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?
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;
