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

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Date:   Thu, 18 May 2017 11:29:30 +0800
From:   Firo Yang <firogm@...il.com>
To:     walter harms <wharms@....de>
Cc:     linux-hams@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] hdlcdrv: fix divide error bug if bitrate is 0

On Wed, May 17, 2017 at 06:08:11PM +0200, walter harms wrote:
>
>
>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.
I agree with this.
>
>
>> 
>>>
>>> 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.
Indeed, ENODEV is more informative to enduser.
I will send a update patch.

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