From 8a40bccffe9e28e211fe996845658f87f5cc60e9 Mon Sep 17 00:00:00 2001
From: Alexander Zubkov <green@qrator.net>
Date: Wed, 26 Jun 2024 16:29:57 +0200
Subject: [PATCH] BFD: Add option to accept zero checksum for IPv6 UDP packets

Some vendors do not fill the checksum for IPv6 UDP packets.
For interoperability with such implementations one can set
UDP_NO_CHECK6_RX socket option on Linux.

Thanks to Ville O for the suggestion.

Minor changes by committer.
---
 doc/bird.sgml        |  9 +++++++++
 lib/socket.h         |  2 ++
 proto/bfd/bfd.c      |  3 ++-
 proto/bfd/bfd.h      |  1 +
 proto/bfd/config.Y   |  3 ++-
 proto/bfd/packets.c  | 10 ++++++++++
 sysdep/bsd/sysio.h   |  6 ++++++
 sysdep/linux/sysio.h |  9 +++++++++
 sysdep/unix/io.c     |  4 ++++
 9 files changed, 45 insertions(+), 2 deletions(-)

diff --git a/doc/bird.sgml b/doc/bird.sgml
index 8035ec18..096e3148 100644
--- a/doc/bird.sgml
+++ b/doc/bird.sgml
@@ -2499,6 +2499,7 @@ milliseconds.
 <code>
 protocol bfd [&lt;name&gt;] {
 	accept [ipv4|ipv6] [direct|multihop];
+	zero udp6 checksum rx &lt;switch&gt;;
 	interface &lt;interface pattern&gt; {
 		interval &lt;time&gt;;
 		min rx interval &lt;time&gt;;
@@ -2548,6 +2549,14 @@ protocol bfd [&lt;name&gt;] {
 	in cases like running multiple BIRD instances on a machine, each
 	handling a different set of interfaces. Default: disabled.
 
+	<tag><label id="bfd-zero-udp6-checksum-rx">zero udp6 checksum rx <m/switch/</tag>
+	UDP checksum computation is optional in IPv4 while it is mandatory in
+	IPv6. Some BFD implementations send UDP datagrams with zero (blank)
+	checksum even in IPv6 case. This option configures BFD listening sockets
+	to accept such datagrams. It is available only on platforms that support
+	the relevant socket option (e.g. <cf/UDP_NO_CHECK6_RX/ on Linux).
+	Default: disabled.
+
 	<tag><label id="bfd-iface">interface <m/pattern/ [, <m/.../] { <m/options/ }</tag>
 	Interface definitions allow to specify options for sessions associated
 	with such interfaces and also may contain interface specific options.
diff --git a/lib/socket.h b/lib/socket.h
index 231c10d8..3417423f 100644
--- a/lib/socket.h
+++ b/lib/socket.h
@@ -131,6 +131,8 @@ extern int sk_priority_control;		/* Suggested priority for control traffic, shou
 #define SKF_HDRINCL	0x400	/* Used internally */
 #define SKF_PKTINFO	0x800	/* Used internally */
 
+#define SKF_UDP6_NO_CSUM_RX	0x1000	/* Accept zero checksums for received UDPv6 packets */
+
 /*
  *	Socket types		     SA SP DA DP IF  TTL SendTo	(?=may, -=must not, *=must)
  */
diff --git a/proto/bfd/bfd.c b/proto/bfd/bfd.c
index 4f8499ba..d08c413d 100644
--- a/proto/bfd/bfd.c
+++ b/proto/bfd/bfd.c
@@ -1149,7 +1149,8 @@ bfd_reconfigure(struct proto *P, struct proto_config *c)
       (new->accept_ipv6 != old->accept_ipv6) ||
       (new->accept_direct != old->accept_direct) ||
       (new->accept_multihop != old->accept_multihop) ||
-      (new->strict_bind != old->strict_bind))
+      (new->strict_bind != old->strict_bind) ||
+      (new->zero_udp6_checksum_rx != old->zero_udp6_checksum_rx))
     return 0;
 
   birdloop_mask_wakeups(p->loop);
diff --git a/proto/bfd/bfd.h b/proto/bfd/bfd.h
index 847c6b14..af31354e 100644
--- a/proto/bfd/bfd.h
+++ b/proto/bfd/bfd.h
@@ -48,6 +48,7 @@ struct bfd_config
   u8 accept_direct;
   u8 accept_multihop;
   u8 strict_bind;
+  u8 zero_udp6_checksum_rx;
 };
 
 struct bfd_iface_config
diff --git a/proto/bfd/config.Y b/proto/bfd/config.Y
index 39e7577f..485ddf07 100644
--- a/proto/bfd/config.Y
+++ b/proto/bfd/config.Y
@@ -24,7 +24,7 @@ CF_DECLS
 CF_KEYWORDS(BFD, MIN, IDLE, RX, TX, INTERVAL, MULTIPLIER, PASSIVE,
 	INTERFACE, MULTIHOP, NEIGHBOR, DEV, LOCAL, AUTHENTICATION,
 	NONE, SIMPLE, METICULOUS, KEYED, MD5, SHA1, IPV4, IPV6, DIRECT,
-	STRICT, BIND)
+	STRICT, BIND, ZERO, UDP6, CHECKSUM, RX)
 
 %type <iface> bfd_neigh_iface
 %type <a> bfd_neigh_local
@@ -51,6 +51,7 @@ bfd_proto_item:
  | MULTIHOP bfd_multihop
  | NEIGHBOR bfd_neighbor
  | STRICT BIND bool { BFD_CFG->strict_bind = $3; }
+ | ZERO UDP6 CHECKSUM RX bool { BFD_CFG->zero_udp6_checksum_rx = $5; }
  ;
 
 bfd_proto_opts:
diff --git a/proto/bfd/packets.c b/proto/bfd/packets.c
index aec91ca6..6097bcae 100644
--- a/proto/bfd/packets.c
+++ b/proto/bfd/packets.c
@@ -416,6 +416,8 @@ bfd_err_hook(sock *sk, int err)
 sock *
 bfd_open_rx_sk(struct bfd_proto *p, int multihop, int af)
 {
+  struct bfd_config *cf = (struct bfd_config *) (p->p.cf);
+
   sock *sk = sk_new(p->tpool);
   sk->type = SK_UDP;
   sk->subtype = af;
@@ -432,6 +434,9 @@ bfd_open_rx_sk(struct bfd_proto *p, int multihop, int af)
   sk->priority = sk_priority_control;
   sk->flags = SKF_THREAD | SKF_LADDR_RX | (!multihop ? SKF_TTL_RX : 0);
 
+  if (cf->zero_udp6_checksum_rx)
+    sk->flags |= SKF_UDP6_NO_CSUM_RX;
+
   if (sk_open(sk) < 0)
     goto err;
 
@@ -447,6 +452,8 @@ err:
 sock *
 bfd_open_rx_sk_bound(struct bfd_proto *p, ip_addr local, struct iface *ifa)
 {
+  struct bfd_config *cf = (struct bfd_config *) (p->p.cf);
+
   sock *sk = sk_new(p->tpool);
   sk->type = SK_UDP;
   sk->saddr = local;
@@ -464,6 +471,9 @@ bfd_open_rx_sk_bound(struct bfd_proto *p, ip_addr local, struct iface *ifa)
   sk->priority = sk_priority_control;
   sk->flags = SKF_THREAD | SKF_BIND | (ifa ? SKF_TTL_RX : 0);
 
+  if (cf->zero_udp6_checksum_rx)
+    sk->flags |= SKF_UDP6_NO_CSUM_RX;
+
   if (sk_open(sk) < 0)
     goto err;
 
diff --git a/sysdep/bsd/sysio.h b/sysdep/bsd/sysio.h
index b6b42b1e..c20c7f99 100644
--- a/sysdep/bsd/sysio.h
+++ b/sysdep/bsd/sysio.h
@@ -309,3 +309,9 @@ sk_set_freebind(sock *s)
 {
   ERR_MSG("Freebind is not supported");
 }
+
+static inline int
+sk_set_udp6_no_csum_rx(sock *s)
+{
+  ERR_MSG("UDPv6 zero checksum is not supported");
+}
diff --git a/sysdep/linux/sysio.h b/sysdep/linux/sysio.h
index f13eda7c..5e71b535 100644
--- a/sysdep/linux/sysio.h
+++ b/sysdep/linux/sysio.h
@@ -285,3 +285,12 @@ sk_set_freebind(sock *s)
 
   return 0;
 }
+
+static inline int
+sk_set_udp6_no_csum_rx(sock *s)
+{
+  int y = 1;
+
+  if (setsockopt(s->fd, SOL_UDP, UDP_NO_CHECK6_RX, &y, sizeof(y)) < 0)
+    ERR("UDP_NO_CHECK6_RX");
+}
diff --git a/sysdep/unix/io.c b/sysdep/unix/io.c
index 9b499020..da2c5492 100644
--- a/sysdep/unix/io.c
+++ b/sysdep/unix/io.c
@@ -1046,6 +1046,10 @@ sk_setup(sock *s)
     if (s->tos >= 0)
       if (sk_set_tos6(s, s->tos) < 0)
 	return -1;
+
+    if ((s->flags & SKF_UDP6_NO_CSUM_RX) && (s->type == SK_UDP))
+      if (sk_set_udp6_no_csum_rx(s) < 0)
+	return -1;
   }
 
   /* Must be after sk_set_tos4() as setting ToS on Linux also mangles priority */