[PATCH] mdio_bus: add NULL check to mdiobus_read/mdiobus_write

[Stefan Kerkmann]

Reviewed-by: Stefan Kerkmann <s.kerkmann at pengutronix.de>

On 14.10.24 10:55, Ahmad Fatoum wrote:
> These functions shouldn't be called with a NULL pointer as argument in
> the first place, but this happened at least twice so far[1][2], because
> drivers weren't tested in fixed-link setups without PHYs.
> 
> To improve user experience, let's return -EIO instead of crashing
> outright. The proper fix is still to adapt these drivers, so they
> do not try to access non-existent PHYs.
> 
> [1]: commit 6269556397 ("net: eqos: let phy_resume handle fixed link phys")
> [2]: https://lore.barebox.org/barebox/20241010-fix-designware-fixed-link-v1-1-de2df5485a25@pengutronix.de/T/#u
> 
> Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
> ---
>  drivers/net/phy/mdio_bus.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/net/phy/mdio_bus.c b/drivers/net/phy/mdio_bus.c
> index 30d5aeacff0d..68652e92a830 100644
> --- a/drivers/net/phy/mdio_bus.c
> +++ b/drivers/net/phy/mdio_bus.c
> @@ -441,6 +441,9 @@ int mdiobus_read(struct mii_bus *bus, int addr, u32 regnum)
>  {
>  	int ret;
>  
> +	if (!bus)
> +		return -EIO;
> +
>  	slice_acquire(&bus->slice);
>  
>  	ret = bus->read(bus, addr, regnum);
> @@ -461,6 +464,9 @@ int mdiobus_write(struct mii_bus *bus, int addr, u32 regnum, u16 val)
>  {
>  	int ret;
>  
> +	if (!bus)
> +		return -EIO;
> +
>  	slice_acquire(&bus->slice);
>  
>  	ret = bus->write(bus, addr, regnum, val);

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