Greetings audit mailing list, I've got an AWS instance running an Amazon Linux kernel, 4.9.77-31.58.amzn1.x86_64 with the base OS being CentOS 6. The instance had one program with the audit handle (Proprietary closed source software, Lacework agent). I installed and started OSQuery which attempted to acquire the audit handle. I'm unsure if osquery was successful or not, because I was unable to ssh in to the server to investigate. I ended up having to restart the instance. Almost immediately after starting osquery, sshd got stuck in D state. syslog has a hung task warning and backtrace that provides some information:
Jun 14 20:54:53 packer_default-10-180-21-138 kernel: [12191989.724101] > INFO: task sshd:1840 blocked for more than 10 seconds. Jun 14 20:54:53 packer_default-10-180-21-138 kernel: [12191989.727856] > Tainted: G E 4.9.77-31.58.amzn1.x86_64 #1 Jun 14 20:54:53 packer_default-10-180-21-138 kernel: [12191989.731856] > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. Jun 14 20:54:53 packer_default-10-180-21-138 kernel: [12191989.736283] > sshd D 0 1840 1839 0x00000080 Jun 14 20:54:53 packer_default-10-180-21-138 kernel: [12191989.736287] > 0000000000000000 ffff8802025c6540 ffff88003684d940 ffff880205f3bb80 Jun 14 20:54:53 packer_default-10-180-21-138 kernel: [12191989.736290] > ffff8802072582c0 ffffc900049bfc60 ffffffff81556e62 0000000000000001 Jun 14 20:54:53 packer_default-10-180-21-138 kernel: [12191989.736292] > 004200ca00000001 ffff8802072582c0 0000000000000000 ffffffff81a65140 Jun 14 20:54:53 packer_default-10-180-21-138 kernel: [12191989.736295] Call > Trace: Jun 14 20:54:53 packer_default-10-180-21-138 kernel: [12191989.736302] > [<ffffffff81556e62>] ? __schedule+0x242/0x700 Jun 14 20:54:53 packer_default-10-180-21-138 kernel: [12191989.736304] > [<ffffffff8155734c>] schedule+0x2c/0x80 Jun 14 20:54:53 packer_default-10-180-21-138 kernel: [12191989.736306] > [<ffffffff815575ee>] schedule_preempt_disabled+0xe/0x10 Jun 14 20:54:53 packer_default-10-180-21-138 kernel: [12191989.736308] > [<ffffffff81558f05>] __mutex_lock_slowpath+0x95/0x110 Jun 14 20:54:53 packer_default-10-180-21-138 kernel: [12191989.736311] > [<ffffffff8147a6f8>] ? __alloc_skb+0x78/0x1e0 Jun 14 20:54:53 packer_default-10-180-21-138 kernel: [12191989.736313] > [<ffffffff81558f97>] mutex_lock+0x17/0x30 Jun 14 20:54:53 packer_default-10-180-21-138 kernel: [12191989.736316] > [<ffffffff811178bd>] audit_receive+0x1d/0x90 Jun 14 20:54:53 packer_default-10-180-21-138 kernel: [12191989.736319] > [<ffffffff814c4976>] netlink_unicast+0x176/0x220 Jun 14 20:54:53 packer_default-10-180-21-138 kernel: [12191989.736320] > [<ffffffff814c4cf6>] netlink_sendmsg+0x2d6/0x390 Jun 14 20:54:53 packer_default-10-180-21-138 kernel: [12191989.736323] > [<ffffffff814719fe>] sock_sendmsg+0x3e/0x50 Jun 14 20:54:53 packer_default-10-180-21-138 kernel: [12191989.736324] > [<ffffffff81471ead>] SYSC_sendto+0x11d/0x150 Jun 14 20:54:53 packer_default-10-180-21-138 kernel: [12191989.736327] > [<ffffffff8111c68b>] ? __audit_syscall_entry+0xbb/0x100 Jun 14 20:54:53 packer_default-10-180-21-138 kernel: [12191989.736330] > [<ffffffff81003478>] ? syscall_trace_enter+0x1c8/0x2c0 Jun 14 20:54:53 packer_default-10-180-21-138 kernel: [12191989.736332] > [<ffffffff814728ee>] SyS_sendto+0xe/0x10 Jun 14 20:54:53 packer_default-10-180-21-138 kernel: [12191989.736333] > [<ffffffff81003b09>] do_syscall_64+0x59/0xc0 Jun 14 20:54:53 packer_default-10-180-21-138 kernel: [12191989.736335] > [<ffffffff8155bd70>] entry_SYSCALL64_slow_path+0x25/0x25 I've been doing some reading (ex. https://www.redhat.com/archives/linux-audit/2016-February/msg00025.html ) and my understanding is that osquery should have been able to acquire the audit handle, trampling lacework's ("Last one wins"), but I don't have access to the Lacework code to know how it might handle that situation (I'm engaging their support separately). I also noticed the patch set for 4.17 seemed to include some changes around the code path in the backtrace. I'm trying to understand this behavior and determine if it's a bug, if said bug has already been fixed by a patch between 4.9.77 and 4.17, or that this issue is a lack of my understanding of the behavior of the audit system. It is surprising to me that an audit system related issue would result in sshd getting stuck in D state. Several other processes on the system continued running without incident. Processed launched out of cron also got stuck in D state. I would be grateful for some expert insight. If this isn't a bug and is a misunderstanding on my part, is there any way to configure the audit system such that an issue won't result in processes getting stuck in D state? Thanks, Preston Bennes
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