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

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Date:   Wed, 17 May 2017 18:08:11 +0200
From:   walter harms <wharms@....de>
To:     Firo Yang <firogm@...il.com>
CC:     linux-hams@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] hdlcdrv: fix divide error bug if bitrate is 0



Am 17.05.2017 15:42, schrieb Firo Yang:
> 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;


I do not want to say you change is not valid but i have learned that it is better to
have an obvious check that to rely on hidden knowledge.


> 
>>
>> Also perhaps !netif_running(dev) should better return ENODEV.
> 
> However, the 'dev' truly exists in this circumstance.
> 

yes and i do not feel good with that but "no permission" will lead
any enduser into a search for user rights.



re,
 wh


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