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

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Message-ID: <CAOQ4uxjV=7=FXuyccBK9Pu1B7o-w-pbc1FQXJxY4q6z8E93KOg@mail.gmail.com>
Date:   Wed, 22 May 2019 21:29:37 +0300
From:   Amir Goldstein <amir73il@...il.com>
To:     Christian Brauner <christian@...uner.io>
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 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.