linux-kernel - Re: [PATCH 07/11] fs: Allow CAP_SYS_ADMIN in s_user

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Date:   Mon, 19 Feb 2018 16:56:56 -0600
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Miklos Szeredi <mszeredi@...hat.com>
Cc:     Dongsu Park <dongsu@...volk.io>,
        lkml <linux-kernel@...r.kernel.org>,
        Linux Containers <containers@...ts.linux-foundation.org>,
        Alban Crequy <alban@...volk.io>,
        Seth Forshee <seth.forshee@...onical.com>,
        Sargun Dhillon <sargun@...gun.me>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH 07/11] fs: Allow CAP_SYS_ADMIN in s_user_ns to freeze and thaw filesystems

Miklos Szeredi <mszeredi@...hat.com> writes:

> On Fri, Dec 22, 2017 at 3:32 PM, Dongsu Park <dongsu@...volk.io> wrote:
>> From: Seth Forshee <seth.forshee@...onical.com>
>>
>> The user in control of a super block should be allowed to freeze
>> and thaw it. Relax the restrictions on the FIFREEZE and FITHAW
>> ioctls to require CAP_SYS_ADMIN in s_user_ns.
>
> Why is this required for unprivileged fuse?
>
> Fuse doesn't support freeze, so this seems to make no sense in the
> context of this patchset.

This isn't required to support fuse.  It is a relaxation in permissions
so it isn't strictly necessary for anything.

Until just recently Seth and I work working through the vfs looking at
what we need in general for unprivileged mounts.  With fuse as our focus
but we were not limiting ourselves to fuse.

I have been putting off relaxation of permissions like this because they
are not necessary for safety.  But in general they do make sense.

In practice I think all we need to worry about for fuse is the last 4 patches.

Eric