linux-kernel - [PATCH 0/2] Re: bpfilter causes a leftover kernel process

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Date:   Sat, 20 Oct 2018 19:39:55 +0200
From:   Olivier Brunel <jjk@...cky.com>
To:     Network Development <netdev@...r.kernel.org>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        "Luis R . Rodriguez" <mcgrof@...nel.org>,
        linux-kernel@...r.kernel.org,
        "David S . Miller" <davem@...emloft.net>,
        Olivier Brunel <jjk@...cky.com>
Subject: [PATCH 0/2] Re: bpfilter causes a leftover kernel process

On Tue, 16 Oct 2018 16:38:56 +0000
Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:

> On Wed, Sep 5, 2018 at 5:05 PM Olivier Brunel <jjk@...cky.com> wrote:
> >
> > You'll see in the end that systemd complains that it can't
> > unmount /oldroot (EBUSY), aka the root fs; and that's because of the
> > bpfilter helper, which wasn't killed because it's seen as a kernel
> > thread due to its empty command line and therefore not signaled.  
> 
> thanks for tracking it down.
> can somebody send a patch to give bpfilter non-empty cmdline?
> I think that would be a better fix than tweaking all pid1s.

So I'm not a kernel dev and this would be my first atttempt at a kernel patch,
but I did have a look and came up with the following patch(es) to fix this.
Hopefully I did things right.

It adds a default command line ("usermodehelper") to such processes, so any &
all such helpers will be seen as user process and not kernel threads, but
there's also the possibility to specify a command line to use, here
"bpfilter_umh"

Cheers,


Olivier Brunel (2):
  umh: Add command line to user mode helpers
  net: bpfilter: Set user mode helper's command line

 include/linux/umh.h          |  1 +
 kernel/umh.c                 | 16 ++++++++++++++--
 net/bpfilter/bpfilter_kern.c |  1 +
 3 files changed, 16 insertions(+), 2 deletions(-)

-- 
2.19.0