audit: make sure we don't let the retry queue grow without bounds

The retry queue is intended to provide a temporary buffer in the case
of transient errors when communicating with auditd, it is not meant
as a long life queue, that functionality is provided by the hold
queue.

This patch fixes a problem identified by Seth where the retry queue
could grow uncontrollably if an auditd instance did not connect to
the kernel to drain the queues.  This commit fixes this by doing the
following:

* Make sure we always call auditd_reset() if we decide the connection
with audit is really dead.  There were some cases in
kauditd_hold_skb() where we did not reset the connection, this patch
relocates the reset calls to kauditd_thread() so all the error
conditions are caught and the connection reset.  As a side effect,
this means we could move auditd_reset() and get rid of the forward
definition at the top of kernel/audit.c.

* We never checked the status of the auditd connection when
processing the main audit queue which meant that the retry queue
could grow unchecked.  This patch adds a call to auditd_reset()
after the main queue has been processed if auditd is not connected,
the auditd_reset() call will make sure the retry and hold queues are
correctly managed/flushed so that the retry queue remains reasonable.

Cc: <stable@vger.kernel.org> # 4.10.x-: 5b52330bReported-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

kernel/audit.c

@@ -160,7 +160,6 @@ static LIST_HEAD(audit_freelist);
 
 /* queue msgs to send via kauditd_task */
 static struct sk_buff_head audit_queue;
-static void kauditd_hold_skb(struct sk_buff *skb);
 /* queue msgs due to temporary unicast send problems */
 static struct sk_buff_head audit_retry_queue;
 /* queue msgs waiting for new auditd connection */
@@ -453,30 +452,6 @@ static void auditd_set(int pid, u32 portid, struct net *net)
 	spin_unlock_irqrestore(&auditd_conn.lock, flags);
 }
 
-/**
- * auditd_reset - Disconnect the auditd connection
- *
- * Description:
- * Break the auditd/kauditd connection and move all the queued records into the
- * hold queue in case auditd reconnects.
- */
-static void auditd_reset(void)
-{
-	struct sk_buff *skb;
-
-	/* if it isn't already broken, break the connection */
-	rcu_read_lock();
-	if (auditd_conn.pid)
-		auditd_set(0, 0, NULL);
-	rcu_read_unlock();
-
-	/* flush all of the main and retry queues to the hold queue */
-	while ((skb = skb_dequeue(&audit_retry_queue)))
-		kauditd_hold_skb(skb);
-	while ((skb = skb_dequeue(&audit_queue)))
-		kauditd_hold_skb(skb);
-}
-
 /**
  * kauditd_print_skb - Print the audit record to the ring buffer
  * @skb: audit record
@@ -505,9 +480,6 @@ static void kauditd_rehold_skb(struct sk_buff *skb)
 {
 	/* put the record back in the queue at the same place */
 	skb_queue_head(&audit_hold_queue, skb);
-
-	/* fail the auditd connection */
-	auditd_reset();
 }
 
 /**
@@ -544,9 +516,6 @@ static void kauditd_hold_skb(struct sk_buff *skb)
 	/* we have no other options - drop the message */
 	audit_log_lost("kauditd hold queue overflow");
 	kfree_skb(skb);
-
-	/* fail the auditd connection */
-	auditd_reset();
 }
 
 /**
@@ -566,6 +535,30 @@ static void kauditd_retry_skb(struct sk_buff *skb)
 	skb_queue_tail(&audit_retry_queue, skb);
 }
 
+/**
+ * auditd_reset - Disconnect the auditd connection
+ *
+ * Description:
+ * Break the auditd/kauditd connection and move all the queued records into the
+ * hold queue in case auditd reconnects.
+ */
+static void auditd_reset(void)
+{
+	struct sk_buff *skb;
+
+	/* if it isn't already broken, break the connection */
+	rcu_read_lock();
+	if (auditd_conn.pid)
+		auditd_set(0, 0, NULL);
+	rcu_read_unlock();
+
+	/* flush all of the main and retry queues to the hold queue */
+	while ((skb = skb_dequeue(&audit_retry_queue)))
+		kauditd_hold_skb(skb);
+	while ((skb = skb_dequeue(&audit_queue)))
+		kauditd_hold_skb(skb);
+}
+
 /**
  * auditd_send_unicast_skb - Send a record via unicast to auditd
  * @skb: audit record
@@ -758,6 +751,7 @@ static int kauditd_thread(void *dummy)
 					NULL, kauditd_rehold_skb);
 		if (rc < 0) {
 			sk = NULL;
+			auditd_reset();
 			goto main_queue;
 		}
 
@@ -767,6 +761,7 @@ static int kauditd_thread(void *dummy)
 					NULL, kauditd_hold_skb);
 		if (rc < 0) {
 			sk = NULL;
+			auditd_reset();
 			goto main_queue;
 		}
 
@@ -775,16 +770,18 @@ static int kauditd_thread(void *dummy)
 		 * unicast, dump failed record sends to the retry queue; if
 		 * sk == NULL due to previous failures we will just do the
 		 * multicast send and move the record to the retry queue */
-		kauditd_send_queue(sk, portid, &audit_queue, 1,
-				   kauditd_send_multicast_skb,
-				   kauditd_retry_skb);
+		rc = kauditd_send_queue(sk, portid, &audit_queue, 1,
+					kauditd_send_multicast_skb,
+					kauditd_retry_skb);
+		if (sk == NULL || rc < 0)
+			auditd_reset();
+		sk = NULL;
 
 		/* drop our netns reference, no auditd sends past this line */
 		if (net) {
 			put_net(net);
 			net = NULL;
 		}
-		sk = NULL;
 
 		/* we have processed all the queues so wake everyone */
 		wake_up(&audit_backlog_wait);