sysctl: Fix data races in proc_doulongvec_minmax().

[ 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@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 bdb2f17..9a68da5 100644 (file)
--- 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);