linux-kernel - Re: [PATCH] fanotify: remove redundant capable(CAP_SYS

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Message-ID: <EB97EF04-D44F-4320-ACDC-C536EED03BA4@brauner.io>
Date:   Wed, 22 May 2019 20:57:32 +0200
From:   Christian Brauner <christian@...uner.io>
To:     Amir Goldstein <amir73il@...il.com>
CC:     Jan Kara <jack@...e.cz>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fanotify: remove redundant capable(CAP_SYS_ADMIN)s

On May 22, 2019 8:29:37 PM GMT+02:00, Amir Goldstein <amir73il@...il.com> wrote:
>On Wed, May 22, 2019 at 7:32 PM Christian Brauner
><christian@...uner.io> wrote:
>>
>> This removes two redundant capable(CAP_SYS_ADMIN) checks from
>> fanotify_init().
>> fanotify_init() guards the whole syscall with capable(CAP_SYS_ADMIN)
>at the
>> beginning. So the other two capable(CAP_SYS_ADMIN) checks are not
>needed.
>
>It's intentional:
>
>commit e7099d8a5a34d2876908a9fab4952dabdcfc5909
>Author: Eric Paris <eparis@...hat.com>
>Date:   Thu Oct 28 17:21:57 2010 -0400
>
>    fanotify: limit the number of marks in a single fanotify group
>
>There is currently no limit on the number of marks a given fanotify
>group
>can have.  Since fanotify is gated on CAP_SYS_ADMIN this was not seen
>as
>a serious DoS threat.  This patch implements a default of 8192, the
>same as
>inotify to work towards removing the CAP_SYS_ADMIN gating and
>eliminating
>    the default DoS'able status.
>
>    Signed-off-by: Eric Paris <eparis@...hat.com>
>
>There idea is to eventually remove the gated CAP_SYS_ADMIN.
>There is no reason that fanotify could not be used by unprivileged
>users
>to setup inotify style watch on an inode or directories children, see:
>https://patchwork.kernel.org/patch/10668299/
>
>>
>> Fixes: 5dd03f55fd2 ("fanotify: allow userspace to override max queue
>depth")
>> Fixes: ac7e22dcfaf ("fanotify: allow userspace to override max
>marks")
>
>Fixes is used to tag bug fixes for stable.
>There is no bug.
>
>Thanks,
>Amir.

Interesting. When do you think the gate can be removed?
I was looking into switching from inotify to fanotify but since it's not useable from
non-initial userns it's a no-no
since we support nested workloads.