linux-kernel - Re: [PATCH] PowerPC: kernel: memory access violation when rtas_data

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Date:	Wed, 24 Apr 2013 15:40:50 +0800
From:	Chen Gang <gang.chen@...anux.com>
To:	Vasant Hegde <hegdevasant@...ux.vnet.ibm.com>
CC:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	"sfr@...b.auug.org.au" <sfr@...b.auug.org.au>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"paulus@...ba.org" <paulus@...ba.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH] PowerPC: kernel: memory access violation when rtas_data_buf
 contents are more than 1026

On 2013年04月24日 15:23, Vasant Hegde wrote:
> On 04/24/2013 12:33 PM, Chen Gang wrote:
>> On 2013年04月24日 14:28, Vasant Hegde wrote:
>>> On 04/23/2013 08:42 AM, Chen Gang wrote:
>>>>
>>>> need set '\0' for 'local_buffer'.
>>>>
>>>> SPLPAR_MAXLENGTH is 1026, RTAS_DATA_BUF_SIZE is 4096. so the
>>>> contents of
>>>> rtas_data_buf may truncated in memcpy.
>>>>
>>>> if contents are really truncated.
>>>>     the splpar_strlen is more than 1026. the next while loop
>>>> checking will
>>>>     not find the end of buffer. that will cause memory access
>>>> violation.
>>>>
>>>
>>> Per parameter length in ibm,get-system-parameter RTAS call is limited to
>>> 1026 bytes (1024 bytes of data + 2 bytes  length). And 'rtas_data_buf'
>>> was set to 0 (first 1026 bytes) before call RTAS call. At the worst if
>>> we get junk in RTAS output length field helps to exit from the while
>>> loop. So I don't think we need this patch.
>>
>> Is get-system-parameter return the NUL terminated string ? if so, it
>> will no issue (just like your discription).
>>
> 
> Length includes the length of the NULL. So (idx < splpar_strlen)
> is safe. IMO existing code is proper.

OK, since it is not an issue, I will try another patches for powerpc POWER7.

  :-)

-- 
Chen Gang

Asianux Corporation
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