netdev - [PATCH net-next 02/13] tcp: fix cookie_init

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Message-ID: <20231020125748.122792-3-edumazet@google.com>
Date: Fri, 20 Oct 2023 12:57:37 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, Neal Cardwell <ncardwell@...gle.com>, 
	Yuchung Cheng <ycheng@...gle.com>, Kevin Yang <yyd@...gle.com>, 
	Soheil Hassas Yeganeh <soheil@...gle.com>, Wei Wang <weiwan@...gle.com>, Van Jacobson <vanj@...gle.com>, 
	Florian Westphal <fw@...len.de>, eric.dumazet@...il.com, Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next 02/13] tcp: fix cookie_init_timestamp() overflows

cookie_init_timestamp() is supposed to return a 64bit timestamp
suitable for both TSval determination and setting of skb->tstamp.

Unfortunately it uses 32bit fields and overflows after
2^32 * 10^6 nsec (~49 days) of uptime.

Generated TSval are still correct, but skb->tstamp might be set
far away in the past, potentially confusing other layers.

tcp_ns_to_ts() is changed to return a full 64bit value,
ts and ts_now variables are changed to u64 type,
and TSMASK is removed in favor of shifts operations.

While we are at it, change this sequence:
		ts >>= TSBITS;
		ts--;
		ts <<= TSBITS;
		ts |= options;
to:
		ts -= (1UL << TSBITS);

Fixes: 9a568de4818d ("tcp: switch TCP TS option (RFC 7323) to 1ms clock")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 include/net/tcp.h     |  2 +-
 net/ipv4/syncookies.c | 20 +++++++-------------
 2 files changed, 8 insertions(+), 14 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index bad304d173a56c768e1f87fa740e8e568d220f00..d47a57a47b50b4bbc7ff45c76371d39cf6207c54 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -805,7 +805,7 @@ static inline u32 tcp_time_stamp(const struct tcp_sock *tp)
 }
 
 /* Convert a nsec timestamp into TCP TSval timestamp (ms based currently) */
-static inline u32 tcp_ns_to_ts(u64 ns)
+static inline u64 tcp_ns_to_ts(u64 ns)
 {
 	return div_u64(ns, NSEC_PER_SEC / TCP_TS_HZ);
 }
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index dc478a0574cbe71d392522ed4a690f12654f3e08..3b4dafefb4b036c661bf52f5e7e304b943a4fd5e 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -41,7 +41,6 @@ static siphash_aligned_key_t syncookie_secret[2];
  * requested/supported by the syn/synack exchange.
  */
 #define TSBITS	6
-#define TSMASK	(((__u32)1 << TSBITS) - 1)
 
 static u32 cookie_hash(__be32 saddr, __be32 daddr, __be16 sport, __be16 dport,
 		       u32 count, int c)
@@ -62,27 +61,22 @@ static u32 cookie_hash(__be32 saddr, __be32 daddr, __be16 sport, __be16 dport,
  */
 u64 cookie_init_timestamp(struct request_sock *req, u64 now)
 {
-	struct inet_request_sock *ireq;
-	u32 ts, ts_now = tcp_ns_to_ts(now);
+	const struct inet_request_sock *ireq = inet_rsk(req);
+	u64 ts, ts_now = tcp_ns_to_ts(now);
 	u32 options = 0;
 
-	ireq = inet_rsk(req);
-
 	options = ireq->wscale_ok ? ireq->snd_wscale : TS_OPT_WSCALE_MASK;
 	if (ireq->sack_ok)
 		options |= TS_OPT_SACK;
 	if (ireq->ecn_ok)
 		options |= TS_OPT_ECN;
 
-	ts = ts_now & ~TSMASK;
+	ts = (ts_now >> TSBITS) << TSBITS;
 	ts |= options;
-	if (ts > ts_now) {
-		ts >>= TSBITS;
-		ts--;
-		ts <<= TSBITS;
-		ts |= options;
-	}
-	return (u64)ts * (NSEC_PER_SEC / TCP_TS_HZ);
+	if (ts > ts_now)
+		ts -= (1UL << TSBITS);
+
+	return ts * (NSEC_PER_SEC / TCP_TS_HZ);
 }
 
 
-- 
2.42.0.655.g421f12c284-goog