linux-kernel - Re: [RFC][PATCH] exec: Use init rlimits for setuid exec

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Date:   Thu, 6 Jul 2017 22:03:53 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Michal Hocko <mhocko@...nel.org>,
        Ben Hutchings <ben@...adent.org.uk>, Willy Tarreau <w@....eu>,
        Hugh Dickins <hughd@...gle.com>,
        Oleg Nesterov <oleg@...hat.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Rik van Riel <riel@...hat.com>,
        Larry Woodman <lwoodman@...hat.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Tony Luck <tony.luck@...el.com>,
        "James E.J. Bottomley" <jejb@...isc-linux.org>,
        Helge Diller <deller@....de>,
        James Hogan <james.hogan@...tec.com>,
        Laura Abbott <labbott@...hat.com>, Greg KH <greg@...ah.com>,
        "security@...nel.org" <security@...nel.org>,
        Qualys Security Advisory <qsa@...lys.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Ximin Luo <infinity0@...ian.org>
Subject: Re: [RFC][PATCH] exec: Use init rlimits for setuid exec

On Thu, Jul 6, 2017 at 9:48 PM, Andy Lutomirski <luto@...nel.org> wrote:
>
> How about a much simpler solution: don't read rlimit at all in
> copy_strings(), let alone try to enforce it.

People have historically relied on E2BIG and then splitting things
into multiple chunks (ie do the whole 'xargs' thing).

But I agree that *if* we abort cleanly with E2BIG, then it's fine if
we copy a bit too much first. It's just that we need to check early
enough that an E2BIG error is possible (ie not after the "point of no
return").

And yes, I think we can get rid of the layout differences based on
rlimit. After all, if I read that right the thing currently clamps
that "gap" thing to 128MB anyway (and that's on the *low* side).

             Linus