linux-kernel - Re: [PATCH] fs/proc/task_mmu.c v1: fix clear_refs

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Message-ID: <20090813084557.GB5663@cr0.nay.redhat.com>
Date:	Thu, 13 Aug 2009 16:45:57 +0800
From:	Amerigo Wang <xiyou.wangcong@...il.com>
To:	Vincent Li <macli@....ubc.ca>
Cc:	Amerigo Wang <xiyou.wangcong@...il.com>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH] fs/proc/task_mmu.c v1: fix clear_refs_write() input
	sanity check

On Wed, Aug 12, 2009 at 10:20:28PM -0700, Vincent Li wrote:
>On Thu, 13 Aug 2009, Amerigo Wang wrote:
>
>> On Wed, Aug 12, 2009 at 04:29:54PM -0700, Vincent Li wrote:
>> >v1 fix the compiling errors and keep the type variable name.
>> >
>> >Andrew Morton pointed out similar string hacking and obfuscated check for zero-length input
>> >at the end of the function, David Rientjes suggested to use strict_strtol to replace
>> >simple_strtol, this patch cover above suggestions, add removing of leading and trailing
>> >whitespace from user input. It does not change function behavious.
>> >
>> 
>> 
>> Sorry, what real benefits can we get from this patch?
>
>It removes the redundant and weird zero-length check at the end of the 
>function since the the function already check the returning value of 
>simple_strtol, if it is zero-length input, the function should already 
>return error -EINVAL. Also using strict_strtol would only accept ascii 
>numbers, not something like:
>>echo 1foo > /proc/pid/clear_refs
>

IIRC, many /proc files can accept input like this...

I sent a patch some time ago to "fix" this, but Andrew pointed out
that things like "1foo" can be hackish. :-/


>
>> 
>> If this is really necessary, why not other files similar to 'clear_refs'?
>> 
>
>I did the same to other functions, but Andrew pointed out making changes 
>without fully understanding the patch impact would be risky and break 
>existing applications, So I need to fully understand what those functions 
>do before I make any changes.
> 


I can't find any strong reason why this one is differernt from others
in accepting input like "1foo"...

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