netdev - Re: [PATCH] ax25: unsigned cannot be less than 0 in ax25_ctl

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Date:	Tue, 13 Oct 2009 11:48:38 +0200
From:	walter harms <wharms@....de>
To:	Kevin Dawson <kevind@....com.au>
Cc:	Roel Kluin <roel.kluin@...il.com>, linux-hams@...r.kernel.org,
	netdev <netdev@...r.kernel.org>, Joerg Reuter <jreuter@...na.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] ax25: unsigned cannot be less than 0 in ax25_ctl_ioctl()



Kevin Dawson schrieb:
> Roel Kluin wrote:
> 
>>>  tmp_arg=ax25_ctl.arg * HZ;
>>>
>>>   if (arg == 0 || arg >  ULONG_MAX )
>>>         goto einval_put;
>>
>> I'm not sure, I think this would only work if we made `arg' an
>> unsigned long long.
> 
> That depends on the possible values of ax25_ctl.arg.
> 
>> +    if (ax25_ctl.arg * HZ > ULONG_MAX && ax25_ctl.cmd != AX25_KILL)
>> +        return -EINVAL;
> 
> Why the need to change arg before comparing it with a constant?  Let the
> compiler do the work:
> 
>     if (ax25_ctl.arg > ULONG_MAX / HZ && ...
> 
> Kevin
> 

i like this because it prevents a wrap around for stupid ax25_ctl.arg values but will not help when
ax25_ctl.arg * HZ is used later. NTL i think HZ does not need to be constant these days but i am not an
expert on that area.

  re,
   wh


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