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Date: Fri, 14 Jan 2022 17:35:18 -0500
From: Paul Moore <paul@...l-moore.com>
To: cuigaosheng <cuigaosheng1@...wei.com>
Cc: linux-audit@...hat.com, Xiujianfeng <xiujianfeng@...wei.com>,
wangweiyang <wangweiyang2@...wei.com>,
linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Flush the hold queue fall into an infinite loop.
On Thu, Jan 13, 2022 at 8:22 PM cuigaosheng <cuigaosheng1@...wei.com> wrote:
>
> I want to stop droping the logs into audit_hold_queue when the auditd is abnormal.it
> seems that this modification goes against the design intent of audit_hold_queue. its
> effect is similar to removing the audit_hold_queue.
>
> diff --git a/kernel/audit.c b/kernel/audit.c
> index 2a38cbaf3ddb..a8091b1a6587 100644
> --- a/kernel/audit.c
> +++ b/kernel/audit.c
> @@ -748,6 +748,7 @@ static int kauditd_send_queue(struct sock *sk, u32
> portid,
> (*err_hook)(skb);
> if (rc == -EAGAIN)
> rc = 0;
> + audit_default = AUDIT_OFF;
> /* continue to drain the queue */
> continue;
> } else
> @@ -755,6 +756,7 @@ static int kauditd_send_queue(struct sock *sk, u32
> portid,
> } else {
> /* skb sent - drop the extra reference and
> continue */
> consume_skb(skb);
> + audit_default = audit_enabled;
> failed = 0;
> }
> }
We can't toggle the audit_default setting like this, that isn't
acceptable upstream. I believe I have a fix, but I need to finish the
testing before I can post it for further review.
> 在 2022/1/13 23:22, Paul Moore 写道:
> > On Thu, Jan 13, 2022 at 6:57 AM cuigaosheng <cuigaosheng1@...wei.com> wrote:
> >> When we add "audit=1" to the cmdline, kauditd will take up 100%
> >> cpu resource.As follows:
> >>
> >> configurations:
> >> auditctl -b 64
> >> auditctl --backlog_wait_time 60000
> >> auditctl -r 0
> >> auditctl -w /root/aaa -p wrx
> >> shell scripts：
> >> #!/bin/bash
> >> i=0
> >> while [ $i -le 66 ]
> >> do
> >> touch /root/aaa
> >> let i++
> >> done
> >> mandatory conditions:
> >>
> >> add "audit=1" to the cmdline, and kill -19 pid_number(for /sbin/auditd).
> >>
> >> As long as we keep the audit_hold_queue non-empty, flush the hold queue will fall into
> >> an infinite loop.
> >>
> >> 713 static int kauditd_send_queue(struct sock *sk, u32 portid,
> >> 714 struct sk_buff_head *queue,
> >> 715 unsigned int retry_limit,
> >> 716 void (*skb_hook)(struct sk_buff *skb),
> >> 717 void (*err_hook)(struct sk_buff *skb))
> >> 718 {
> >> 719 int rc = 0;
> >> 720 struct sk_buff *skb;
> >> 721 unsigned int failed = 0;
> >> 722
> >> 723 /* NOTE: kauditd_thread takes care of all our locking, we just use
> >> 724 * the netlink info passed to us (e.g. sk and portid) */
> >> 725
> >> 726 while ((skb = skb_dequeue(queue))) {
> >> 727 /* call the skb_hook for each skb we touch */
> >> 728 if (skb_hook)
> >> 729 (*skb_hook)(skb);
> >> 730
> >> 731 /* can we send to anyone via unicast? */
> >> 732 if (!sk) {
> >> 733 if (err_hook)
> >> 734 (*err_hook)(skb);
> >> 735 continue;
> >> 736 }
> >> 737
> >> 738 retry:
> >> 739 /* grab an extra skb reference in case of error */
> >> 740 skb_get(skb);
> >> 741 rc = netlink_unicast(sk, skb, portid, 0);
> >> 742 if (rc < 0) {
> >> 743 /* send failed - try a few times unless fatal error */
> >> 744 if (++failed >= retry_limit ||
> >> 745 rc == -ECONNREFUSED || rc == -EPERM) {
> >> 746 sk = NULL;
> >> 747 if (err_hook)
> >> 748 (*err_hook)(skb);
> >> 749 if (rc == -EAGAIN)
> >> 750 rc = 0;
> >> 751 /* continue to drain the queue */
> >> 752 continue;
> >> 753 } else
> >> 754 goto retry;
> >> 755 } else {
> >> 756 /* skb sent - drop the extra reference and continue */
> >> 757 consume_skb(skb);
> >> 758 failed = 0;
> >> 759 }
> >> 760 }
> >> 761
> >> 762 return (rc >= 0 ? 0 : rc);
> >> 763 }
> >>
> >> When kauditd attempt to flush the hold queue, the queue parameter is &audit_hold_queue,
> >> and if netlink_unicast(line 741 ) return -EAGAIN, sk will be NULL(line 746), so err_hook(kauditd_rehold_skb)
> >> will be call. Then continue, skb_dequeue(line 726) and err_hook(kauditd_rehold_skb,line 733) will
> >> fall into an infinite loop.
> >> I don't really understand the value of audit_hold_queue, can we remove it, or stop droping the logs
> >> into kauditd_rehold_skb when the auditd is abnormal?
> > Thanks Gaosheng for the bug report, I'm able to reproduce this and I'm
> > looking into it now. I'll report back when I have a better idea of
> > the problem and a potential fix.
> >
--
paul moore
www.paul-moore.com
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