networkd: validate NTP server strings configured in .network files

Let's be a bit stricter, and make sure users only configure proper DNS names or
IP addresses, but not any other strings.

src/network/networkd-network-gperf.gperf

@@ -54,7 +54,7 @@ Network.LLMNR,                          config_parse_resolve_support,
 Network.MulticastDNS,                   config_parse_resolve_support,                   0,                             offsetof(Network, mdns)
 Network.DNSSEC,                         config_parse_dnssec_mode,                       0,                             offsetof(Network, dnssec_mode)
 Network.DNSSECNegativeTrustAnchors,     config_parse_dnssec_negative_trust_anchors,     0,                             0
-Network.NTP,                            config_parse_strv,                              0,                             offsetof(Network, ntp)
+Network.NTP,                            config_parse_ntp,                               0,                             offsetof(Network, ntp)
 Network.IPForward,                      config_parse_address_family_boolean_with_kernel,0,                             offsetof(Network, ip_forward)
 Network.IPMasquerade,                   config_parse_bool,                              0,                             offsetof(Network, ip_masquerade)
 Network.IPv6PrivacyExtensions,          config_parse_ipv6_privacy_extensions,           0,                             offsetof(Network, ipv6_privacy_extensions)

src/network/networkd-network.c

@@ -1084,6 +1084,59 @@ int config_parse_dnssec_negative_trust_anchors(
         return 0;
 }
 
+int config_parse_ntp(
+                const char *unit,
+                const char *filename,
+                unsigned line,
+                const char *section,
+                unsigned section_line,
+                const char *lvalue,
+                int ltype,
+                const char *rvalue,
+                void *data,
+                void *userdata) {
+
+        char ***l = data;
+        int r;
+
+        assert(l);
+        assert(lvalue);
+        assert(rvalue);
+
+        if (isempty(rvalue)) {
+                *l = strv_free(*l);
+                return 0;
+        }
+
+        for (;;) {
+                _cleanup_free_ char *w = NULL;
+
+                r = extract_first_word(&rvalue, &w, NULL, 0);
+                if (r == -ENOMEM)
+                        return log_oom();
+                if (r < 0) {
+                        log_syntax(unit, LOG_ERR, filename, line, r, "Failed to extract NTP server name, ignoring: %s", rvalue);
+                        break;
+                }
+                if (r == 0)
+                        break;
+
+                r = dns_name_is_valid_or_address(w);
+                if (r <= 0) {
+                        log_syntax(unit, LOG_ERR, filename, line, r, "%s is not a valid domain name or IP address, ignoring.", w);
+                        continue;
+                }
+
+                r = strv_push(l, w);
+                if (r < 0)
+                        return log_oom();
+
+                w = NULL;
+        }
+
+        return 0;
+}
+
 int config_parse_dhcp_route_table(const char *unit,
                                   const char *filename,
                                   unsigned line,

src/network/networkd-network.h

@@ -233,6 +233,7 @@ int config_parse_dnssec_negative_trust_anchors(const char *unit, const char *fil
 int config_parse_dhcp_use_domains(const char *unit, const char *filename, unsigned line, const char *section, unsigned section_line, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
 int config_parse_lldp_mode(const char *unit, const char *filename, unsigned line, const char *section, unsigned section_line, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
 int config_parse_dhcp_route_table(const char *unit, const char *filename, unsigned line, const char *section, unsigned section_line, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
+int config_parse_ntp(const char *unit, const char *filename, unsigned line, const char *section, unsigned section_line, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
 
 /* Legacy IPv4LL support */
 int config_parse_ipv4ll(const char *unit, const char *filename, unsigned line, const char *section, unsigned section_line, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);