udp_io, traceroute: Standardise IPv6 PKTINFO handling to be portable

The current standard (RFC 3542) is for IPV6_RECVPKTINFO to be given to
setsockopt, and IPV6_PKTINFO to be used as the packet type. Previously,
RFC 2292 required IPV6_PKTINFO to be used for both, but RFC 3542
re-purposed IPV6_PKTINFO when given to setsockopt. The special
Linux-specific IPV6_2292PKTINFO has the same semantics as IPV6_PKTINFO
in RFC 2292, but was introduced at the same time as IPV6_RECVPKTINFO.

Therefore, if we have IPV6_RECVPKTINFO available, we can use the RFC
3542 style, and if not, we assume that only the RFC 2292 API is
available, using IPV6_PKTINFO for both.

Signed-off-by: James Clarke <jrtc27@jrtc27.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/libbb/udp_io.c b/libbb/udp_io.c
index 6e3ef484e..68355e6c4 100644
--- a/libbb/udp_io.c
+++ b/libbb/udp_io.c
@@ -8,6 +8,10 @@
  */
 #include "libbb.h"
 
+#if defined(IPV6_PKTINFO) && !defined(IPV6_RECVPKTINFO)
+# define IPV6_RECVPKTINFO IPV6_PKTINFO
+#endif
+
 /*
  * This asks kernel to let us know dst addr/port of incoming packets
  * We don't check for errors here. Not supported == won't be used
@@ -18,8 +22,8 @@ socket_want_pktinfo(int fd UNUSED_PARAM)
 #ifdef IP_PKTINFO
         setsockopt_1(fd, IPPROTO_IP, IP_PKTINFO);
 #endif
-#if ENABLE_FEATURE_IPV6 && defined(IPV6_PKTINFO)
-        setsockopt_1(fd, IPPROTO_IPV6, IPV6_PKTINFO);
+#if ENABLE_FEATURE_IPV6 && defined(IPV6_RECVPKTINFO)
+        setsockopt_1(fd, IPPROTO_IPV6, IPV6_RECVPKTINFO);
 #endif
 }