Also try lo0 as a fallback interface. Fixes default use on OpenBSD

Background:

Libnet usually needs init before we have searched for the real
interface. In that case, first we just give a NULL pointer as the
interface. But libnet sometimes fails to find an interface (no idea
why), so we try to put in "lo".

This commit adds "lo0" as an interface checked, as that is the name on
OpenBSD.

1 files changed, 51 insertions, 17 deletions

diff --git a/src/arping.c b/src/arping.c
index e2c157f..5e21303 100644
--- a/src/arping.c
+++ b/src/arping.c
@@ -626,17 +626,48 @@ strip_newline(char* s) {
 
 /**
  * Init libnet with specified ifname. Destroy if already inited.
- * If this function retries with different parameter it will preserve
- * the original error message and print that.
+ *
+ * Libnet usually needs init before we have searched for the real
+ * interface. In that case, first we just give a NULL pointer as the
+ * interface. But libnet sometimes fails to find an interface (no idea
+ * why), so then we try to use "lo" and "lo0" explicitly.
+ *
+ * If even loopback fails, then it'll preserve the original error
+ * message.
+ *
  * Call with recursive=0.
  */
 void
-do_libnet_init(const char *ifname, int recursive)
+do_libnet_init(const char *inifname, int recursive)
 {
+        const char* ifname = inifname;
+        int last = 0;
+        switch (recursive) {
+        case 0:
+                break;
+        case 1:
+                ifname = "lo"; // E.g. Linux.
+                break;
+        case 2:
+                ifname = "lo0"; // E.g. OpenBSD.
+                break;
+        default:
+                last = 1;
+                break;
+        }
+
+        // If we're given an interface name then always use that.
+        // No need to be recursive about it.
+        if (inifname != NULL && recursive == 0) {
+                ifname = inifname;
+                last = 1;
+        }
+
 	char ebuf[LIBNET_ERRBUF_SIZE];
         ebuf[0] = 0;
 	if (verbose > 1) {
-                printf("arping: libnet_init(%s)\n", ifname ? ifname : "<null>");
+                printf("arping: trying libnet_init(LIBNET_LINK, %s)\n",
+                       ifname ? ifname : "<null>");
 	}
 	if (libnet) {
 		/* Probably going to switch interface from temp to real. */
@@ -644,28 +675,31 @@ do_libnet_init(const char *ifname, int recursive)
 		libnet = 0;
 	}
 
-        /* Try libnet_init() even though we aren't root. We may have
+        /* Try libnet_init() even though we maybe aren't root. We may have
          * a capability or something. */
 	if (!(libnet = libnet_init(LIBNET_LINK,
 				   (char*)ifname,
 				   ebuf))) {
                 strip_newline(ebuf);
-                if (!ifname) {
-                        /* Sometimes libnet guesses an interface that it then
-                         * can't use. Work around that by attempting to
-                         * use "lo". */
-                        do_libnet_init("lo", 1);
+                if (verbose) {
+                        fprintf(stderr,
+                                "arping: libnet_init(LIBNET_LINK, %s): %s\n",
+                                ifname ? ifname : "<null>",
+                                *ebuf ? ebuf : "<no error message>");
+                }
+                if (!last) {
+                        do_libnet_init(ifname, recursive+1);
                         if (libnet != NULL) {
                                 return;
                         }
-                } else if (recursive) {
-                        /* Continue original execution to get that
-                         * error message. */
-                        return;
                 }
-                fprintf(stderr, "arping: libnet_init(LIBNET_LINK, %s): %s\n",
-                        ifname ? ifname : "<null>",
-                        *ebuf ? ebuf : "<no error message>");
+                if (!verbose) {
+                        // Prevent double-print when verbose.
+                        fprintf(stderr,
+                                "arping: libnet_init(LIBNET_LINK, %s): %s\n",
+                                ifname ? ifname : "<null>",
+                                *ebuf ? ebuf : "<no error message>");
+                }
                 if (getuid() && geteuid()) {
                         fprintf(stderr,
                                 "arping: you may need to run as root\n");