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Commit f09ac9db authored by Eric Paris's avatar Eric Paris Committed by Al Viro
Browse files

Audit: stop deadlock from signals under load 



A deadlock is possible between kauditd and auditd under load if auditd
receives a signal.  When auditd receives a signal it sends a netlink
message to the kernel asking for information about the sender of the
signal.  In that same context the audit system will attempt to send a
netlink message back to the userspace auditd.  If kauditd has already
filled the socket buffer (see netlink_attachskb()) auditd will now put
itself to sleep waiting for room to send the message.  Since auditd is
responsible for draining that socket we have a deadlock.  The fix, since
the response from the kernel does not need to be synchronous is to send
the signal information back to auditd in a separate thread.  And thus
auditd can continue to drain the audit queue normally.

Signed-off-by: default avatarEric Paris <eparis@redhat.com>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent f3d357b0

kernel/audit.c

+35 −5
Original line number Diff line number Diff line
@@ -156,6 +156,11 @@ struct audit_buffer { 
	gfp_t		     gfp_mask;

};



struct audit_reply {

	int pid;

	struct sk_buff *skb;

};



static void audit_set_pid(struct audit_buffer *ab, pid_t pid)

{

	if (ab) {
@@ -528,6 +533,19 @@ struct sk_buff *audit_make_reply(int pid, int seq, int type, int done, 
	return NULL;

}



static int audit_send_reply_thread(void *arg)

{

	struct audit_reply *reply = (struct audit_reply *)arg;



	mutex_lock(&audit_cmd_mutex);

	mutex_unlock(&audit_cmd_mutex);



	/* Ignore failure. It'll only happen if the sender goes away,

	   because our timeout is set to infinite. */

	netlink_unicast(audit_sock, reply->skb, reply->pid, 0);

	kfree(reply);

	return 0;

}

/**

 * audit_send_reply - send an audit reply message via netlink

 * @pid: process id to send reply to
@@ -545,13 +563,25 @@ void audit_send_reply(int pid, int seq, int type, int done, int multi, 
		      void *payload, int size)

{

	struct sk_buff *skb;

	struct task_struct *tsk;

	struct audit_reply *reply = kmalloc(sizeof(struct audit_reply),

					    GFP_KERNEL);



	if (!reply)

		return;



	skb = audit_make_reply(pid, seq, type, done, multi, payload, size);

	if (!skb)

		return;

	/* Ignore failure. It'll only happen if the sender goes away,

	   because our timeout is set to infinite. */

	netlink_unicast(audit_sock, skb, pid, 0);

	return;



	reply->pid = pid;

	reply->skb = skb;



	tsk = kthread_run(audit_send_reply_thread, reply, "audit_send_reply");

	if (IS_ERR(tsk)) {

		kfree(reply);

		kfree_skb(skb);

	}

}



/*