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 <joech...@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 <joech...@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 <joech...@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;