Hi Alejandro, Alejandro Colomar wrote on Sat, Dec 31, 2022 at 05:56:27PM +0100:
> I've started auditing the OpenBSD source code after the discussion on > arc4random_uniform(3) and my suggestion of arc4random_range() on the glibc > mailing list. > > I found some cases where it seems like there's an off-by-one bug, which > would be solved by providing arc4random_range(). I'll show here one, > to confirm that it's a bug, and if you confirm it, I'll continue fixing > similar bugs around the OpenBSD tree. > > Here's the first one I found, which I hope is fixed by my patch: > > > diff --git a/usr.sbin/rad/engine.c b/usr.sbin/rad/engine.c > index ceb11d574e3..a61ea3835a6 100644 > --- a/usr.sbin/rad/engine.c > +++ b/usr.sbin/rad/engine.c > @@ -641,8 +641,7 @@ iface_timeout(int fd, short events, void *arg) > struct imsg_send_ra send_ra; > struct timeval tv; > > - tv.tv_sec = MIN_RTR_ADV_INTERVAL + > - arc4random_uniform(MAX_RTR_ADV_INTERVAL - MIN_RTR_ADV_INTERVAL); > + tv.tv_sec = arc4random_range(MIN_RTR_ADV_INTERVAL, > MAX_RTR_ADV_INTERVAL); > tv.tv_usec = arc4random_uniform(1000000); Currently, the code puts a number in the range [200, 600) in tv_sec and a random number of microseconds into tv_usec, i.e. the timeout will be greater than or equal to 200 seconds and strictly less than 600 seconds with a uniform distribution. Isn't that exactly what is intended? > log_debug("%s new timeout in %lld", __func__, tv.tv_sec); > > > If I'm correct, it should have been 'min + (max - min + 1)' instead > of 'min + (max - min)'. Please confirm. With your change, the timeout could go up to 600.999999, i.e. almost 601 seconds. I don't know the protocol and can't say whether the change would matter, but naively, exceeding the MAX_ feels surprising to me. Really, this doesn't look like a bug to me... Yours, Ingo