From 1fa1b758606e8ec927bc5ce571c9e53612ee5feb Mon Sep 17 00:00:00 2001
From: Steve Grubb <sgrubb@redhat.com>
Date: Tue, 17 Oct 2017 18:29:22 -0400
Subject: [PATCH] audit: Allow auditd to set pid to 0 to end auditing
Git-commit: 33e8a907804428109ce1d12301c3365d619cc4df
Patch-mainline: v4.15-rc1
References: bsc#1158094

The API to end auditing has historically been for auditd to set the
pid to 0. This patch restores that functionality.

See: https://github.com/linux-audit/audit-kernel/issues/69

Reviewed-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Steve Grubb <sgrubb@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Oscar Salvador <osalvador@suse.de>

---
 kernel/audit.c | 29 ++++++++++++++++-------------
 1 file changed, 16 insertions(+), 13 deletions(-)

diff --git a/kernel/audit.c b/kernel/audit.c
index a9ef1dfc5ac7..c30633a8a1f5 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -1190,25 +1190,28 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 			pid_t auditd_pid;
 			struct pid *req_pid = task_tgid(current);
 
-			/* sanity check - PID values must match */
-			if (new_pid != pid_vnr(req_pid))
+			/* sanity check - PID values must match. Setting
+			   pid to 0 is how auditd ends auditing. */
+			if (new_pid && (new_pid != pid_vnr(req_pid)))
 				return -EINVAL;
 
 			/* test the auditd connection */
 			audit_replace(req_pid);
 
 			auditd_pid = auditd_pid_vnr();
-			/* only the current auditd can unregister itself */
-			if ((!new_pid) && (new_pid != auditd_pid)) {
-				audit_log_config_change("audit_pid", new_pid,
-							auditd_pid, 0);
-				return -EACCES;
-			}
-			/* replacing a healthy auditd is not allowed */
-			if (auditd_pid && new_pid) {
-				audit_log_config_change("audit_pid", new_pid,
-							auditd_pid, 0);
-				return -EEXIST;
+			if (auditd_pid) {
+				/* replacing a healthy auditd is not allowed */
+				if (new_pid) {
+					audit_log_config_change("audit_pid", new_pid,
+								auditd_pid, 0);
+					return -EEXIST;
+				}
+				/* only the current auditd can unregister itself */
+				if (pid_vnr(req_pid) != auditd_pid) {
+					audit_log_config_change("audit_pid", new_pid,
+								auditd_pid, 0);
+					return -EACCES;
+				}
 			}
 
 			if (new_pid) {
-- 
2.23.0