linux-kernel - [PATCH v2] net: phy: Fix use after free in phy

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Date:   Mon, 28 Nov 2016 15:18:31 +0100
From:   Geert Uytterhoeven <geert+renesas@...der.be>
To:     Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Josh Cartwright <josh.cartwright@...com>,
        Nathan Sullivan <nathan.sullivan@...com>,
        Zach Brown <zach.brown@...com>
Cc:     Woojung Huh <woojung.huh@...rochip.com>, netdev@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Geert Uytterhoeven <geert+renesas@...der.be>
Subject: [PATCH v2] net: phy: Fix use after free in phy_detach()

If device_release_driver(&phydev->mdio.dev) is called, it releases all
resources belonging to the PHY device. Hence the subsequent call to
phy_led_triggers_unregister() will access already freed memory when
unregistering the LEDs.

Move the call to phy_led_triggers_unregister() before the possible call
to device_release_driver() to fix this.

Fixes: 2e0bc452f4721520 ("net: phy: leds: add support for led triggers on phy link state change")
Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
---
This is v2 of "[RFC] net: phy: Fix double free in phy_detach()".

v2:
  - Dropped RFC,
  - Reworded, as commit a7dac9f9c1695d74 ("phy: fix error case of
    phy_led_triggers_(un)register") fixed the double free, and thus the
    warning I was seeing during "poweroff" on sh73a0/kzm9g,
  - Verified use after free using CONFIG_DEBUG_DEVRES, log_devres = 1,
    and additional debug code printing the address of
    phy->phy_led_triggers. Adding poisoning of freed memory to
    devres_log() will cause a crash.
---
 drivers/net/phy/phy_device.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
index ba86c191a13ea81c..a1d6e13b1b4113a4 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c
@@ -981,6 +981,8 @@ void phy_detach(struct phy_device *phydev)
 	phydev->attached_dev = NULL;
 	phy_suspend(phydev);
 
+	phy_led_triggers_unregister(phydev);
+
 	/* If the device had no specific driver before (i.e. - it
 	 * was using the generic driver), we unbind the device
 	 * from the generic driver so that there's a chance a
@@ -994,8 +996,6 @@ void phy_detach(struct phy_device *phydev)
 		}
 	}
 
-	phy_led_triggers_unregister(phydev);
-
 	/*
 	 * The phydev might go away on the put_device() below, so avoid
 	 * a use-after-free bug by reading the underlying bus first.
-- 
1.9.1