USB: serial: io_edgeport: fix slab-out-of-bounds read in edge_interrupt_callback

Fix slab-out-of-bounds read in the interrupt-URB completion handler.

The boundary condition should be (length - 1) as we access
data[position + 1].

Reported-and-tested-by: syzbot+37ba33391ad5f3935bbd@syzkaller.appspotmail.com
Signed-off-by: Qiujun Huang <hqjagain@gmail.com>
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Johan Hovold <johan@kernel.org>

diff --git a/drivers/usb/serial/io_edgeport.c b/drivers/usb/serial/io_edgeport.c
index 5737add..4cca0b8 100644 (file)
--- a/drivers/usb/serial/io_edgeport.c
+++ b/drivers/usb/serial/io_edgeport.c
@@ -710,7 +710,7 @@ static void edge_interrupt_callback(struct urb *urb)
                /* grab the txcredits for the ports if available */
                position = 2;
                portNumber = 0;
-               while ((position < length) &&
+               while ((position < length - 1) &&
                                (portNumber < edge_serial->serial->num_ports)) {
                        txCredits = data[position] | (data[position+1] << 8);
                        if (txCredits) {