linux-kernel - Re: [PATCH] ipmi: Fix kernel panic at ipmi_ssif

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Message-ID: <6d686ff9-e94b-ddc0-cf9f-13a839acbb08@acm.org>
Date:   Fri, 24 Mar 2017 21:53:16 -0500
From:   Corey Minyard <minyard@....org>
To:     Joeseph Chang <joechang@....qualcomm.com>,
        openipmi-developer@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Cc:     anjiandi@....qualcomm.com, Joeseph Chang <joechang@...eaurora.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@...eaurora.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@...eaurora.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;