[PATCH v2] net: arc_emac: Fix use after free in arc_mdio_probe()

[PATCH v2] net: arc_emac: Fix use after free in arc_mdio_probe()

[Jianglei Nie]

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 name in a local variable and make the
bus->name point to the rodata section "name",then use the name in the
error message without referring to bus to avoid the uaf.

Signed-off-by: Jianglei Nie <niejianglei2021@163.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..87f40c2ba904 100644
--- a/drivers/net/ethernet/arc/emac_mdio.c
+++ b/drivers/net/ethernet/arc/emac_mdio.c
@@ -132,6 +132,7 @@ int arc_mdio_probe(struct arc_emac_priv *priv)
 {
 	struct arc_emac_mdio_bus_data *data = &priv->bus_data;
 	struct device_node *np = priv->dev->of_node;
+	const char *name = "Synopsys MII Bus";
 	struct mii_bus *bus;
 	int error;
 
@@ -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

Re: [PATCH v2] net: arc_emac: Fix use after free in arc_mdio_probe()

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (master)
by Jakub Kicinski <kuba@kernel.org>:

On Wed,  9 Mar 2022 20:18:24 +0800 you wrote:
> 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 name in a local variable and make the
> bus->name point to the rodata section "name",then use the name in the
> error message without referring to bus to avoid the uaf.
> 
> [...]

Here is the summary with links:
  - [v2] net: arc_emac: Fix use after free in arc_mdio_probe()
    https://git.kernel.org/netdev/net/c/bc0e610a6eb0

You are awesome, thank you!
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