linux-hardening - Re: [PATCH v4 0/6] binfmt_elf: Support segments with 0 filesz and misaligned starts

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Date: Fri, 29 Sep 2023 10:09:17 -0700
From: Kees Cook <keescook@...omium.org>
To: Sebastian Ott <sebott@...hat.com>
Cc: Eric Biederman <ebiederm@...ssion.com>,
	Thomas Weißschuh <linux@...ssschuh.net>,
	Pedro Falcato <pedro.falcato@...il.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v4 0/6] binfmt_elf: Support segments with 0 filesz and
 misaligned starts

On Fri, Sep 29, 2023 at 01:33:50PM +0200, Sebastian Ott wrote:
> Hello Kees,
> 
> On Thu, 28 Sep 2023, Kees Cook wrote:
> > This is the continuation of the work Eric started for handling
> > "p_memsz > p_filesz" in arbitrary segments (rather than just the last,
> > BSS, segment). I've added the suggested changes:
> > 
> > - drop unused "elf_bss" variable
> > - refactor load_elf_interp() to use elf_load()
> > - refactor load_elf_library() to use elf_load()
> > - report padzero() errors when PROT_WRITE is present
> > - drop vm_brk()
> 
> While I was debugging the initial issue I stumbled over the following
> - care to take it as part of this series?
> ----->8
> [PATCH] mm: vm_brk_flags don't bail out while holding lock
> 
> Calling vm_brk_flags() with flags set other than VM_EXEC
> will exit the function without releasing the mmap_write_lock.
> 
> Just do the sanity check before the lock is acquired. This
> doesn't fix an actual issue since no caller sets a flag other
> than VM_EXEC.

Oh, eek. Yeah, that seems like a good idea. :)

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

-Kees

-- 
Kees Cook