usblp: fix race between disconnect() and read()

read() needs to check whether the device has been
disconnected before it tries to talk to the device.

Signed-off-by: Oliver Neukum <[e-mail]>
Reported-by: [e-mail]
Link: https://lore.kernel.org/r/[e-mail]
Cc: stable <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/class/usblp.c

···
 	if (rv < 0)
 		return rv;
 
+	if (!usblp->present) {
+		count = -ENODEV;
+		goto done;
+	}
+
 	if ((avail = usblp->rstatus) < 0) {
 		printk(KERN_ERR "usblp%d: error %d reading from printer\n",
 		    usblp->minor, (int)avail);