From: Kuniyuki Iwashima <kuniyu@amazon.com>
Date: Tue, 12 Jul 2022 00:15:19 +0000 (-0700)
Subject: sysctl: Fix data-races in proc_dou8vec_minmax().
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=e58b02e445463065b4078bf621561da75197853f;p=linux.git

sysctl: Fix data-races in proc_dou8vec_minmax().

[ 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@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 5be8108a9a45e..357900d0cef9a 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1138,13 +1138,13 @@ 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);