On Mon, May 15, 2017 at 03:49:55PM +0200, Mike Belopuhov wrote:
> On Sun, May 07, 2017 at 18:59 -0500, Matthew Martin wrote:
> > RFC 4861 specifies ReachableTime "should be a uniformly distributed
> > random value between MIN_RANDOM_FACTOR and MAX_RANDOM_FACTOR times
> > BaseReachableTime milliseconds." I think the author intended to do the
> > multiplication by (x>>10) outside the mask, but it's still missing a -1.
> >
> > - Matthew Martin
> >
> >
> >
> > diff --git nd6.h nd6.h
> > index 4274cd4dd07..8eea089a40c 100644
> > --- nd6.h
> > +++ nd6.h
> > @@ -162,8 +162,8 @@ struct llinfo_nd6 {
> > #define MIN_RANDOM_FACTOR 512 /* 1024 * 0.5 */
> > #define MAX_RANDOM_FACTOR 1536 /* 1024 * 1.5 */
> > #define ND_COMPUTE_RTIME(x) \
> > - (((MIN_RANDOM_FACTOR * (x >> 10)) + (arc4random() & \
> > - ((MAX_RANDOM_FACTOR - MIN_RANDOM_FACTOR) * (x >> 10)))) /1000)
> > + (((arc4random() & (MAX_RANDOM_FACTOR - MIN_RANDOM_FACTOR - 1)) \
> > + + MIN_RANDOM_FACTOR) * (x >> 10) / 1000)
> >
> > TAILQ_HEAD(nd_drhead, nd_defrouter);
> > struct nd_defrouter {
> >
>
> Hmm, how about we use an arc4random_uniform here? It will generate
> numbers less than the upper bound specified as an argument so I don't
> need to -1 there.
>
> I don't think they wanted to do a multiplication by (x>>10) outside
> the mask and in this case as well we want arc4random_uniform to operate
> on an extended range.
>
> Does this look good?
Sure. In the past[1] tb@ had raised concern about using
arc4random_uniform in the kernel since it can loop indefinitely. If
that's not a concern here, the only reason to possibly not go with
arc4random_uniform is for portability with other projects that use the
KAME code which appears to have arc4random but not arc4random_uniform.
1: http://marc.info/?l=openbsd-tech&m=144947731311613&w=2
> diff --git sys/netinet6/nd6.h sys/netinet6/nd6.h
> index 4274cd4dd07..01c0fe2c7af 100644
> --- sys/netinet6/nd6.h
> +++ sys/netinet6/nd6.h
> @@ -160,12 +160,12 @@ struct llinfo_nd6 {
> #define REACHABLE_TIME 30000 /* msec */
> #define RETRANS_TIMER 1000 /* msec */
> #define MIN_RANDOM_FACTOR 512 /* 1024 * 0.5 */
> #define MAX_RANDOM_FACTOR 1536 /* 1024 * 1.5 */
> #define ND_COMPUTE_RTIME(x) \
> - (((MIN_RANDOM_FACTOR * (x >> 10)) + (arc4random() & \
> - ((MAX_RANDOM_FACTOR - MIN_RANDOM_FACTOR) * (x >> 10)))) /1000)
> + ((arc4random_uniform((MAX_RANDOM_FACTOR - MIN_RANDOM_FACTOR) * \
> + (x >> 10)) + MIN_RANDOM_FACTOR * (x >> 10)) / 1000)
>
> TAILQ_HEAD(nd_drhead, nd_defrouter);
> struct nd_defrouter {
> TAILQ_ENTRY(nd_defrouter) dr_entry;
> struct in6_addr rtaddr;
