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From:   Josh Snyder <joshs@netflix.com>
Date:   Tue, 15 Jan 2019 23:52:25 -0800
Message-ID: <CA+t-nXTfdo07EBvVo+mu8SRhrVyB=mEPLDQikHfpJue1jALJtQ@mail.gmail.com>
Subject: Re: [PATCH] mm/mincore: allow for making sys_mincore() privileged
To:     Dominique Martinet <asmadeus@codewreck.org>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Andy Lutomirski <luto@amacapital.net>,
        Dave Chinner <david@fromorbit.com>,
        Jiri Kosina <jikos@kernel.org>,
        Matthew Wilcox <willy@infradead.org>,
        Jann Horn <jannh@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Greg KH <gregkh@linuxfoundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Michal Hocko <mhocko@suse.com>, Linux-MM <linux-mm@kvack.org>,
        kernel list <linux-kernel@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>
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On Tue, Jan 15, 2019 at 10:34 PM Dominique Martinet <asmadeus@codewreck.org>
wrote:
>
> There is a difference with your previous patch though, that used to list no
> page in core when it didn't know; this patch lists pages as in core when it
> refuses to tell. I don't think that's very important, though.

Is there a reason not to return -EPERM in this case?

>
> If anything, the 0400 user-owner file might be a problem in some edge
> case (e.g. if you're preloading git directories, many objects are 0444);
> should we *also* check ownership?...

Yes, this seems valuable. Some databases with immutable files (e.g. git, as
you've mentioned) conceivably operate this way.

Josh