*.localdomain != localhost

".localdomain" is not a reserved suffix (or prefix). I'm not aware of any
product expecting *.localdomain to resolve to localhost, however I am aware of
at least one product that defaults to ".localdomain" as its DNS suffix provided
via DHCP (pfSense). This leads to unexpected results when attempting to access
a host that's offline (or a host that's online, when nsswitch.conf is
[mis-]configured to have myhostname ahead of DNS).

Operate on:
localhost (and localhost.)
*.localhost (and *.localhost.)
localhost.localdomain (and localhost.localdomain.)
*.localhost.localdomain (and *.localhost.localdomain.)

We should not cover:
*.localdomain (nor *.localdomain.)
localdomain (nor localdomain.)

diff --git a/man/nss-myhostname.xml b/man/nss-myhostname.xml
index 251bdec..e339e6b 100644 (file)
--- a/man/nss-myhostname.xml
+++ b/man/nss-myhostname.xml
@@ -71,9 +71,10 @@
       is on the local loopback) and the IPv6 address ::1 (which is the
       local host).</para></listitem>
 
-      <listitem><para>The hostname <literal>localhost</literal> (as well as any hostname ending in
-      <literal>.localhost</literal>, <literal>.localdomain</literal> or equal to <literal>localdomain</literal>) is
-      resolved to the IP addresses 127.0.0.1 and ::1.</para></listitem>
+      <listitem><para>The hostnames <literal>localhost</literal> and
+      <literal>localhost.localdomain</literal> (as well as any hostname
+      ending in <literal>.localhost</literal> or <literal>.localhost.localdomain</literal>)
+      are resolved to the IP addresses 127.0.0.1 and ::1.</para></listitem>
 
       <listitem><para>The hostname <literal>gateway</literal> is
       resolved to all current default routing gateway addresses,

diff --git a/man/systemd-resolved.service.xml b/man/systemd-resolved.service.xml
index 7a9e23a..829729c 100644 (file)
--- a/man/systemd-resolved.service.xml
+++ b/man/systemd-resolved.service.xml
@@ -87,9 +87,10 @@
       is on the local loopback) and the IPv6 address ::1 (which is the
       local host).</para></listitem>
 
-      <listitem><para>The hostname <literal>localhost</literal> (as well as any hostname ending in
-      <literal>.localhost</literal>, <literal>.localdomain</literal> or equal to <literal>localdomain</literal>) is
-      resolved to the IP addresses 127.0.0.1 and ::1.</para></listitem>
+      <listitem><para>The hostnames <literal>localhost</literal> and
+      <literal>localhost.localdomain</literal> (as well as any hostname
+      ending in <literal>.localhost</literal> or <literal>.localhost.localdomain</literal>)
+      are resolved to the IP addresses 127.0.0.1 and ::1.</para></listitem>
 
       <listitem><para>The hostname <literal>gateway</literal> is
       resolved to all current default routing gateway addresses,

diff --git a/src/basic/hostname-util.c b/src/basic/hostname-util.c
index 7bb2344..4fe6a72 100644 (file)
--- a/src/basic/hostname-util.c
+++ b/src/basic/hostname-util.c
@@ -150,16 +150,16 @@ bool is_localhost(const char *hostname) {
         assert(hostname);
 
         /* This tries to identify local host and domain names
-         * described in RFC6761 plus the redhatism of .localdomain */
+         * described in RFC6761 plus the redhatism of localdomain */
 
         return strcaseeq(hostname, "localhost") ||
                strcaseeq(hostname, "localhost.") ||
-               strcaseeq(hostname, "localdomain.") ||
-               strcaseeq(hostname, "localdomain") ||
+               strcaseeq(hostname, "localhost.localdomain") ||
+               strcaseeq(hostname, "localhost.localdomain.") ||
                endswith_no_case(hostname, ".localhost") ||
                endswith_no_case(hostname, ".localhost.") ||
-               endswith_no_case(hostname, ".localdomain") ||
-               endswith_no_case(hostname, ".localdomain.");
+               endswith_no_case(hostname, ".localhost.localdomain") ||
+               endswith_no_case(hostname, ".localhost.localdomain.");
 }
 
 bool is_gateway_hostname(const char *hostname) {