From c382d39a85c1edbaf96f0cd84385cd6549c0bde2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ond=C5=99ej=20Sur=C3=BD?= <ondrej@sury.org>
Date: Fri, 29 May 2020 10:17:32 +0200
Subject: [PATCH] linux,udp: enable full ICMP error reporting

The Linux kernel suppresses some ICMP error messages by default for UDP
sockets. This commit sets IP_RECVERR/IPV6_RECVERR on the socket to
enable full ICMP error reporting, hopefully resulting in faster failover
to working name servers.

PR-URL: https://github.com/libuv/libuv/pull/2872
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>
---
 docs/src/udp.rst | 11 ++++++++++-
 include/uv.h     |  9 ++++++++-
 src/unix/udp.c   | 30 +++++++++++++++++++++++++++++-
 3 files changed, 47 insertions(+), 3 deletions(-)

diff --git a/docs/src/udp.rst b/docs/src/udp.rst
index 827fbaad..3a7c6db4 100644
--- a/docs/src/udp.rst
+++ b/docs/src/udp.rst
@@ -53,6 +53,14 @@ Data types
              * in uv_udp_recv_cb, nread will always be 0 and addr will always be NULL.
              */
             UV_UDP_MMSG_FREE = 16,
+            /*
+             * Indicates if IP_RECVERR/IPV6_RECVERR will be set when binding the handle.
+             * This sets IP_RECVERR for IPv4 and IPV6_RECVERR for IPv6 UDP sockets on
+             * Linux. This stops the Linux kernel from supressing some ICMP error messages
+             * and enables full ICMP error reporting for faster failover.
+             * This flag is no-op on platforms other than Linux.
+             */
+            UV_UDP_LINUX_RECVERR = 32,
             /*
             * Indicates that recvmmsg should be used, if available.
             */
@@ -178,7 +186,8 @@ API
         with the address and port to bind to.
 
     :param flags: Indicate how the socket will be bound,
-        ``UV_UDP_IPV6ONLY`` and ``UV_UDP_REUSEADDR`` are supported.
+        ``UV_UDP_IPV6ONLY``, ``UV_UDP_REUSEADDR``, and ``UV_UDP_RECVERR``
+        are supported.
 
     :returns: 0 on success, or an error code < 0 on failure.
 
diff --git a/include/uv.h b/include/uv.h
index 1e1fc94b..cbdf1b02 100644
--- a/include/uv.h
+++ b/include/uv.h
@@ -626,7 +626,14 @@ enum uv_udp_flags {
    * in uv_udp_recv_cb, nread will always be 0 and addr will always be NULL.
    */
   UV_UDP_MMSG_FREE = 16,
-
+  /*
+   * Indicates if IP_RECVERR/IPV6_RECVERR will be set when binding the handle.
+   * This sets IP_RECVERR for IPv4 and IPV6_RECVERR for IPv6 UDP sockets on
+   * Linux. This stops the Linux kernel from supressing some ICMP error messages
+   * and enables full ICMP error reporting for faster failover.
+   * This flag is no-op on platforms other than Linux.
+   */
+  UV_UDP_LINUX_RECVERR = 32,
   /*
    * Indicates that recvmmsg should be used, if available.
    */
diff --git a/src/unix/udp.c b/src/unix/udp.c
index 7d699a16..5d0ec8d3 100644
--- a/src/unix/udp.c
+++ b/src/unix/udp.c
@@ -504,6 +504,28 @@ static int uv__set_reuse(int fd) {
   return 0;
 }
 
+/*
+ * The Linux kernel suppresses some ICMP error messages by default for UDP
+ * sockets. Setting IP_RECVERR/IPV6_RECVERR on the socket enables full ICMP
+ * error reporting, hopefully resulting in faster failover to working name
+ * servers.
+ */
+static int uv__set_recverr(int fd, sa_family_t ss_family) {
+#if defined(__linux__)
+  int yes;
+
+  yes = 1;
+  if (ss_family == AF_INET) {
+    if (setsockopt(fd, IPPROTO_IP, IP_RECVERR, &yes, sizeof(yes)))
+      return UV__ERR(errno);
+  } else if (ss_family == AF_INET6) {
+    if (setsockopt(fd, IPPROTO_IPV6, IPV6_RECVERR, &yes, sizeof(yes)))
+       return UV__ERR(errno);
+  }
+#endif
+  return 0;
+}
+
 
 int uv__udp_bind(uv_udp_t* handle,
                  const struct sockaddr* addr,
@@ -514,7 +536,7 @@ int uv__udp_bind(uv_udp_t* handle,
   int fd;
 
   /* Check for bad flags. */
-  if (flags & ~(UV_UDP_IPV6ONLY | UV_UDP_REUSEADDR))
+  if (flags & ~(UV_UDP_IPV6ONLY | UV_UDP_REUSEADDR | UV_UDP_LINUX_RECVERR))
     return UV_EINVAL;
 
   /* Cannot set IPv6-only mode on non-IPv6 socket. */
@@ -530,6 +552,12 @@ int uv__udp_bind(uv_udp_t* handle,
     handle->io_watcher.fd = fd;
   }
 
+  if (flags & UV_UDP_LINUX_RECVERR) {
+    err = uv__set_recverr(fd, addr->sa_family);
+    if (err)
+      return err;
+  }
+
   if (flags & UV_UDP_REUSEADDR) {
     err = uv__set_reuse(fd);
     if (err)