util-lib: add new ifname_valid() call that validates interface names

Make use of this in nspawn at a couple of places. A later commit should port
more code over to this, including networkd.

src/nspawn/nspawn-network.c

@@ -29,6 +29,8 @@
 #include "netlink-util.h"
 #include "nspawn-network.h"
 #include "siphash24.h"
+#include "socket-util.h"
+#include "stat-util.h"
 #include "string-util.h"
 #include "udev-util.h"
 #include "util.h"
@@ -515,13 +517,13 @@ int veth_extra_parse(char ***l, const char *p) {
         r = extract_first_word(&p, &a, ":", EXTRACT_DONT_COALESCE_SEPARATORS);
         if (r < 0)
                 return r;
-        if (r == 0 || isempty(a))
+        if (r == 0 || !ifname_valid(a))
                 return -EINVAL;
 
         r = extract_first_word(&p, &b, ":", EXTRACT_DONT_COALESCE_SEPARATORS);
         if (r < 0)
                 return r;
-        if (r == 0 || isempty(b)) {
+        if (r == 0 || !ifname_valid(b)) {
                 free(b);
                 b = strdup(a);
                 if (!b)

src/nspawn/nspawn.c

@@ -467,6 +467,12 @@ static int parse_argv(int argc, char *argv[]) {
                         break;
 
                 case ARG_NETWORK_BRIDGE:
+
+                        if (!ifname_valid(optarg)) {
+                                log_error("Bridge interface name not valid: %s", optarg);
+                                return -EINVAL;
+                        }
+
                         r = free_and_strdup(&arg_network_bridge, optarg);
                         if (r < 0)
                                 return log_oom();
@@ -489,6 +495,12 @@ static int parse_argv(int argc, char *argv[]) {
                         break;
 
                 case ARG_NETWORK_INTERFACE:
+
+                        if (!ifname_valid(optarg)) {
+                                log_error("Network interface name not valid: %s", optarg);
+                                return -EINVAL;
+                        }
+
                         if (strv_extend(&arg_network_interfaces, optarg) < 0)
                                 return log_oom();
 
@@ -497,6 +509,12 @@ static int parse_argv(int argc, char *argv[]) {
                         break;
 
                 case ARG_NETWORK_MACVLAN:
+
+                        if (!ifname_valid(optarg)) {
+                                log_error("MACVLAN network interface name not valid: %s", optarg);
+                                return -EINVAL;
+                        }
+
                         if (strv_extend(&arg_network_macvlan, optarg) < 0)
                                 return log_oom();
 
@@ -505,6 +523,12 @@ static int parse_argv(int argc, char *argv[]) {
                         break;
 
                 case ARG_NETWORK_IPVLAN:
+
+                        if (!ifname_valid(optarg)) {
+                                log_error("IPVLAN network interface name not valid: %s", optarg);
+                                return -EINVAL;
+                        }
+
                         if (strv_extend(&arg_network_ipvlan, optarg) < 0)
                                 return log_oom();