Re: [PATCH net v2] net: mdio-ipq4019: fix possible invalid pointer dereference

[Hui Tang]

On 2022/11/17 21:57, Andrew Lunn wrote:
> On Thu, Nov 17, 2022 at 05:05:14PM +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@xxxxxxxxxx>
> > ---
> > v1 -> v2: set priv->eth_ldo_rdy NULL, if devm_ioremap_resource() failed
> > ---
> >  drivers/net/mdio/mdio-ipq4019.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/mdio/mdio-ipq4019.c b/drivers/net/mdio/mdio-ipq4019.c
> > index 4eba5a91075c..dfd1647eac36 100644
> > --- a/drivers/net/mdio/mdio-ipq4019.c
> > +++ b/drivers/net/mdio/mdio-ipq4019.c
> > @@ -231,8 +231,11 @@ static int ipq4019_mdio_probe(struct platform_device *pdev)
> >  	/* The platform resource is provided on the chipset IPQ5018 */
> >  	/* This resource is optional */
> >  	res = platform_get_resource(pdev, IORESOURCE_MEM, 1);
> > -	if (res)
> > +	if (res) {
> >  		priv->eth_ldo_rdy = devm_ioremap_resource(&pdev->dev, res);
> > +		if (IS_ERR(priv->eth_ldo_rdy))
> > +			priv->eth_ldo_rdy = NULL;
> > +	}
>
> As i said, please add devm_ioremap_resource_optional().  Follow the
> concept of devm_clk_get_optional(), devm_gpiod_get_optional(),
> devm_reset_control_get_optional(), devm_reset_control_get_optional(),
> platform_get_irq_byname_optional() etc.
>
> All these will not return an error if the resource you are trying to
> get does not exist. They instead return NULL, or something which other
> API members understand as does not exist, but thats O.K.
>
> These functions however do return errors for real problem, ENOMEM,
> EINVAL etc. These should not be ignored.
>
> You should then use this new function for all your other patches where
> the resource is optional.


I finally understand what you mean now.

I need add devm_ioremap_resource_optional() helper, which return NULL
if the resource does not exist, and if it return other errors we need
to deal with errors. In my case, it returns -ENOMEM if the resource
does not exist.

So, the code should be as follows, is that right?

+	void __iomem *devm_ioremap_resource_optional(struct device *dev,
+                                    	     const struct resource *res)
+	{
+		void __iomem *base;
+
+		base = __devm_ioremap_resource(dev, res, DEVM_IOREMAP);
+		if (IS_ERR(base) && PTR_ERR(base) == -ENOMEM)
+			return NULL;
+
+		return base;
+	}


[...]
	res = platform_get_resource(pdev, IORESOURCE_MEM, 1);
-	if (res)
+	if (res) {
+		priv->eth_ldo_rdy = devm_ioremap_resource_optional(&pdev->dev, res)
+		if (IS_ERR(priv->eth_ldo_rdy))
+			return PTR_ERR(priv->eth_ldo_rdy);
+	}
[...]

thanks.