestamp offsets for each connection

[Florian Westphal]

jiffies based timestamps allow for easy inference of number of devices
behind NAT translators and also makes tracking of hosts simpler.

commit ceaa1fef65a7c2e ("tcp: adding a per-socket timestamp offset")
added the main infrastructure that is needed for per-connection ts
randomization, in particular writing/reading the on-wire tcp header
format takes the offset into account so rest of stack can use normal
tcp_time_stamp (jiffies).

So only two items are left:
 - add a tsoffset for request sockets
 - extend the tcp isn generator to also return another 32bit number
   in addition to the ISN.

Re-use of ISN generator also means timestamps are still monotonically
increasing for same connection quadruple, i.e. PAWS will still work.

Includes fixes from Eric Dumazet.

Signed-off-by: Florian Westphal <fw@strlen.de>
Acked-by: Eric Dumazet <edumazet@google.com>
Acked-by: Yuchung Cheng <ycheng@google.com>
---
 No changes since v1.

 include/linux/tcp.h      |  1 +
 include/net/secure_seq.h |  8 ++++----
 include/net/tcp.h        |  2 +-
 net/core/secure_seq.c    | 10 ++++++----
 net/ipv4/syncookies.c    |  1 +
 net/ipv4/tcp_input.c     |  7 ++++++-
 net/ipv4/tcp_ipv4.c      |  9 +++++----
 net/ipv4/tcp_minisocks.c |  4 +++-
 net/ipv4/tcp_output.c    |  2 +-
 net/ipv6/syncookies.c    |  1 +
 net/ipv6/tcp_ipv6.c      | 10 ++++++----
 11 files changed, 35 insertions(+), 20 deletions(-)

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 00e0ee8f001f..734bab4c3bef 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -123,6 +123,7 @@ struct tcp_request_sock {
 	u32				txhash;
 	u32				rcv_isn;
 	u32				snt_isn;
+	u32				ts_off;
 	u32				last_oow_ack_time; /* last SYNACK */
 	u32				rcv_nxt; /* the ack # by SYNACK. For
 						  * FastOpen it's the seq#
diff --git a/include/net/secure_seq.h b/include/net/secure_seq.h
index 3f36d45b714a..0caee631a836 100644
--- a/include/net/secure_seq.h
+++ b/include/net/secure_seq.h
@@ -6,10 +6,10 @@
 u32 secure_ipv4_port_ephemeral(__be32 saddr, __be32 daddr, __be16 dport);
 u32 secure_ipv6_port_ephemeral(const __be32 *saddr, const __be32 *daddr,
 			       __be16 dport);
-__u32 secure_tcp_sequence_number(__be32 saddr, __be32 daddr,
-				 __be16 sport, __be16 dport);
-__u32 secure_tcpv6_sequence_number(const __be32 *saddr, const __be32 *daddr,
-				   __be16 sport, __be16 dport);
+u32 secure_tcp_sequence_number(__be32 saddr, __be32 daddr,
+			       __be16 sport, __be16 dport, u32 *tsoff);
+u32 secure_tcpv6_sequence_number(const __be32 *saddr, const __be32 *daddr,
+				 __be16 sport, __be16 dport, u32 *tsoff);
 u64 secure_dccp_sequence_number(__be32 saddr, __be32 daddr,
 				__be16 sport, __be16 dport);
 u64 secure_dccpv6_sequence_number(__be32 *saddr, __be32 *daddr,
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 3e097e39d4d2..207147b4c6b2 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1827,7 +1827,7 @@ struct tcp_request_sock_ops {
 	struct dst_entry *(*route_req)(const struct sock *sk, struct flowi *fl,
 				       const struct request_sock *req,
 				       bool *strict);
-	__u32 (*init_seq)(const struct sk_buff *skb);
+	__u32 (*init_seq)(const struct sk_buff *skb, u32 *tsoff);
 	int (*send_synack)(const struct sock *sk, struct dst_entry *dst,
 			   struct flowi *fl, struct request_sock *req,
 			   struct tcp_fastopen_cookie *foc,
diff --git a/net/core/secure_seq.c b/net/core/secure_seq.c
index fd3ce461fbe6..a8d6062cbb4a 100644
--- a/net/core/secure_seq.c
+++ b/net/core/secure_seq.c
@@ -40,8 +40,8 @@ static u32 seq_scale(u32 seq)
 #endif
 
 #if IS_ENABLED(CONFIG_IPV6)
-__u32 secure_tcpv6_sequence_number(const __be32 *saddr, const __be32 *daddr,
-				   __be16 sport, __be16 dport)
+u32 secure_tcpv6_sequence_number(const __be32 *saddr, const __be32 *daddr,
+				 __be16 sport, __be16 dport, u32 *tsoff)
 {
 	u32 secret[MD5_MESSAGE_BYTES / 4];
 	u32 hash[MD5_DIGEST_WORDS];
@@ -58,6 +58,7 @@ __u32 secure_tcpv6_sequence_number(const __be32 *saddr, const __be32 *daddr,
 
 	md5_transform(hash, secret);
 
+	*tsoff = hash[1];
 	return seq_scale(hash[0]);
 }
 EXPORT_SYMBOL(secure_tcpv6_sequence_number);
@@ -86,8 +87,8 @@ EXPORT_SYMBOL(secure_ipv6_port_ephemeral);
 
 #ifdef CONFIG_INET
 
-__u32 secure_tcp_sequence_number(__be32 saddr, __be32 daddr,
-				 __be16 sport, __be16 dport)
+u32 secure_tcp_sequence_number(__be32 saddr, __be32 daddr,
+			       __be16 sport, __be16 dport, u32 *tsoff)
 {
 	u32 hash[MD5_DIGEST_WORDS];
 
@@ -99,6 +100,7 @@ __u32 secure_tcp_sequence_number(__be32 saddr, __be32 daddr,
 
 	md5_transform(hash, net_secret);
 
+	*tsoff = hash[1];
 	return seq_scale(hash[0]);
 }
 
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index 0dc6286272aa..3e88467d70ee 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -334,6 +334,7 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
 	treq = tcp_rsk(req);
 	treq->rcv_isn		= ntohl(th->seq) - 1;
 	treq->snt_isn		= cookie;
+	treq->ts_off		= 0;
 	req->mss		= mss;
 	ireq->ir_num		= ntohs(th->dest);
 	ireq->ir_rmt_port	= th->source;
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 56fe736fd64d..2257de244622 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6307,6 +6307,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
 		goto drop;
 
 	tcp_rsk(req)->af_specific = af_ops;
+	tcp_rsk(req)->ts_off = 0;
 
 	tcp_clear_options(&tmp_opt);
 	tmp_opt.mss_clamp = af_ops->mss_clamp;
@@ -6328,6 +6329,9 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
 	if (security_inet_conn_request(sk, skb, req))
 		goto drop_and_free;
 
+	if (isn && tmp_opt.tstamp_ok)
+		af_ops->init_seq(skb, &tcp_rsk(req)->ts_off);
+
 	if (!want_cookie && !isn) {
 		/* VJ's idea. We save last timestamp seen
 		 * from the destination in peer table, when entering
@@ -6368,7 +6372,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
 			goto drop_and_release;
 		}
 
-		isn = af_ops->init_seq(skb);
+		isn = af_ops->init_seq(skb, &tcp_rsk(req)->ts_off);
 	}
 	if (!dst) {
 		dst = af_ops->route_req(sk, &fl, req, NULL);
@@ -6380,6 +6384,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
 
 	if (want_cookie) {
 		isn = cookie_init_sequence(af_ops, sk, skb, &req->mss);
+		tcp_rsk(req)->ts_off = 0;
 		req->cookie_ts = tmp_opt.tstamp_ok;
 		if (!tmp_opt.tstamp_ok)
 			inet_rsk(req)->ecn_ok = 0;
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 5555eb86e549..b50f05905ced 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -95,12 +95,12 @@ static int tcp_v4_md5_hash_hdr(char *md5_hash, const struct tcp_md5sig_key *key,
 struct inet_hashinfo tcp_hashinfo;
 EXPORT_SYMBOL(tcp_hashinfo);
 
-static  __u32 tcp_v4_init_sequence(const struct sk_buff *skb)
+static u32 tcp_v4_init_sequence(const struct sk_buff *skb, u32 *tsoff)
 {
 	return secure_tcp_sequence_number(ip_hdr(skb)->daddr,
 					  ip_hdr(skb)->saddr,
 					  tcp_hdr(skb)->dest,
-					  tcp_hdr(skb)->source);
+					  tcp_hdr(skb)->source, tsoff);
 }
 
 int tcp_twsk_unique(struct sock *sk, struct sock *sktw, void *twp)
@@ -237,7 +237,8 @@ int tcp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
 		tp->write_seq = secure_tcp_sequence_number(inet->inet_saddr,
 							   inet->inet_daddr,
 							   inet->inet_sport,
-							   usin->sin_port);
+							   usin->sin_port,
+							   &tp->tsoffset);
 
 	inet->inet_id = tp->write_seq ^ jiffies;
 
@@ -824,7 +825,7 @@ static void tcp_v4_reqsk_send_ack(const struct sock *sk, struct sk_buff *skb,
 	tcp_v4_send_ack(sk, skb, seq,
 			tcp_rsk(req)->rcv_nxt,
 			req->rsk_rcv_wnd >> inet_rsk(req)->rcv_wscale,
-			tcp_time_stamp,
+			tcp_time_stamp + tcp_rsk(req)->ts_off,
 			req->ts_recent,
 			0,
 			tcp_md5_do_lookup(sk, (union tcp_md5_addr *)&ip_hdr(skb)->daddr,
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 6234ebaa7db1..28ce5ee831f5 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -532,7 +532,7 @@ struct sock *tcp_create_openreq_child(const struct sock *sk,
 			newtp->rx_opt.ts_recent_stamp = 0;
 			newtp->tcp_header_len = sizeof(struct tcphdr);
 		}
-		newtp->tsoffset = 0;
+		newtp->tsoffset = treq->ts_off;
 #ifdef CONFIG_TCP_MD5SIG
 		newtp->md5sig_info = NULL;	/*XXX*/
 		if (newtp->af_specific->md5_lookup(sk, newsk))
@@ -581,6 +581,8 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
 
 		if (tmp_opt.saw_tstamp) {
 			tmp_opt.ts_recent = req->ts_recent;
+			if (tmp_opt.rcv_tsecr)
+				tmp_opt.rcv_tsecr -= tcp_rsk(req)->ts_off;
 			/* We do not store true stamp, but it is not required,
 			 * it can be estimated (approximately)
 			 * from another data.
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index d3545d0cff75..c7adcb57654e 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -640,7 +640,7 @@ static unsigned int tcp_synack_options(struct request_sock *req,
 	}
 	if (likely(ireq->tstamp_ok)) {
 		opts->options |= OPTION_TS;
-		opts->tsval = tcp_skb_timestamp(skb);
+		opts->tsval = tcp_skb_timestamp(skb) + tcp_rsk(req)->ts_off;
 		opts->tsecr = req->ts_recent;
 		remaining -= TCPOLEN_TSTAMP_ALIGNED;
 	}
diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
index 97830a6a9cbb..a4d49760bf43 100644
--- a/net/ipv6/syncookies.c
+++ b/net/ipv6/syncookies.c
@@ -209,6 +209,7 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
 	treq->snt_synack.v64	= 0;
 	treq->rcv_isn = ntohl(th->seq) - 1;
 	treq->snt_isn = cookie;
+	treq->ts_off = 0;
 
 	/*
 	 * We need to lookup the dst_entry to get the correct window size.
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 28ec0a2e7b72..a2185a214abc 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -101,12 +101,12 @@ static void inet6_sk_rx_dst_set(struct sock *sk, const struct sk_buff *skb)
 	}
 }
 
-static __u32 tcp_v6_init_sequence(const struct sk_buff *skb)
+static u32 tcp_v6_init_sequence(const struct sk_buff *skb, u32 *tsoff)
 {
 	return secure_tcpv6_sequence_number(ipv6_hdr(skb)->daddr.s6_addr32,
 					    ipv6_hdr(skb)->saddr.s6_addr32,
 					    tcp_hdr(skb)->dest,
-					    tcp_hdr(skb)->source);
+					    tcp_hdr(skb)->source, tsoff);
 }
 
 static int tcp_v6_connect(struct sock *sk, struct sockaddr *uaddr,
@@ -283,7 +283,8 @@ static int tcp_v6_connect(struct sock *sk, struct sockaddr *uaddr,
 		tp->write_seq = secure_tcpv6_sequence_number(np->saddr.s6_addr32,
 							     sk->sk_v6_daddr.s6_addr32,
 							     inet->inet_sport,
-							     inet->inet_dport);
+							     inet->inet_dport,
+							     &tp->tsoffset);
 
 	err = tcp_connect(sk);
 	if (err)
@@ -956,7 +957,8 @@ static void tcp_v6_reqsk_send_ack(const struct sock *sk, struct sk_buff *skb,
 			tcp_rsk(req)->snt_isn + 1 : tcp_sk(sk)->snd_nxt,
 			tcp_rsk(req)->rcv_nxt,
 			req->rsk_rcv_wnd >> inet_rsk(req)->rcv_wscale,
-			tcp_time_stamp, req->ts_recent, sk->sk_bound_dev_if,
+			tcp_time_stamp + tcp_rsk(req)->ts_off,
+			req->ts_recent, sk->sk_bound_dev_if,
 			tcp_v6_md5_do_lookup(sk, &ipv6_hdr(skb)->daddr),
 			0, 0);
 }
-- 
2.7.3

[PATCH net-next v3 2/2] tcp: allow to turn tcp timestamp randomization off

[Florian Westphal]

Eric says: "By looking at tcpdump, and TS val of xmit packets of multiple
flows, we can deduct the relative qdisc delays (think of fq pacing).
This should work even if we have one flow per remote peer."

Having random per flow (or host) offsets doesn't allow that anymore so add
a way to turn this off.

Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Acked-by: Yuchung Cheng <ycheng@google.com>
---
 change since v2:
 - make 2 the new 'non-random' mode, suggested by Yuchung.
 1 is now still the default but it will use per-offset randomization.

 Tested:
 sysctl_tcp_timestamps=2, tcpdump on lo, both ends have same ts value.

 change since v1: do check in secure_tcpv4/6_sequence_number so outgoing
 syn packets won't have a random offset either in if randomization is off.

 Documentation/networking/ip-sysctl.txt | 9 +++++++--
 net/core/secure_seq.c                  | 5 +++--
 net/ipv4/tcp_input.c                   | 1 +
 3 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 5af48dd7c5fc..5ca567fa6b8c 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -610,8 +610,13 @@ tcp_syn_retries - INTEGER
 	with the current initial RTO of 1second. With this the final timeout
 	for an active TCP connection attempt will happen after 127seconds.
 
-tcp_timestamps - BOOLEAN
-	Enable timestamps as defined in RFC1323.
+tcp_timestamps - INTEGER
+Enable timestamps as defined in RFC1323.
+	0: Disabled.
+	1: Enable timestamps as defined in RFC1323 and use random offset for
+	each connection rather than only using the current time.
+	2: Like 1, but without random offsets.
+	Default: 1
 
 tcp_min_tso_segs - INTEGER
 	Minimal number of segments per TSO frame.
diff --git a/net/core/secure_seq.c b/net/core/secure_seq.c
index a8d6062cbb4a..88a8e429fc3e 100644
--- a/net/core/secure_seq.c
+++ b/net/core/secure_seq.c
@@ -12,6 +12,7 @@
 #include <net/secure_seq.h>
 
 #if IS_ENABLED(CONFIG_IPV6) || IS_ENABLED(CONFIG_INET)
+#include <net/tcp.h>
 #define NET_SECRET_SIZE (MD5_MESSAGE_BYTES / 4)
 
 static u32 net_secret[NET_SECRET_SIZE] ____cacheline_aligned;
@@ -58,7 +59,7 @@ u32 secure_tcpv6_sequence_number(const __be32 *saddr, const __be32 *daddr,
 
 	md5_transform(hash, secret);
 
-	*tsoff = hash[1];
+	*tsoff = sysctl_tcp_timestamps == 1 ? hash[1] : 0;
 	return seq_scale(hash[0]);
 }
 EXPORT_SYMBOL(secure_tcpv6_sequence_number);
@@ -100,7 +101,7 @@ u32 secure_tcp_sequence_number(__be32 saddr, __be32 daddr,
 
 	md5_transform(hash, net_secret);
 
-	*tsoff = hash[1];
+	*tsoff = sysctl_tcp_timestamps == 1 ? hash[1] : 0;
 	return seq_scale(hash[0]);
 }
 
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 2257de244622..fe668c1b9ced 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -85,6 +85,7 @@ int sysctl_tcp_dsack __read_mostly = 1;
 int sysctl_tcp_app_win __read_mostly = 31;
 int sysctl_tcp_adv_win_scale __read_mostly = 1;
 EXPORT_SYMBOL(sysctl_tcp_adv_win_scale);
+EXPORT_SYMBOL(sysctl_tcp_timestamps);
 
 /* rfc5961 challenge ack rate limiting */
 int sysctl_tcp_challenge_ack_limit = 1000;
-- 
2.7.3

Re: [PATCH net-next v3 1/2] tcp: randomize tcp timestamp offsets for each connection

[David Miller]

From: Florian Westphal <fw@strlen.de>
Date: Thu,  1 Dec 2016 11:32:06 +0100

> jiffies based timestamps allow for easy inference of number of devices
> behind NAT translators and also makes tracking of hosts simpler.
> 
> commit ceaa1fef65a7c2e ("tcp: adding a per-socket timestamp offset")
> added the main infrastructure that is needed for per-connection ts
> randomization, in particular writing/reading the on-wire tcp header
> format takes the offset into account so rest of stack can use normal
> tcp_time_stamp (jiffies).
> 
> So only two items are left:
>  - add a tsoffset for request sockets
>  - extend the tcp isn generator to also return another 32bit number
>    in addition to the ISN.
> 
> Re-use of ISN generator also means timestamps are still monotonically
> increasing for same connection quadruple, i.e. PAWS will still work.
> 
> Includes fixes from Eric Dumazet.
> 
> Signed-off-by: Florian Westphal <fw@strlen.de>
> Acked-by: Eric Dumazet <edumazet@google.com>
> Acked-by: Yuchung Cheng <ycheng@google.com>

Applied.

Re: [PATCH net-next v3 2/2] tcp: allow to turn tcp timestamp randomization off

[David Miller]

From: Florian Westphal <fw@strlen.de>
Date: Thu,  1 Dec 2016 11:32:07 +0100

> Eric says: "By looking at tcpdump, and TS val of xmit packets of multiple
> flows, we can deduct the relative qdisc delays (think of fq pacing).
> This should work even if we have one flow per remote peer."
> 
> Having random per flow (or host) offsets doesn't allow that anymore so add
> a way to turn this off.
> 
> Suggested-by: Eric Dumazet <edumazet@google.com>
> Signed-off-by: Florian Westphal <fw@strlen.de>
> Acked-by: Yuchung Cheng <ycheng@google.com>

Applied.