bug#13298: 24.3.50; Cannot write backup file; backing up in ~\.emacs.d\%backup%~

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sat, 29 Dec 2012 20:05:23 +0400
> From: Dmitry Gutov <dgutov@yandex.ru>
> CC: 13298@debbugs.gnu.org
> 
> On 29.12.2012 18:44, Eli Zaretskii wrote:
> >> Date: Sat, 29 Dec 2012 17:55:58 +0400
> >> From: Dmitry Gutov <dgutov@yandex.ru>
> >> CC: 13298@debbugs.gnu.org
> >>
> >> On 29.12.2012 17:51, Eli Zaretskii wrote:
> >>>> Date: Sat, 29 Dec 2012 17:42:55 +0400
> >>>> From: Dmitry Gutov <dgutov@yandex.ru>
> >>>> CC: 13298@debbugs.gnu.org
> >>>>
> >>>>> Can you step with a debugger (e.g., Edebug) through
> >>>>> backup-buffer-copy, and see why it errors out?  My crystal ball says
> >>>>> it happens because of set-file-extended-attributes, in which case
> >>>>> please tell what is the value of extended-attributes argument passed
> >>>>> to backup-buffer-copy.
> >>>>
> >>>> Indeed, it happens after a call to set-file-acl.
> >>>>
> >>>> ((acl .
> >>>> "O:BAG:S-1-5-21-909999172-181315677-756075521-513D:(A;;FA;;;SY)(A;;FA;;;BA)(A;;FA;;;S-1-5-21-909999172-181315677-756075521-1000)")
> >>>> (selinux-context nil nil nil nil))
> >>>
> >>> And if, before the call to set-file-acl inside
> >>> set-file-extended-attributes, you evaluate the expression
> >>>
> >>>     (file-acl filename)
> >>>
> >>> what does it return?
> >>
> >> "O:S-1-5-21-909999172-181315677-756075521-1000G:S-1-5-21-909999172-181315677-756075521-513D:(A;;FA;;;SY)(A;;FA;;;BA)(A;;FA;;;S-1-5-21-909999172-181315677-756075521-1000)"
> >
> > I guess this happens because all of the following:
> >
> >    . your user is a local Administrator
> >
> >    . you took ownership of your ~/.emacs.d directory, instead of
> >      leaving it owned by the Administrators group
> 
> The above is true. But /Users/gutov is owned by SYSTEM, FWIW.
> 
> >    . you didn't (or cannot) enable the "take ownership" privilege in
> >      your local security policy
> 
> This policy's security setting says "Administrators", and my user 
> belongs to that group (I'm looking in Local Policies/User Rights 
> Assignment, is that right?).

You could try explicitly allowing the privilege for your user, but I'm
not sure it would help.  That's the "cannot" part above: for users who
are members of the Administrators group, enabling that privilege does
nothing, AFAIK.  Windows doesn't let such users this privilege without
elevation.  You can only avoid the problem by running Emacs "as
Administrator" or from a shell that was run "as Administrator".

> > I installed as trunk revision 111369 a set of changes that should fix
> > this for you.  Please test.  (I could only approximate the problem on
> > my machine, so I cannot be sure the changes indeed fix it.)
> 
> It's better, but now I see these messages:
> 
> Saving file c:/Users/gutov/.newsrc...
> Error: (file-error "Setting ACL" "operation not permitted" 

This is what the changes intended to accomplish.  In this discussion:

  http://lists.gnu.org/archive/html/emacs-devel/2012-12/msg00568.html

I suggested to ignore these errors entirely, but others felt this was
too radical, since there could be real security issues involved here.
Stefan suggested using with-demoted-errors here:

  http://lists.gnu.org/archive/html/emacs-devel/2012-12/msg00645.html

which is what Emacs does after my changes.

> Like I described, I don't think my situation is exceptional, so seeing 
> the error messages is misleading.

Why misleading?  We asked Emacs to preserve the ACLs of the original
file, and it couldn't.  Shouldn't the user be informed about that?

If you think this is bad behavior, lobby on emacs-devel to allow some
kind of user options for ignoring these errors (which means you don't
care about security of access to your files).