Re: [PATCH] PowerPC: kernel: memory access violation when rtas_data_bufcontents are more than 1026

From: Vasant Hegde
Date: Wed Apr 24 2013 - 03:24:18 EST

On 04/24/2013 12:33 PM, Chen Gang wrote:
On 2013å04æ24æ 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.


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----------------------------------


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