netdev - [PATCH] net: arc_emac: Fix use after free in arc_mdio

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Date:   Tue,  8 Mar 2022 19:10:05 +0800
From:   Jianglei Nie <niejianglei2021@....com>
To:     davem@...emloft.net, kuba@...nel.org, caihuoqing@...du.com
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jianglei Nie <niejianglei2021@....com>
Subject: [PATCH] net: arc_emac: Fix use after free in arc_mdio_probe()

If bus->state is equal to MDIOBUS_ALLOCATED, mdiobus_free(bus) will free
the "bus". But bus->name is still used in the next line, which will lead
to a use after free.

We can fix it by putting the bus->name in a local variable and then use
the name in the error message without referring to bus to avoid the uaf.

Signed-off-by: Jianglei Nie <niejianglei2021@....com>
---
 drivers/net/ethernet/arc/emac_mdio.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/arc/emac_mdio.c b/drivers/net/ethernet/arc/emac_mdio.c
index 9acf589b1178..33fd63d227ef 100644
--- a/drivers/net/ethernet/arc/emac_mdio.c
+++ b/drivers/net/ethernet/arc/emac_mdio.c
@@ -134,6 +134,7 @@ int arc_mdio_probe(struct arc_emac_priv *priv)
 	struct device_node *np = priv->dev->of_node;
 	struct mii_bus *bus;
 	int error;
+	const char *name = "Synopsys MII Bus";
 
 	bus = mdiobus_alloc();
 	if (!bus)
@@ -142,7 +143,7 @@ int arc_mdio_probe(struct arc_emac_priv *priv)
 	priv->bus = bus;
 	bus->priv = priv;
 	bus->parent = priv->dev;
-	bus->name = "Synopsys MII Bus";
+	bus->name = name;
 	bus->read = &arc_mdio_read;
 	bus->write = &arc_mdio_write;
 	bus->reset = &arc_mdio_reset;
@@ -167,7 +168,7 @@ int arc_mdio_probe(struct arc_emac_priv *priv)
 	if (error) {
 		mdiobus_free(bus);
 		return dev_err_probe(priv->dev, error,
-				     "cannot register MDIO bus %s\n", bus->name);
+				     "cannot register MDIO bus %s\n", name);
 	}
 
 	return 0;
-- 
2.25.1