[PATCH] USB: serial: keyspan: fix NULL-derefs on open() and write()

[Johan Hovold]

Fix NULL-pointer dereferences on open() and write() which can be
triggered by a malicious USB device.

The current URB allocation helper would fail to initialise the newly
allocated URB if the device has unexpected endpoint descriptors,
something which could lead NULL-pointer dereferences in a number of
open() and write() paths when accessing the URB. For example:

        BUG: kernel NULL pointer dereference, address: 0000000000000000
        ...
        RIP: 0010:usb_clear_halt+0x11/0xc0
        ...
        Call Trace:
         ? tty_port_open+0x4d/0xd0
         keyspan_open+0x70/0x160 [keyspan]
         serial_port_activate+0x5b/0x80 [usbserial]
         tty_port_open+0x7b/0xd0
         ? check_tty_count+0x43/0xa0
         tty_open+0xf1/0x490

        BUG: kernel NULL pointer dereference, address: 0000000000000000
        ...
        RIP: 0010:keyspan_write+0x14e/0x1f3 [keyspan]
        ...
        Call Trace:
         serial_write+0x43/0xa0 [usbserial]
         n_tty_write+0x1af/0x4f0
         ? do_wait_intr_irq+0x80/0x80
         ? process_echoes+0x60/0x60
         tty_write+0x13f/0x2f0

        BUG: kernel NULL pointer dereference, address: 0000000000000000
        ...
        RIP: 0010:keyspan_usa26_send_setup+0x298/0x305 [keyspan]
        ...
        Call Trace:
         keyspan_open+0x10f/0x160 [keyspan]
         serial_port_activate+0x5b/0x80 [usbserial]
         tty_port_open+0x7b/0xd0
         ? check_tty_count+0x43/0xa0
         tty_open+0xf1/0x490

Fixes: fdcba53e2d58 ("fix for bugzilla #7544 (keyspan USB-to-serial converter)")
Cc: stable <sta...@vger.kernel.org>     # 2.6.21
Signed-off-by: Johan Hovold <jo...@kernel.org>
---
 drivers/usb/serial/keyspan.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/serial/keyspan.c b/drivers/usb/serial/keyspan.c
index d34779fe4a8d..e66a59ef43a1 100644
--- a/drivers/usb/serial/keyspan.c
+++ b/drivers/usb/serial/keyspan.c
@@ -1741,8 +1741,8 @@ static struct urb *keyspan_setup_urb(struct usb_serial 
*serial, int endpoint,
 
        ep_desc = find_ep(serial, endpoint);
        if (!ep_desc) {
-               /* leak the urb, something's wrong and the callers don't care */
-               return urb;
+               usb_free_urb(urb);
+               return NULL;
        }
        if (usb_endpoint_xfer_int(ep_desc)) {
                ep_type_name = "INT";
-- 
2.23.0