mei: check for error returned from mei_hbuf_empty_slots()

mei_hbuf_empty_slots() may return with an error in case
of circular buffer overflow. This type of error may
be caused only by a bug. However currently, the error
won't be detected due signed type promotion in comparison to u32.
We add explicit check for less then zero and explicit cast
in comparison to suppress singn-compare warning.
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/mei/client.c

@@ -865,8 +865,10 @@ int mei_cl_irq_disconnect(struct mei_cl *cl, struct mei_cl_cb *cb,
 
 	msg_slots = mei_data2slots(sizeof(struct hbm_client_connect_request));
 	slots = mei_hbuf_empty_slots(dev);
+	if (slots < 0)
+		return -EOVERFLOW;
 
-	if (slots < msg_slots)
+	if ((u32)slots < msg_slots)
 		return -EMSGSIZE;
 
 	ret = mei_cl_send_disconnect(cl, cb);
@@ -1054,12 +1056,15 @@ int mei_cl_irq_connect(struct mei_cl *cl, struct mei_cl_cb *cb,
 	int rets;
 
 	msg_slots = mei_data2slots(sizeof(struct hbm_client_connect_request));
-	slots = mei_hbuf_empty_slots(dev);
 
 	if (mei_cl_is_other_connecting(cl))
 		return 0;
 
-	if (slots < msg_slots)
+	slots = mei_hbuf_empty_slots(dev);
+	if (slots < 0)
+		return -EOVERFLOW;
+
+	if ((u32)slots < msg_slots)
 		return -EMSGSIZE;
 
 	rets = mei_cl_send_connect(cl, cb);
@@ -1296,8 +1301,10 @@ int mei_cl_irq_notify(struct mei_cl *cl, struct mei_cl_cb *cb,
 
 	msg_slots = mei_data2slots(sizeof(struct hbm_client_connect_request));
 	slots = mei_hbuf_empty_slots(dev);
+	if (slots < 0)
+		return -EOVERFLOW;
 
-	if (slots < msg_slots)
+	if ((u32)slots < msg_slots)
 		return -EMSGSIZE;
 
 	request = mei_cl_notify_fop2req(cb->fop_type);
@@ -1573,6 +1580,9 @@ int mei_cl_irq_write(struct mei_cl *cl, struct mei_cl_cb *cb,
 	}
 
 	slots = mei_hbuf_empty_slots(dev);
+	if (slots < 0)
+		return -EOVERFLOW;
+
 	len = buf->size - cb->buf_idx;
 	msg_slots = mei_data2slots(len);
 
@@ -1581,11 +1591,11 @@ int mei_cl_irq_write(struct mei_cl *cl, struct mei_cl_cb *cb,
 	mei_hdr.reserved = 0;
 	mei_hdr.internal = cb->internal;
 
-	if (slots >= msg_slots) {
+	if ((u32)slots >= msg_slots) {
 		mei_hdr.length = len;
 		mei_hdr.msg_complete = 1;
 	/* Split the message only if we can write the whole host buffer */
-	} else if (slots == dev->hbuf_depth) {
+	} else if ((u32)slots == dev->hbuf_depth) {
 		msg_slots = slots;
 		len = (slots * sizeof(u32)) - sizeof(struct mei_msg_hdr);
 		mei_hdr.length = len;

drivers/misc/mei/hw-me.c

@@ -540,8 +540,11 @@ static int mei_me_hbuf_write(struct mei_device *dev,
 	empty_slots = mei_hbuf_empty_slots(dev);
 	dev_dbg(dev->dev, "empty slots = %hu.\n", empty_slots);
 
+	if (empty_slots < 0)
+		return -EOVERFLOW;
+
 	dw_cnt = mei_data2slots(length);
-	if (empty_slots < 0 || dw_cnt > empty_slots)
+	if (dw_cnt > (u32)empty_slots)
 		return -EMSGSIZE;
 
 	mei_me_hcbww_write(dev, *((u32 *) header));

drivers/misc/mei/hw-txe.c

@@ -709,7 +709,7 @@ static int mei_txe_write(struct mei_device *dev,
 	struct mei_txe_hw *hw = to_txe_hw(dev);
 	unsigned long rem;
 	unsigned long length;
-	int slots = dev->hbuf_depth;
+	u32 slots = dev->hbuf_depth;
 	u32 *reg_buf = (u32 *)buf;
 	u32 dw_cnt;
 	int i;

drivers/misc/mei/interrupt.c

@@ -173,10 +173,12 @@ static int mei_cl_irq_disconnect_rsp(struct mei_cl *cl, struct mei_cl_cb *cb,
 	int slots;
 	int ret;
 
-	slots = mei_hbuf_empty_slots(dev);
 	msg_slots = mei_data2slots(sizeof(struct hbm_client_connect_response));
+	slots = mei_hbuf_empty_slots(dev);
+	if (slots < 0)
+		return -EOVERFLOW;
 
-	if (slots < msg_slots)
+	if ((u32)slots < msg_slots)
 		return -EMSGSIZE;
 
 	ret = mei_hbm_cl_disconnect_rsp(dev, cl);
@@ -208,8 +210,10 @@ static int mei_cl_irq_read(struct mei_cl *cl, struct mei_cl_cb *cb,
 
 	msg_slots = mei_data2slots(sizeof(struct hbm_flow_control));
 	slots = mei_hbuf_empty_slots(dev);
+	if (slots < 0)
+		return -EOVERFLOW;
 
-	if (slots < msg_slots)
+	if ((u32)slots < msg_slots)
 		return -EMSGSIZE;
 
 	ret = mei_hbm_cl_flow_control_req(dev, cl);
@@ -365,7 +369,10 @@ int mei_irq_write_handler(struct mei_device *dev, struct list_head *cmpl_list)
 		return 0;
 
 	slots = mei_hbuf_empty_slots(dev);
-	if (slots <= 0)
+	if (slots < 0)
+		return -EOVERFLOW;
+
+	if (slots == 0)
 		return -EMSGSIZE;
 
 	/* complete all waiting for write CB */