Re: [PATCH] USB2NET: SR9700: fix uninitialized variable use in sr_mdio_read

[Shigeru Yoshida]

On Tue, 23 Jul 2024 22:04:34 +0800, Ma Ke wrote:
> It could lead to error happen because the variable res is not updated if
> the call to sr_share_read_word returns an error. In this particular case
> error code was returned and res stayed uninitialized.
> 
> This can be avoided by checking the return value of sr_share_read_word
> and propagating the error if the read operation failed.
> 
> Fixes: c9b37458e956 ("USB2NET : SR9700 : One chip USB 1.1 USB2NET SR9700Device Driver Support")
> Signed-off-by: Ma Ke <make24@xxxxxxxxxxx>
> ---
>  drivers/net/usb/sr9700.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/usb/sr9700.c b/drivers/net/usb/sr9700.c
> index 0a662e42ed96..d5bc596f4521 100644
> --- a/drivers/net/usb/sr9700.c
> +++ b/drivers/net/usb/sr9700.c
> @@ -179,6 +179,7 @@ static int sr_mdio_read(struct net_device *netdev, int phy_id, int loc)
>  	struct usbnet *dev = netdev_priv(netdev);
>  	__le16 res;
>  	int rc = 0;
> +	int err;
>  
>  	if (phy_id) {
>  		netdev_dbg(netdev, "Only internal phy supported\n");
> @@ -193,7 +194,10 @@ static int sr_mdio_read(struct net_device *netdev, int phy_id, int loc)
>  		if (value & NSR_LINKST)
>  			rc = 1;
>  	}
> -	sr_share_read_word(dev, 1, loc, &res);
> +	err = sr_share_read_word(dev, 1, loc, &res);
> +	if (err < 0)
> +		return err;
> +

The patch looks good to me.  But I think the following sr_read_reg()
has the same uninit-value access issue.  If sr_read_reg() returns an
error, value may be uninitialized:

static int sr_mdio_read(struct net_device *netdev, int phy_id, int loc)
{
[...]
	/* Access NSR_LINKST bit for link status instead of MII_BMSR */
	if (loc == MII_BMSR) {
		u8 value;

		sr_read_reg(dev, SR_NSR, &value);
		if (value & NSR_LINKST)
			rc = 1;
	}

Why don't we fix it together?

Thanks,
Shigeru

>  	if (rc == 1)
>  		res = le16_to_cpu(res) | BMSR_LSTATUS;
>  	else
> -- 
> 2.25.1
> 
>