linux-kernel - Re: [PATCH 0/2] fix the traced mt-exec deadlock

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Date:   Fri, 24 Feb 2017 17:03:54 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Aleksa Sarai <asarai@...e.com>,
        Andy Lutomirski <luto@...capital.net>,
        Attila Fazekas <afazekas@...hat.com>,
        Jann Horn <jann@...jh.net>, Kees Cook <keescook@...omium.org>,
        Michal Hocko <mhocko@...nel.org>,
        Ulrich Obergfell <uobergfe@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] fix the traced mt-exec deadlock

Eric,

our discussion was a bit confusing, and it seems that we did not
fully convince each other. So let me ask what do you finally think
about this fix.

Let me repeat. Even if I do not agree with some of your objections,
I do agree that 1/2 does not look nice and clean. And we seem to
agree that either way, with or without this fix, we need more changes
in this area.

But we need a simple and backportable fix for stable trees, say for
rhel7. This bug was reported many times, and this is the simplest
solution I was able to find.

Oleg.


On 02/13, Oleg Nesterov wrote:
>
> Hello,
>
> Lets finally fix this problem, it was reported several times. I still think that
> in the longer term we should (try to) rework the security hooks and (partially)
> revert this change, but this is not trivial and we need something backportable
> anyway.
>
> Eric, Jann, we already discussed this change. 1/2 is the same patch I suggested 3
> months ago except now it compiles and moves flush_signal_handlers() to de_thread().
>
> Both patches ask for subsequent cleanups, see the changelogs.
>
> Oleg.
>
>  arch/x86/ia32/ia32_aout.c |   3 ++
>  fs/binfmt_aout.c          |   3 ++
>  fs/binfmt_elf.c           |   6 ++-
>  fs/binfmt_elf_fdpic.c     |   4 ++
>  fs/binfmt_flat.c          |   3 ++
>  fs/exec.c                 | 128 +++++++++++++++++++++++-----------------------
>  include/linux/binfmts.h   |   1 +
>  kernel/exit.c             |   5 +-
>  kernel/signal.c           |  21 +++++---
>  9 files changed, 101 insertions(+), 73 deletions(-)