USB: w1 ds2490: Fix bug caused by improper use of altsetting array

The syzkaller USB fuzzer spotted a slab-out-of-bounds bug in the
ds2490 driver.  This bug is caused by improper use of the altsetting
array in the usb_interface structure (the array's entries are not
always stored in numerical order), combined with a naive assumption
that all interfaces probed by the driver will have the expected number
of altsettings.

The bug can be fixed by replacing references to the possibly
non-existent intf->altsetting[alt] entry with the guaranteed-to-exist
intf->cur_altsetting entry.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-and-tested-by: syzbot+d65f673b847a1a96cdba@syzkaller.appspotmail.com
CC: <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/w1/masters/ds2490.c

@@ -1016,15 +1016,15 @@ static int ds_probe(struct usb_interface *intf,
 	/* alternative 3, 1ms interrupt (greatly speeds search), 64 byte bulk */
 	alt = 3;
 	err = usb_set_interface(dev->udev,
-		intf->altsetting[alt].desc.bInterfaceNumber, alt);
+		intf->cur_altsetting->desc.bInterfaceNumber, alt);
 	if (err) {
 		dev_err(&dev->udev->dev, "Failed to set alternative setting %d "
 			"for %d interface: err=%d.\n", alt,
-			intf->altsetting[alt].desc.bInterfaceNumber, err);
+			intf->cur_altsetting->desc.bInterfaceNumber, err);
 		goto err_out_clear;
 	}
 
-	iface_desc = &intf->altsetting[alt];
+	iface_desc = intf->cur_altsetting;
 	if (iface_desc->desc.bNumEndpoints != NUM_EP-1) {
 		pr_info("Num endpoints=%d. It is not DS9490R.\n",
 			iface_desc->desc.bNumEndpoints);