From: Alexander Bluhm <bluhm@openbsd.org>
Subject: Re: Unlock IPCTL_ARPTIMEOUT case of ip_sysctl()
To: Vitaliy Makkoveev <mvs@openbsd.org>
Cc: tech@openbsd.org
Date: Tue, 15 Jul 2025 23:57:48 +0200

On Tue, Jul 15, 2025 at 11:52:15PM +0300, Vitaliy Makkoveev wrote:
> `arpt_keep' is already marked with [a], so use atomic_load_int() and
> move the assignment out of netlock. Both arpresolve() and arpcache()
> belong to different paths.

OK bluhm@

> Index: sys/netinet/if_ether.c
> ===================================================================
> RCS file: /cvs/src/sys/netinet/if_ether.c,v
> retrieving revision 1.274
> diff -u -p -r1.274 if_ether.c
> --- sys/netinet/if_ether.c	8 Jul 2025 00:47:41 -0000	1.274
> +++ sys/netinet/if_ether.c	15 Jul 2025 20:24:46 -0000
> @@ -384,7 +384,7 @@ arpresolve(struct ifnet *ifp, struct rte
>  
>  		/* refresh ARP entry when timeout gets close */
>  		if (rt->rt_expire != 0 &&
> -		    rt->rt_expire - arpt_keep / 8 < uptime) {
> +		    rt->rt_expire - atomic_load_int(&arpt_keep) / 8 < uptime) {
>  
>  			mtx_enter(&arp_mtx);
>  			la = (struct llinfo_arp *)rt->rt_llinfo;
> @@ -709,7 +709,7 @@ arpcache(struct ifnet *ifp, struct ether
>  	sdl->sdl_alen = sizeof(ea->arp_sha);
>  	memcpy(LLADDR(sdl), ea->arp_sha, sizeof(ea->arp_sha));
>  	if (rt->rt_expire)
> -		rt->rt_expire = uptime + arpt_keep;
> +		rt->rt_expire = uptime + atomic_load_int(&arpt_keep);
>  	rt->rt_flags &= ~RTF_REJECT;
>  
>  	/* Notify userland that an ARP resolution has been done. */
> Index: sys/netinet/ip_input.c
> ===================================================================
> RCS file: /cvs/src/sys/netinet/ip_input.c,v
> retrieving revision 1.419
> diff -u -p -r1.419 ip_input.c
> --- sys/netinet/ip_input.c	15 Jul 2025 18:28:57 -0000	1.419
> +++ sys/netinet/ip_input.c	15 Jul 2025 20:24:46 -0000
> @@ -125,10 +125,10 @@ const struct sysctl_bounded_args ipctl_v
>  	{ IPCTL_IPPORT_HILASTAUTO, &ipport_hilastauto, 0, 65535 },
>  	{ IPCTL_IPPORT_MAXQUEUE, &ip_maxqueue, 0, 10000 },
>  	{ IPCTL_MFORWARDING, &ipmforwarding, 0, 1 },
> +	{ IPCTL_ARPTIMEOUT, &arpt_keep, 0, INT_MAX },
>  };
>  
>  const struct sysctl_bounded_args ipctl_vars[] = {
> -	{ IPCTL_ARPTIMEOUT, &arpt_keep, 0, INT_MAX },
>  	{ IPCTL_ARPDOWN, &arpt_down, 0, INT_MAX },
>  };
>  #endif /* SMALL_KERNEL */
> @@ -1845,6 +1845,7 @@ ip_sysctl(int *name, u_int namelen, void
>  	case IPCTL_IPPORT_HILASTAUTO:
>  	case IPCTL_IPPORT_MAXQUEUE:
>  	case IPCTL_MFORWARDING:
> +	case IPCTL_ARPTIMEOUT:
>  		return (sysctl_bounded_arr(
>  		    ipctl_vars_unlocked, nitems(ipctl_vars_unlocked),
>  		    name, namelen, oldp, oldlenp, newp, newlen));
> 
>