Security hole in cros_ec_dev.c on 32bit chrome hosts

[Alan Cox <alan@lxorguk.ukuu.org.uk>]

This was reported to Google on Feb 2nd with no action but an
acknowledgement.

Making public since so as we are close to release


/* Ioctls */
static long ec_device_ioctl_xcmd(struct cros_ec_dev *ec, void __user *arg)
{
        long ret;  
        struct cros_ec_command u_cmd;
        struct cros_ec_command *s_cmd;

        if (copy_from_user(&u_cmd, arg, sizeof(u_cmd)))
                return -EFAULT;
 
        s_cmd = kmalloc(sizeof(*s_cmd) + max(u_cmd.outsize, u_cmd.insize),
                        GFP_KERNEL);

Pass u_cmd.insize as a very large value so that it overflows with the
sizeof to a small number which we kmalloc

	 if (!s_cmd)
                return -ENOMEM;

and copy u_cmd.outsize bytes into it.

        if (copy_from_user(s_cmd, arg, sizeof(*s_cmd) + u_cmd.outsize)) {
                ret = -EFAULT;
                goto exit;
        }


Alan