ctdb-common: Use POSIX if_nameindex() to check interface existence

This works as an unprivileged user, so avoids unnecessary errors when
running in test mode (and not as root):

  2022-02-18T12:21:12.436491+11:00 node.0 ctdbd[6958]: ctdb_sys_check_iface_exists: Failed to open raw socket
  2022-02-18T12:21:12.436534+11:00 node.0 ctdbd[6958]: ctdb_sys_check_iface_exists: Failed to open raw socket
  2022-02-18T12:21:12.436557+11:00 node.0 ctdbd[6958]: ctdb_sys_check_iface_exists: Failed to open raw socket
  2022-02-18T12:21:12.436577+11:00 node.0 ctdbd[6958]: ctdb_sys_check_iface_exists: Failed to open raw socket

The corresponding porting test would now become pointless because it
would just confirm that "fake" does not exist.  Attempt to make it
useful by using a less likely name than "fake" and attempting to
detect the loopback interface.

Signed-off-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Amitay Isaacs <amitay@gmail.com>

3 files changed, 33 insertions, 38 deletions

diff --git a/ctdb/common/system.c b/ctdb/common/system.c
index 650b62bab16..08dc68284fd 100644
--- a/ctdb/common/system.c
+++ b/ctdb/common/system.c
@@ -148,32 +148,36 @@ void ctdb_wait_for_process_to_exit(pid_t pid)
 	}
 }
 
-#ifdef HAVE_AF_PACKET
+#ifdef HAVE_IF_NAMEINDEX
 
 bool ctdb_sys_check_iface_exists(const char *iface)
 {
-	int s;
-	struct ifreq ifr;
+	struct if_nameindex *ifnis, *ifni;
+	bool found = false;
 
-	s = socket(AF_PACKET, SOCK_RAW, 0);
-	if (s == -1){
-		/* We don't know if the interface exists, so assume yes */
-		DBG_ERR("Failed to open raw socket\n");
-		return true;
+	ifnis = if_nameindex();
+	if (ifnis == NULL) {
+		DBG_ERR("Failed to retrieve inteface list\n");
+		return false;
 	}
 
-	strlcpy(ifr.ifr_name, iface, sizeof(ifr.ifr_name));
-	if (ioctl(s, SIOCGIFINDEX, &ifr) < 0 && errno == ENODEV) {
-		DBG_ERR("Interface '%s' not found\n", iface);
-		close(s);
-		return false;
+	for (ifni = ifnis;
+	     ifni->if_index != 0 || ifni->if_name != NULL;
+	     ifni++) {
+		int cmp = strcmp(iface, ifni->if_name);
+		if (cmp == 0) {
+			found = true;
+			goto done;
+		}
 	}
-	close(s);
 
-	return true;
+done:
+	if_freenameindex(ifnis);
+
+	return found;
 }
 
-#else /* HAVE_AF_PACKET */
+#else /* HAVE_IF_NAMEINDEX */
 
 bool ctdb_sys_check_iface_exists(const char *iface)
 {
@@ -181,7 +185,7 @@ bool ctdb_sys_check_iface_exists(const char *iface)
 	return true;
 }
 
-#endif /* HAVE_AF_PACKET */
+#endif /* HAVE_IF_NAMEINDEX */
 
 #ifdef HAVE_PEERCRED
 
diff --git a/ctdb/tests/UNIT/cunit/porting_tests_001.sh b/ctdb/tests/UNIT/cunit/porting_tests_001.sh
index 52291b20cc6..bdb7fc531d4 100755
--- a/ctdb/tests/UNIT/cunit/porting_tests_001.sh
+++ b/ctdb/tests/UNIT/cunit/porting_tests_001.sh
@@ -11,16 +11,5 @@ remove_socket ()
 
 test_cleanup remove_socket
 
-os=$(uname)
-if [ "$os" = "Linux" ] ; then
-	uid=$(id -u)
-	if [ "$uid" -eq 0 ] ; then
-		ok "ctdb_sys_check_iface_exists: Interface 'fake' not found"
-	else
-		ok "ctdb_sys_check_iface_exists: Failed to open raw socket"
-	fi
-else
-	ok_null
-fi
-
-unit_test porting_tests --socket=${socket}
+ok_null
+unit_test porting_tests --socket="$socket"
diff --git a/ctdb/tests/src/porting_tests.c b/ctdb/tests/src/porting_tests.c
index 8902c34dfc2..00618d2c4a7 100644
--- a/ctdb/tests/src/porting_tests.c
+++ b/ctdb/tests/src/porting_tests.c
@@ -171,15 +171,17 @@ static int fork_helper(void)
 */
 static int test_ctdb_sys_check_iface_exists(void)
 {
-	const char *fakename = "fake";
-	bool test;
+	bool test1, test2;
+
+	test1 = ctdb_sys_check_iface_exists("unlikely123xyz");
+	assert(!test1);
+
+	/* Linux and others */
+	test1 = ctdb_sys_check_iface_exists("lo");
+	/* FreeBSD */
+	test2 = ctdb_sys_check_iface_exists("lo0");
+	assert(test1 || test2);
 
-	test = ctdb_sys_check_iface_exists(fakename);
-	if (geteuid() == 0) {
-		assert(test == false);
-	} else {
-		assert(test == true);
-	}
 	return 0;
 }