linux-kernel - Re: + mm-relax-ptrace-mode-in-process_vm

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Message-ID: <20180306180319.GC2080@avx2>
Date:   Tue, 6 Mar 2018 21:03:19 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Jann Horn <jann@...jh.net>, linux-kernel@...r.kernel.org
Subject: Re: + mm-relax-ptrace-mode-in-process_vm_readv2.patch added to -mm
 tree

On Tue, Mar 06, 2018 at 08:42:19PM +0300, Alexey Dobriyan wrote:
> On Mon, Mar 05, 2018 at 05:02:08PM -0800, Kees Cook wrote:
> > On Mon, Mar 5, 2018 at 4:07 PM,  <akpm@...ux-foundation.org> wrote:
> 
> > > It is more natural to check for read-from-memory permissions in case of
> > > process_vm_readv() as PTRACE_MODE_ATTACH is equivalent to write
> > > permissions.
> > 
> > NAK, this weakens the existing permission model for reading
> 
> What if existing permission model is overezealous?
> 
> /proc/*/auxv, /proc/*/environ, /proc*/cmdline, /proc/*/mem opened
> for reading and process_vm_readv(2) should do PTRACE_MODE_READ and
> everything else should do PTRACE_MODE_ATTACH.

Or in other words:

what if there should be 3 levels:
1) permission to write to address space
2) permission to read arbitrarily from adress space
3) permission to read auxv, argv and envp

Current code conflates (1) and (2).