linux-kernel - Re: [PATCH] mm/mincore: allow for making sys

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Date:   Wed, 16 Jan 2019 04:36:07 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Josh Snyder <joshs@...flix.com>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Dave Chinner <david@...morbit.com>,
        Jiri Kosina <jikos@...nel.org>, Jann Horn <jannh@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Michal Hocko <mhocko@...e.com>, Linux-MM <linux-mm@...ck.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH] mm/mincore: allow for making sys_mincore() privileged

On Wed, Jan 16, 2019 at 05:00:25PM +1200, Linus Torvalds wrote:
> And if you're not the owner of the file, do you have another
> suggestion for that "Yes, I have the right to see what's in-core for
> this file". Because the problem is literally that if it's some random
> read-only system file, the kernel shouldn't leak access patterns to
> it..

This probably isn't a good heuristic, but thought I'd mention it
anyway ...  if the file is executable and you're not the owner, mincore
always/never says its pages are resident.  That'd fix all library leaks,
but then there's probably a smart way of figuring out something from
access patterns to a data file of some kind (/etc/passwd?)