batman-adv: Utilize prandom_u32_max for random [0, max) values

The kernel provides a function to create random values from 0 - (max-1)
since commit f337db64af ("random32: add prandom_u32_max and convert open
coded users"). Simply use this function to replace code sections which use
prandom_u32 and a handcrafted method to map it to the correct range.

Signed-off-by: Sven Eckelmann <sven@narfation.org>

net/batman-adv/bat_iv_ogm.c

@@ -280,7 +280,7 @@ batadv_iv_ogm_emit_send_time(const struct batadv_priv *bat_priv)
 	unsigned int msecs;
 
 	msecs = atomic_read(&bat_priv->orig_interval) - BATADV_JITTER;
-	msecs += prandom_u32() % (2 * BATADV_JITTER);
+	msecs += prandom_u32_max(2 * BATADV_JITTER);
 
 	return jiffies + msecs_to_jiffies(msecs);
 }
@@ -288,7 +288,7 @@ batadv_iv_ogm_emit_send_time(const struct batadv_priv *bat_priv)
 /* when do we schedule a ogm packet to be sent */
 static unsigned long batadv_iv_ogm_fwd_send_time(void)
 {
-	return jiffies + msecs_to_jiffies(prandom_u32() % (BATADV_JITTER / 2));
+	return jiffies + msecs_to_jiffies(prandom_u32_max(BATADV_JITTER / 2));
 }
 
 /* apply hop penalty for a normal link */

net/batman-adv/bat_v_elp.c

@@ -49,7 +49,7 @@ static void batadv_v_elp_start_timer(struct batadv_hard_iface *hard_iface)
 	unsigned int msecs;
 
 	msecs = atomic_read(&hard_iface->bat_v.elp_interval) - BATADV_JITTER;
-	msecs += prandom_u32() % (2 * BATADV_JITTER);
+	msecs += prandom_u32_max(2 * BATADV_JITTER);
 
 	queue_delayed_work(batadv_event_workqueue, &hard_iface->bat_v.elp_wq,
 			   msecs_to_jiffies(msecs));

net/batman-adv/bat_v_ogm.c

@@ -88,7 +88,7 @@ static void batadv_v_ogm_start_queue_timer(struct batadv_hard_iface *hard_iface)
 	unsigned int msecs = BATADV_MAX_AGGREGATION_MS * 1000;
 
 	/* msecs * [0.9, 1.1] */
-	msecs += prandom_u32() % (msecs / 5) - (msecs / 10);
+	msecs += prandom_u32_max(msecs / 5) - (msecs / 10);
 	queue_delayed_work(batadv_event_workqueue, &hard_iface->bat_v.aggr_wq,
 			   msecs_to_jiffies(msecs / 1000));
 }
@@ -107,7 +107,7 @@ static void batadv_v_ogm_start_timer(struct batadv_priv *bat_priv)
 		return;
 
 	msecs = atomic_read(&bat_priv->orig_interval) - BATADV_JITTER;
-	msecs += prandom_u32() % (2 * BATADV_JITTER);
+	msecs += prandom_u32_max(2 * BATADV_JITTER);
 	queue_delayed_work(batadv_event_workqueue, &bat_priv->bat_v.ogm_wq,
 			   msecs_to_jiffies(msecs));
 }