linux-kernel - [PATCH v2] net: phy: phy_led_triggers: Fix a possible null-pointer dereference in phy_led_trigger_change

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Message-Id: <20190730080813.15363-1-baijiaju1990@gmail.com>
Date:   Tue, 30 Jul 2019 16:08:13 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     andrew@...n.ch, f.fainelli@...il.com, hkallweit1@...il.com,
        davem@...emloft.net
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jia-Ju Bai <baijiaju1990@...il.com>
Subject: [PATCH v2] net: phy: phy_led_triggers: Fix a possible null-pointer dereference in phy_led_trigger_change_speed()

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@...il.com>
---
v2:
* Add the organization of the tool's authors.
  Thank David and Andrew for helpful advice.

---
 drivers/net/phy/phy_led_triggers.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/phy/phy_led_triggers.c b/drivers/net/phy/phy_led_triggers.c
index b86a4b2116f8..59a94e07e7c5 100644
--- a/drivers/net/phy/phy_led_triggers.c
+++ b/drivers/net/phy/phy_led_triggers.c
@@ -48,8 +48,9 @@ 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;
 	}
-- 
2.17.0