linux-kernel - Re: [PATCH] ELF: fix overflow in total mapping size calculation

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Message-ID: <YV8qp6J+HW0ciLVP@localhost.localdomain>
Date:   Thu, 7 Oct 2021 20:13:11 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] ELF: fix overflow in total mapping size calculation

On Tue, Oct 05, 2021 at 05:21:29PM -0700, Andrew Morton wrote:
> On Sun, 3 Oct 2021 15:11:24 +0300 Alexey Dobriyan <adobriyan@...il.com> wrote:
> 
> > Kernel assumes that ELF program headers are ordered by mapping address,
> > but doesn't enforce it. It is possible to make mapping size extremely huge
> > by simply shuffling first and last PT_LOAD segments.
> > 
> > As long as PT_LOAD segments do not overlap, it is silly to require
> > sorting by v_addr anyway because mmap() doesn't care.
> > 
> > Don't assume PT_LOAD segments are sorted and calculate min and max
> > addresses correctly.
> 
> It sounds good, but why do I have the feeling this will explode in some
> unexpected fashion?  Because it's elf, and that's what it does :(

Good news, it is ELF, we'll hear about breakage immediately. :^)

Kernel "enforces" PT_LOAD ordering: if total mapping size overflows,
then mmap will reject it. I hope every ELF binary maintains ordering.

But! total_mapping_size() only looks at first and the last PT_LOAD
segments which is obviously incorrect.