From be4c5eb267ee73ef1d70c25c6d648625e96eb477 Mon Sep 17 00:00:00 2001
From: Johan Hovold <johan@kernel.org>
Date: Tue, 29 Sep 2020 12:42:39 +0200
Subject: [PATCH] USB: serial: qcserial: fix altsetting probing
Git-commit: be4c5eb267ee73ef1d70c25c6d648625e96eb477
Patch-mainline: v5.10-rc1
References: git-fixes

Drivers should not assume that interface descriptors have been parsed in
any particular order so use the interface number to look up the second
alternate setting. That number is also what the driver later use to
switch setting.

Note that although the driver could end up verifying the existence of
the expected endpoints on the wrong interface, a later sanity check in
usb_wwan_port_probe() would have caught this before it could cause any
real damage.

Fixes: a78b42824dd7 ("USB: serial: add qualcomm wireless modem driver")
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/usb/serial/qcserial.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/serial/qcserial.c b/drivers/usb/serial/qcserial.c
index c8d1ea0e6e6f..83da8236e3c8 100644
--- a/drivers/usb/serial/qcserial.c
+++ b/drivers/usb/serial/qcserial.c
@@ -243,11 +243,11 @@ static int qcprobe(struct usb_serial *serial, const struct usb_device_id *id)
 		/* QDL mode */
 		/* Gobi 2000 has a single altsetting, older ones have two */
 		if (serial->interface->num_altsetting == 2)
-			intf = &serial->interface->altsetting[1];
+			intf = usb_altnum_to_altsetting(serial->interface, 1);
 		else if (serial->interface->num_altsetting > 2)
 			goto done;
 
-		if (intf->desc.bNumEndpoints == 2 &&
+		if (intf && intf->desc.bNumEndpoints == 2 &&
 		    usb_endpoint_is_bulk_in(&intf->endpoint[0].desc) &&
 		    usb_endpoint_is_bulk_out(&intf->endpoint[1].desc)) {
 			dev_dbg(dev, "QDL port found\n");
-- 
2.16.4