Re: [PATCH] ipmi: Fix kernel panic at ipmi_ssif_thread()

[joechang@codeaurora.org]

Hi Corey,

Thanks your feedback and suggestion. :)
I think you are right. It is better to allocate one new local variable 
to store i2c data and size that will be sent...
I create new patch in following according to your suggestion.
Could you help to review the patch again?

 From eec31f51acc7e019fd0dcc512febda86870268d2 Mon Sep 17 00:00:00 2001
 From: Joeseph Chang <joechang@codeaurora.org>
Date: Mon, 27 Mar 2017 10:46:42 +0800
Subject: [PATCH] ipmi: Fix kernel panic at ipmi_ssif_thread()

msg_written_handler() may set ssif_info->multi_data to NULL
when using ipmitool to write fru.

Fix kernel panic at ipmi_ssif_thread() and incorrect
ssif_info->multi_pos by adding one local pointer i2c_data to store i2c
data and size to send before calling ssif_i2c_send().

With this change, can avoid concurrent access to ssif_info->multi_pos 
and
ssif_info->multi_data at msg_written_handler.
Because msg_written_handler can be called at any time after 
ssif_i2c_send().
---
  drivers/char/ipmi/ipmi_ssif.c | 4 +++-
  1 file changed, 3 insertions(+), 1 deletion(-)
  mode change 100644 => 100755 drivers/char/ipmi/ipmi_ssif.c

diff --git a/drivers/char/ipmi/ipmi_ssif.c 
b/drivers/char/ipmi/ipmi_ssif.c
old mode 100644
new mode 100755
index cca6e5b..f36f018
--- a/drivers/char/ipmi/ipmi_ssif.c
+++ b/drivers/char/ipmi/ipmi_ssif.c
@@ -852,6 +852,7 @@ static void msg_written_handler(struct ssif_info 
*ssif_info, int result,
                  unsigned char *data, unsigned int len)
  {
      int rv;
+    unsigned char *i2c_data;

      /* We are single-threaded here, so no need for a lock. */
      if (result < 0) {
@@ -899,6 +900,7 @@ static void msg_written_handler(struct ssif_info 
*ssif_info, int result,
              left = 32;
          /* Length byte. */
          ssif_info->multi_data[ssif_info->multi_pos] = left;
+        i2c_data = ssif_info->multi_data + ssif_info->multi_pos;
          ssif_info->multi_pos += left;
          if (left < 32)
              /*
@@ -912,7 +914,7 @@ static void msg_written_handler(struct ssif_info 
*ssif_info, int result,
          rv = ssif_i2c_send(ssif_info, msg_written_handler,
                    I2C_SMBUS_WRITE,
                    SSIF_IPMI_MULTI_PART_REQUEST_MIDDLE,
-                  ssif_info->multi_data + ssif_info->multi_pos,
+                  i2c_data,
                    I2C_SMBUS_BLOCK_DATA);
          if (rv < 0) {
              /* request failed, just return the error. */
-- 
1.9.1


Thank you,
Joseph.

Corey Minyard 於 2017-03-25 10:53 寫到:
> This is incorrect.  These values *must* be set before ssif_i2c_send() 
> is done.
> Once ssif_i2c_send() is called, msg_written_handler can be called at 
> any
> time after that, including before where you moved the new code.
> 
> If I understand this correctly, I think you need to add a variable,
> maybe named "bytes_to_write" and do
> 
>   bytes_to_write = ssif_info->multi_data + ssif_info->multi_pos;
> 
> before the comparison and pass bytes_to_write into
> ssif_i2c_send().
> 
> Thanks,
> 
> -corey
> 
> On 03/23/2017 02:07 AM, Joeseph Chang wrote:
>> From: Joeseph Chang <joechang@codeaurora.org>
>> 
>> msg_written_handler() may set ssif_info->multi_data to NULL
>> when using ipmitool to write fru.
>> Change the ssif i2c send data sequence in msg_written_handler()
>> to fix NULL pointer kernel panic and incorrect ssif_info->multi_pos.
>> 
>> Signed-off-by: Joeseph Chang <joechang@codeaurora.org>
>> ---
>>   drivers/char/ipmi/ipmi_ssif.c | 20 +++++++++++---------
>>   1 file changed, 11 insertions(+), 9 deletions(-)
>> 
>> diff --git a/drivers/char/ipmi/ipmi_ssif.c 
>> b/drivers/char/ipmi/ipmi_ssif.c
>> index cca6e5b..39346ee 100644
>> --- a/drivers/char/ipmi/ipmi_ssif.c
>> +++ b/drivers/char/ipmi/ipmi_ssif.c
>> @@ -899,21 +899,13 @@ static void msg_written_handler(struct ssif_info 
>> *ssif_info, int result,
>>   			left = 32;
>>   		/* Length byte. */
>>   		ssif_info->multi_data[ssif_info->multi_pos] = left;
>> -		ssif_info->multi_pos += left;
>> -		if (left < 32)
>> -			/*
>> -			 * Write is finished.  Note that we must end
>> -			 * with a write of less than 32 bytes to
>> -			 * complete the transaction, even if it is
>> -			 * zero bytes.
>> -			 */
>> -			ssif_info->multi_data = NULL;
>>     		rv = ssif_i2c_send(ssif_info, msg_written_handler,
>>   				  I2C_SMBUS_WRITE,
>>   				  SSIF_IPMI_MULTI_PART_REQUEST_MIDDLE,
>>   				  ssif_info->multi_data + ssif_info->multi_pos,
>>   				  I2C_SMBUS_BLOCK_DATA);
>> +
>>   		if (rv < 0) {
>>   			/* request failed, just return the error. */
>>   			ssif_inc_stat(ssif_info, send_errors);
>> @@ -922,6 +914,16 @@ static void msg_written_handler(struct ssif_info 
>> *ssif_info, int result,
>>   				pr_info("Error from i2c_non_blocking_op(3)\n");
>>   			msg_done_handler(ssif_info, -EIO, NULL, 0);
>>   		}
>> +
>> +		ssif_info->multi_pos += left;
>> +		if (left < 32)
>> +			/*
>> +			 * Write is finished.  Note that we must end
>> +			 * with a write of less than 32 bytes to
>> +			 * complete the transaction, even if it is
>> +			 * zero bytes.
>> +			 */
>> +			ssif_info->multi_data = NULL;
>>   	} else {
>>   		/* Ready to request the result. */
>>   		unsigned long oflags, *flags;