From mboxrd@z Thu Jan  1 00:00:00 1970
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S965489AbeAMJPH (ORCPT <rfc822;ralf@linux-mips.org> + 1 other);
        Sat, 13 Jan 2018 04:15:07 -0500
Received: from mail-wr0-f178.google.com ([209.85.128.178]:47038 "EHLO
        mail-wr0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S965373AbeAMJPD (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Sat, 13 Jan 2018 04:15:03 -0500
X-Google-Smtp-Source: ACJfBovA40R8uCV5H49NJzvufUstNwfPVHDkTdCKZFhtUy0k1VCVQAi0Xnvn8iAg7xpAbzlryZN4tA==
Date: Sat, 13 Jan 2018 12:14:59 +0300
From: Alexey Dobriyan <adobriyan@gmail.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH] elf: fix NT_FILE integer overflow
Message-ID: <20180113091458.GA2533@avx2>
References: <20180112203427.GA9109@avx2>
 <20180112145208.b054caf00c6fa666cc1a1c9c@linux-foundation.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20180112145208.b054caf00c6fa666cc1a1c9c@linux-foundation.org>
User-Agent: Mutt/1.7.2 (2016-11-26)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Return-Path: <linux-kernel-owner@vger.kernel.org>

On Fri, Jan 12, 2018 at 02:52:08PM -0800, Andrew Morton wrote:
> On Fri, 12 Jan 2018 23:34:27 +0300 Alexey Dobriyan <adobriyan@gmail.com> wrote:
> 
> > If vm.max_map_count bumped above 2^26 (67+ mil) and system has enough
> > RAM to allocate all the VMAs (~12.8 GB on Fedora 27 with 200-byte VMAs),
> > then it should be possible to overflow 32-bit "size", pass paranoia check,
> > allocate very little vmalloc space and oops while writing into vmalloc
> > guard page...
> > 
> > But I didn't test this, only coredump of regular process.
> > 
> > ...
> >
> > --- a/fs/binfmt_elf.c
> > +++ b/fs/binfmt_elf.c
> > @@ -1599,6 +1599,8 @@ static int fill_files_note(struct memelfnote *note)
> >  
> >  	/* *Estimated* file count and total data size needed */
> >  	count = current->mm->map_count;
> > +	if (count > UINT_MAX / 64)
> > +		return -EINVAL;
> >  	size = count * 64;
> >  
> >  	names_ofs = (2 + 3 * count) * sizeof(data[0]);
> 
> Why not make `size' a ulong (or size_t)?  That seems to be the
> appropriate type and the code will then immediately barf over the
> MAX_FILE_NOTE_SIZE comparison anyway.

You can do it, but MAX_FILE_NOTE_SIZE is only 4 MB, and 32-bit code is
smaller than 64-bit code.