linux-kernel - Re: [PATCH v6 4/5] fuse: Ensure posix acls are translated outside of init_user

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Message-ID: <87inao6dfa.fsf@xmission.com>
Date:   Thu, 22 Feb 2018 13:18:33 -0600
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Miklos Szeredi <mszeredi@...hat.com>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Linux Containers <containers@...ts.linux-foundation.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Alban Crequy <alban@...volk.io>,
        Seth Forshee <seth.forshee@...onical.com>,
        Sargun Dhillon <sargun@...gun.me>,
        Dongsu Park <dongsu@...volk.io>,
        "Serge E. Hallyn" <serge@...lyn.com>
Subject: Re: [PATCH v6 4/5] fuse: Ensure posix acls are translated outside of init_user_ns

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

> On Wed, Feb 21, 2018 at 9:29 PM, Eric W. Biederman
> <ebiederm@...ssion.com> wrote:
>> Ensure the translation happens by failing to read or write
>> posix acls when the filesystem has not indicated it supports
>> posix acls.
>
> For the first iteration this is fine, but  we could convert the raw
> xattrs as well, if we later want to, right?

I will say maybe.  This is tricky.   The code would not be too hard,
and the function to do the work posix_acl_fix_xattr_userns already
exists in fs/posix_acl.c

I don't actually expect that to work longterm.  I expect the direction
the kernel internals are moving is that all filesystems that implement
posix acls will be expected to implement .get_acl and .set_acl.

I would have to reread the old thread that got us to this point with
posix acls before I could really understand the backwards compatible
fuse use case, and I would have to reread the rest of the acl processing
in the kernel before I could recall exactly what makes sense.

If there was an obvious way to whitelist xattrs that fuse can support
for user namespaces I think I would go for that.  Just to avoid future
problems with future xattrs.

Eric