net: phy: phy_led_triggers: Fix a possible null-pointer dereference in phy_led_trigger_change_speed()

[ Upstream commit 271da132e29b5341c31eca6ba6a72ea1302ebac8 ]

In phy_led_trigger_change_speed(), there is an if statement on line 48
to check whether phy->last_triggered is NULL:
    if (!phy->last_triggered)

When phy->last_triggered is NULL, it is used on line 52:
    led_trigger_event(&phy->last_triggered->trigger, LED_OFF);

Thus, a possible null-pointer dereference may occur.

To fix this bug, led_trigger_event(&phy->last_triggered->trigger,
LED_OFF) is called when phy->last_triggered is not NULL.

This bug is found by a static analysis tool STCheck written by
the OSLAB group in Tsinghua University.

Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/net/phy/phy_led_triggers.c

@@ -58,8 +58,9 @@ void phy_led_trigger_change_speed(struct phy_device *phy)
 		if (!phy->last_triggered)
 			led_trigger_event(&phy->led_link_trigger->trigger,
 					  LED_FULL);
+		else
+			led_trigger_event(&phy->last_triggered->trigger, LED_OFF);
 
-		led_trigger_event(&phy->last_triggered->trigger, LED_OFF);
 		led_trigger_event(&plt->trigger, LED_FULL);
 		phy->last_triggered = plt;
 	}