Merge tag 'audit-pr-20240105' of git://git.kernel.org/pub/scm/linux/kernel/git/pcmoore/audit

Pull audit updates from Paul Moore:
 "The audit updates are fairly minor with only two patches:

   - Send an audit ACK to userspace immediately upon receiving an auditd
     registration event as opposed to waiting until the registration has
     been fully processed and the audit backlog starts filling the
     netlink buffers.

     Sending the ACK earlier, as done here, is still safe as the
     operation should not fail at the point when the ACK is done, and
     doing so helps avoid the ACK being dropped in extreme situations.

   - Update the audit MAINTAINERS entry with additional information.

     There isn't anything in this update that should be new to regular
     contributors or list subscribers, but I'm pushing to start
     documenting our processes, conventions, etc. and this seems like an
     important part of that"

* tag 'audit-pr-20240105' of git://git.kernel.org/pub/scm/linux/kernel/git/pcmoore/audit:
  MAINTAINERS: update the audit entry
  audit: Send netlink ACK before setting connection in auditd_set

1 files changed, 24 insertions, 7 deletions

diff --git a/kernel/audit.c b/kernel/audit.c
index 16205dd29843..9c8e5f732c4c 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -487,15 +487,19 @@ static void auditd_conn_free(struct rcu_head *rcu)
  * @pid: auditd PID
  * @portid: auditd netlink portid
  * @net: auditd network namespace pointer
+ * @skb: the netlink command from the audit daemon
+ * @ack: netlink ack flag, cleared if ack'd here
  *
  * Description:
  * This function will obtain and drop network namespace references as
  * necessary.  Returns zero on success, negative values on failure.
  */
-static int auditd_set(struct pid *pid, u32 portid, struct net *net)
+static int auditd_set(struct pid *pid, u32 portid, struct net *net,
+		      struct sk_buff *skb, bool *ack)
 {
 	unsigned long flags;
 	struct auditd_connection *ac_old, *ac_new;
+	struct nlmsghdr *nlh;
 
 	if (!pid || !net)
 		return -EINVAL;
@@ -507,6 +511,13 @@ static int auditd_set(struct pid *pid, u32 portid, struct net *net)
 	ac_new->portid = portid;
 	ac_new->net = get_net(net);
 
+	/* send the ack now to avoid a race with the queue backlog */
+	if (*ack) {
+		nlh = nlmsg_hdr(skb);
+		netlink_ack(skb, nlh, 0, NULL);
+		*ack = false;
+	}
+
 	spin_lock_irqsave(&auditd_conn_lock, flags);
 	ac_old = rcu_dereference_protected(auditd_conn,
 					   lockdep_is_held(&auditd_conn_lock));
@@ -1200,7 +1211,8 @@ static int audit_replace(struct pid *pid)
 	return auditd_send_unicast_skb(skb);
 }
 
-static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
+static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
+			     bool *ack)
 {
 	u32			seq;
 	void			*data;
@@ -1293,7 +1305,8 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 				/* register a new auditd connection */
 				err = auditd_set(req_pid,
 						 NETLINK_CB(skb).portid,
-						 sock_net(NETLINK_CB(skb).sk));
+						 sock_net(NETLINK_CB(skb).sk),
+						 skb, ack);
 				if (audit_enabled != AUDIT_OFF)
 					audit_log_config_change("audit_pid",
 								new_pid,
@@ -1538,9 +1551,10 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
  * Parse the provided skb and deal with any messages that may be present,
  * malformed skbs are discarded.
  */
-static void audit_receive(struct sk_buff  *skb)
+static void audit_receive(struct sk_buff *skb)
 {
 	struct nlmsghdr *nlh;
+	bool ack;
 	/*
 	 * len MUST be signed for nlmsg_next to be able to dec it below 0
 	 * if the nlmsg_len was not aligned
@@ -1553,9 +1567,12 @@ static void audit_receive(struct sk_buff  *skb)
 
 	audit_ctl_lock();
 	while (nlmsg_ok(nlh, len)) {
-		err = audit_receive_msg(skb, nlh);
-		/* if err or if this message says it wants a response */
-		if (err || (nlh->nlmsg_flags & NLM_F_ACK))
+		ack = nlh->nlmsg_flags & NLM_F_ACK;
+		err = audit_receive_msg(skb, nlh, &ack);
+
+		/* send an ack if the user asked for one and audit_receive_msg
+		 * didn't already do it, or if there was an error. */
+		if (ack || err)
 			netlink_ack(skb, nlh, err, NULL);
 
 		nlh = nlmsg_next(nlh, &len);