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

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Date:	Wed, 24 Apr 2013 15:03:52 +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 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).

If it will not return NUL terminated string, please see line 326:

  "while ((*local_buffer) && (idx < splpar_strlen))"
  (when idx == 1024, *local_buffer is memory access violation).

Since we use the first 2 bytes as length, and also be sure of the real
length will never more than 1024, I suggest to:

---------------------------patch begin--------------------------------

diff --git a/arch/powerpc/kernel/lparcfg.c b/arch/powerpc/kernel/lparcfg.c
index 801a757..f8bd7cf 100644
--- a/arch/powerpc/kernel/lparcfg.c
+++ b/arch/powerpc/kernel/lparcfg.c
@@ -323,7 +323,7 @@ static void parse_system_parameter_string(struct seq_file *m)
 
 		w_idx = 0;
 		idx = 0;
-		while ((*local_buffer) && (idx < splpar_strlen)) {
+		while (idx < splpar_strlen) {
 			workbuffer[w_idx++] = local_buffer[idx++];
 			if ((local_buffer[idx] == ',')
 			    || (local_buffer[idx] == '\0')) {

---------------------------patch end----------------------------------

Thanks.

-- 
Chen Gang

Asianux Corporation
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