bug#10403: epg--make-temp-file permissions race condition fixes

[Chong Yidong]

Could you review the patch posted by Paul?  Thanks.


Paul Eggert <eggert@cs.ucla.edu> writes:

> === modified file 'lisp/ChangeLog'
> --- lisp/ChangeLog    2011-12-29 21:55:33 +0000
> +++ lisp/ChangeLog    2011-12-29 22:08:29 +0000
> @@ -1,5 +1,8 @@
>  2011-12-29  Paul Eggert  <eggert@cs.ucla.edu>
>  
> +     * epg.el (epg--make-temp-file): Avoid permission race conditions
> +     when creating temporary directories and files on older Emacs.
> +
>       * files.el (move-file-to-trash): Preserve default file modes on error.
>       (Bug#10401)
>  
>
> === modified file 'lisp/epg.el'
> --- lisp/epg.el       2011-11-23 07:03:56 +0000
> +++ lisp/epg.el       2011-12-29 22:08:29 +0000
> @@ -1951,14 +1951,16 @@
>  of PREFIX, and expanding against `temporary-file-directory' if necessary),
>  is guaranteed to point to a newly created empty file.
>  You can then use `write-region' to write new data into the file."
> -      (let (tempdir tempfile)
> +      (let (tempdir tempfile orig-modes)
>       (setq prefix (expand-file-name prefix
>                                      (if (featurep 'xemacs)
>                                          (temp-directory)
>                                        temporary-file-directory)))
> +     (setq orig-modes (default-file-modes))
>       (unwind-protect
>           (let (file)
>             ;; First, create a temporary directory.
> +           (set-default-file-modes #o700)
>             (while (condition-case ()
>                        (progn
>                          (setq tempdir (make-temp-name
> @@ -1969,14 +1971,12 @@
>                          (make-directory tempdir))
>                      ;; let's try again.
>                      (file-already-exists t)))
> -           (set-file-modes tempdir 448)
>             ;; Second, create a temporary file in the tempdir.
>             ;; There *is* a race condition between `make-temp-name'
>             ;; and `write-region', but we don't care it since we are
>             ;; in a private directory now.
>             (setq tempfile (make-temp-name (concat tempdir "/EMU")))
>             (write-region "" nil tempfile nil 'silent)
> -           (set-file-modes tempfile 384)
>             ;; Finally, make a hard-link from the tempfile.
>             (while (condition-case ()
>                        (progn
> @@ -1986,6 +1986,7 @@
>                      ;; let's try again.
>                      (file-already-exists t)))
>             file)
> +       (set-default-file-modes orig-modes)
>         ;; Cleanup the tempfile.
>         (and tempfile
>              (file-exists-p tempfile)