netdev - [PATCHv2 next] ipv6: add icmpv6_error_anycast_as

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Message-ID: <20230419013238.2691167-1-maheshb@google.com>
Date:   Tue, 18 Apr 2023 18:32:38 -0700
From:   Mahesh Bandewar <maheshb@...gle.com>
To:     Netdev <netdev@...r.kernel.org>, David Ahern <dsahern@...nel.org>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     Jonathan Corbet <corbet@....net>,
        Mahesh Bandewar <mahesh@...dewar.net>,
        Kuniyuki Iwashima <kuniyu@...zon.com>,
        Mahesh Bandewar <maheshb@...gle.com>,
        "Maciej Żenczykowski" <maze@...gle.com>
Subject: [PATCHv2 next] ipv6: add icmpv6_error_anycast_as_unicast for ICMPv6

ICMPv6 error packets are not sent to the anycast destinations and this
prevents things like traceroute from working. So create a setting similar
to ECHO when dealing with Anycast sources (icmpv6_echo_ignore_anycast).

Signed-off-by: Mahesh Bandewar <maheshb@...gle.com>
CC: Maciej Żenczykowski <maze@...gle.com>
---
 Documentation/networking/ip-sysctl.rst |  7 +++++++
 include/net/netns/ipv6.h               |  1 +
 net/ipv6/af_inet6.c                    |  1 +
 net/ipv6/icmp.c                        | 15 +++++++++++++--
 4 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index 87dd1c5283e6..b2a563ef0789 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -2719,6 +2719,13 @@ echo_ignore_anycast - BOOLEAN
 
 	Default: 0
 
+error_anycast_as_unicast - BOOLEAN
+	If set to 1, then the kernel will respond with ICMP Errors
+	resulting from requests sent to it over the IPv6 protocol destined
+	to anycast address essentially treating anycast as unicast.
+
+	Default: 0
+
 xfrm6_gc_thresh - INTEGER
 	(Obsolete since linux-4.14)
 	The threshold at which we will start garbage collecting for IPv6
diff --git a/include/net/netns/ipv6.h b/include/net/netns/ipv6.h
index b4af4837d80b..3cceb3e9320b 100644
--- a/include/net/netns/ipv6.h
+++ b/include/net/netns/ipv6.h
@@ -55,6 +55,7 @@ struct netns_sysctl_ipv6 {
 	u64 ioam6_id_wide;
 	bool skip_notify_on_dev_down;
 	u8 fib_notify_on_flag_change;
+	u8 icmpv6_error_anycast_as_unicast;
 };
 
 struct netns_ipv6 {
diff --git a/net/ipv6/af_inet6.c b/net/ipv6/af_inet6.c
index 38689bedfce7..2b7ac752afc2 100644
--- a/net/ipv6/af_inet6.c
+++ b/net/ipv6/af_inet6.c
@@ -952,6 +952,7 @@ static int __net_init inet6_net_init(struct net *net)
 	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.sysctl.icmpv6_error_anycast_as_unicast = 0;
 
 	/* By default, rate limit error messages.
 	 * Except for pmtu discovery, it would break it.
diff --git a/net/ipv6/icmp.c b/net/ipv6/icmp.c
index f32bc98155bf..1465a211e592 100644
--- a/net/ipv6/icmp.c
+++ b/net/ipv6/icmp.c
@@ -362,9 +362,10 @@ static struct dst_entry *icmpv6_route_lookup(struct net *net,
 
 	/*
 	 * We won't send icmp if the destination is known
-	 * anycast.
+	 * anycast unless we need to treat anycast as unicast.
 	 */
-	if (ipv6_anycast_destination(dst, &fl6->daddr)) {
+	if (!READ_ONCE(net->ipv6.sysctl.icmpv6_error_anycast_as_unicast) &&
+	    ipv6_anycast_destination(dst, &fl6->daddr)) {
 		net_dbg_ratelimited("icmp6_send: acast source\n");
 		dst_release(dst);
 		return ERR_PTR(-EINVAL);
@@ -1192,6 +1193,15 @@ static struct ctl_table ipv6_icmp_table_template[] = {
 		.mode		= 0644,
 		.proc_handler = proc_do_large_bitmap,
 	},
+	{
+		.procname	= "error_anycast_as_unicast",
+		.data		= &init_net.ipv6.sysctl.icmpv6_error_anycast_as_unicast,
+		.maxlen		= sizeof(u8),
+		.mode		= 0644,
+		.proc_handler	= proc_dou8vec_minmax,
+		.extra1		= SYSCTL_ZERO,
+		.extra2		= SYSCTL_ONE,
+	},
 	{ },
 };
 
@@ -1209,6 +1219,7 @@ struct ctl_table * __net_init ipv6_icmp_sysctl_init(struct net *net)
 		table[2].data = &net->ipv6.sysctl.icmpv6_echo_ignore_multicast;
 		table[3].data = &net->ipv6.sysctl.icmpv6_echo_ignore_anycast;
 		table[4].data = &net->ipv6.sysctl.icmpv6_ratemask_ptr;
+		table[5].data = &net->ipv6.sysctl.icmpv6_error_anycast_as_unicast;
 	}
 	return table;
 }
-- 
2.40.0.634.g4ca3ef3211-goog