bug#25419: give better message when trying to go to forbidden areas

bug#25419: give better message when trying to go to forbidden areas

[積丹尼 Dan Jacobson]

Do C-x C-f ~root
You will see:
Setting current directory: Success, /root/

But that is about all.

Because normally,

$ cd ~root
bash: cd: /root: Permission denied

Which better reflects reality.

bug#25419: give better message when trying to go to forbidden areas

[Eli Zaretskii]

> From: 積丹尼 Dan Jacobson
> 	<jidanni@jidanni.org>
> Date: Wed, 11 Jan 2017 22:44:08 +0800
> 
> Do C-x C-f ~root
> You will see:
> Setting current directory: Success, /root/

That's because /root has a file-name handler,
tramp-completion-file-name-handler, and although that handler turns
around and calls file-accessible-directory-p, the value of errno is
lost in transition:

  /* If the file name has special constructs in it,
     call the corresponding file handler.  */
  handler = Ffind_file_name_handler (absname, Qfile_accessible_directory_p);
  if (!NILP (handler))
    {
      Lisp_Object r = call2 (handler, Qfile_accessible_directory_p, absname);
      errno = 0;
      return r;
    }

Is there any better way than arbitrarily set errno to EACCES if the
handler returns something other than t?

bug#25419: give better message when trying to go to forbidden areas

[npostavs]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: 積丹尼 Dan Jacobson
>> 	<jidanni@jidanni.org>
>> Date: Wed, 11 Jan 2017 22:44:08 +0800
>> 
>> Do C-x C-f ~root
>> You will see:
>> Setting current directory: Success, /root/
>
> That's because /root has a file-name handler,
> tramp-completion-file-name-handler, and although that handler turns
> around and calls file-accessible-directory-p, the value of errno is
> lost in transition:
>
>   /* If the file name has special constructs in it,
>      call the corresponding file handler.  */
>   handler = Ffind_file_name_handler (absname, Qfile_accessible_directory_p);
>   if (!NILP (handler))
>     {
>       Lisp_Object r = call2 (handler, Qfile_accessible_directory_p, absname);
>       errno = 0;
>       return r;
>     }
>
> Is there any better way than arbitrarily set errno to EACCES if the
> handler returns something other than t?

AFAICT, not without changing the interface of
file-accessible-directory-p file handler, no.

bug#25419: give better message when trying to go to forbidden areas

[Eli Zaretskii]

> From: npostavs@users.sourceforge.net
> Cc: 積丹尼 Dan Jacobson <jidanni@jidanni.org>,
>   25419@debbugs.gnu.org
> Date: Wed, 18 Jan 2017 22:28:17 -0500
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> From: 積丹尼 Dan Jacobson
> >> 	<jidanni@jidanni.org>
> >> Date: Wed, 11 Jan 2017 22:44:08 +0800
> >> 
> >> Do C-x C-f ~root
> >> You will see:
> >> Setting current directory: Success, /root/
> >
> > That's because /root has a file-name handler,
> > tramp-completion-file-name-handler, and although that handler turns
> > around and calls file-accessible-directory-p, the value of errno is
> > lost in transition:
> >
> >   /* If the file name has special constructs in it,
> >      call the corresponding file handler.  */
> >   handler = Ffind_file_name_handler (absname, Qfile_accessible_directory_p);
> >   if (!NILP (handler))
> >     {
> >       Lisp_Object r = call2 (handler, Qfile_accessible_directory_p, absname);
> >       errno = 0;
> >       return r;
> >     }
> >
> > Is there any better way than arbitrarily set errno to EACCES if the
> > handler returns something other than t?
> 
> AFAICT, not without changing the interface of
> file-accessible-directory-p file handler, no.

OK, thanks.  I made that change, and I'm marking this bug done.