Re: [patch] [media] dvb-core: check ->msg_len for diseqc_send_master_cmd()

[Dan Carpenter <dan.carpenter@oracle.com>]

Oops.  I send this to Mauro's old email address.  Sorry about that.

regards,
dan carpenter

On Tue, Apr 01, 2014 at 05:38:07PM +0300, Dan Carpenter wrote:
> I'd like to send this patch except that it "breaks"
> cx24116_send_diseqc_msg().  The cx24116 driver accepts ->msg_len values
> up to 24 but it looks like it's just copying 16 bytes past the end of
> the ->msg[] array so it's already broken.
> 
> cmd->msg_len is an unsigned char.  The comment next to the struct
> declaration says that valid values are are 3-6.  Some of the drivers
> check that this is true, but most don't and it could cause memory
> corruption.
> 
> Some examples of functions which don't check are:
> ttusbdecfe_dvbs_diseqc_send_master_cmd()
> cx24123_send_diseqc_msg()
> ds3000_send_diseqc_msg()
> etc.
> 
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> Reviewed-by: Antti Palosaari <crope@iki.fi>
> ---
> This is a static checker fix and I haven't tested it but the security
> implications are quite bad so we should fix this.
> 
> diff --git a/drivers/media/dvb-core/dvb_frontend.c b/drivers/media/dvb-core/dvb_frontend.c
> index 57601c0..3d1eee6 100644
> --- a/drivers/media/dvb-core/dvb_frontend.c
> +++ b/drivers/media/dvb-core/dvb_frontend.c
> @@ -2267,7 +2267,13 @@ static int dvb_frontend_ioctl_legacy(struct file *file,
>  
>  	case FE_DISEQC_SEND_MASTER_CMD:
>  		if (fe->ops.diseqc_send_master_cmd) {
> -			err = fe->ops.diseqc_send_master_cmd(fe, (struct dvb_diseqc_master_cmd*) parg);
> +			struct dvb_diseqc_master_cmd *cmd = parg;
> +
> +			if (cmd->msg_len >= 3 && cmd->msg_len <= 6)
> +				err = fe->ops.diseqc_send_master_cmd(fe, cmd);
> +			else
> +				err = -EINVAL;
> +
>  			fepriv->state = FESTATE_DISEQC;
>  			fepriv->status = 0;
>  		}