dhcp (dhclient): honor ipv4.dhcp-client-id=none

If the client-id has been set to "none", the DHCP client-id option
(option 61) mustn't be sent. Honor this when the dhclient plugin is
used.

If dhclient has been called with the -i option (Use  a DUID with DHCPv4
clients), it will send a Client-ID even without setting one in dhclient.conf.
In this case, this option needs to be explicitly overwritten with:
  send dhcp-client-identifier = "";

At least in RHEL 8, dhclient is launched with `-i` turned on by default.

4 files changed, 109 insertions, 8 deletions

diff --git a/src/core/dhcp/nm-dhcp-dhclient-utils.c b/src/core/dhcp/nm-dhcp-dhclient-utils.c
index ea8943fa1e..286f7aa19f 100644
--- a/src/core/dhcp/nm-dhcp-dhclient-utils.c
+++ b/src/core/dhcp/nm-dhcp-dhclient-utils.c
@@ -120,7 +120,10 @@ add_ip4_config(GString            *str,
         }
 
         g_string_append(str, CLIENTID_TAG " ");
-        if (i < l) {
+        if (l == 0) {
+            /* An empty value effectively unsets the client-id to avoid sending it */
+            g_string_append(str, "\"\"");
+        } else if (i < l) {
             /* Unprintable; convert to a hex string */
             for (i = 0; i < l; i++) {
                 if (i > 0)
@@ -293,6 +296,7 @@ char *
 nm_dhcp_dhclient_create_config(const char         *interface,
                                int                 addr_family,
                                GBytes             *client_id,
+                               gboolean            send_client_id,
                                const char         *anycast_address,
                                const char         *hostname,
                                guint32             timeout,
@@ -391,8 +395,8 @@ nm_dhcp_dhclient_create_config(const char         *interface,
                 continue;
 
             if (NM_STR_HAS_PREFIX(p, CLIENTID_TAG)) {
-                /* Override config file "dhcp-client-id" and use one from the connection */
-                if (client_id)
+                /* Skip "dhcp-client-id" if the connection has defined a custom one or "none" */
+                if (client_id || !send_client_id)
                     continue;
 
                 /* Otherwise, capture and return the existing client id */
@@ -477,6 +481,8 @@ nm_dhcp_dhclient_create_config(const char         *interface,
     }
 
     if (addr_family == AF_INET) {
+        nm_auto_unref_bytes GBytes *client_id_none = NULL;
+        client_id = send_client_id ? client_id : (client_id_none = g_bytes_new_static("", 0));
         add_ip4_config(new_contents, client_id, hostname, use_fqdn, hostname_flags);
         add_request(reqs, "rfc3442-classless-static-routes");
         add_request(reqs, "ms-classless-static-routes");
diff --git a/src/core/dhcp/nm-dhcp-dhclient-utils.h b/src/core/dhcp/nm-dhcp-dhclient-utils.h
index 6187cce0fb..34b2617512 100644
--- a/src/core/dhcp/nm-dhcp-dhclient-utils.h
+++ b/src/core/dhcp/nm-dhcp-dhclient-utils.h
@@ -12,6 +12,7 @@
 char *nm_dhcp_dhclient_create_config(const char         *interface,
                                      int                 addr_family,
                                      GBytes             *client_id,
+                                     gboolean            send_client_id,
                                      const char         *anycast_addr,
                                      const char         *hostname,
                                      guint32             timeout,
diff --git a/src/core/dhcp/nm-dhcp-dhclient.c b/src/core/dhcp/nm-dhcp-dhclient.c
index e6357871ef..2a3af10a56 100644
--- a/src/core/dhcp/nm-dhcp-dhclient.c
+++ b/src/core/dhcp/nm-dhcp-dhclient.c
@@ -233,6 +233,7 @@ create_dhclient_config(NMDhcpDhclient     *self,
                        const char         *iface,
                        const char         *uuid,
                        GBytes             *client_id,
+                       gboolean            send_client_id,
                        const char         *anycast_address,
                        const char         *hostname,
                        guint32             timeout,
@@ -271,6 +272,7 @@ create_dhclient_config(NMDhcpDhclient     *self,
     new_content = nm_dhcp_dhclient_create_config(iface,
                                                  addr_family,
                                                  client_id,
+                                                 send_client_id,
                                                  anycast_address,
                                                  hostname,
                                                  timeout,
@@ -515,6 +517,7 @@ ip4_start(NMDhcpClient *client, GError **error)
                                              client_config->iface,
                                              client_config->uuid,
                                              client_config->client_id,
+                                             client_config->v4.send_client_id,
                                              client_config->anycast_address,
                                              client_config->hostname,
                                              client_config->timeout,
@@ -557,6 +560,7 @@ ip6_start(NMDhcpClient *client, const struct in6_addr *ll_addr, GError **error)
                                              config->iface,
                                              config->uuid,
                                              NULL,
+                                             TRUE,
                                              config->anycast_address,
                                              config->hostname,
                                              config->timeout,
diff --git a/src/core/dhcp/tests/test-dhcp-dhclient.c b/src/core/dhcp/tests/test-dhcp-dhclient.c
index e95f218e6e..0edcc296b4 100644
--- a/src/core/dhcp/tests/test-dhcp-dhclient.c
+++ b/src/core/dhcp/tests/test-dhcp-dhclient.c
@@ -36,11 +36,14 @@ test_config(const char         *orig,
             const char         *anycast_addr,
             const char         *mud_url)
 {
-    gs_free char *new                    = NULL;
-    gs_unref_bytes GBytes *client_id     = NULL;
-    gs_unref_bytes GBytes *new_client_id = NULL;
-
-    if (dhcp_client_id) {
+    gs_free char *new                     = NULL;
+    gs_unref_bytes GBytes *client_id      = NULL;
+    gs_unref_bytes GBytes *new_client_id  = NULL;
+    gboolean               send_client_id = TRUE;
+
+    if (nm_streq0(dhcp_client_id, "none")) {
+        send_client_id = FALSE;
+    } else if (dhcp_client_id) {
         client_id = nm_dhcp_utils_client_id_string_to_bytes(dhcp_client_id);
         g_assert(client_id);
     }
@@ -48,6 +51,7 @@ test_config(const char         *orig,
     new = nm_dhcp_dhclient_create_config(iface,
                                          addr_family,
                                          client_id,
+                                         send_client_id,
                                          anycast_addr,
                                          hostname,
                                          timeout,
@@ -502,6 +506,90 @@ test_existing_ascii_client_id(void)
                 NULL,
                 NULL);
 }
+
+/*****************************************************************************/
+
+static const char *none_client_id_orig = "send dhcp-client-identifier 10:30:04:20:7A:08;\n";
+
+static const char *none_client_id_expected =
+    "# Created by NetworkManager\n"
+    "# Merged from /path/to/dhclient.conf\n"
+    "\n"
+    "send dhcp-client-identifier \"\"; # added by NetworkManager\n"
+    "\n"
+    "option rfc3442-classless-static-routes code 121 = array of unsigned integer 8;\n"
+    "option ms-classless-static-routes code 249 = array of unsigned integer 8;\n"
+    "option wpad code 252 = string;\n"
+    "\n"
+    "also request rfc3442-classless-static-routes;\n"
+    "also request ms-classless-static-routes;\n"
+    "also request static-routes;\n"
+    "also request wpad;\n"
+    "also request ntp-servers;\n"
+    "also request root-path;\n"
+    "\n";
+
+static void
+test_none_client_id(void)
+{
+    const char            *connection_client_id = "none";
+    gs_unref_bytes GBytes *expected_client_id   = NULL;
+
+    test_config(none_client_id_orig,
+                none_client_id_expected,
+                AF_INET,
+                NULL,
+                0,
+                FALSE,
+                NM_DHCP_HOSTNAME_FLAG_NONE,
+                connection_client_id,
+                expected_client_id,
+                "eth0",
+                NULL,
+                NULL);
+}
+
+/*****************************************************************************/
+
+static const char *missing_client_id_orig = "";
+
+static const char *missing_client_id_expected =
+    "# Created by NetworkManager\n"
+    "# Merged from /path/to/dhclient.conf\n"
+    "\n"
+    "\n"
+    "option rfc3442-classless-static-routes code 121 = array of unsigned integer 8;\n"
+    "option ms-classless-static-routes code 249 = array of unsigned integer 8;\n"
+    "option wpad code 252 = string;\n"
+    "\n"
+    "also request rfc3442-classless-static-routes;\n"
+    "also request ms-classless-static-routes;\n"
+    "also request static-routes;\n"
+    "also request wpad;\n"
+    "also request ntp-servers;\n"
+    "also request root-path;\n"
+    "\n";
+
+static void
+test_missing_client_id(void)
+{
+    const char            *connection_client_id = NULL;
+    gs_unref_bytes GBytes *expected_client_id   = NULL;
+
+    test_config(missing_client_id_orig,
+                missing_client_id_expected,
+                AF_INET,
+                NULL,
+                0,
+                FALSE,
+                NM_DHCP_HOSTNAME_FLAG_NONE,
+                connection_client_id,
+                expected_client_id,
+                "eth0",
+                NULL,
+                NULL);
+}
+
 /*****************************************************************************/
 
 static const char *fqdn_expected =
@@ -1364,6 +1452,8 @@ main(int argc, char **argv)
     g_test_add_func("/dhcp/dhclient/existing-hex-client-id", test_existing_hex_client_id);
     g_test_add_func("/dhcp/dhclient/existing-client-id", test_existing_escaped_client_id);
     g_test_add_func("/dhcp/dhclient/existing-ascii-client-id", test_existing_ascii_client_id);
+    g_test_add_func("/dhcp/dhclient/none-client-id", test_none_client_id);
+    g_test_add_func("/dhcp/dhclient/missing-client-id", test_missing_client_id);
     g_test_add_func("/dhcp/dhclient/fqdn", test_fqdn);
     g_test_add_func("/dhcp/dhclient/fqdn_options_override", test_fqdn_options_override);
     g_test_add_func("/dhcp/dhclient/override_hostname", test_override_hostname);