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

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Date:   Mon, 26 Feb 2018 15:51:16 -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

ebiederm@...ssion.com (Eric W. Biederman) writes:

> Miklos Szeredi <mszeredi@...hat.com> writes:
>
>> On Thu, Feb 22, 2018 at 11:50 PM, Eric W. Biederman
>> <ebiederm@...ssion.com> wrote:
>>
>>> So if we could figure out how to use the generic acl support for the old
>>> brand of fuse filesystems that don't set FUSE_POSIX_ACL it would be much
>>> easier to support them long term.
>>
>> Simplest and most robust way seems to be to do everything the same (as
>> with FUSE_POSIX_ACL) but tell the vfs not to cache the acl.
>
> Good point.  That sounds like for the !fc->posix_acl case we just
> need a careful use of "forget_all_cached_acls(inode)".
>
> I will take a quick look at that, and see if that is easy/sufficient to
> cover the legacy fuse case.  Otherwise I will go with what I already
> have here.
>
> That feels like a better path.  And internally I would call what is
> today fc->posix_acl fc->cached_posix_acl.  To better convey the intent.
> Fingers crossed.

It looks like simply setting
"inode->i_acl = inode->i_default_acl = ACL_DONT_CACHE;" is the secret
sauce needed to disable caching in the legacy case and make everything
work.

I had to tweak the calls to forget_all_cached_acls so that won't clear
the ACL_DONT_CACHE status but otherwise that was an absolutely trivial
change to combine those two code paths.

I will post my updated patches shortly.

Eric