audit: do not panic on invalid boot parameter

If you pass in an invalid audit boot parameter value, e.g. "audit=off",
the kernel panics very early in boot before the regular console is
initialized.  Unless you have earlyprintk enabled, there is no
indication of what the problem is on the console.

Convert the panic() calls to pr_err(), and leave auditing enabled if an
invalid parameter value was passed in.

Modify the parameter to also accept "on" or "off" as valid values, and
update the documentation accordingly.
Signed-off-by: Greg Edwards <gedwards@ddn.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

Documentation/admin-guide/kernel-parameters.txt

@@ -387,15 +387,15 @@
 			Use software keyboard repeat
 
 	audit=		[KNL] Enable the audit sub-system
-			Format: { "0" | "1" } (0 = disabled, 1 = enabled)
-			0 - kernel audit is disabled and can not be enabled
-			    until the next reboot
+			Format: { "0" | "1" | "off" | "on" }
+			0 | off - kernel audit is disabled and can not be
+			    enabled until the next reboot
 			unset - kernel audit is initialized but disabled and
 			    will be fully enabled by the userspace auditd.
-			1 - kernel audit is initialized and partially enabled,
-			    storing at most audit_backlog_limit messages in
-			    RAM until it is fully enabled by the userspace
-			    auditd.
+			1 | on - kernel audit is initialized and partially
+			    enabled, storing at most audit_backlog_limit
+			    messages in RAM until it is fully enabled by the
+			    userspace auditd.
 			Default: unset
 
 	audit_backlog_limit= [KNL] Set the audit queue size limit.

kernel/audit.c

@@ -1615,19 +1615,26 @@ static int __init audit_init(void)
 }
 postcore_initcall(audit_init);
 
-/* Process kernel command-line parameter at boot time.  audit=0 or audit=1. */
+/*
+ * Process kernel command-line parameter at boot time.
+ * audit={0|off} or audit={1|on}.
+ */
 static int __init audit_enable(char *str)
 {
-	long val;
-
-	if (kstrtol(str, 0, &val))
-		panic("audit: invalid 'audit' parameter value (%s)\n", str);
-	audit_default = (val ? AUDIT_ON : AUDIT_OFF);
+	if (!strcasecmp(str, "off") || !strcmp(str, "0"))
+		audit_default = AUDIT_OFF;
+	else if (!strcasecmp(str, "on") || !strcmp(str, "1"))
+		audit_default = AUDIT_ON;
+	else {
+		pr_err("audit: invalid 'audit' parameter value (%s)\n", str);
+		audit_default = AUDIT_ON;
+	}
 
 	if (audit_default == AUDIT_OFF)
 		audit_initialized = AUDIT_DISABLED;
 	if (audit_set_enabled(audit_default))
-		panic("audit: error setting audit state (%d)\n", audit_default);
+		pr_err("audit: error setting audit state (%d)\n",
+		       audit_default);
 
 	pr_info("%s\n", audit_default ?
 		"enabled (after initialization)" : "disabled (until reboot)");