[PATCH] (1/2) new audit filter allows excluding messages by type (kernel)

[Dustin Kirkland]

Kernel patch is pretty simple, straightforward...

- Add a new, 5th filter called "exclude".
- And add a new field AUDIT_MSGTYPE.
- Define a new function audit_filter_exclude() that takes a message type
as input and examines all rules in the filter.  It returns '1' if the
message is to be excluded, and '0' otherwise.
- Call the audit_filter_exclude() function near the top of
audit_log_start() just after asserting audit_initialized.  If the
message type is not to be audited, return NULL very early, before doing
a lot of work.

Comments welcome.

:-Dustin



diff -urpN linux-2.6.14-rc4-audit_ops/include/linux/audit.h
linux-2.6.14-rc4-audit_ops-exclude/include/linux/audit.h
--- linux-2.6.14-rc4-audit_ops/include/linux/audit.h	2005-10-26 16:12:42.000000000 -0500
+++ linux-2.6.14-rc4-audit_ops-exclude/include/linux/audit.h	2005-10-31 15:51:02.000000000 -0600
@@ -81,8 +81,9 @@
 #define AUDIT_FILTER_ENTRY	0x02	/* Apply rule at syscall entry */
 #define AUDIT_FILTER_WATCH	0x03	/* Apply rule to file system watches */
 #define AUDIT_FILTER_EXIT	0x04	/* Apply rule at syscall exit */
+#define AUDIT_FILTER_EXCLUDE	0x05	/* Apply rule early, at audit_log_start */
 
-#define AUDIT_NR_FILTERS	5
+#define AUDIT_NR_FILTERS	6
 
 #define AUDIT_FILTER_PREPEND	0x10	/* Prepend to front of list */
 
@@ -121,6 +122,7 @@
 #define AUDIT_LOGINUID	9
 #define AUDIT_PERS	10
 #define AUDIT_ARCH	11
+#define AUDIT_MSGTYPE	12
 
 				/* These are ONLY useful when checking
 				 * at syscall exit time (AUDIT_AT_EXIT). */
@@ -265,6 +267,7 @@ extern int audit_sockaddr(int len, void 
 extern int audit_avc_path(struct dentry *dentry, struct vfsmount *mnt);
 extern void audit_signal_info(int sig, struct task_struct *t);
 extern int audit_filter_user(struct netlink_skb_parms *cb, int type);
+extern int audit_filter_exclude(int type);
 #else
 #define audit_alloc(t) ({ 0; })
 #define audit_free(t) do { ; } while (0)
diff -urpN linux-2.6.14-rc4-audit_ops/kernel/audit.c linux-2.6.14-rc4-audit_ops-exclude/kernel/audit.c
--- linux-2.6.14-rc4-audit_ops/kernel/audit.c	2005-10-21 12:35:50.000000000 -0500
+++ linux-2.6.14-rc4-audit_ops-exclude/kernel/audit.c	2005-11-01 16:01:57.000000000 -0600
@@ -659,6 +659,10 @@ struct audit_buffer *audit_log_start(str
 	if (!audit_initialized)
 		return NULL;
 
+	if (unlikely(audit_filter_exclude(type))) {
+		return NULL;
+	}
+
 	if (gfp_mask & __GFP_WAIT)
 		reserve = 0;
 	else
diff -urpN linux-2.6.14-rc4-audit_ops/kernel/auditsc.c linux-2.6.14-rc4-audit_ops-exclude/kernel/auditsc.c
--- linux-2.6.14-rc4-audit_ops/kernel/auditsc.c	2005-10-27 14:17:41.000000000 -0500
+++ linux-2.6.14-rc4-audit_ops-exclude/kernel/auditsc.c	2005-11-01 14:02:25.000000000 -0600
@@ -181,7 +181,8 @@ static struct list_head audit_filter_lis
 	LIST_HEAD_INIT(audit_filter_list[2]),
 	LIST_HEAD_INIT(audit_filter_list[3]),
 	LIST_HEAD_INIT(audit_filter_list[4]),
-#if AUDIT_NR_FILTERS != 5
+	LIST_HEAD_INIT(audit_filter_list[5]),
+#if AUDIT_NR_FILTERS != 6
 #error Fix audit_filter_list initialiser
 #endif
 };
@@ -663,6 +664,33 @@ int audit_filter_user(struct netlink_skb
 	return ret; /* Audit by default */
 }
 
+int audit_filter_exclude(int type)
+{
+	struct audit_entry *e;
+	int result = 0;
+	
+	rcu_read_lock();
+	list_for_each_entry_rcu(e, &audit_filter_list[AUDIT_FILTER_EXCLUDE], list) {
+		struct audit_rule *rule = &e->rule;
+		int i;
+		for (i = 0; i < rule->field_count; i++) {
+			u32 field  = rule->fields[i] & ~AUDIT_OPERATORS;
+			u32 op  = rule->fields[i] & AUDIT_OPERATORS;
+			u32 value  = rule->values[i];
+			if ( field == AUDIT_MSGTYPE ) {
+				result = audit_comparator(type, op, value); 
+				if (!result) {
+					rcu_read_unlock();
+					return result;
+				}
+			}
+		}
+	}
+	rcu_read_unlock();
+	return result;
+}
+
+
 /* This should be called with task_lock() held. */
 static inline struct audit_context *audit_get_context(struct task_struct *tsk,
 						      int return_valid,
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