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

[Joseph Chang <joechang@qti.qualcomm.com>]

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 to be send...
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.
-----Original Message-----
From: Corey Minyard [mailto:tcminyard@gmail.com] On Behalf Of Corey Minyard
Sent: Saturday, March 25, 2017 10:53 AM
To: Joseph Chang <joechang@qti.qualcomm.com>; openipmi-developer@lists.sourceforge.net; linux-kernel@vger.kernel.org
Cc: Jiandi An <anjiandi@qti.qualcomm.com>; Joeseph Chang <joechang@codeaurora.org>
Subject: Re: [PATCH] ipmi: Fix kernel panic at ipmi_ssif_thread()

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;