msg could be null without checking null and return, but still dereference
msg->rsp[2] and will lead to a null pointer trigger.

Signed-off-by: Haowen Bai <baihaowen@meizu.com>
---
V1->V2: check msg both cases that also uses msg; add logs;

 drivers/char/ipmi/ipmi_ssif.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/drivers/char/ipmi/ipmi_ssif.c b/drivers/char/ipmi/ipmi_ssif.c
index f199cc194844..eb6bdd44b69e 100644
--- a/drivers/char/ipmi/ipmi_ssif.c
+++ b/drivers/char/ipmi/ipmi_ssif.c
@@ -758,8 +758,11 @@ static void msg_done_handler(struct ssif_info *ssif_info, int result,
 	switch (ssif_info->ssif_state) {
 	case SSIF_NORMAL:
 		ipmi_ssif_unlock_cond(ssif_info, flags);
-		if (!msg)
+		if (!msg) {
+			dev_dbg(&ssif_info->client->dev,
+				"msg was null, case SSIF_NORMAL\n");
 			break;
+		}
 
 		if (result < 0)
 			return_hosed_msg(ssif_info, msg);
@@ -814,6 +817,13 @@ static void msg_done_handler(struct ssif_info *ssif_info, int result,
 		break;
 
 	case SSIF_GETTING_EVENTS:
+		if (!msg) {
+			ipmi_ssif_unlock_cond(ssif_info, flags);
+			dev_dbg(&ssif_info->client->dev,
+				"msg was null, case SSIF_GETTING_EVENTS\n");
+			break;
+		}
+
 		if ((result < 0) || (len < 3) || (msg->rsp[2] != 0)) {
 			/* Error getting event, probably done. */
 			msg->done(msg);
@@ -838,6 +848,13 @@ static void msg_done_handler(struct ssif_info *ssif_info, int result,
 		break;
 
 	case SSIF_GETTING_MESSAGES:
+		if (!msg) {
+			ipmi_ssif_unlock_cond(ssif_info, flags);
+			dev_dbg(&ssif_info->client->dev,
+				"msg was null, case SSIF_GETTING_MESSAGES\n");
+			break;
+		}
+
 		if ((result < 0) || (len < 3) || (msg->rsp[2] != 0)) {
 			/* Error getting event, probably done. */
 			msg->done(msg);
-- 
2.7.4