batman-adv: tp_meter: annotate last_recv_time access with READ/WRITE_ONCE

commit d67c728 upstream.

The last_recv_time field for batadv_tp_receiver tracks the jiffies value of
the most recent activity and is used to detect timeouts. These accesses are
not consistently protected by a lock, so READ_ONCE/WRITE_ONCE must be used
to prevent data races caused by compiler optimizations.

Cc: stable@kernel.org
Fixes: 33a3bb4 ("batman-adv: throughput meter implementation")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: ecsv

net/batman-adv/tp_meter.c

@@ -1183,7 +1183,7 @@ static void batadv_tp_receiver_shutdown(struct timer_list *t)
 	bat_priv = tp_vars->bat_priv;
 
 	/* if there is recent activity rearm the timer */
-	if (!batadv_has_timed_out(tp_vars->last_recv_time,
+	if (!batadv_has_timed_out(READ_ONCE(tp_vars->last_recv_time),
 				  BATADV_TP_RECV_TIMEOUT)) {
 		/* reset the receiver shutdown timer */
 		batadv_tp_reset_receiver_timer(tp_vars);
@@ -1424,7 +1424,7 @@ batadv_tp_init_recv(struct batadv_priv *bat_priv,
 	tp_vars = batadv_tp_list_find_session(bat_priv, icmp->orig,
 					      icmp->session, BATADV_TP_RECEIVER);
 	if (tp_vars) {
-		tp_vars->last_recv_time = jiffies;
+		WRITE_ONCE(tp_vars->last_recv_time, jiffies);
 		goto out_unlock;
 	}
 
@@ -1455,7 +1455,7 @@ batadv_tp_init_recv(struct batadv_priv *bat_priv,
 	kref_get(&tp_vars->refcount);
 	timer_setup(&tp_vars->timer, batadv_tp_receiver_shutdown, 0);
 
-	tp_vars->last_recv_time = jiffies;
+	WRITE_ONCE(tp_vars->last_recv_time, jiffies);
 
 	kref_get(&tp_vars->refcount);
 	hlist_add_head_rcu(&tp_vars->list, &bat_priv->tp_list);
@@ -1506,7 +1506,7 @@ static void batadv_tp_recv_msg(struct batadv_priv *bat_priv,
 			goto out;
 		}
 
-		tp_vars->last_recv_time = jiffies;
+		WRITE_ONCE(tp_vars->last_recv_time, jiffies);
 	}
 
 	/* if the packet is a duplicate, it may be the case that an ACK has been