linux-kernel - [PATCH 4.19 179/229] tcp: annotate data-race around tcp_md5sig_pool

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Message-Id: <20221024113004.886317136@linuxfoundation.org>
Date:   Mon, 24 Oct 2022 13:31:38 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Abhishek Shah <abhishek.shah@...umbia.edu>,
        Eric Dumazet <edumazet@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.19 179/229] tcp: annotate data-race around tcp_md5sig_pool_populated

From: Eric Dumazet <edumazet@...gle.com>

[ Upstream commit aacd467c0a576e5e44d2de4205855dc0fe43f6fb ]

tcp_md5sig_pool_populated can be read while another thread
changes its value.

The race has no consequence because allocations
are protected with tcp_md5sig_mutex.

This patch adds READ_ONCE() and WRITE_ONCE() to document
the race and silence KCSAN.

Reported-by: Abhishek Shah <abhishek.shah@...umbia.edu>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 net/ipv4/tcp.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index e25130812cc8..1a6c55441627 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3692,12 +3692,16 @@ static void __tcp_alloc_md5sig_pool(void)
 	 * to memory. See smp_rmb() in tcp_get_md5sig_pool()
 	 */
 	smp_wmb();
-	tcp_md5sig_pool_populated = true;
+	/* Paired with READ_ONCE() from tcp_alloc_md5sig_pool()
+	 * and tcp_get_md5sig_pool().
+	*/
+	WRITE_ONCE(tcp_md5sig_pool_populated, true);
 }
 
 bool tcp_alloc_md5sig_pool(void)
 {
-	if (unlikely(!tcp_md5sig_pool_populated)) {
+	/* Paired with WRITE_ONCE() from __tcp_alloc_md5sig_pool() */
+	if (unlikely(!READ_ONCE(tcp_md5sig_pool_populated))) {
 		mutex_lock(&tcp_md5sig_mutex);
 
 		if (!tcp_md5sig_pool_populated)
@@ -3705,7 +3709,8 @@ bool tcp_alloc_md5sig_pool(void)
 
 		mutex_unlock(&tcp_md5sig_mutex);
 	}
-	return tcp_md5sig_pool_populated;
+	/* Paired with WRITE_ONCE() from __tcp_alloc_md5sig_pool() */
+	return READ_ONCE(tcp_md5sig_pool_populated);
 }
 EXPORT_SYMBOL(tcp_alloc_md5sig_pool);
 
@@ -3721,7 +3726,8 @@ struct tcp_md5sig_pool *tcp_get_md5sig_pool(void)
 {
 	local_bh_disable();
 
-	if (tcp_md5sig_pool_populated) {
+	/* Paired with WRITE_ONCE() from __tcp_alloc_md5sig_pool() */
+	if (READ_ONCE(tcp_md5sig_pool_populated)) {
 		/* coupled with smp_wmb() in __tcp_alloc_md5sig_pool() */
 		smp_rmb();
 		return this_cpu_ptr(&tcp_md5sig_pool);
-- 
2.35.1