[PATCH] char: ipmi: Fix possible pointer dereferences in msg_done_handler()

[Jia-Ju Bai <baijiaju1990@gmail.com>]

In msg_done_handler(), there is an if statement on line 778 to check
whether msg is NULL:
    if (msg)

When msg is NULL, it is used on line 845:
    if ((result < 0) || (len < 3) || (msg->rsp[2] != 0))
and line 869:
    if ((result < 0) || (len < 3) || (msg->rsp[2] != 0))

Thus, possible null-pointer dereferences may occur.

To fix these bugs, msg is checked before being used.

These bugs are found by a static analysis tool STCheck written by us.

Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
---
 drivers/char/ipmi/ipmi_ssif.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/char/ipmi/ipmi_ssif.c b/drivers/char/ipmi/ipmi_ssif.c
index 305fa5054274..2e40a98d9939 100644
--- a/drivers/char/ipmi/ipmi_ssif.c
+++ b/drivers/char/ipmi/ipmi_ssif.c
@@ -842,6 +842,8 @@ static void msg_done_handler(struct ssif_info *ssif_info, int result,
 		break;
 
 	case SSIF_GETTING_EVENTS:
+		if (!msg)
+			break;
 		if ((result < 0) || (len < 3) || (msg->rsp[2] != 0)) {
 			/* Error getting event, probably done. */
 			msg->done(msg);
@@ -866,6 +868,8 @@ static void msg_done_handler(struct ssif_info *ssif_info, int result,
 		break;
 
 	case SSIF_GETTING_MESSAGES:
+		if (!msg)
+			break;
 		if ((result < 0) || (len < 3) || (msg->rsp[2] != 0)) {
 			/* Error getting event, probably done. */
 			msg->done(msg);
-- 
2.17.0