USB: fix DoS in pwc USB video driver

the pwc driver has a disconnect method that waits for user space to
close the device. This opens up an opportunity for a DoS attack,
blocking the USB subsystem and making khubd's task busy wait in
kernel space. This patch shifts freeing resources to close if an opened
device is disconnected.

Signed-off-by: Oliver Neukum <oneukum@suse.de>
CC: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/media/video/pwc/pwc.h

@@ -193,6 +193,7 @@ struct pwc_device
    char vsnapshot;		/* snapshot mode */
    char vsync;			/* used by isoc handler */
    char vmirror;		/* for ToUCaM series */
+	char unplugged;
 
    int cmd_len;
    unsigned char cmd_buf[13];