Re: [PATCH] net: mdio-ipq4019: fix possible invalid pointer dereference

[Andrew Lunn <andrew@lunn.ch>]

On Tue, Nov 15, 2022 at 12:50:28PM +0800, Hui Tang wrote:
> priv->eth_ldo_rdy is saved the return value of devm_ioremap_resource(),
> which !IS_ERR() should be used to check.
> 
> Fixes: 23a890d493e3 ("net: mdio: Add the reset function for IPQ MDIO driver")
> Signed-off-by: Hui Tang <tanghui20@huawei.com>
> ---
>  drivers/net/mdio/mdio-ipq4019.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/mdio/mdio-ipq4019.c b/drivers/net/mdio/mdio-ipq4019.c
> index 4eba5a91075c..d7a1f7c56f97 100644
> --- a/drivers/net/mdio/mdio-ipq4019.c
> +++ b/drivers/net/mdio/mdio-ipq4019.c
> @@ -188,7 +188,7 @@ static int ipq_mdio_reset(struct mii_bus *bus)
>  	/* To indicate CMN_PLL that ethernet_ldo has been ready if platform resource 1
>  	 * is specified in the device tree.
>  	 */
> -	if (priv->eth_ldo_rdy) {
> +	if (!IS_ERR(priv->eth_ldo_rdy)) {
>  		val = readl(priv->eth_ldo_rdy);
>  		val |= BIT(0);
>  		writel(val, priv->eth_ldo_rdy);

There is a general pattern in the kernel that optional things are set
to NULL if the resource does not exist. Often there is a
get_foo_optional() which will return a NULL point if the things does
not exist, the thing if it does exist, or an error code if a real
error happened.

So please follow this patterns. Check the return value in
ipq4019_mdio_probe(). Looking at __devm_ioremap_resource() i _think_
it returns -ENOMEM if the resource does not exist? So maybe any other
error is a real error, and should be reported, and -ENOMEM should
result in eth_ldo_rdy set to NULL?

       Andrew