netdev - Re: [patch] isdn: fix a wrapping bug in isdn_ppp

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Date:	Fri, 12 Oct 2012 09:49:52 +0200
From:	Karsten Keil <kkeil@...ux-pingi.de>
To:	Joe Perches <joe@...ches.com>
CC:	David Laight <David.Laight@...LAB.COM>,
	Andreas Schwab <schwab@...ux-m68k.org>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	Karsten Keil <isdn@...ux-pingi.de>,
	"David S. Miller" <davem@...emloft.net>,
	Masanari Iida <standby24x7@...il.com>, netdev@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [patch] isdn: fix a wrapping bug in isdn_ppp_ioctl()

Hi,
Am 10.10.2012 17:52, schrieb Joe Perches:
> On Wed, 2012-10-10 at 16:44 +0100, David Laight wrote:
>>> On Wed, 2012-10-10 at 15:59 +0100, David Laight wrote:
>>>> Seems to me the code is expecting 256 bits of data, not any multiple of int,
>>>> long or anything else.
>>>
>>> include/linux/isdn_ppp.h:#define PPPIOCGCOMPRESSORS _IOR('t',134,unsigned long [8])
>>
>> That doesn't mean the whole thing makes any sense on 64bit systems.
>> A whole load of historic code used 'long' to ensure 32bit.
>> Some of that might have crept into Linux sources.
> 
> Very true, but it's exported via copy_to_user.
> 
>> Since I suspect there are a maximum of 256 bits on both 32 and 64bit
>> systems, I wouldn't like to guess exactly how any particular 64bit
>> application chooses to check the bitmap.
>>
>> The ioctl constant may be wrong on 64 bit systems.
> 
> shrug.  Not much to do about it now.
> isdn isn't very active.
> 
> Karsten?  What do you think?
> 

I use ipppd as testbench to test remote connections via different PPP
clients running on a 64 bit system without problems so far - but I did
not use any compressions for some years, so maybe this code was never
tested on 64 bit and at least not on mixed 32/64 bit systems.
If I will find some time, I will check if the compression works.
I did not wrote this part, so I cannot say how the code should work
correctly out of the box, I  need to analyze this first by myself.

Karsten

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