AUDIT: Optimise the audit-disabled case for discarding user messages

Also exempt USER_AVC message from being discarded to preserve 
existing behaviour for SE Linux.
Signed-off-by: David Woodhouse <dwmw2@infradead.org>

include/linux/audit.h

@@ -51,7 +51,8 @@
 #define AUDIT_WATCH_LIST	1009	/* List all file/dir watches */
 #define AUDIT_SIGNAL_INFO	1010	/* Get info about sender of signal to auditd */
 
-#define AUDIT_FIRST_USER_MSG	1100	/* Userspace messages uninteresting to kernel */
+#define AUDIT_FIRST_USER_MSG	1100	/* Userspace messages mostly uninteresting to kernel */
+#define AUDIT_USER_AVC		1107	/* We filter this differently */
 #define AUDIT_LAST_USER_MSG	1199
  
 #define AUDIT_DAEMON_START      1200    /* Daemon startup record */
@@ -235,7 +236,7 @@ extern int audit_socketcall(int nargs, unsigned long *args);
 extern int audit_sockaddr(int len, void *addr);
 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 task_struct *tsk, int type);
+extern int audit_filter_user(int pid, int type);
 #else
 #define audit_alloc(t) ({ 0; })
 #define audit_free(t) do { ; } while (0)
@@ -252,7 +253,7 @@ extern int audit_filter_user(struct task_struct *tsk, int type);
 #define audit_sockaddr(len, addr) ({ 0; })
 #define audit_avc_path(dentry, mnt) ({ 0; })
 #define audit_signal_info(s,t) do { ; } while (0)
-#define audit_filter_user(struct ({ 1; })
+#define audit_filter_user(p,t) ({ 1; })
 #endif
 
 #ifdef CONFIG_AUDIT

kernel/audit.c

@@ -429,25 +429,21 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 		break;
 	case AUDIT_USER:
 	case AUDIT_FIRST_USER_MSG...AUDIT_LAST_USER_MSG:
-		read_lock(&tasklist_lock);
-		tsk = find_task_by_pid(pid);
-		if (tsk)
-			get_task_struct(tsk);
-		read_unlock(&tasklist_lock);
-		if (!tsk)
-			return -ESRCH;
-
-		if (audit_enabled && audit_filter_user(tsk, msg_type)) {
-			    ab = audit_log_start(NULL, msg_type);
-			    if (ab) {
-				    audit_log_format(ab,
-						     "user pid=%d uid=%u auid=%u msg='%.1024s'",
-						     pid, uid, loginuid, (char *)data);
-				    audit_set_pid(ab, pid);
-				    audit_log_end(ab);
-			    }
+		if (!audit_enabled && msg_type != AUDIT_USER_AVC)
+			return 0;
+
+		err = audit_filter_user(pid, msg_type);
+		if (err == 1) {
+			err = 0;
+			ab = audit_log_start(NULL, msg_type);
+			if (ab) {
+				audit_log_format(ab,
+						 "user pid=%d uid=%u auid=%u msg='%.1024s'",
+						 pid, uid, loginuid, (char *)data);
+				audit_set_pid(ab, pid);
+				audit_log_end(ab);
+			}
 		}
-		put_task_struct(tsk);
 		break;
 	case AUDIT_ADD:
 	case AUDIT_DEL:

kernel/auditsc.c

@@ -530,22 +530,33 @@ static enum audit_state audit_filter_syscall(struct task_struct *tsk,
 	return AUDIT_BUILD_CONTEXT;
 }
 
-int audit_filter_user(struct task_struct *tsk, int type)
+int audit_filter_user(int pid, int type)
 {
+	struct task_struct *tsk;
 	struct audit_entry *e;
 	enum audit_state   state;
+	int ret = 1;
 
-	if (audit_pid && tsk->pid == audit_pid)
-		return AUDIT_DISABLED;
+	read_lock(&tasklist_lock);
+	tsk = find_task_by_pid(pid);
+	if (tsk)
+		get_task_struct(tsk);
+	read_unlock(&tasklist_lock);
+
+	if (!tsk)
+		return -ESRCH;
 
 	rcu_read_lock();
 	list_for_each_entry_rcu(e, &audit_filter_list[AUDIT_FILTER_USER], list) {
 		if (audit_filter_rules(tsk, &e->rule, NULL, &state)) {
-			rcu_read_unlock();
-			return state != AUDIT_DISABLED;
+			if (state == AUDIT_DISABLED)
+				ret = 0;
+			break;
 		}
 	}
 	rcu_read_unlock();
+	put_task_struct(tsk);
+
 	return 1; /* Audit by default */
 
 }