netdev - [PATCH net] phylib: fix potential use-after-free

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Message-Id: <20220119162748.32418-1-kabel@kernel.org>
Date:   Wed, 19 Jan 2022 17:27:48 +0100
From:   Marek Behún <kabel@...nel.org>
To:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Cc:     Russell King <rmk+kernel@...linux.org.uk>,
        Andrew Lunn <andrew@...n.ch>,
        Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        "David S . Miller" <davem@...emloft.net>,
        Marek Behún <kabel@...nel.org>
Subject: [PATCH net] phylib: fix potential use-after-free

Commit bafbdd527d56 ("phylib: Add device reset GPIO support") added call
to phy_device_reset(phydev) after the put_device() call in phy_detach().

The comment before the put_device() call says that the phydev might go
away with put_device().

Fix potential use-after-free by calling phy_device_reset() before
put_device().

Fixes: bafbdd527d56 ("phylib: Add device reset GPIO support")
Signed-off-by: Marek Behún <kabel@...nel.org>
---
 drivers/net/phy/phy_device.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
index 74d8e1dc125f..ce0bb5951b81 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c
@@ -1746,6 +1746,9 @@ void phy_detach(struct phy_device *phydev)
 	    phy_driver_is_genphy_10g(phydev))
 		device_release_driver(&phydev->mdio.dev);
 
+	/* Assert the reset signal */
+	phy_device_reset(phydev, 1);
+
 	/*
 	 * The phydev might go away on the put_device() below, so avoid
 	 * a use-after-free bug by reading the underlying bus first.
@@ -1757,9 +1760,6 @@ void phy_detach(struct phy_device *phydev)
 		ndev_owner = dev->dev.parent->driver->owner;
 	if (ndev_owner != bus->owner)
 		module_put(bus->owner);
-
-	/* Assert the reset signal */
-	phy_device_reset(phydev, 1);
 }
 EXPORT_SYMBOL(phy_detach);
 
-- 
2.34.1