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

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Date:	Wed, 24 Apr 2013 11:58:04 +0530
From:	Vasant Hegde <hegdevasant@...ux.vnet.ibm.com>
To:	Chen Gang <gang.chen@...anux.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 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.

-Vasant

>
> Signed-off-by: Chen Gang<gang.chen@...anux.com>
> ---
>   arch/powerpc/kernel/lparcfg.c |    1 +
>   1 files changed, 1 insertions(+), 0 deletions(-)
>
> diff --git a/arch/powerpc/kernel/lparcfg.c b/arch/powerpc/kernel/lparcfg.c
> index 801a757..d92f387 100644
> --- a/arch/powerpc/kernel/lparcfg.c
> +++ b/arch/powerpc/kernel/lparcfg.c
> @@ -299,6 +299,7 @@ static void parse_system_parameter_string(struct seq_file *m)
>   				__pa(rtas_data_buf),
>   				RTAS_DATA_BUF_SIZE);
>   	memcpy(local_buffer, rtas_data_buf, SPLPAR_MAXLENGTH);
> +	local_buffer[SPLPAR_MAXLENGTH - 1] = '\0';
>   	spin_unlock(&rtas_data_buf_lock);
>
>   	if (call_status != 0) {

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