linux-kernel - [PATCH 5.18 109/231] sysctl: Fix data-races in proc_dou8vec

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Date:   Tue, 19 Jul 2022 13:53:14 +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, Kuniyuki Iwashima <kuniyu@...zon.com>,
        "David S. Miller" <davem@...emloft.net>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.18 109/231] sysctl: Fix data-races in proc_dou8vec_minmax().

From: Kuniyuki Iwashima <kuniyu@...zon.com>

[ Upstream commit 7dee5d7747a69aa2be41f04c6a7ecfe3ac8cdf18 ]

A sysctl variable is accessed concurrently, and there is always a chance
of data-race.  So, all readers and writers need some basic protection to
avoid load/store-tearing.

This patch changes proc_dou8vec_minmax() to use READ_ONCE() and
WRITE_ONCE() internally to fix data-races on the sysctl side.  For now,
proc_dou8vec_minmax() itself is tolerant to a data-race, but we still
need to add annotations on the other subsystem's side.

Fixes: cb9444130662 ("sysctl: add proc_dou8vec_minmax()")
Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 kernel/sysctl.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 878b1122cb89..54ec36e69907 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1079,13 +1079,13 @@ int proc_dou8vec_minmax(struct ctl_table *table, int write,
 
 	tmp.maxlen = sizeof(val);
 	tmp.data = &val;
-	val = *data;
+	val = READ_ONCE(*data);
 	res = do_proc_douintvec(&tmp, write, buffer, lenp, ppos,
 				do_proc_douintvec_minmax_conv, &param);
 	if (res)
 		return res;
 	if (write)
-		*data = val;
+		WRITE_ONCE(*data, val);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(proc_dou8vec_minmax);
-- 
2.35.1