Messages in this thread | | | From | Paul Moore <> | Date | Fri, 14 Jan 2022 17:35:18 -0500 | Subject | Re: Flush the hold queue fall into an infinite loop. |
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On Thu, Jan 13, 2022 at 8:22 PM cuigaosheng <cuigaosheng1@huawei.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@huawei.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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