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From:   Kuniyuki Iwashima <kuniyu@amazon.com>
To:     "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Iurii Zaikin <yzaikin@google.com>
CC:     Kuniyuki Iwashima <kuniyu@amazon.com>,
        Kuniyuki Iwashima <kuni1840@gmail.com>,
        <netdev@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: [PATCH v2 net 01/12] sysctl: Fix data races in proc_dointvec().
Date:   Wed, 6 Jul 2022 16:39:52 -0700
Message-ID: <20220706234003.66760-2-kuniyu@amazon.com>
In-Reply-To: <20220706234003.66760-1-kuniyu@amazon.com>
References: <20220706234003.66760-1-kuniyu@amazon.com>
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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_dointvec() to use READ_ONCE() and WRITE_ONCE()
internally to fix data-races on the sysctl side.  For now, proc_dointvec()
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@amazon.com>
---
 kernel/sysctl.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index e52b6e372c60..c8a05655ae60 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -446,14 +446,14 @@ static int do_proc_dointvec_conv(bool *negp, unsigned long *lvalp,
 		if (*negp) {
 			if (*lvalp > (unsigned long) INT_MAX + 1)
 				return -EINVAL;
-			*valp = -*lvalp;
+			WRITE_ONCE(*valp, -*lvalp);
 		} else {
 			if (*lvalp > (unsigned long) INT_MAX)
 				return -EINVAL;
-			*valp = *lvalp;
+			WRITE_ONCE(*valp, *lvalp);
 		}
 	} else {
-		int val = *valp;
+		int val = READ_ONCE(*valp);
 		if (val < 0) {
 			*negp = true;
 			*lvalp = -(unsigned long)val;
-- 
2.30.2