Merge branch 'icmp-better-deal-with-ddos'

Eric Dumazet says:

====================
icmp: better deal with DDOS

When dealing with death of big UDP servers, admins might want to
increase net.ipv4.icmp_msgs_per_sec and net.ipv4.icmp_msgs_burst
to big values (2,000,000 or more).

They also might need to tune the per-host ratelimit to 1ms or 0ms
in favor of the global rate limit.

This series fixes bugs showing up in all these needs.
====================

Link: https://patch.msgid.link/20260216142832.3834174-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: kuba-moo

Documentation/networking/ip-sysctl.rst

@@ -3234,12 +3234,13 @@ enhanced_dad - BOOLEAN
 ===========
 
 ratelimit - INTEGER
-	Limit the maximal rates for sending ICMPv6 messages.
+	Limit the maximal rates for sending ICMPv6 messages to a particular
+	peer.
 
 	0 to disable any limiting,
-	otherwise the minimal space between responses in milliseconds.
+	otherwise the space between responses in milliseconds.
 
-	Default: 1000
+	Default: 100
 
 ratemask - list of comma separated ranges
 	For ICMPv6 message types matching the ranges in the ratemask, limit

include/net/netns/ipv4.h

@@ -88,6 +88,12 @@ struct netns_ipv4 {
 	int sysctl_tcp_rcvbuf_low_rtt;
 	__cacheline_group_end(netns_ipv4_read_rx);
 
+	/* ICMP rate limiter hot cache line. */
+	__cacheline_group_begin_aligned(icmp);
+	atomic_t	icmp_global_credit;
+	u32		icmp_global_stamp;
+	__cacheline_group_end_aligned(icmp);
+
 	struct inet_timewait_death_row tcp_death_row;
 	struct udp_table *udp_table;
 
@@ -141,8 +147,7 @@ struct netns_ipv4 {
 	int sysctl_icmp_ratemask;
 	int sysctl_icmp_msgs_per_sec;
 	int sysctl_icmp_msgs_burst;
-	atomic_t icmp_global_credit;
-	u32 icmp_global_stamp;
+
 	u32 ip_rt_min_pmtu;
 	int ip_rt_mtu_expires;
 	int ip_rt_min_advmss;

net/ipv4/icmp.c

@@ -250,7 +250,8 @@ bool icmp_global_allow(struct net *net)
 	if (delta < HZ / 50)
 		return false;
 
-	incr = READ_ONCE(net->ipv4.sysctl_icmp_msgs_per_sec) * delta / HZ;
+	incr = READ_ONCE(net->ipv4.sysctl_icmp_msgs_per_sec);
+	incr = div_u64((u64)incr * delta, HZ);
 	if (!incr)
 		return false;
 
@@ -315,23 +316,29 @@ static bool icmpv4_xrlim_allow(struct net *net, struct rtable *rt,
 	struct dst_entry *dst = &rt->dst;
 	struct inet_peer *peer;
 	struct net_device *dev;
+	int peer_timeout;
 	bool rc = true;
 
 	if (!apply_ratelimit)
 		return true;
 
+	peer_timeout = READ_ONCE(net->ipv4.sysctl_icmp_ratelimit);
+	if (!peer_timeout)
+		goto out;
+
 	/* No rate limit on loopback */
 	rcu_read_lock();
 	dev = dst_dev_rcu(dst);
 	if (dev && (dev->flags & IFF_LOOPBACK))
-		goto out;
+		goto out_unlock;
 
 	peer = inet_getpeer_v4(net->ipv4.peers, fl4->daddr,
 			       l3mdev_master_ifindex_rcu(dev));
-	rc = inet_peer_xrlim_allow(peer,
-				   READ_ONCE(net->ipv4.sysctl_icmp_ratelimit));
-out:
+	rc = inet_peer_xrlim_allow(peer, peer_timeout);
+
+out_unlock:
 	rcu_read_unlock();
+out:
 	if (!rc)
 		__ICMP_INC_STATS(net, ICMP_MIB_RATELIMITHOST);
 	else

net/ipv6/af_inet6.c

@@ -952,7 +952,7 @@ static int __net_init inet6_net_init(struct net *net)
 	int err = 0;
 
 	net->ipv6.sysctl.bindv6only = 0;
-	net->ipv6.sysctl.icmpv6_time = 1*HZ;
+	net->ipv6.sysctl.icmpv6_time = HZ / 10;
 	net->ipv6.sysctl.icmpv6_echo_ignore_all = 0;
 	net->ipv6.sysctl.icmpv6_echo_ignore_multicast = 0;
 	net->ipv6.sysctl.icmpv6_echo_ignore_anycast = 0;

net/ipv6/icmp.c

@@ -217,16 +217,15 @@ static bool icmpv6_xrlim_allow(struct sock *sk, u8 type,
 	} else if (dev && (dev->flags & IFF_LOOPBACK)) {
 		res = true;
 	} else {
-		struct rt6_info *rt = dst_rt6_info(dst);
-		int tmo = net->ipv6.sysctl.icmpv6_time;
+		int tmo = READ_ONCE(net->ipv6.sysctl.icmpv6_time);
 		struct inet_peer *peer;
 
-		/* Give more bandwidth to wider prefixes. */
-		if (rt->rt6i_dst.plen < 128)
-			tmo >>= ((128 - rt->rt6i_dst.plen)>>5);
-
-		peer = inet_getpeer_v6(net->ipv6.peers, &fl6->daddr);
-		res = inet_peer_xrlim_allow(peer, tmo);
+		if (!tmo) {
+			res = true;
+		} else {
+			peer = inet_getpeer_v6(net->ipv6.peers, &fl6->daddr);
+			res = inet_peer_xrlim_allow(peer, tmo);
+		}
 	}
 	rcu_read_unlock();
 	if (!res)