linux-kernel - [PATCH 0/5] Infrastructure to allow fixing exec deadlocks

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Message-ID: <87v9ne5y4y.fsf_-_@x220.int.ebiederm.org>
Date:   Sun, 08 Mar 2020 16:34:37 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Bernd Edlinger <bernd.edlinger@...mail.de>
Cc:     Christian Brauner <christian.brauner@...ntu.com>,
        Kees Cook <keescook@...omium.org>,
        Jann Horn <jannh@...gle.com>, Jonathan Corbet <corbet@....net>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Oleg Nesterov <oleg@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Andrei Vagin <avagin@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        "Peter Zijlstra \(Intel\)" <peterz@...radead.org>,
        Yuyang Du <duyuyang@...il.com>,
        David Hildenbrand <david@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Anshuman Khandual <anshuman.khandual@....com>,
        David Howells <dhowells@...hat.com>,
        James Morris <jamorris@...ux.microsoft.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Christian Kellner <christian@...lner.me>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Aleksa Sarai <cyphar@...har.com>,
        "Dmitry V. Levin" <ldv@...linux.org>,
        "linux-doc\@vger.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-fsdevel\@vger.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-mm\@kvack.org" <linux-mm@...ck.org>,
        "stable\@vger.kernel.org" <stable@...r.kernel.org>,
        "linux-api\@vger.kernel.org" <linux-api@...r.kernel.org>
Subject: [PATCH 0/5] Infrastructure to allow fixing exec deadlocks


Bernd, everyone

This is how I think the infrastructure change should look that makes way
for fixing this issue.

- Cleanup and reorder the code so code that can potentially wait
  indefinitely for userspace comes at the beginning for flush_old_exec.
- Add a new mutex and take it after we have passed any potential
  indefinite waits for userspace.

Then I think it is just going through the existing users of
cred_guard_mutex and fixing them to use the new one.

There really aren't that many users of cred_guard_mutex so we should be
able to get through the easy ones fairly quickly.  And anything that
isn't easy we can wait until we have a good fix.

The users of cred_guard_mutex that I saw were:
    fs/proc/base.c:
       proc_pid_attr_write
       do_io_accounting
       proc_pid_stack
       proc_pid_syscall
       proc_pid_personality
    
    perf_event_open
    mm_access
    kcmp
    pidfd_fget
    seccomp_set_mode_filter

Bernd I think I have addressed the issues you pointed out in v1.
Please let me know if you see anything else.

Eric W. Biederman (5):
      exec: Only compute current once in flush_old_exec
      exec: Factor unshare_sighand out of de_thread and call it separately
      exec: Move cleanup of posix timers on exec out of de_thread
      exec: Move exec_mmap right after de_thread in flush_old_exec
      exec: Add a exec_update_mutex to replace cred_guard_mutex

 fs/exec.c                    | 65 ++++++++++++++++++++++++++++++--------------
 include/linux/sched/signal.h |  9 +++++-
 init/init_task.c             |  1 +
 kernel/fork.c                |  1 +
 4 files changed, 54 insertions(+), 22 deletions(-)