Re: bpfilter blocks root unmount during shutdown

Andrei Borzenkov
2018-09-24T16:30:02Z

24.09.2018 16:20, Lennart Poettering пишет:
> On So, 23.09.18 10:38, Andrei Borzenkov (arvidjaar@gmail.com) wrote:
>
>> Dracut /shutdown script first tries to kill all processes still running
>> off old root. Unfortunately this fails for special user process that
>> runs bpfilter because it does not include reference to /oldroot in
>> places where dracut looks for in kilall_proc_mountpoint()
>
> Hmm, when we invoke the /shutdown executable we already executed our
> process killing spree as part of systemd-shutdown. How come your
> processes even survive that long?

p = procfs_file_alloca(pid, "cmdline");
f = fopen(p, "re");
if (!f)
return true; /* not really, but has the desired effect */

count = fread(&c, 1, 1, f);

/* Kernel threads have an empty cmdline */
if (count <= 0)
return true;

This process is spawned as special kernel thread, even though it is
otherwise normal user process.

net/bpfilter/bpfilter_kern.c:load_umh():

/* fork usermode process */
err = fork_usermode_blob(&bpfilter_umh_start,
&bpfilter_umh_end - &bpfilter_umh_start,
&info);
if (err)
return err;
pr_info("Loaded bpfilter_umh pid %d\n", info.pid);