linux-kernel - [PATCH 3.16 143/148] tcp: Protect accesses to .ts_recent_stamp with {READ,WRITE}

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Message-ID: <lsq.1581185941.148021438@decadent.org.uk>
Date:   Sat, 08 Feb 2020 18:21:22 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "Eric Dumazet" <edumazet@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        "Guillaume Nault" <gnault@...hat.com>
Subject: [PATCH 3.16 143/148] tcp: Protect accesses to .ts_recent_stamp
 with {READ,WRITE}_ONCE()

3.16.82-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Guillaume Nault <gnault@...hat.com>

commit 721c8dafad26ccfa90ff659ee19755e3377b829d upstream.

Syncookies borrow the ->rx_opt.ts_recent_stamp field to store the
timestamp of the last synflood. Protect them with READ_ONCE() and
WRITE_ONCE() since reads and writes aren't serialised.

Use of .rx_opt.ts_recent_stamp for storing the synflood timestamp was
introduced by a0f82f64e269 ("syncookies: remove last_synq_overflow from
struct tcp_sock"). But unprotected accesses were already there when
timestamp was stored in .last_synq_overflow.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Guillaume Nault <gnault@...hat.com>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
[bwh: Backported to 3.16: Use ACCESS_ONCE() instead of {READ,WRITE}_ONCE()]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 include/net/tcp.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -482,17 +482,17 @@ struct sock *cookie_v4_check(struct sock
  */
 static inline void tcp_synq_overflow(struct sock *sk)
 {
-	unsigned long last_overflow = tcp_sk(sk)->rx_opt.ts_recent_stamp;
+	unsigned long last_overflow = ACCESS_ONCE(tcp_sk(sk)->rx_opt.ts_recent_stamp);
 	unsigned long now = jiffies;
 
 	if (!time_between32(now, last_overflow, last_overflow + HZ))
-		tcp_sk(sk)->rx_opt.ts_recent_stamp = now;
+		ACCESS_ONCE(tcp_sk(sk)->rx_opt.ts_recent_stamp) = now;
 }
 
 /* syncookies: no recent synqueue overflow on this listening socket? */
 static inline bool tcp_synq_no_recent_overflow(const struct sock *sk)
 {
-	unsigned long last_overflow = tcp_sk(sk)->rx_opt.ts_recent_stamp;
+	unsigned long last_overflow = ACCESS_ONCE(tcp_sk(sk)->rx_opt.ts_recent_stamp);
 
 	return time_after(jiffies, last_overflow + TCP_SYNCOOKIE_VALID);
 }