linux-kernel - Re: [PATCH] proc: Enable smaps

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Message-Id: <20220908145934.4565620db7cbc3b9ceb90e3b@linux-foundation.org>
Date:   Thu, 8 Sep 2022 14:59:34 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Vincent Whitchurch <vincent.whitchurch@...s.com>
Cc:     <kernel@...s.com>, <adobriyan@...il.com>, <vbabka@...e.cz>,
        <dancol@...gle.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH] proc: Enable smaps_rollup without ptrace rights

On Thu, 8 Sep 2022 11:39:19 +0200 Vincent Whitchurch <vincent.whitchurch@...s.com> wrote:

> smaps_rollup is currently only allowed on processes which the user has
> ptrace permissions for, since it uses a common proc open function used
> by other files like mem and smaps.
> 
> However, while smaps provides detailed, individual information about
> each memory map in the process (justifying its ptrace rights
> requirement), smaps_rollup only provides a summary of the memory usage,
> which is not unlike the information available from other places like the
> status and statm files, which do not need ptrace permissions.
> 
> The first line of smaps_rollup could however be sensitive, since it
> exposes the randomized start and end of the process' address space.
> This information however does not seem essential to smap_rollup's
> purpose and could be replaced with placeholder values to preserve the
> format without leaking information.  (I could not find any user space in
> Debian or Android which uses the information in the first line.)
> 
> Replace the start with 0 and end with ~0 and allow smaps_rollup to be
> opened and read regardless of ptrace permissions.

What is the motivation for this?  Use case?  End-user value and such?