From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neil Horman Subject: [PATCH] net: implement emergency route cache rebulds when gc_elasticity is exceeded Date: Mon, 29 Sep 2008 15:12:54 -0400 Message-ID: <20080929191254.GA20074@hmsreliant.think-freely.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: kuznet@ms2.inr.ac.ru, davem@davemloft.net, pekkas@netcore.fi, jmorris@namei.org, yoshfuji@linux-ipv6.org, kaber@trash.net, nhorman@tuxdriver.com To: netdev@vger.kernel.org Return-path: Received: from charlotte.tuxdriver.com ([70.61.120.58]:37322 "EHLO smtp.tuxdriver.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752141AbYI2TPF (ORCPT ); Mon, 29 Sep 2008 15:15:05 -0400 Content-Disposition: inline Sender: netdev-owner@vger.kernel.org List-ID: Hey all- We currently have the ability to disable our route cache secret interval rebuild timer (by setting it to zero), but if we do that its possible for an attacker (if they guess our route cache hash secret, to fill our system with routes that all hash to the same bucket, destroying our performance. This patch provides a backstop for that issues. In the event that our rebuild interval is disabled (or very large), if any hash chain exceeds ip_rt_gc_elasticity, we do an emergency hash rebuild. During the hash rebuild we: 1) warn the user of the emergency 2) disable the rebuild timer 3) invalidate the route caches 4) re-enable the rebuild timer with its old value Regards Neil Signed-off-by: Neil Horman route.c | 36 +++++++++++++++++++++++++++++++++++- 1 file changed, 35 insertions(+), 1 deletion(-) diff --git a/net/ipv4/route.c b/net/ipv4/route.c index 6ee5354..b95e02a 100644 --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -145,7 +145,7 @@ static struct dst_entry *ipv4_negative_advice(struct dst_entry *dst); static void ipv4_link_failure(struct sk_buff *skb); static void ip_rt_update_pmtu(struct dst_entry *dst, u32 mtu); static int rt_garbage_collect(struct dst_ops *ops); - +static void rt_emergency_hash_rebuild(void); static struct dst_ops ipv4_dst_ops = { .family = AF_INET, @@ -1056,6 +1056,15 @@ restart: *candp = cand->u.dst.rt_next; rt_free(cand); } + } else if (chain_length > ip_rt_gc_elasticity) { + /* + * We didn't find a route entry we could safely free, + * yet our chain length is over our elasticity value. + * Someone may have guessed our hash secret and is artifically + * filling up our route cache. Lets do an emergency rebuild + * to be safe + */ + rt_emergency_hash_rebuild(); } /* Try to bind route to arp only if it is output @@ -2946,6 +2955,31 @@ static void rt_secret_reschedule(int old) rtnl_unlock(); } +static void rt_secret_rebuild_oneshot(void) { + struct net *net; + int old_interval = ip_rt_secret_interval; + + ip_rt_secret_interval = 0; + + rt_secret_reschedule(old_interval); + + for_each_net(net) + rt_cache_invalidate(net); + + ip_rt_secret_interval = old_interval; + + rt_secret_reschedule(0); +} + +static void rt_emergency_hash_rebuild(void) { + if (net_ratelimit()) { + printk(KERN_WARNING "Route hash chain too long!\n"); + printk(KERN_WARNING "Adjust your secret_interval!\n"); + } + + rt_secret_rebuild_oneshot(); +} + static int ipv4_sysctl_rt_secret_interval(ctl_table *ctl, int write, struct file *filp, void __user *buffer, size_t *lenp, -- /**************************************************** * Neil Horman * Software Engineer, Red Hat ****************************************************/