mwifiex: fix division by zero in fw download path

Add the missing endpoint sanity checks to probe() to avoid division by
zero in mwifiex_write_data_sync() in case a malicious device has broken
descriptors (or when doing descriptor fuzz testing).

Only add checks for the firmware-download boot stage, which require both
command endpoints, for now. The driver looks like it will handle a
missing endpoint during normal operation without oopsing, albeit not
very gracefully as it will try to submit URBs to the default pipe and
fail.

Note that USB core will reject URBs submitted for endpoints with zero
wMaxPacketSize but that drivers doing packet-size calculations still
need to handle this (cf. commit 2548288 ("USB: Fix: Don't skip
endpoint descriptors with maxpacket=0")).

Fixes: 4daffe3 ("mwifiex: add support for Marvell USB8797 chipset")
Cc: stable@vger.kernel.org      # 3.5
Cc: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20211027080819.6675-4-johan@kernel.org

drivers/net/wireless/marvell/mwifiex/usb.c

@@ -505,6 +505,22 @@ static int mwifiex_usb_probe(struct usb_interface *intf,
 		}
 	}
 
+	switch (card->usb_boot_state) {
+	case USB8XXX_FW_DNLD:
+		/* Reject broken descriptors. */
+		if (!card->rx_cmd_ep || !card->tx_cmd_ep)
+			return -ENODEV;
+		if (card->bulk_out_maxpktsize == 0)
+			return -ENODEV;
+		break;
+	case USB8XXX_FW_READY:
+		/* Assume the driver can handle missing endpoints for now. */
+		break;
+	default:
+		WARN_ON(1);
+		return -ENODEV;
+	}
+
 	usb_set_intfdata(intf, card);
 
 	ret = mwifiex_add_card(card, &card->fw_done, &usb_ops,