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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 9 insertions, 5 deletions

diff --git a/drivers/usb/serial/digi_acceleport.c b/drivers/usb/serial/digi_acceleport.c
index 6a1df9e824ca..3b610f1e3f7c 100644
--- a/drivers/usb/serial/digi_acceleport.c
+++ b/drivers/usb/serial/digi_acceleport.c
@@ -1482,16 +1482,20 @@ 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;
 
+        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];
 
                 dev_dbg(&port->dev, "digi_read_oob_callback: opcode=%d, line=%d, status=%d, val=%d\n",
                         opcode, line, status, val);