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From:   ebiederm@xmission.com (Eric W. Biederman)
To:     Kees Cook <keescook@chromium.org>
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Date:   Tue, 10 Mar 2020 16:09:07 -0500
In-Reply-To: <202003101344.8777D43A44@keescook> (Kees Cook's message of "Tue,
        10 Mar 2020 13:47:51 -0700")
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Subject: Re: [PATCH v2 4/5] exec: Move exec_mmap right after de_thread in flush_old_exec
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Kees Cook <keescook@chromium.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