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

[joechang]

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@xxxxxxxxxxxxxx>
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 æ 2017-03-25 10:53 åå:
> 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@xxxxxxxxxxxxxx>
> >
> > 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@xxxxxxxxxxxxxx>
> > ---
> >   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;