USB: serial: digi_acceleport: fix OOB data sanity check

commit 2d380889215fe20b8523345649dee0579821800c upstream.

Make sure to check for short transfers to avoid underflow in a loop
condition when parsing the receive buffer.

Also fix an off-by-one error in the incomplete sanity check which could
lead to invalid data being parsed.

Fixes: 8c209e6782ca ("USB: make actual_length in struct urb field u32")
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/usb/serial/digi_acceleport.c b/drivers/usb/serial/digi_acceleport.c
index e59bd95..24c9fc8 100644 (file)
--- a/drivers/usb/serial/digi_acceleport.c
+++ b/drivers/usb/serial/digi_acceleport.c
@@ -1746,6 +1746,7 @@ static int digi_read_oob_callback(struct urb *urb)
        struct usb_serial *serial = port->serial;
        struct tty_struct *tty;
        struct digi_port *priv = usb_get_serial_port_data(port);
+       unsigned char *buf = urb->transfer_buffer;
        int opcode, line, status, val;
        int i;
        unsigned int rts;
@@ -1753,12 +1754,15 @@ static int digi_read_oob_callback(struct urb *urb)
        dbg("digi_read_oob_callback: port=%d, len=%d",
                        priv->dp_port_num, urb->actual_length);
 
+       if (urb->actual_length < 4)
+               return -1;
+
        /* handle each oob command */
-       for (i = 0; i < urb->actual_length - 3;) {
-               opcode = ((unsigned char *)urb->transfer_buffer)[i++];
-               line = ((unsigned char *)urb->transfer_buffer)[i++];
-               status = ((unsigned char *)urb->transfer_buffer)[i++];
-               val = ((unsigned char *)urb->transfer_buffer)[i++];
+       for (i = 0; i < urb->actual_length - 4; i += 4) {
+               opcode = buf[i];
+               line = buf[i + 1];
+               status = buf[i + 2];
+               val = buf[i + 3];
 
                dbg("digi_read_oob_callback: opcode=%d, line=%d, status=%d, val=%d",
                        opcode, line, status, val);