Re: [PATCH] can: bcm: check timer values before ktime conversion

[Oliver Hartkopp <socketcan@xxxxxxxxxxxx>]

Hi Andre,

just wondered whether it makes sense to limit this value for sending 
cyclic messages or for detecting a timeout on reception.

4.294.967.295 seconds would be ~136 years - this makes no sense to me 
and I would assume someone applied some (unintended?) stuff into the 
timeval.

Don't you think?

Best,
Oliver

On 1/12/19 11:16 PM, Andre Naujoks wrote:
> Hi.
>
> The 15 minute limit seems arbitrary to me. I'd be surprised if an
> (R|T)X_SETUP failed because of a timeout greater than this. Are there
> any problems with allowing larger timeouts? If not, I do not see a
> reason to restrict this.
>
> Regards
>    Andre
>
> On 1/12/19 10:57 PM, Oliver Hartkopp wrote:
> > Kyungtae Kim detected a potential integer overflow in bcm_[rx|tx]_setup() when
> > the conversion into ktime multiplies the given value with NSEC_PER_USEC (1000).
> >
> > Reference: https://marc.info/?l=linux-can&m=154732118819828&w=2
> >
> > Add a check for the given tv_usec, so that the value stays below one second.
> > Additionally limit the tv_sec value to a reasonable value for CAN related
> > use-cases of 15 minutes.
> >
> > Reported-by: Kyungtae Kim <kt0755@xxxxxxxxx>
> > Tested-by: Oliver Hartkopp <socketcan@xxxxxxxxxxxx>
> > Signed-off-by: Oliver Hartkopp <socketcan@xxxxxxxxxxxx>
> > Cc: linux-stable <stable@xxxxxxxxxxxxxxx> # >= 2.6.26
> > ---
> >   net/can/bcm.c | 23 +++++++++++++++++++++++
> >   1 file changed, 23 insertions(+)
> >
> > diff --git a/net/can/bcm.c b/net/can/bcm.c
> > index 0af8f0db892a..ff3799be077b 100644
> > --- a/net/can/bcm.c
> > +++ b/net/can/bcm.c
> > @@ -67,6 +67,9 @@
> >    */
> >   #define MAX_NFRAMES 256
> >   
> > +/* limit timers to 15 minutes for sending/timeouts */
> > +#define BCM_TIMER_SEC_MAX (15*60)
> > +
> >   /* use of last_frames[index].flags */
> >   #define RX_RECV    0x40 /* received data for this element */
> >   #define RX_THR     0x80 /* element not been sent due to throttle feature */
> > @@ -140,6 +143,18 @@ static inline ktime_t bcm_timeval_to_ktime(struct bcm_timeval tv)
> >   	return ktime_set(tv.tv_sec, tv.tv_usec * NSEC_PER_USEC);
> >   }
> >   
> > +/* check limitations for timeval provided by user */
> > +static int bcm_is_invalid_tv(struct bcm_msg_head *msg_head)
> > +{
> > +	if ((msg_head->ival1.tv_sec > BCM_TIMER_SEC_MAX) ||
> > +	    (msg_head->ival1.tv_usec >= USEC_PER_SEC) ||
> > +	    (msg_head->ival2.tv_sec > BCM_TIMER_SEC_MAX) ||
> > +	    (msg_head->ival2.tv_usec >= USEC_PER_SEC))
> > +		return 1;
> > +
> > +	return 0;
> > +}
> > +
> >   #define CFSIZ(flags) ((flags & CAN_FD_FRAME) ? CANFD_MTU : CAN_MTU)
> >   #define OPSIZ sizeof(struct bcm_op)
> >   #define MHSIZ sizeof(struct bcm_msg_head)
> > @@ -873,6 +888,10 @@ static int bcm_tx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
> >   	if (msg_head->nframes < 1 || msg_head->nframes > MAX_NFRAMES)
> >   		return -EINVAL;
> >   
> > +	/* check timeval limitations */
> > +	if ((msg_head->flags & SETTIMER) && bcm_is_invalid_tv(msg_head))
> > +		return -EINVAL;
> > +
> >   	/* check the given can_id */
> >   	op = bcm_find_op(&bo->tx_ops, msg_head, ifindex);
> >   	if (op) {
> > @@ -1053,6 +1072,10 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
> >   	     (!(msg_head->can_id & CAN_RTR_FLAG))))
> >   		return -EINVAL;
> >   
> > +	/* check timeval limitations */
> > +	if ((msg_head->flags & SETTIMER) && bcm_is_invalid_tv(msg_head))
> > +		return -EINVAL;
> > +
> >   	/* check the given can_id */
> >   	op = bcm_find_op(&bo->rx_ops, msg_head, ifindex);
> >   	if (op) {