drivers:misc:ti-st: protect against bad packets

We encounter situations where we got bad packet type from the
UART (probably due to platform problem or UART driver issues)
which caused us out of boundary array access,
which eventually led to kernel panic.

Signed-off-by: Amir Ayun <[e-mail]>
Signed-off-by: Pavan Savoy <[e-mail]>
Signed-off-by: Leonid Iziumtsev <[e-mail]>
Signed-off-by: Gigi Joseph <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/misc/ti-st/st_core.c

···
 			/* Unknow packet? */
 		default:
 			type = *ptr;
-			if (st_gdata->list[type] == NULL) {
-				pr_err("chip/interface misbehavior dropping"
-					" frame starting with 0x%02x", type);
-				goto done;
 
+			/* Default case means non-HCILL packets,
+			 * possibilities are packets for:
+			 * (a) valid protocol -  Supported Protocols within
+			 *     the ST_MAX_CHANNELS.
+			 * (b) registered protocol - Checked by
+			 *     "st_gdata->list[type] == NULL)" are supported
+			 *     protocols only.
+			 *  Rules out any invalid protocol and
+			 *  unregistered protocols with channel ID < 16.
+			 */
+
+			if ((type >= ST_MAX_CHANNELS) ||
+					(st_gdata->list[type] == NULL)) {
+				pr_err("chip/interface misbehavior: "
+						"dropping frame starting "
+						"with 0x%02x\n", type);
+				goto done;
 			}
+
 			st_gdata->rx_skb = alloc_skb(
 					st_gdata->list[type]->max_frame_size,
 					GFP_ATOMIC);
···
 		kfree(st_gdata);
 	}
 }
-
-