bus: mhi: core: Add range check for channel id received in event ring

MHI data completion handler function reads channel id from event
ring element. Value is under the control of MHI devices and can be
any value between 0 and 255. In order to prevent out of bound access
add a bound check against the max channel supported by controller
and skip processing of that event ring element.
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>
Signed-off-by: Bhaumik Bhatt <bbhatt@codeaurora.org>
Reviewed-by: Jeffrey Hugo <jhugo@codeaurora.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/20200521170249.21795-4-manivannan.sadhasivam@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/bus/mhi/core/main.c

@@ -775,9 +775,18 @@ int mhi_process_ctrl_ev_ring(struct mhi_controller *mhi_cntrl,
 		}
 		case MHI_PKT_TYPE_TX_EVENT:
 			chan = MHI_TRE_GET_EV_CHID(local_rp);
-			mhi_chan = &mhi_cntrl->mhi_chan[chan];
-			parse_xfer_event(mhi_cntrl, local_rp, mhi_chan);
-			event_quota--;
+
+			WARN_ON(chan >= mhi_cntrl->max_chan);
+
+			/*
+			 * Only process the event ring elements whose channel
+			 * ID is within the maximum supported range.
+			 */
+			if (chan < mhi_cntrl->max_chan) {
+				mhi_chan = &mhi_cntrl->mhi_chan[chan];
+				parse_xfer_event(mhi_cntrl, local_rp, mhi_chan);
+				event_quota--;
+			}
 			break;
 		default:
 			dev_err(dev, "Unhandled event type: %d\n", type);
@@ -820,14 +829,23 @@ int mhi_process_data_event_ring(struct mhi_controller *mhi_cntrl,
 		enum mhi_pkt_type type = MHI_TRE_GET_EV_TYPE(local_rp);
 
 		chan = MHI_TRE_GET_EV_CHID(local_rp);
-		mhi_chan = &mhi_cntrl->mhi_chan[chan];
-
-		if (likely(type == MHI_PKT_TYPE_TX_EVENT)) {
-			parse_xfer_event(mhi_cntrl, local_rp, mhi_chan);
-			event_quota--;
-		} else if (type == MHI_PKT_TYPE_RSC_TX_EVENT) {
-			parse_rsc_event(mhi_cntrl, local_rp, mhi_chan);
-			event_quota--;
+
+		WARN_ON(chan >= mhi_cntrl->max_chan);
+
+		/*
+		 * Only process the event ring elements whose channel
+		 * ID is within the maximum supported range.
+		 */
+		if (chan < mhi_cntrl->max_chan) {
+			mhi_chan = &mhi_cntrl->mhi_chan[chan];
+
+			if (likely(type == MHI_PKT_TYPE_TX_EVENT)) {
+				parse_xfer_event(mhi_cntrl, local_rp, mhi_chan);
+				event_quota--;
+			} else if (type == MHI_PKT_TYPE_RSC_TX_EVENT) {
+				parse_rsc_event(mhi_cntrl, local_rp, mhi_chan);
+				event_quota--;
+			}
 		}
 
 		mhi_recycle_ev_ring_element(mhi_cntrl, ev_ring);