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>

1 files changed, 14 insertions, 4 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,