tcp: introduce TCP_PAWS_WRAP

tcp_paws_check() uses TCP_PAWS_24DAYS constant to detect if TCP TS
values might have wrapped after a long idle period.

This mechanism is described in RFC 7323 5.5 (Outdated Timestamps)

TCP_PAWS_24DAYS value was based on the assumption of a clock
of 1 Khz.

As we want to adopt a 1 Mhz clock in the future, we reduce
this constant.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/tcp.h b/include/net/tcp.h
index af72c1dc37f3dd4cd6858e9c8f6aa7ef31541652..0ab577869d7ac61c5c3b687e98068a16b69bb3af 100644 (file)
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -166,7 +166,12 @@ static_assert((1 << ATO_BITS) > TCP_DELACK_MAX);
 #define MAX_TCP_KEEPCNT                127
 #define MAX_TCP_SYNCNT         127
 
-#define TCP_PAWS_24DAYS        (60 * 60 * 24 * 24)
+/* Ensure that TCP PAWS checks are relaxed after ~2147 seconds
+ * to avoid overflows. This assumes a clock smaller than 1 Mhz.
+ * Default clock is 1 Khz, tcp_usec_ts uses 1 Mhz.
+ */
+#define TCP_PAWS_WRAP (INT_MAX / USEC_PER_SEC)
+
 #define TCP_PAWS_MSL   60              /* Per-host timestamps are invalidated
                                         * after this time. It should be equal
                                         * (or greater than) TCP_TIMEWAIT_LEN
@@ -1619,7 +1624,7 @@ static inline bool tcp_paws_check(const struct tcp_options_received *rx_opt,
        if ((s32)(rx_opt->ts_recent - rx_opt->rcv_tsval) <= paws_win)
                return true;
        if (unlikely(!time_before32(ktime_get_seconds(),
-                                   rx_opt->ts_recent_stamp + TCP_PAWS_24DAYS)))
+                                   rx_opt->ts_recent_stamp + TCP_PAWS_WRAP)))
                return true;
        /*
         * Some OSes send SYN and SYNACK messages with tsval=0 tsecr=0,