linux-kernel - Re: [PATCH v2] net: asix: fix uninit value in asix_mdio

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Message-ID: <20210813155226.651c74f0@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Fri, 13 Aug 2021 15:52:26 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Pavel Skripkin <paskripkin@...il.com>
Cc:     davem@...emloft.net, linux@...pel-privat.de,
        himadrispandya@...il.com, andrew@...n.ch,
        linux-usb@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        syzbot+a631ec9e717fb0423053@...kaller.appspotmail.com,
        Robert Foss <robert.foss@...labora.com>,
        Vincent Palatin <vpalatin@...omium.org>
Subject: Re: [PATCH v2] net: asix: fix uninit value in asix_mdio_read

On Sat, 14 Aug 2021 01:42:19 +0300 Pavel Skripkin wrote:
> Syzbot reported uninit-value in asix_mdio_read(). The problem was in
> missing error handling. asix_read_cmd() should initialize passed stack
> variable smsr, but it can fail in some cases. Then while condidition
> checks possibly uninit smsr variable.
> 
> Since smsr is uninitialized stack variable, driver can misbehave,
> because smsr will be random in case of asix_read_cmd() failure.
> Fix it by adding error cheking and just continue the loop instead of
> checking uninit value.
> 
> Fixes: 8a46f665833a ("net: asix: Avoid looping when the device is disconnected")

This is not the right tag, the Fixes tag should point to the commit
where the problem is introduced. Robert/Vincent only added some error
checking, the issue was there before, right?

Once you locate the right starting point for the fix please make sure
to add the author to CC.

Thanks!

> Reported-by: syzbot+a631ec9e717fb0423053@...kaller.appspotmail.com
> Signed-off-by: Pavel Skripkin <paskripkin@...il.com>

>  drivers/net/usb/asix_common.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/usb/asix_common.c b/drivers/net/usb/asix_common.c
> index ac92bc52a85e..7019c25e591c 100644
> --- a/drivers/net/usb/asix_common.c
> +++ b/drivers/net/usb/asix_common.c
> @@ -468,18 +468,25 @@ int asix_mdio_read(struct net_device *netdev, int phy_id, int loc)
>  	struct usbnet *dev = netdev_priv(netdev);
>  	__le16 res;
>  	u8 smsr;
> -	int i = 0;
> +	int i;
>  	int ret;

nit: move i after ret, reverse xmas tree style

>  	mutex_lock(&dev->phy_mutex);
> -	do {
> +	for (i = 0; i < 30; ++i) {
>  		ret = asix_set_sw_mii(dev, 0);
>  		if (ret == -ENODEV || ret == -ETIMEDOUT)
>  			break;
>  		usleep_range(1000, 1100);
>  		ret = asix_read_cmd(dev, AX_CMD_STATMNGSTS_REG,
>  				    0, 0, 1, &smsr, 0);
> -	} while (!(smsr & AX_HOST_EN) && (i++ < 30) && (ret != -ENODEV));
> +		if (ret == -ENODEV)
> +			break;
> +		else if (ret < 0)
> +			continue;
> +		else if (smsr & AX_HOST_EN)
> +			break;
> +	}
> +
>  	if (ret == -ENODEV || ret == -ETIMEDOUT) {
>  		mutex_unlock(&dev->phy_mutex);
>  		return ret;

Code LGTM, do other functions which Robert/Vincent touched not need the
same treatment tho?