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Re: [PATCH v27 03/21] vfs: Add MAY_DELETE_SELF and MAY_DELETE_CHILD permission flags

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  Re: [PATCH v27 03/21] vfs: Add MAY_DELETE_SELF and MAY_DELETE_CHILD  permission flags Andreas Gruenbacher <agruenba@redhat.com> - 2017-02-13 16:50 +0100

#1579892 — Re: [PATCH v27 03/21] vfs: Add MAY_DELETE_SELF and MAY_DELETE_CHILD permission flags

On Tue, Dec 6, 2016 at 10:25 PM, Miklos Szeredi <miklos@szeredi.hu> wrote:
> 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.

Yes, MAY_DELETE_SELF applies to delete as well as rename; otherwise
rename() would behave different from link() + unlink(); when a user
has the appropriate permissions, the result should be the same though.

Thanks,
Andreas

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