From: Paul Moore <paul@paul-moore.com>
Date: Mon, 13 Dec 2021 15:45:20 -0500
Subject: [PATCH] audit: ensure userspace is penalized the same as the kernel
 when under pressure
Git-commit: 8f110f530635af44fff1f4ee100ecef0bac62510
References: bsc#1204514
Patch-mainline: v5.16-rc6

Due to the audit control mutex necessary for serializing audit
userspace messages we haven't been able to block/penalize userspace
processes that attempt to send audit records while the system is
under audit pressure.  The result is that privileged userspace
applications have a priority boost with respect to audit as they are
not bound by the same audit queue throttling as the other tasks on
the system.

This patch attempts to restore some balance to the system when under
audit pressure by blocking these privileged userspace tasks after
they have finished their audit processing, and dropped the audit
control mutex, but before they return to userspace.

Reported-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Tested-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Reviewed-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
Acked-by: Enzo Matsumiya <ematsumiya@suse.de>
---
 kernel/audit.c |   18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -1477,6 +1477,20 @@ static void audit_receive(struct sk_buff
 		nlh = nlmsg_next(nlh, &len);
 	}
 	mutex_unlock(&audit_cmd_mutex);
+
+	/* can't block with the ctrl lock, so penalize the sender now */
+	if (audit_backlog_limit &&
+	    (skb_queue_len(&audit_queue) > audit_backlog_limit)) {
+		DECLARE_WAITQUEUE(wait, current);
+
+		/* wake kauditd to try and flush the queue */
+		wake_up_interruptible(&kauditd_wait);
+
+		add_wait_queue_exclusive(&audit_backlog_wait, &wait);
+		set_current_state(TASK_UNINTERRUPTIBLE);
+		schedule_timeout(audit_backlog_wait_time);
+		remove_wait_queue(&audit_backlog_wait, &wait);
+	}
 }
 
 /* Run custom bind function on netlink socket group connect or bind requests. */
@@ -1706,7 +1720,9 @@ struct audit_buffer *audit_log_start(str
 	 *    task_tgid_vnr() since auditd_pid is set in audit_receive_msg()
 	 *    using a PID anchored in the caller's namespace
 	 * 2. generator holding the audit_cmd_mutex - we don't want to block
-	 *    while holding the mutex */
+	 *    while holding the mutex, although we do penalize the sender
+	 *    later in audit_receive() when it is safe to block
+	 */
 	if (!(auditd_test_task(current) ||
 	      (current == __mutex_owner(&audit_cmd_mutex)))) {
 		long stime = audit_backlog_wait_time;