USB: usblp: return error when setting unsupported protocol

JIRA: https://issues.redhat.com/browse/RHEL-78828

commit 7a3d76a
Author: Jun Yan <jerrysteve1101@gmail.com>
Date: Thu, 12 Dec 2024 22:38:52 +0800

  Fix the regression introduced by commit d8c6edf ("USB:
  usblp: don't call usb_set_interface if there's a single alt"),
  which causes that unsupported protocols can also be set via
  ioctl when the num_altsetting of the device is 1.

  Move the check for protocol support to the earlier stage.

  Fixes: d8c6edf ("USB: usblp: don't call usb_set_interface if there's a single alt")
  Cc: stable <stable@kernel.org>
  Signed-off-by: Jun Yan <jerrysteve1101@gmail.com>
  Link: https://lore.kernel.org/r/20241212143852.671889-1-jerrysteve1101@gmail.com
  Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Signed-off-by: Desnes Nunes <desnesn@redhat.com>

Author: Desnes Nunes

drivers/usb/class/usblp.c

@@ -1337,11 +1337,12 @@ static int usblp_set_protocol(struct usblp *usblp, int protocol)
 	if (protocol < USBLP_FIRST_PROTOCOL || protocol > USBLP_LAST_PROTOCOL)
 		return -EINVAL;
 
+	alts = usblp->protocol[protocol].alt_setting;
+	if (alts < 0)
+		return -EINVAL;
+
 	/* Don't unnecessarily set the interface if there's a single alt. */
 	if (usblp->intf->num_altsetting > 1) {
-		alts = usblp->protocol[protocol].alt_setting;
-		if (alts < 0)
-			return -EINVAL;
 		r = usb_set_interface(usblp->dev, usblp->ifnum, alts);
 		if (r < 0) {
 			printk(KERN_ERR "usblp: can't set desired altsetting %d on interface %d\n",