[PATCH] Audit: make audit=0 actually turn off audit

Currently audit=0 on the kernel command line does absolutely nothing.
Audit always loads and always uses its resources such as creating the
kernel netlink socket.  This patch causes audit=0 to actually disable
audit.  Audit will use no resources and starting the userspace auditd
daemon will not cause the kernel audit system to activate.

Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

kernel/audit.c

@@ -61,8 +61,11 @@
 
 #include "audit.h"
 
-/* No auditing will take place until audit_initialized != 0.
+/* No auditing will take place until audit_initialized == AUDIT_INITIALIZED.
  * (Initialization happens after skb_init is called.) */
+#define AUDIT_DISABLED		-1
+#define AUDIT_UNINITIALIZED	0
+#define AUDIT_INITIALIZED	1
 static int	audit_initialized;
 
 #define AUDIT_OFF	0
@@ -965,6 +968,9 @@ static int __init audit_init(void)
 {
 	int i;
 
+	if (audit_initialized == AUDIT_DISABLED)
+		return 0;
+
 	printk(KERN_INFO "audit: initializing netlink socket (%s)\n",
 	       audit_default ? "enabled" : "disabled");
 	audit_sock = netlink_kernel_create(&init_net, NETLINK_AUDIT, 0,
@@ -976,7 +982,7 @@ static int __init audit_init(void)
 
 	skb_queue_head_init(&audit_skb_queue);
 	skb_queue_head_init(&audit_skb_hold_queue);
-	audit_initialized = 1;
+	audit_initialized = AUDIT_INITIALIZED;
 	audit_enabled = audit_default;
 	audit_ever_enabled |= !!audit_default;
 
@@ -999,13 +1005,21 @@ __initcall(audit_init);
 static int __init audit_enable(char *str)
 {
 	audit_default = !!simple_strtol(str, NULL, 0);
-	printk(KERN_INFO "audit: %s%s\n",
-	       audit_default ? "enabled" : "disabled",
-	       audit_initialized ? "" : " (after initialization)");
-	if (audit_initialized) {
+	if (!audit_default)
+		audit_initialized = AUDIT_DISABLED;
+
+	printk(KERN_INFO "audit: %s", audit_default ? "enabled" : "disabled");
+
+	if (audit_initialized == AUDIT_INITIALIZED) {
 		audit_enabled = audit_default;
 		audit_ever_enabled |= !!audit_default;
+	} else if (audit_initialized == AUDIT_UNINITIALIZED) {
+		printk(" (after initialization)");
+	} else {
+		printk(" (until reboot)");
 	}
+	printk("\n");
+
 	return 1;
 }
 
@@ -1146,7 +1160,7 @@ struct audit_buffer *audit_log_start(struct audit_context *ctx, gfp_t gfp_mask,
 	int reserve;
 	unsigned long timeout_start = jiffies;
 
-	if (!audit_initialized)
+	if (audit_initialized != AUDIT_INITIALIZED)
 		return NULL;
 
 	if (unlikely(audit_filter_type(type)))