emacs: fix an auto-save permissions race condition

* fileio.c (auto_saving_dir_umask): New static var.
(Fmake_directory_internal): Use it.
(do_auto_save_make_dir): Set it, instead of invoking chmod after
creating the directory.  The old code temporarily assigns
too-generous permissions to the directory.
(do_auto_save_eh): Clear it.
(Fdo_auto_save): Catch all errrors, not just file errors, so
that the var is always cleared.

2 files changed, 23 insertions, 6 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index f10e2955164..6c0185b7386 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,15 @@
+2011-12-29  Paul Eggert  <eggert@cs.ucla.edu>
+
+        emacs: fix an auto-save permissions race condition
+        * fileio.c (auto_saving_dir_umask): New static var.
+        (Fmake_directory_internal): Use it.
+        (do_auto_save_make_dir): Set it, instead of invoking chmod after
+        creating the directory.  The old code temporarily assigns
+        too-generous permissions to the directory.
+        (do_auto_save_eh): Clear it.
+        (Fdo_auto_save): Catch all errrors, not just file errors, so
+        that the var is always cleared.
+
 2011-12-28  Kenichi Handa  <handa@m17n.org>
 
         * coding.c (Fdefine_coding_system_internal): Make an utf-8 base
diff --git a/src/fileio.c b/src/fileio.c
index 3306085491e..27ae8b82204 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -90,6 +90,9 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 /* Nonzero during writing of auto-save files */
 static int auto_saving;
 
+/* Nonzero umask during creation of auto-save directories */
+static int auto_saving_dir_umask;
+
 /* Set by auto_save_1 to mode of original file so Fwrite_region will create
    a new file with the same mode as the original */
 static int auto_save_mode_bits;
@@ -2062,7 +2065,7 @@ DEFUN ("make-directory-internal", Fmake_directory_internal,
 #ifdef WINDOWSNT
   if (mkdir (dir) != 0)
 #else
-  if (mkdir (dir, 0777) != 0)
+  if (mkdir (dir, 0777 & ~auto_saving_dir_umask) != 0)
 #endif
     report_file_error ("Creating directory", list1 (directory));
 
@@ -5205,16 +5208,18 @@ do_auto_save_unwind_1 (Lisp_Object value)  /* used as unwind-protect function */
 static Lisp_Object
 do_auto_save_make_dir (Lisp_Object dir)
 {
-  Lisp_Object mode;
+  Lisp_Object result;
 
-  call2 (Qmake_directory, dir, Qt);
-  XSETFASTINT (mode, 0700);
-  return Fset_file_modes (dir, mode);
+  auto_saving_dir_umask = 077;
+  result = call2 (Qmake_directory, dir, Qt);
+  auto_saving_dir_umask = 0;
+  return result;
 }
 
 static Lisp_Object
 do_auto_save_eh (Lisp_Object ignore)
 {
+  auto_saving_dir_umask = 0;
   return Qnil;
 }
 
@@ -5282,7 +5287,7 @@ A non-nil CURRENT-ONLY argument means save only current buffer.  */)
           dir = Ffile_name_directory (listfile);
           if (NILP (Ffile_directory_p (dir)))
             internal_condition_case_1 (do_auto_save_make_dir,
-                                       dir, Fcons (Fcons (Qfile_error, Qnil), Qnil),
+                                       dir, Qt,
                                        do_auto_save_eh);
           UNGCPRO;
         }