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Date: Thu, 06 May 2010 19:32:35 +0200
From: Eric Dumazet <eric.dumazet@...il.com>
To: Neil Horman <nhorman@...driver.com>
Cc: netdev@...r.kernel.org, davem@...emloft.net, kuznet@....inr.ac.ru,
jmorris@...ei.org, yoshfuji@...ux-ipv6.org, kaber@...sh.net
Subject: Re: [PATCH] ipv4: remove ip_rt_secret timer
Le jeudi 06 mai 2010 à 13:16 -0400, Neil Horman a écrit :
> A while back there was a discussion regarding the rt_secret_interval timer.
> Given that we've had the ability to do emergency route cache rebuilds for awhile
> now, based on a statistical analysis of the various hash chain lengths in the
> cache, the use of the flush timer is somewhat redundant. This patch removes the
> rt_secret_interval sysctl, allowing us to rely solely on the statistical
> analysis mechanism to determine the need for route cache flushes.
>
> Signed-off-by: Neil Horman <nhorman@...driver.com>
>
>
Nice cleanup try Neil, but this gives to attackers more time to hit the
cache (infinite time should be enough as a matter of fact ;) )
Hints :
- What is the initial value of rt_genid ?
- How/When is it changed (full 32 bits are changed or small
perturbations ? check rt_cache_invalidate())
Thanks
> include/net/netns/ipv4.h | 1
> net/ipv4/route.c | 108 -----------------------------------------------
> 2 files changed, 2 insertions(+), 107 deletions(-)
>
> diff --git a/include/net/netns/ipv4.h b/include/net/netns/ipv4.h
> index ae07fee..d68c3f1 100644
> --- a/include/net/netns/ipv4.h
> +++ b/include/net/netns/ipv4.h
> @@ -55,7 +55,6 @@ struct netns_ipv4 {
> int sysctl_rt_cache_rebuild_count;
> int current_rt_cache_rebuild_count;
>
> - struct timer_list rt_secret_timer;
> atomic_t rt_genid;
>
> #ifdef CONFIG_IP_MROUTE
> diff --git a/net/ipv4/route.c b/net/ipv4/route.c
> index a947428..ffd3da1 100644
> --- a/net/ipv4/route.c
> +++ b/net/ipv4/route.c
> @@ -129,7 +129,6 @@ static int ip_rt_gc_elasticity __read_mostly = 8;
> static int ip_rt_mtu_expires __read_mostly = 10 * 60 * HZ;
> static int ip_rt_min_pmtu __read_mostly = 512 + 20 + 20;
> static int ip_rt_min_advmss __read_mostly = 256;
> -static int ip_rt_secret_interval __read_mostly = 10 * 60 * HZ;
> static int rt_chain_length_max __read_mostly = 20;
>
> static struct delayed_work expires_work;
> @@ -918,32 +917,11 @@ void rt_cache_flush_batch(void)
> rt_do_flush(!in_softirq());
> }
>
> -/*
> - * We change rt_genid and let gc do the cleanup
> - */
> -static void rt_secret_rebuild(unsigned long __net)
> -{
> - struct net *net = (struct net *)__net;
> - rt_cache_invalidate(net);
> - mod_timer(&net->ipv4.rt_secret_timer, jiffies + ip_rt_secret_interval);
> -}
> -
> -static void rt_secret_rebuild_oneshot(struct net *net)
> -{
> - del_timer_sync(&net->ipv4.rt_secret_timer);
> - rt_cache_invalidate(net);
> - if (ip_rt_secret_interval)
> - mod_timer(&net->ipv4.rt_secret_timer, jiffies + ip_rt_secret_interval);
> -}
> -
> static void rt_emergency_hash_rebuild(struct net *net)
> {
> - if (net_ratelimit()) {
> + if (net_ratelimit())
> printk(KERN_WARNING "Route hash chain too long!\n");
> - printk(KERN_WARNING "Adjust your secret_interval!\n");
> - }
> -
> - rt_secret_rebuild_oneshot(net);
> + rt_cache_invalidate(net);
> }
>
> /*
> @@ -3101,48 +3079,6 @@ static int ipv4_sysctl_rtcache_flush(ctl_table *__ctl, int write,
> return -EINVAL;
> }
>
> -static void rt_secret_reschedule(int old)
> -{
> - struct net *net;
> - int new = ip_rt_secret_interval;
> - int diff = new - old;
> -
> - if (!diff)
> - return;
> -
> - rtnl_lock();
> - for_each_net(net) {
> - int deleted = del_timer_sync(&net->ipv4.rt_secret_timer);
> - long time;
> -
> - if (!new)
> - continue;
> -
> - if (deleted) {
> - time = net->ipv4.rt_secret_timer.expires - jiffies;
> -
> - if (time <= 0 || (time += diff) <= 0)
> - time = 0;
> - } else
> - time = new;
> -
> - mod_timer(&net->ipv4.rt_secret_timer, jiffies + time);
> - }
> - rtnl_unlock();
> -}
> -
> -static int ipv4_sysctl_rt_secret_interval(ctl_table *ctl, int write,
> - void __user *buffer, size_t *lenp,
> - loff_t *ppos)
> -{
> - int old = ip_rt_secret_interval;
> - int ret = proc_dointvec_jiffies(ctl, write, buffer, lenp, ppos);
> -
> - rt_secret_reschedule(old);
> -
> - return ret;
> -}
> -
> static ctl_table ipv4_route_table[] = {
> {
> .procname = "gc_thresh",
> @@ -3251,13 +3187,6 @@ static ctl_table ipv4_route_table[] = {
> .mode = 0644,
> .proc_handler = proc_dointvec,
> },
> - {
> - .procname = "secret_interval",
> - .data = &ip_rt_secret_interval,
> - .maxlen = sizeof(int),
> - .mode = 0644,
> - .proc_handler = ipv4_sysctl_rt_secret_interval,
> - },
> { }
> };
>
> @@ -3337,36 +3266,6 @@ static __net_initdata struct pernet_operations sysctl_route_ops = {
> #endif
>
>
> -static __net_init int rt_secret_timer_init(struct net *net)
> -{
> - atomic_set(&net->ipv4.rt_genid,
> - (int) ((num_physpages ^ (num_physpages>>8)) ^
> - (jiffies ^ (jiffies >> 7))));
> -
> - net->ipv4.rt_secret_timer.function = rt_secret_rebuild;
> - net->ipv4.rt_secret_timer.data = (unsigned long)net;
> - init_timer_deferrable(&net->ipv4.rt_secret_timer);
> -
> - if (ip_rt_secret_interval) {
> - net->ipv4.rt_secret_timer.expires =
> - jiffies + net_random() % ip_rt_secret_interval +
> - ip_rt_secret_interval;
> - add_timer(&net->ipv4.rt_secret_timer);
> - }
> - return 0;
> -}
> -
> -static __net_exit void rt_secret_timer_exit(struct net *net)
> -{
> - del_timer_sync(&net->ipv4.rt_secret_timer);
> -}
> -
> -static __net_initdata struct pernet_operations rt_secret_timer_ops = {
> - .init = rt_secret_timer_init,
> - .exit = rt_secret_timer_exit,
> -};
> -
> -
> #ifdef CONFIG_NET_CLS_ROUTE
> struct ip_rt_acct __percpu *ip_rt_acct __read_mostly;
> #endif /* CONFIG_NET_CLS_ROUTE */
> @@ -3424,9 +3323,6 @@ int __init ip_rt_init(void)
> schedule_delayed_work(&expires_work,
> net_random() % ip_rt_gc_interval + ip_rt_gc_interval);
>
> - if (register_pernet_subsys(&rt_secret_timer_ops))
> - printk(KERN_ERR "Unable to setup rt_secret_timer\n");
> -
> if (ip_rt_proc_init())
> printk(KERN_ERR "Unable to create route proc files\n");
> #ifdef CONFIG_XFRM
> --
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