linux-kernel - Re: [PATCH v2 4/5] exec: Move exec_mmap right after de_thread in flush_old

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Message-ID: <87r1xzrk7g.fsf@x220.int.ebiederm.org>
Date:   Tue, 10 Mar 2020 16:09:07 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Kees Cook <keescook@...omium.org>
Cc:     Bernd Edlinger <bernd.edlinger@...mail.de>,
        Christian Brauner <christian.brauner@...ntu.com>,
        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: Re: [PATCH v2 4/5] exec: Move exec_mmap right after de_thread in flush_old_exec

Kees Cook <keescook@...omium.org> writes:

> On Sun, Mar 08, 2020 at 04:38:00PM -0500, Eric W. Biederman wrote:
>> Futher this consolidates all of the possible indefinite waits for
>> userspace together at the top of flush_old_exec.  The possible wait
>> for a ptracer on PTRACE_EVENT_EXIT, the possible wait for a page fault
>> to be resolved in clear_child_tid, and the possible wait for a page
>> fault in exit_robust_list.
>
> I forgot to mention, just as a point of clarity, there are lots of
> other page faults possible, but they're _before_ flush_old_exec()
> (i.e. all the copy_strings() calls). Is it worth clarifying this to
> "before or at the top of flush_old_exec()" or do you mean something
> else? (And as always: perhaps expand flush_old_exec()'s comment to
> describe the newly intended state.)

Yes.  Before or at the start of flush_old_exec where the mutex
is taken.  That is the point.  I will see if I can come up with
and appropriate comment.

Eric