From 318acb0f6cb77a32aad5d7f79e06f3c5065ac702 Mon Sep 17 00:00:00 2001
From: "Ondrej Zajicek (work)" <santiago@crfreenet.org>
Date: Sat, 28 Jul 2018 16:54:06 +0200
Subject: [PATCH] BSD: Use MSG_DONTROUTE for unicast packets on FreeBSD

BSD systems cannot use SO_DONTROUTE, because it does not work properly
with multicast packets (perhaps it tries to find iface based on multicast
group address). But we can use MSG_DONTROUTE sendmsg() flag for unicast
packets. Works on FreeBSD, is ignored on OpenBSD and is broken on NetBSD
(i guess due to integrated routing table and ARP table).
---
 lib/ip.h           | 3 +++
 sysdep/bsd/sysio.h | 5 +++++
 sysdep/cf/README   | 1 +
 sysdep/unix/io.c   | 8 +++++++-
 4 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/lib/ip.h b/lib/ip.h
index 5cfce1f1..c3f3e905 100644
--- a/lib/ip.h
+++ b/lib/ip.h
@@ -241,6 +241,9 @@ static inline int ip6_is_v4mapped(ip6_addr a)
 #define ipa_classify(x) ip6_classify(&(x))
 #define ipa_is_link_local(x) ip6_is_link_local(x)
 
+static inline int ip4_is_unicast(ip4_addr a)
+{ return _I(a) < 0xe0000000; }
+
 /* XXXX remove */
 static inline int ipa_classify_net(ip_addr a)
 { return ipa_zero2(a) ? (IADDR_HOST | SCOPE_UNIVERSE) : ipa_classify(a); }
diff --git a/sysdep/bsd/sysio.h b/sysdep/bsd/sysio.h
index 68296e65..a5d161ba 100644
--- a/sysdep/bsd/sysio.h
+++ b/sysdep/bsd/sysio.h
@@ -12,6 +12,11 @@
 #include <sys/param.h>
 
 
+#ifdef __FreeBSD__
+/* Should be defined in sysdep/cf/bsd.h, but it is flavor-specific */
+#define CONFIG_DONTROUTE_UNICAST
+#endif
+
 #ifdef __NetBSD__
 
 #ifndef IP_RECVTTL
diff --git a/sysdep/cf/README b/sysdep/cf/README
index e62c3481..9a7a4afa 100644
--- a/sysdep/cf/README
+++ b/sysdep/cf/README
@@ -11,6 +11,7 @@ CONFIG_MC_PROPER_SRC	Multicast packets have source address according to socket s
 CONFIG_SKIP_MC_BIND	Don't call bind on multicast socket (def for *BSD)
 CONFIG_NO_IFACE_BIND	Bind to iface is not available, use workarounds (def for *BSD)
 CONFIG_UNIX_DONTROUTE	Use setsockopts DONTROUTE (undef for *BSD)
+CONFIG_DONTROUTE_UNICAST Use MSG_DONTROUTE flag for unicast packets (def for FreeBSD)
 CONFIG_USE_HDRINCL	Use IP_HDRINCL instead of control messages for source address on raw IP sockets.
 
 CONFIG_RESTRICTED_PRIVILEGES	Implements restricted privileges using drop_uid()
diff --git a/sysdep/unix/io.c b/sysdep/unix/io.c
index 11a0d6f1..a960b7f8 100644
--- a/sysdep/unix/io.c
+++ b/sysdep/unix/io.c
@@ -1541,6 +1541,7 @@ sk_sendmsg(sock *s)
   struct iovec iov = {s->tbuf, s->tpos - s->tbuf};
   byte cmsg_buf[CMSG_TX_SPACE];
   sockaddr dst;
+  int flags = 0;
 
   sockaddr_fill(&dst, s->af, s->daddr, s->iface, s->dport);
 
@@ -1551,6 +1552,11 @@ sk_sendmsg(sock *s)
     .msg_iovlen = 1
   };
 
+#ifdef CONFIG_DONTROUTE_UNICAST
+  if (ipa_is_ip4(s->daddr) && ip4_is_unicast(ipa_to_ip4(s->daddr)))
+    flags = MSG_DONTROUTE;
+#endif
+
 #ifdef CONFIG_USE_HDRINCL
   byte hdr[20];
   struct iovec iov2[2] = { {hdr, 20}, iov };
@@ -1566,7 +1572,7 @@ sk_sendmsg(sock *s)
   if (s->flags & SKF_PKTINFO)
     sk_prepare_cmsgs(s, &msg, cmsg_buf, sizeof(cmsg_buf));
 
-  return sendmsg(s->fd, &msg, 0);
+  return sendmsg(s->fd, &msg, flags);
 }
 
 static inline int