linux-kernel - Re: [PATCH 6/7] exec: Move most of setup_new_exec into flush_old

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Date:   Thu, 7 May 2020 22:50:53 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>, Jann Horn <jannh@...gle.com>,
        Greg Ungerer <gerg@...ux-m68k.org>,
        Rob Landley <rob@...dley.net>,
        Bernd Edlinger <bernd.edlinger@...mail.de>,
        linux-fsdevel@...r.kernel.org, Al Viro <viro@...IV.linux.org.uk>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 6/7] exec: Move most of setup_new_exec into flush_old_exec

On Thu, May 07, 2020 at 04:51:13PM -0500, Eric W. Biederman wrote:
> I intend to the following text to the changelog.  At this point I
> believe I have read through everything and nothing raises any concerns
> for me:
> 
> --- text begin ---
> 
> To see why it is safe to move this code please note that effectively
> this change moves the personality setting in the binfmt and the following
> three lines of code after everything except unlocking the mutexes:
>         arch_pick_mmap_layout
>         arch_setup_new_exec
>         mm->task_size = TASK_SIZE
> 
> The function arch_pick_mmap_layout at most sets:
>         mm->get_unmapped_area
>         mm->mmap_base
>         mm->mmap_legacy_base
>         mm->mmap_compat_base
>         mm->mmap_compat_legacy_base
> which nothing in flush_old_exec or setup_new_exec depends on.
> 
> The function arch_setup_new_exec only sets architecture specific
> state and the rest of the functions only deal in state that applies
> to all architectures.
> 
> The last line just sets mm->task_size and again nothing in flush_old_exec
> or setup_new_exec depend on task_size.
> 
> --- text end ---
> [...]
> > So, with a bit larger changelog discussing what's moving "earlier",
> > I think this looks good:
> 
> Please see above.

Awesome! Thanks for checking my checking of your checking. ;)

Acked-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook