audit: implement generic feature setting and retrieving

The audit_status structure was not designed with extensibility in mind.
Define a new AUDIT_SET_FEATURE message type which takes a new structure
of bits where things can be enabled/disabled/locked one at a time.  This
structure should be able to grow in the future while maintaining forward
and backward compatibility (based loosly on the ideas from capabilities
and prctl)

This does not actually add any features, but is just infrastructure to
allow new on/off types of audit system features.

Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Eric Paris <eparis@redhat.com>

1 files changed, 109 insertions, 0 deletions

diff --git a/kernel/audit.c b/kernel/audit.c
index 74550ff..29ee6a4 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -139,6 +139,15 @@ static struct task_struct *kauditd_task;
 static DECLARE_WAIT_QUEUE_HEAD(kauditd_wait);
 static DECLARE_WAIT_QUEUE_HEAD(audit_backlog_wait);
 
+static struct audit_features af = {.vers = AUDIT_FEATURE_VERSION,
+				   .mask = -1,
+				   .features = 0,
+				   .lock = 0,};
+
+static char *audit_feature_names[0] = {
+};
+
+
 /* Serialize requests from userspace. */
 DEFINE_MUTEX(audit_cmd_mutex);
 
@@ -583,6 +592,8 @@ static int audit_netlink_ok(struct sk_buff *skb, u16 msg_type)
 		return -EOPNOTSUPP;
 	case AUDIT_GET:
 	case AUDIT_SET:
+	case AUDIT_GET_FEATURE:
+	case AUDIT_SET_FEATURE:
 	case AUDIT_LIST_RULES:
 	case AUDIT_ADD_RULE:
 	case AUDIT_DEL_RULE:
@@ -627,6 +638,94 @@ static int audit_log_common_recv_msg(struct audit_buffer **ab, u16 msg_type)
 	return rc;
 }
 
+int is_audit_feature_set(int i)
+{
+	return af.features & AUDIT_FEATURE_TO_MASK(i);
+}
+
+
+static int audit_get_feature(struct sk_buff *skb)
+{
+	u32 seq;
+
+	seq = nlmsg_hdr(skb)->nlmsg_seq;
+
+	audit_send_reply(NETLINK_CB(skb).portid, seq, AUDIT_GET, 0, 0,
+			 &af, sizeof(af));
+
+	return 0;
+}
+
+static void audit_log_feature_change(int which, u32 old_feature, u32 new_feature,
+				     u32 old_lock, u32 new_lock, int res)
+{
+	struct audit_buffer *ab;
+
+	ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_FEATURE_CHANGE);
+	audit_log_format(ab, "feature=%s new=%d old=%d old_lock=%d new_lock=%d res=%d",
+			 audit_feature_names[which], !!old_feature, !!new_feature,
+			 !!old_lock, !!new_lock, res);
+	audit_log_end(ab);
+}
+
+static int audit_set_feature(struct sk_buff *skb)
+{
+	struct audit_features *uaf;
+	int i;
+
+	BUILD_BUG_ON(AUDIT_LAST_FEATURE + 1 > sizeof(audit_feature_names)/sizeof(audit_feature_names[0]));
+	uaf = nlmsg_data(nlmsg_hdr(skb));
+
+	/* if there is ever a version 2 we should handle that here */
+
+	for (i = 0; i <= AUDIT_LAST_FEATURE; i++) {
+		u32 feature = AUDIT_FEATURE_TO_MASK(i);
+		u32 old_feature, new_feature, old_lock, new_lock;
+
+		/* if we are not changing this feature, move along */
+		if (!(feature & uaf->mask))
+			continue;
+
+		old_feature = af.features & feature;
+		new_feature = uaf->features & feature;
+		new_lock = (uaf->lock | af.lock) & feature;
+		old_lock = af.lock & feature;
+
+		/* are we changing a locked feature? */
+		if ((af.lock & feature) && (new_feature != old_feature)) {
+			audit_log_feature_change(i, old_feature, new_feature,
+						 old_lock, new_lock, 0);
+			return -EPERM;
+		}
+	}
+	/* nothing invalid, do the changes */
+	for (i = 0; i <= AUDIT_LAST_FEATURE; i++) {
+		u32 feature = AUDIT_FEATURE_TO_MASK(i);
+		u32 old_feature, new_feature, old_lock, new_lock;
+
+		/* if we are not changing this feature, move along */
+		if (!(feature & uaf->mask))
+			continue;
+
+		old_feature = af.features & feature;
+		new_feature = uaf->features & feature;
+		old_lock = af.lock & feature;
+		new_lock = (uaf->lock | af.lock) & feature;
+
+		if (new_feature != old_feature)
+			audit_log_feature_change(i, old_feature, new_feature,
+						 old_lock, new_lock, 1);
+
+		if (new_feature)
+			af.features |= feature;
+		else
+			af.features &= ~feature;
+		af.lock |= new_lock;
+	}
+
+	return 0;
+}
+
 static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 {
 	u32			seq;
@@ -698,6 +797,16 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 		if (status_get->mask & AUDIT_STATUS_BACKLOG_LIMIT)
 			err = audit_set_backlog_limit(status_get->backlog_limit);
 		break;
+	case AUDIT_GET_FEATURE:
+		err = audit_get_feature(skb);
+		if (err)
+			return err;
+		break;
+	case AUDIT_SET_FEATURE:
+		err = audit_set_feature(skb);
+		if (err)
+			return err;
+		break;
 	case AUDIT_USER:
 	case AUDIT_FIRST_USER_MSG ... AUDIT_LAST_USER_MSG:
 	case AUDIT_FIRST_USER_MSG2 ... AUDIT_LAST_USER_MSG2: