From: Miklos Szeredi <miklos@szeredi.hu>
Subject: Re: [PATCH v27 03/21] vfs: Add MAY_DELETE_SELF and MAY_DELETE_CHILD
 permission flags
Date: Tue, 6 Dec 2016 22:25:22 +0100
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References: <1476190256-1677-1-git-send-email-agruenba@redhat.com>
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 <20161206201529.GA1203@fieldses.org> <20161206203347.GC4498@jra3>
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Cc: "J. Bruce Fields" <bfields@fieldses.org>,
        Andreas Gruenbacher <agruenba@redhat.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Christoph Hellwig <hch@infradead.org>,
        "Theodore Ts'o" <tytso@mit.edu>,
        Andreas Dilger <adilger.kernel@dilger.ca>,
        Jeff Layton <jlayton@poochiereds.net>,
        Trond Myklebust <trond.myklebust@primarydata.com>,
        Anna Schumaker <anna.schumaker@netapp.com>,
        Dave Chinner <david@fromorbit.com>,
        "linux-ext4@vger.kernel.org" <linux-ext4@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linux NFS list <linux-nfs@vger.kernel.org>,
        linux-cifs@vger.kernel.org, Linux API <linux-api@vger.kernel.org>
To: Jeremy Allison <jra@samba.org>
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <20161206203347.GC4498@jra3>
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On Tue, Dec 6, 2016 at 10:13 PM, Jeremy Allison <jra@samba.org> wrote:
> On Tue, Dec 06, 2016 at 03:15:29PM -0500, J. Bruce Fields wrote:
>> On Fri, Dec 02, 2016 at 10:57:42AM +0100, Miklos Szeredi wrote:
>> > On Tue, Oct 11, 2016 at 2:50 PM, Andreas Gruenbacher
>> > <agruenba@redhat.com> wrote:
>> > > Normally, deleting a file requires MAY_WRITE access to the parent
>> > > directory.  With richacls, a file may be deleted with MAY_DELETE_CHILD access
>> > > to the parent directory or with MAY_DELETE_SELF access to the file.
>> > >
>> > > To support that, pass the MAY_DELETE_CHILD mask flag to inode_permission()
>> > > when checking for delete access inside a directory, and MAY_DELETE_SELF
>> > > when checking for delete access to a file itself.
>> > >
>> > > The MAY_DELETE_SELF permission overrides the sticky directory check.
>> >
>> > And MAY_DELETE_SELF seems totally inappropriate to any kind of rename,
>> > since from the point of view of the inode we are not doing anything at
>> > all.  The modifications are all in the parent(s), and that's where the
>> > permission checks need to be.
>>
>> I'm having a hard time finding an authoritative reference here (Samba
>> people might be able to help), but my understanding is that Windows
>> gives this a meaning something like "may I delete a link to this file".
>>
>> (And not even "may I delete the *last* link to this file", which might
>> also sound more logical.)
>
> I just did a recent patch here. In Samba we now check for
> SEC_DIR_ADD_FILE/SEC_DIR_ADD_SUBDIR on the target directory
> (depending on if the object being moved is a file or dir).

And MAY_DELETE_SELF as well, for rename?  That's really counterintuitive for me.

Thanks,
Miklos