[PATCH] ipmi/powernv: Fix potential invalid pointer dereference

If the OPAL call to receive the ipmi message fails, then we free up the
smi message and return. But, the driver still holds the reference to
old smi message in the 'cur_msg' which can potentially be accessed later
and freed again leading to kernel oops. To fix it up,

The kernel driver should reset the 'cur_msg' and send reply to the user
in addition to freeing the message.

Signed-off-by: Neelesh Gupta <redacted>
---
 drivers/char/ipmi/ipmi_powernv.c |   13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/char/ipmi/ipmi_powernv.c b/drivers/char/ipmi/ipmi_powernv.c
index 9b409c0..637486d 100644
--- a/drivers/char/ipmi/ipmi_powernv.c
+++ b/drivers/char/ipmi/ipmi_powernv.c

@@ -143,9 +143,16 @@ static int ipmi_powernv_recv(struct ipmi_smi_powernv *smi)
 	pr_devel("%s:   -> %d (size %lld)\n", __func__,
 			rc, rc == 0 ? size : 0);
 	if (rc) {
-		spin_unlock_irqrestore(&smi->msg_lock, flags);
-		ipmi_free_smi_msg(msg);
-		return 0;
+		/* If came via the poll, and response was not yet ready */
+		if (rc == OPAL_EMPTY) {
+			spin_unlock_irqrestore(&smi->msg_lock, flags);
+			return 0;
+		} else {
+			smi->cur_msg = NULL;
+			spin_unlock_irqrestore(&smi->msg_lock, flags);
+			send_error_reply(smi, msg, IPMI_ERR_UNSPECIFIED);
+			return 0;
+		}
 	}
 
 	if (size < sizeof(*opal_msg)) {

Ok, this looks fine.  A couple of question...

Do I need to send this upstream right now?  How well has this been tested?

Do you want this backported to 4.0 stable?

-corey

On 07/16/2015 06:16 AM, Neelesh Gupta wrote:

Hi Corey,

On 07/16/2015 08:31 PM, Corey Minyard wrote:

Ok, this looks fine.  A couple of question...

Do I need to send this upstream right now?  How well has this been tested?

I would want either Jeremy or Alistair to review this patch before you 
send this
upstream. There is also firmware piece 
http://patchwork.ozlabs.org/patch/496645/
awaiting review.

In the testing front, I manually made the opal_ipmi_recv() function to 
fail for testing
the error path and see if the driver recovers from it and subsequent 
ipmi commands
work all good.

Do you want this backported to 4.0 stable?

Yes, I want this to be be backported to 4.0 stable.

Thanks,
Neelesh.

-corey

On 07/16/2015 06:16 AM, Neelesh Gupta wrote:

quoted

If the OPAL call to receive the ipmi message fails, then we free up the
smi message and return. But, the driver still holds the reference to
old smi message in the 'cur_msg' which can potentially be accessed later
and freed again leading to kernel oops. To fix it up,

The kernel driver should reset the 'cur_msg' and send reply to the user
in addition to freeing the message.

Signed-off-by: Neelesh Gupta <redacted>
---
  drivers/char/ipmi/ipmi_powernv.c |   13 ++++++++++---
  1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/char/ipmi/ipmi_powernv.c b/drivers/char/ipmi/ipmi_powernv.c
index 9b409c0..637486d 100644
--- a/drivers/char/ipmi/ipmi_powernv.c
+++ b/drivers/char/ipmi/ipmi_powernv.c

@@ -143,9 +143,16 @@ static int ipmi_powernv_recv(struct ipmi_smi_powernv *smi)
  	pr_devel("%s:   -> %d (size %lld)\n", __func__,
  			rc, rc == 0 ? size : 0);
  	if (rc) {
-		spin_unlock_irqrestore(&smi->msg_lock, flags);
-		ipmi_free_smi_msg(msg);
-		return 0;
+		/* If came via the poll, and response was not yet ready */
+		if (rc == OPAL_EMPTY) {
+			spin_unlock_irqrestore(&smi->msg_lock, flags);
+			return 0;
+		} else {
+			smi->cur_msg = NULL;
+			spin_unlock_irqrestore(&smi->msg_lock, flags);
+			send_error_reply(smi, msg, IPMI_ERR_UNSPECIFIED);
+			return 0;
+		}
  	}
  
  	if (size < sizeof(*opal_msg)) {