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

[Neelesh Gupta <neelegup@linux.vnet.ibm.com>]

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 <neelegup@linux.vnet.ibm.com>
---
 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)) {