linux-kernel - Re: [PATCH] ptrace: restore smp_rmb() in __ptrace_may

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Message-ID: <CAG48ez0Qu2CDhP4MPXTxxqLjTpk0X5ZubQQDfNRoP0JRrYt4Og@mail.gmail.com>
Date:   Wed, 29 May 2019 18:01:50 +0200
From:   Jann Horn <jannh@...gle.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Oleg Nesterov <oleg@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        David Howells <dhowells@...hat.com>,
        kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ptrace: restore smp_rmb() in __ptrace_may_access()

On Wed, May 29, 2019 at 5:59 PM Eric W. Biederman <ebiederm@...ssion.com> wrote:
> Jann Horn <jannh@...gle.com> writes:
>
> > Restore the read memory barrier in __ptrace_may_access() that was deleted
> > a couple years ago. Also add comments on this barrier and the one it pairs
> > with to explain why they're there (as far as I understand).
>
> My bad.
>
> When I made that change I could not figure out what that barrier was
> for, and it did not appear necessary.
>
> Do you happen to know of any real world problems?

No, this is just from reading the code and trying to make other
changes to it. (I'm trying to figure out how to finally deal with some
of the other issues in the ptrace access check, so I've been staring
at that code a lot over the last couple days.)