tcp: randomize tcp timestamp offsets for each connection

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>
Signed-off-by: David S. Miller <davem@davemloft.net>

8 files changed, 29 insertions, 15 deletions

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);
 }