resolv: Enable full ICMP errors for UDP DNS sockets [BZ #24047]

The Linux kernel suppresses some ICMP error messages by default for
UDP sockets.  This commit enables full ICMP error reporting,
hopefully resulting in faster failover to working name servers.

1 files changed, 37 insertions, 0 deletions

diff --git a/resolv/res_enable_icmp.c b/resolv/res_enable_icmp.c
new file mode 100644
index 0000000000..bdc9220f08
--- /dev/null
+++ b/resolv/res_enable_icmp.c
@@ -0,0 +1,37 @@
+/* Enable full ICMP errors on a socket.
+   Copyright (C) 2019 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <netinet/in.h>
+#include <sys/socket.h>
+
+int
+__res_enable_icmp (int family, int fd)
+{
+  int one = 1;
+  switch (family)
+    {
+    case AF_INET:
+      return setsockopt (fd, SOL_IP, IP_RECVERR, &one, sizeof (one));
+    case AF_INET6:
+      return setsockopt (fd, SOL_IPV6, IPV6_RECVERR, &one, sizeof (one));
+    default:
+      __set_errno (EAFNOSUPPORT);
+      return -1;
+    }
+}