Enforce *no networking* in single-user mode, runlevel 1

This is a quite intrusive change.  In addition to the already reserved
runlevels 0 and 6, halt and reboot, respectively, this patch reserves
runlevel 1 as *no networking*, like the traditional SysV init did.  One
of the reasons for this change is the new 'single' user mode, introduced
earlier.  Most users when entering 'S' or 'single' on the kernel cmdline
expect the single user mode (runlevel 1) to be without networking.

This leaves 2, 3, 4, 5, and 7, 8, 9 as fully user-configurable runlevels
with networking.

Of course, networking can still be enabled in runlevel 1 using ifconfig
or ifupdown, or change runlevel.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

src/helpers.c

@@ -212,6 +212,77 @@ done:
 		sethostname(*hostname, strlen(*hostname));
 }
 
+static void ifup(char *ifname, int updown)
+{
+	char cmd[80];
+
+	if (updown) {
+		snprintf(cmd, sizeof(cmd), "ifup %s", ifname);
+		run_interactive(cmd, "Bringing up interface %s", ifname);
+	} else {
+		snprintf(cmd, sizeof(cmd), "ifdown -f %s", ifname);
+		run_interactive(cmd, "Taking down interface %s", ifname);
+	}
+}
+
+/*
+ * Bring up networking, but only if not single-user or rescue mode
+ */
+void networking(int updown)
+{
+	FILE *fp;
+
+	if (updown)
+		_d("Setting up networking ...");
+	else
+		_d("Taking down networking ...");
+
+	/* Run user network start script if enabled */
+	if (updown && network) {
+		run_interactive(network, "Starting networking: %s", network);
+		goto done;
+	}
+
+	/* Debian/Ubuntu/Busybox/RH/Suse */
+	if (!whichp("ifup"))
+		goto done;
+
+	fp = fopen("/etc/network/interfaces", "r");
+	if (fp) {
+		char buf[160];
+
+		/* Bring up, or down, all 'auto' interfaces */
+		while (fgets(buf, sizeof(buf), fp)) {
+			char *line, *ifname = NULL;
+
+			chomp(buf);
+			line = strip_line(buf);
+
+			if (!strncmp(line, "auto", 4))
+				ifname = &line[5];
+			if (!strncmp(line, "allow-hotplug", 13))
+				ifname = &line[14];
+
+			if (!ifname)
+				continue;
+
+			ifup(ifname, updown);
+		}
+
+		fclose(fp);
+	}
+
+done:
+	/* Fall back to bring up at least loopback */
+	ifconfig("lo", "127.0.0.1", "255.0.0.0", updown);
+
+	/* Hooks that rely on loopback, or basic networking being up. */
+	if (updown) {
+		_d("Calling all network up hooks ...");
+		plugin_run_hooks(HOOK_NETWORK_UP);
+	}
+}
+
 #ifndef HAVE_GETFSENT
 static lfile_t *fstab = NULL;