Hello Florian, Ingo, On 1/1/23 08:24, Florian Obser wrote:
On 2022-12-31 23:54 +01, Ingo Schwarze <schwa...@usta.de> wrote: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...Unfortunately the OP did not explain why they think this is a bug.
Sorry; my bad; I should have explained it.The thing that led me to believe that it was a bug is that variables or constants called *max* (normally) refer to the maximum value allowed in a range, for which there usually is a *min* counterpart (when it's not simply 0).
In this case, it seems MAX_* is really the maximum+1. I don't know what the code is about, so 200 and 600 just look like magic numbers to me, and I don't know if the maximum is 600 or actually 599.
Yours, Ingo
Cheers, Alex -- <http://www.alejandro-colomar.es/>
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