netrom: Fix a data-race around sysctl_netrom_transport_busy_delay

[ Upstream commit 43547d8699439a67b78d6bb39015113f7aa360fd ]

We need to protect the reader reading the sysctl value because the
value can be changed concurrently.

Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Signed-off-by: Jason Xing <kernelxing@tencent.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

net/netrom/af_netrom.c

@@ -459,7 +459,7 @@ static int nr_create(struct net *net, struct socket *sock, int protocol,
 	nr->n2     =
 		msecs_to_jiffies(READ_ONCE(sysctl_netrom_transport_maximum_tries));
 	nr->t4     =
-		msecs_to_jiffies(sysctl_netrom_transport_busy_delay);
+		msecs_to_jiffies(READ_ONCE(sysctl_netrom_transport_busy_delay));
 	nr->idle   =
 		msecs_to_jiffies(sysctl_netrom_transport_no_activity_timeout);
 	nr->window = sysctl_netrom_transport_requested_window_size;