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

From Andy Lutomirski <luto@kernel.org>
Newsgroups linux.kernel
Subject Re: [RFC][PATCH] exec: Use init rlimits for setuid exec
Date 2017-07-07 17:00 +0200
Message-ID <u0CTF-5qc-39@gated-at.bofh.it> (permalink)
References (5 earlier) <u0tnj-7hv-1@gated-at.bofh.it> <u0tQl-7Je-3@gated-at.bofh.it> <u0tQl-7Je-1@gated-at.bofh.it> <u0u9H-7Qw-9@gated-at.bofh.it> <u0ujn-7Uj-13@gated-at.bofh.it>
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On Thu, Jul 6, 2017 at 10:45 PM, Kees Cook <keescook@chromium.org> wrote:
> On Thu, Jul 6, 2017 at 10:36 PM, Andy Lutomirski <luto@kernel.org> wrote:
>> Aren't there real use cases that use many megs of arguments?
>
> They'd be relatively new since the args were pretty limited before.
> I'd be curious to see them.
>
>> We could probably get away with saying max(rlimit(RLIMIT_STACK), 2MB)
>> as long as we make sure later on that we don't screw up if we've
>> overallocated?
>
> min, not max, but yeah. Here's part of what I have for get_arg_page():
>
>                 rlim = current->signal->rlim;
> -               if (size > READ_ONCE(rlim[RLIMIT_STACK].rlim_cur) / 4)
> +               arg_stack = READ_ONCE(rlim[RLIMIT_STACK].rlim_cur);
> +               arg_stack = min_t(unsigned long, arg_stack, _STK_LIM) / 4;
> +               if (size > arg_stack)
>                         goto fail;

I really did mean max, the idea being that, if we're going to increase
rlim_cur, it's a bit odd to fail the exec if it would have worked
under the higher value.  That being said, I see no real exploit vector
here if just rlimit(RLIMIT_STACK) is used.

(Can you just use rlimit()?  The open-coding seems entirely useless.)

I thought of another approach, though: change the rlimit macros so
that a secureexec program always gets at least 8MB stack.  Might be
less regression-prone.

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Thread

[RFC][PATCH] exec: Use init rlimits for setuid exec Kees Cook <keescook@chromium.org> - 2017-07-06 06:40 +0200
  Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Andy Lutomirski <luto@kernel.org> - 2017-07-06 07:00 +0200
    Re: [RFC][PATCH] exec: Use init rlimits for setuid exec ebiederm@xmission.com (Eric W. Biederman) - 2017-07-06 15:00 +0200
      Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Andy Lutomirski <luto@kernel.org> - 2017-07-06 17:30 +0200
  Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Willy Tarreau <w@1wt.eu> - 2017-07-06 07:50 +0200
  Re: [RFC][PATCH] exec: Use init rlimits for setuid exec ebiederm@xmission.com (Eric W. Biederman) - 2017-07-06 14:50 +0200
    Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Andy Lutomirski <luto@kernel.org> - 2017-07-06 17:40 +0200
  Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Linus Torvalds <torvalds@linux-foundation.org> - 2017-07-06 18:40 +0200
    Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Linus Torvalds <torvalds@linux-foundation.org> - 2017-07-06 19:00 +0200
    Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Kees Cook <keescook@chromium.org> - 2017-07-06 19:30 +0200
      Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Linus Torvalds <torvalds@linux-foundation.org> - 2017-07-06 20:00 +0200
        Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Kees Cook <keescook@chromium.org> - 2017-07-06 21:20 +0200
          Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Andy Lutomirski <luto@kernel.org> - 2017-07-07 06:50 +0200
            Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Linus Torvalds <torvalds@linux-foundation.org> - 2017-07-07 07:10 +0200
            Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Kees Cook <keescook@chromium.org> - 2017-07-07 07:20 +0200
              Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Linus Torvalds <torvalds@linux-foundation.org> - 2017-07-07 07:40 +0200
                Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Kees Cook <keescook@chromium.org> - 2017-07-07 07:50 +0200
                Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Kees Cook <keescook@chromium.org> - 2017-07-07 08:50 +0200
                Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Linus Torvalds <torvalds@linux-foundation.org> - 2017-07-07 18:30 +0200
                Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Kees Cook <keescook@chromium.org> - 2017-07-07 20:30 +0200
              Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Andy Lutomirski <luto@kernel.org> - 2017-07-07 07:40 +0200
                Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Kees Cook <keescook@chromium.org> - 2017-07-07 07:50 +0200
                Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Linus Torvalds <torvalds@linux-foundation.org> - 2017-07-07 08:10 +0200
                Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Kees Cook <keescook@chromium.org> - 2017-07-07 08:20 +0200
                Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Linus Torvalds <torvalds@linux-foundation.org> - 2017-07-07 18:10 +0200
                Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Kees Cook <keescook@chromium.org> - 2017-07-07 20:30 +0200
                Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Andy Lutomirski <luto@kernel.org> - 2017-07-07 17:00 +0200
            Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Kees Cook <keescook@chromium.org> - 2017-07-07 07:20 +0200
          Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Michal Hocko <mhocko@kernel.org> - 2017-07-10 10:50 +0200
            Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Linus Torvalds <torvalds@linux-foundation.org> - 2017-07-10 18:20 +0200
              Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Willy Tarreau <w@1wt.eu> - 2017-07-10 19:00 +0200
            Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Kees Cook <keescook@chromium.org> - 2017-07-10 18:20 +0200
              Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Michal Hocko <mhocko@kernel.org> - 2017-07-10 18:30 +0200
                Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Michal Hocko <mhocko@kernel.org> - 2017-07-10 20:20 +0200
                Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Rik van Riel <riel@redhat.com> - 2017-07-10 20:40 +0200
    Re: [RFC][PATCH] exec: Use init rlimits for setuid exec Alan Cox <gnomes@lxorguk.ukuu.org.uk> - 2017-07-13 02:00 +0200

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