tcp: consolidate paws check

Wow, it was quite tricky to merge that stream of negations
but I think I finally got it right:

check & replace_ts_recent:
(s32)(rcv_tsval - ts_recent) >= 0                  => 0
(s32)(ts_recent - rcv_tsval) <= 0                  => 0

discard:
(s32)(ts_recent - rcv_tsval)  > TCP_PAWS_WINDOW    => 1
(s32)(ts_recent - rcv_tsval) <= TCP_PAWS_WINDOW    => 0

I toggled the return values of tcp_paws_check around since
the old encoding added yet-another negation making tracking
of truth-values really complicated.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 21 insertions, 12 deletions

diff --git a/include/net/tcp.h b/include/net/tcp.h
index d74ac301e6bc..255ca35bea05 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -997,11 +997,21 @@ static inline int tcp_fin_time(const struct sock *sk)
         return fin_timeout;
 }
 
-static inline int tcp_paws_check(const struct tcp_options_received *rx_opt, int rst)
+static inline int tcp_paws_check(const struct tcp_options_received *rx_opt,
+                                 int paws_win)
 {
-        if ((s32)(rx_opt->rcv_tsval - rx_opt->ts_recent) >= 0)
-                return 0;
-        if (get_seconds() >= rx_opt->ts_recent_stamp + TCP_PAWS_24DAYS)
+        if ((s32)(rx_opt->ts_recent - rx_opt->rcv_tsval) <= paws_win)
+                return 1;
+        if (unlikely(get_seconds() >= rx_opt->ts_recent_stamp + TCP_PAWS_24DAYS))
+                return 1;
+
+        return 0;
+}
+
+static inline int tcp_paws_reject(const struct tcp_options_received *rx_opt,
+                                  int rst)
+{
+        if (tcp_paws_check(rx_opt, 0))
                 return 0;
 
         /* RST segments are not recommended to carry timestamp,
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index f527a16a7b33..b7d02c5dd6da 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3883,8 +3883,7 @@ static inline void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
                  * Not only, also it occurs for expired timestamps.
                  */
 
-                if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) >= 0 ||
-                   get_seconds() >= tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS)
+                if (tcp_paws_check(&tp->rx_opt, 0))
                         tcp_store_ts_recent(tp);
         }
 }
@@ -3936,9 +3935,9 @@ static inline int tcp_paws_discard(const struct sock *sk,
                                    const struct sk_buff *skb)
 {
         const struct tcp_sock *tp = tcp_sk(sk);
-        return ((s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) > TCP_PAWS_WINDOW &&
-                get_seconds() < tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS &&
-                !tcp_disordered_ack(sk, skb));
+
+        return !tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW) &&
+               !tcp_disordered_ack(sk, skb);
 }
 
 /* Check segment sequence number for validity.
@@ -5513,7 +5512,7 @@ discard:
 
         /* PAWS check. */
         if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp &&
-            tcp_paws_check(&tp->rx_opt, 0))
+            tcp_paws_reject(&tp->rx_opt, 0))
                 goto discard_and_undo;
 
         if (th->syn) {
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 4b0df3e6b609..43bbba7926ee 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -107,7 +107,7 @@ tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb,
                 if (tmp_opt.saw_tstamp) {
                         tmp_opt.ts_recent       = tcptw->tw_ts_recent;
                         tmp_opt.ts_recent_stamp = tcptw->tw_ts_recent_stamp;
-                        paws_reject = tcp_paws_check(&tmp_opt, th->rst);
+                        paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
                 }
         }
 
@@ -511,7 +511,7 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
                          * from another data.
                          */
                         tmp_opt.ts_recent_stamp = get_seconds() - ((TCP_TIMEOUT_INIT/HZ)<<req->retrans);
-                        paws_reject = tcp_paws_check(&tmp_opt, th->rst);
+                        paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
                 }
         }