Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20210203124112.1182614-1-mszeredi@redhat.com> <20210203130501.GY308988@casper.infradead.org>
 <CAJfpegs3YWybmH7iKDLQ-KwmGieS1faO1uSZ-ADB0UFYOFPEnQ@mail.gmail.com>
 <20210203135827.GZ308988@casper.infradead.org> <CAJfpegvHFHcCPtyJ+w6uRx+hLH9JAT46WJktF_nez-ZZAria7A@mail.gmail.com>
 <20210203142802.GA308988@casper.infradead.org>
In-Reply-To: <20210203142802.GA308988@casper.infradead.org>
From:   Miklos Szeredi <miklos@szeredi.hu>
Date:   Wed, 3 Feb 2021 15:38:54 +0100
Message-ID: <CAJfpegtW5-XObARX87A8siTJNxTCkzXG=QY5tTRXVUvHXXZn3g@mail.gmail.com>
Subject: Re: [PATCH 00/18] new API for FS_IOC_[GS]ETFLAGS/FS_IOC_FS[GS]ETXATTR
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Miklos Szeredi <mszeredi@redhat.com>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        Al Viro <viro@zeniv.linux.org.uk>,
        Andreas Dilger <adilger@dilger.ca>,
        Andreas Gruenbacher <agruenba@redhat.com>,
        Christoph Hellwig <hch@lst.de>,
        "Darrick J . Wong" <djwong@kernel.org>,
        Dave Kleikamp <shaggy@kernel.org>,
        David Sterba <dsterba@suse.com>,
        Jaegeuk Kim <jaegeuk@kernel.org>, Jan Kara <jack@suse.cz>,
        Joel Becker <jlbec@evilplan.org>,
        Matthew Garrett <matthew.garrett@nebula.com>,
        Mike Marshall <hubcap@omnibond.com>,
        Richard Weinberger <richard@nod.at>,
        Ryusuke Konishi <konishi.ryusuke@gmail.com>,
        "Theodore Ts'o" <tytso@mit.edu>, Tyler Hicks <code@tyhicks.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Wed, Feb 3, 2021 at 3:28 PM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Wed, Feb 03, 2021 at 03:13:29PM +0100, Miklos Szeredi wrote:
> > On Wed, Feb 3, 2021 at 2:58 PM Matthew Wilcox <willy@infradead.org> wrote:
> >
> > > Network filesystems frequently need to use the credentials attached to
> > > a struct file in order to communicate with the server.  There's no point
> > > fighting this reality.
> >
> > IDGI.  Credentials can be taken from the file and from the task.  In
> > this case every filesystem except cifs looks at task creds. Why are
> > network filesystem special in this respect?
>
> I don't necessarily mean 'struct cred'.  I mean "the authentication
> that the client has performed to the server".  Which is not a per-task
> thing, it's stored in the struct file, which is why we have things like
>
>         int (*write_begin)(struct file *, struct address_space *mapping,
>                                 loff_t pos, unsigned len, unsigned flags,
>                                 struct page **pagep, void **fsdata);
>
> disk filesystems ignore the struct file argument, but network filesystems
> very much use it.

Fine for file I/O.  That's authorized at open time for all
filesystems, not just network ones.

Not fine for metadata operations (IMO).   I.e. ->[gs]etattr() don't
take a file argument either, even though on the uAPI there are plenty
of open file based variants.

Thanks,
Miklos