netdev - Re: [PATCH] hdlcdrv: fix divide error bug if bitrate is 0

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Date:   Wed, 17 May 2017 21:42:46 +0800
From:   Firo Yang <firogm@...il.com>
To:     walter harms <wharms@....de>
Cc:     t.sailer@...mni.ethz.ch, davem@...emloft.net,
        gregkh@...uxfoundation.org, linux-hams@...r.kernel.org,
        netdev@...r.kernel.org, dvyukov@...gle.com,
        syzkaller@...glegroups.com
Subject: Re: [PATCH] hdlcdrv: fix divide error bug if bitrate is 0

On Wed, May 17, 2017 at 02:59:39PM +0200, walter harms wrote:
>
>
>Am 17.05.2017 14:35, schrieb Firo Yang:
>> The divisor s->par.bitrate will always be 0 until initialized by
>> ndo_open() and hdlcdrv_open().
>> 
>> In order to fix this divide zero error, check whether the netdevice
>> was opened by ndo_open() before performing divide.
>> 
>> Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
>> Signed-off-by: Firo Yang <firogm@...il.com>
>> ---
>>  drivers/net/hamradio/hdlcdrv.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/drivers/net/hamradio/hdlcdrv.c b/drivers/net/hamradio/hdlcdrv.c
>> index 8c3633c..3c783fd 100644
>> --- a/drivers/net/hamradio/hdlcdrv.c
>> +++ b/drivers/net/hamradio/hdlcdrv.c
>> @@ -574,7 +574,7 @@ static int hdlcdrv_ioctl(struct net_device *dev, struct ifreq *ifr, int cmd)
>>  		break;		
>>  
>>  	case HDLCDRVCTL_CALIBRATE:
>> -		if(!capable(CAP_SYS_RAWIO))
>> +		if (!capable(CAP_SYS_RAWIO) || !netif_running(dev))
>>  			return -EPERM;
>>  		if (bi.data.calibrate > INT_MAX / s->par.bitrate)
>>  			return -EINVAL;
>
>I would still check for s->par.bitrate > 0 later changes may affect the setting of it
>and it is much more obvious.

I think 0 is not valid value for bitrate, so we should check it in
other places, like what ser12_open() did:
429         if (bc->baud < 300 || bc->baud > 4800) {
430                 printk(KERN_INFO "baycom_ser_fdx: invalid baudrate "
431                                 "(300...4800)\n");
432                 return -EINVAL;
433         }
...
440         bc->hdrv.par.bitrate = bc->baud;

>
>Also perhaps !netif_running(dev) should better return ENODEV.

However, the 'dev' truly exists in this circumstance.

Thanks,
Firo

>
>
>just my 2 cents,
>re,
> wh
>