linux-kernel - [PATCH 5.15 055/167] sysctl: Fix data races in proc_doulongvec

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Message-Id: <20220719114701.918591935@linuxfoundation.org>
Date:   Tue, 19 Jul 2022 13:53:07 +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 5.15 055/167] sysctl: Fix data races in proc_doulongvec_minmax().

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

[ Upstream commit c31bcc8fb89fc2812663900589c6325ba35d9a65 ]

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

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
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 bdb2f17b723f..9a68da5e1551 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1281,9 +1281,9 @@ static int __do_proc_doulongvec_minmax(void *data, struct ctl_table *table,
 				err = -EINVAL;
 				break;
 			}
-			*i = val;
+			WRITE_ONCE(*i, val);
 		} else {
-			val = convdiv * (*i) / convmul;
+			val = convdiv * READ_ONCE(*i) / convmul;
 			if (!first)
 				proc_put_char(&buffer, &left, '\t');
 			proc_put_long(&buffer, &left, val, false);
-- 
2.35.1