[PATCH] audit config lockdown

The following patch adds a new mode to the audit system. It uses the
audit_enabled config option to introduce the idea of audit enabled, but
configuration is immutable. Any attempt to change the configuration
while in this mode is audited. To change the audit rules, you'd need to
reboot the machine.

To use this option, you'd need a modified version of auditctl and use "-e 2".
This is intended to go at the end of the audit.rules file for people that
want an immutable configuration.

This patch also adds "res=" to a number of configuration commands that did not
have it before.
Signed-off-by: Steve Grubb <sgrubb@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

kernel/audit.c

@@ -2,7 +2,7 @@
  * Gateway between the kernel (e.g., selinux) and the user-space audit daemon.
  * System-call specific features have moved to auditsc.c
  *
- * Copyright 2003-2004 Red Hat Inc., Durham, North Carolina.
+ * Copyright 2003-2007 Red Hat Inc., Durham, North Carolina.
  * All Rights Reserved.
  *
  * This program is free software; you can redistribute it and/or modify
@@ -65,7 +65,9 @@
  * (Initialization happens after skb_init is called.) */
 static int	audit_initialized;
 
-/* No syscall auditing will take place unless audit_enabled != 0. */
+/* 0 - no auditing
+ * 1 - auditing enabled
+ * 2 - auditing enabled and configuration is locked/unchangeable. */
 int		audit_enabled;
 
 /* Default state when kernel boots without any parameters. */
@@ -239,102 +241,150 @@ void audit_log_lost(const char *message)
 
 static int audit_set_rate_limit(int limit, uid_t loginuid, u32 sid)
 {
-	int old	= audit_rate_limit;
+	int res, rc = 0, old = audit_rate_limit;
+
+	/* check if we are locked */
+	if (audit_enabled == 2)
+		res = 0;
+	else
+		res = 1;
 
 	if (sid) {
 		char *ctx = NULL;
 		u32 len;
-		int rc;
-		if ((rc = selinux_sid_to_string(sid, &ctx, &len)))
-			return rc;
-		else
+		if ((rc = selinux_sid_to_string(sid, &ctx, &len)) == 0) {
 			audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
-				"audit_rate_limit=%d old=%d by auid=%u subj=%s",
-				limit, old, loginuid, ctx);
-		kfree(ctx);
-	} else
-		audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
-			"audit_rate_limit=%d old=%d by auid=%u",
-			limit, old, loginuid);
-	audit_rate_limit = limit;
-	return 0;
+				"audit_rate_limit=%d old=%d by auid=%u"
+				" subj=%s res=%d",
+				limit, old, loginuid, ctx, res);
+			kfree(ctx);
+		} else
+			res = 0; /* Something weird, deny request */
+	}
+	audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
+		"audit_rate_limit=%d old=%d by auid=%u res=%d",
+		limit, old, loginuid, res);
+
+	/* If we are allowed, make the change */
+	if (res == 1)
+		audit_rate_limit = limit;
+	/* Not allowed, update reason */
+	else if (rc == 0)
+		rc = -EPERM;
+	return rc;
 }
 
 static int audit_set_backlog_limit(int limit, uid_t loginuid, u32 sid)
 {
-	int old	= audit_backlog_limit;
+	int res, rc = 0, old = audit_backlog_limit;
+
+	/* check if we are locked */
+	if (audit_enabled == 2)
+		res = 0;
+	else
+		res = 1;
 
 	if (sid) {
 		char *ctx = NULL;
 		u32 len;
-		int rc;
-		if ((rc = selinux_sid_to_string(sid, &ctx, &len)))
-			return rc;
-		else
+		if ((rc = selinux_sid_to_string(sid, &ctx, &len)) == 0) {
 			audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
-			    "audit_backlog_limit=%d old=%d by auid=%u subj=%s",
-				limit, old, loginuid, ctx);
-		kfree(ctx);
-	} else
-		audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
-			"audit_backlog_limit=%d old=%d by auid=%u",
-			limit, old, loginuid);
-	audit_backlog_limit = limit;
-	return 0;
+				"audit_backlog_limit=%d old=%d by auid=%u"
+				" subj=%s res=%d",
+				limit, old, loginuid, ctx, res);
+			kfree(ctx);
+		} else
+			res = 0; /* Something weird, deny request */
+	}
+	audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
+		"audit_backlog_limit=%d old=%d by auid=%u res=%d",
+		limit, old, loginuid, res);
+
+	/* If we are allowed, make the change */
+	if (res == 1)
+		audit_backlog_limit = limit;
+	/* Not allowed, update reason */
+	else if (rc == 0)
+		rc = -EPERM;
+	return rc;
 }
 
 static int audit_set_enabled(int state, uid_t loginuid, u32 sid)
 {
-	int old = audit_enabled;
+	int res, rc = 0, old = audit_enabled;
 
-	if (state != 0 && state != 1)
+	if (state < 0 || state > 2)
 		return -EINVAL;
 
+	/* check if we are locked */
+	if (audit_enabled == 2)
+		res = 0;
+	else
+		res = 1;
+
 	if (sid) {
 		char *ctx = NULL;
 		u32 len;
-		int rc;
-		if ((rc = selinux_sid_to_string(sid, &ctx, &len)))
-			return rc;
-		else
+		if ((rc = selinux_sid_to_string(sid, &ctx, &len)) == 0) {
 			audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
-				"audit_enabled=%d old=%d by auid=%u subj=%s",
-				state, old, loginuid, ctx);
-		kfree(ctx);
-	} else
-		audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
-			"audit_enabled=%d old=%d by auid=%u",
-			state, old, loginuid);
-	audit_enabled = state;
-	return 0;
+				"audit_enabled=%d old=%d by auid=%u"
+				" subj=%s res=%d",
+				state, old, loginuid, ctx, res);
+			kfree(ctx);
+		} else
+			res = 0; /* Something weird, deny request */
+	}
+	audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
+		"audit_enabled=%d old=%d by auid=%u res=%d",
+		state, old, loginuid, res);
+
+	/* If we are allowed, make the change */
+	if (res == 1)
+		audit_enabled = state;
+	/* Not allowed, update reason */
+	else if (rc == 0)
+		rc = -EPERM;
+	return rc;
 }
 
 static int audit_set_failure(int state, uid_t loginuid, u32 sid)
 {
-	int old = audit_failure;
+	int res, rc = 0, old = audit_failure;
 
 	if (state != AUDIT_FAIL_SILENT
 	    && state != AUDIT_FAIL_PRINTK
 	    && state != AUDIT_FAIL_PANIC)
 		return -EINVAL;
 
+	/* check if we are locked */
+	if (audit_enabled == 2)
+		res = 0;
+	else
+		res = 1;
+
 	if (sid) {
 		char *ctx = NULL;
 		u32 len;
-		int rc;
-		if ((rc = selinux_sid_to_string(sid, &ctx, &len)))
-			return rc;
-		else
+		if ((rc = selinux_sid_to_string(sid, &ctx, &len)) == 0) {
 			audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
-				"audit_failure=%d old=%d by auid=%u subj=%s",
-				state, old, loginuid, ctx);
-		kfree(ctx);
-	} else
-		audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
-			"audit_failure=%d old=%d by auid=%u",
-			state, old, loginuid);
-	audit_failure = state;
-	return 0;
+				"audit_failure=%d old=%d by auid=%u"
+				" subj=%s res=%d",
+				state, old, loginuid, ctx, res);
+			kfree(ctx);
+		} else
+			res = 0; /* Something weird, deny request */
+	}
+	audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
+		"audit_failure=%d old=%d by auid=%u res=%d",
+		state, old, loginuid, res);
+
+	/* If we are allowed, make the change */
+	if (res == 1)
+		audit_failure = state;
+	/* Not allowed, update reason */
+	else if (rc == 0)
+		rc = -EPERM;
+	return rc;
 }
 
 static int kauditd_thread(void *dummy)
@@ -599,6 +649,30 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 	case AUDIT_DEL:
 		if (nlmsg_len(nlh) < sizeof(struct audit_rule))
 			return -EINVAL;
+		if (audit_enabled == 2) {
+			ab = audit_log_start(NULL, GFP_KERNEL,
+					AUDIT_CONFIG_CHANGE);
+			if (ab) {
+				audit_log_format(ab,
+						 "pid=%d uid=%u auid=%u",
+						 pid, uid, loginuid);
+				if (sid) {
+					if (selinux_sid_to_string(
+							sid, &ctx, &len)) {
+						audit_log_format(ab,
+							" ssid=%u", sid);
+						/* Maybe call audit_panic? */
+					} else
+						audit_log_format(ab,
+							" subj=%s", ctx);
+					kfree(ctx);
+				}
+				audit_log_format(ab, " audit_enabled=%d res=0",
+					audit_enabled);
+				audit_log_end(ab);
+			}
+			return -EPERM;
+		}
 		/* fallthrough */
 	case AUDIT_LIST:
 		err = audit_receive_filter(nlh->nlmsg_type, NETLINK_CB(skb).pid,
@@ -609,6 +683,30 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 	case AUDIT_DEL_RULE:
 		if (nlmsg_len(nlh) < sizeof(struct audit_rule_data))
 			return -EINVAL;
+		if (audit_enabled == 2) {
+			ab = audit_log_start(NULL, GFP_KERNEL,
+					AUDIT_CONFIG_CHANGE);
+			if (ab) {
+				audit_log_format(ab,
+						 "pid=%d uid=%u auid=%u",
+						 pid, uid, loginuid);
+				if (sid) {
+					if (selinux_sid_to_string(
+							sid, &ctx, &len)) {
+						audit_log_format(ab,
+							" ssid=%u", sid);
+						/* Maybe call audit_panic? */
+					} else
+						audit_log_format(ab,
+							" subj=%s", ctx);
+					kfree(ctx);
+				}
+				audit_log_format(ab, " audit_enabled=%d res=0",
+					audit_enabled);
+				audit_log_end(ab);
+			}
+			return -EPERM;
+		}
 		/* fallthrough */
 	case AUDIT_LIST_RULES:
 		err = audit_receive_filter(nlh->nlmsg_type, NETLINK_CB(skb).pid,