tty: rocket, avoid OOB access

init_r_port can access pc104 array out of bounds. pc104 is a 2D array
defined to have 4 members. Each member has 8 submembers.
* we can have more than 4 (PCI) boards, i.e. [board] can be OOB
* line is not modulo-ed by anything, so the first line on the second
  board can be 4, on the 3rd 12 or alike (depending on previously
  registered boards). It's zero only on the first line of the first
  board. So even [line] can be OOB, quite soon (with the 2nd registered
  board already).

This code is broken for ages, so just avoid the OOB accesses and don't
try to fix it as we would need to find out the correct line number. Use
the default: RS232, if we are out.

Generally, if anyone needs to set the interface types, a module parameter
is past the last thing that should be used for this purpose. The
parameters' description says it's for ISA cards anyway.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: stable <stable@vger.kernel.org>
Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Link: https://lore.kernel.org/r/20200417105959.15201-2-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/rocket.c

@@ -632,18 +632,21 @@ init_r_port(int board, int aiop, int chan, struct pci_dev *pci_dev)
 	tty_port_init(&info->port);
 	info->port.ops = &rocket_port_ops;
 	info->flags &= ~ROCKET_MODE_MASK;
-	switch (pc104[board][line]) {
-	case 422:
-		info->flags |= ROCKET_MODE_RS422;
-		break;
-	case 485:
-		info->flags |= ROCKET_MODE_RS485;
-		break;
-	case 232:
-	default:
+	if (board < ARRAY_SIZE(pc104) && line < ARRAY_SIZE(pc104_1))
+		switch (pc104[board][line]) {
+		case 422:
+			info->flags |= ROCKET_MODE_RS422;
+			break;
+		case 485:
+			info->flags |= ROCKET_MODE_RS485;
+			break;
+		case 232:
+		default:
+			info->flags |= ROCKET_MODE_RS232;
+			break;
+		}
+	else
 		info->flags |= ROCKET_MODE_RS232;
-		break;
-	}
 
 	info->intmask = RXF_TRIG | TXFIFO_MT | SRC_INT | DELTA_CD | DELTA_CTS | DELTA_DSR;
 	if (sInitChan(ctlp, &info->channel, aiop, chan) == 0) {