Re: [Patch] Off by one in drivers/usb/serial/usb-serial.c

Mikael Pettersson
2006-06-22T13:32:19Z

On Wed, 21 Jun 2006 23:28:17 +0200, Eric Sesterhenn wrote:
> this fixes coverity id #554. since serial table
> is defines as serial_table[SERIAL_TTY_MINORS] we
> should make sure we dont acess with an index
> of SERIAL_TTY_MINORS.
>
> Signed-off-by: Eric Sesterhenn <snakebyte@gmx.de>
>
> --- linux-2.6.17-git2/drivers/usb/serial/usb-serial.c.orig 2006-06-21 23:24:07.000000000 +0200
> +++ linux-2.6.17-git2/drivers/usb/serial/usb-serial.c 2006-06-21 23:25:12.000000000 +0200
> @@ -83,7 +83,7 @@ static struct usb_serial *get_free_seria
>
> good_spot = 1;
> for (j = 1; j <= num_ports-1; ++j)
> - if ((i+j >= SERIAL_TTY_MINORS) || (serial_table[i+j])) {
> + if ((i+j >= SERIAL_TTY_MINORS-1)||(serial_table[i+j])) {
> good_spot = 0;
> i += j;
> break;

Where is the access coverity complained about? If it's the serial_table[i+j]
quoted above, then the original code is OK since i+j < SERIAL_TTY_MINORS is
an invariant in that subexpression.

And the other accesses to serial_table[] in get_free_serial() are also only
done when the index is < SERIAL_TTY_MINORS.

/Mikael