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Backport support for update-game-score to run sgid instead of suid.
This comprises parts of the following commits from upstream git:

commit dbde138155118344b33dfd2db95f688a24a42fec
Author: Ulrich Müller <ulm@gentoo.org>
Date:   Sun Feb 8 21:00:49 2015 +0100

    configure --with-gameuser now defaults to games group.

commit 74ab488ff2e57f31eb5290266f0f3b1995ebf83e
Author: Paul Eggert <eggert@cs.ucla.edu>
Date:   Thu Jan 22 00:39:30 2015 -0800

    Check exit statuses in lib-src/Makefile

commit 7f4e7dd378c456b498c270b47b46aaae365a72ab
Author: Ulrich Müller <ulm@gentoo.org>
Date:   Thu Jan 22 08:24:42 2015 +0100

    Don't fail if chown or chgrp for 'update-game-score' is unsuccessful.

commit 20f66485526b69eb26f2e70bd835a5e1333559d5
Author: Ulrich Müller <ulm@gentoo.org>
Date:   Fri Jan 16 09:25:25 2015 +0100

    Allow update-game-score to run sgid instead of suid.

--- emacs-24.4-orig/configure.ac
+++ emacs-24.4/configure.ac
@@ -313,10 +313,20 @@
 fi
 
 AC_ARG_WITH(gameuser,dnl
-[AS_HELP_STRING([--with-gameuser=USER],[user for shared game score files])])
-test "X${with_gameuser}" != X && test "${with_gameuser}" != yes \
-  && gameuser="${with_gameuser}"
-test "X$gameuser" = X && gameuser=games
+[AS_HELP_STRING([--with-gameuser=USER_OR_GROUP],
+		[user for shared game score files.
+		An argument prefixed by ':' specifies a group instead.])])
+gameuser=
+gamegroup=
+# We don't test if we can actually chown/chgrp here, because configure
+# may run without root privileges.  lib-src/Makefile.in will handle
+# any errors due to missing user/group gracefully.
+case ${with_gameuser} in
+  no) ;;
+  "" | yes) gamegroup=games ;;
+  :*) gamegroup=`echo "${with_gameuser}" | sed -e "s/://"` ;;
+  *) gameuser=${with_gameuser} ;;
+esac
 
 AC_ARG_WITH([gnustep-conf],dnl
 [AS_HELP_STRING([--with-gnustep-conf=FILENAME],
@@ -4658,6 +4668,7 @@
 AC_SUBST(bitmapdir)
 AC_SUBST(gamedir)
 AC_SUBST(gameuser)
+AC_SUBST(gamegroup)
 ## FIXME? Nothing uses @LD_SWITCH_X_SITE@.
 ## src/Makefile.in did add LD_SWITCH_X_SITE (as a cpp define) to the
 ## end of LIBX_BASE, but nothing ever set it.
--- emacs-24.4-orig/lib-src/Makefile.in
+++ emacs-24.4/lib-src/Makefile.in
@@ -101,6 +101,7 @@
 
 gamedir=@gamedir@
 gameuser=@gameuser@
+gamegroup=@gamegroup@
 
 # ==================== Utility Programs for the Build =================
 
@@ -243,10 +244,25 @@
 	umask 022; ${MKDIR_P} "$(DESTDIR)${gamedir}"; \
 	touch "$(DESTDIR)${gamedir}/snake-scores"; \
 	touch "$(DESTDIR)${gamedir}/tetris-scores"
-	-if chown ${gameuser} "$(DESTDIR)${archlibdir}/update-game-score${EXEEXT}" && chmod u+s "$(DESTDIR)${archlibdir}/update-game-score${EXEEXT}"; then \
-	  chown ${gameuser} "$(DESTDIR)${gamedir}"; \
+ifneq ($(gameuser),)
+	if chown ${gameuser} \
+	     "$(DESTDIR)${archlibdir}/update-game-score${EXEEXT}" && \
+	   chmod u+s,go-r \
+	     "$(DESTDIR)${archlibdir}/update-game-score${EXEEXT}"; \
+	then \
+	  chown ${gameuser} "$(DESTDIR)${gamedir}" && \
+	  chmod u=rwx,g=rx,o=rx "$(DESTDIR)${gamedir}"; \
+	fi
+else ifneq ($(gamegroup),)
+	if chgrp ${gamegroup} \
+	     "$(DESTDIR)${archlibdir}/update-game-score${EXEEXT}" && \
+	   chmod g+s,o-r \
+	     "$(DESTDIR)${archlibdir}/update-game-score${EXEEXT}"; \
+	then \
+	  chgrp ${gamegroup} "$(DESTDIR)${gamedir}" && \
 	  chmod u=rwx,g=rwx,o=rx "$(DESTDIR)${gamedir}"; \
 	fi
+endif
 	exp_archlibdir=`cd "$(DESTDIR)${archlibdir}" && /bin/pwd`; \
 	if [ "$$exp_archlibdir" != "`cd ${srcdir} && /bin/pwd`" ]; then \
 	  for file in ${SCRIPTS}; do \
--- emacs-24.4-orig/lib-src/update-game-score.c
+++ emacs-24.4/lib-src/update-game-score.c
@@ -21,8 +21,8 @@
 
 
 /* This program allows a game to securely and atomically update a
-   score file.  It should be installed setuid, owned by an appropriate
-   user like `games'.
+   score file.  It should be installed either setuid or setgid, owned
+   by an appropriate user or group like `games'.
 
    Alternatively, it can be compiled without HAVE_SHARED_GAME_DIR
    defined, and in that case it will store scores in the user's home
@@ -89,7 +89,7 @@
 		       ptrdiff_t *size, struct score_entry const *newscore);
 static void sort_scores (struct score_entry *scores, ptrdiff_t count,
 			 bool reverse);
-static int write_scores (const char *filename,
+static int write_scores (const char *filename, mode_t mode,
 			 const struct score_entry *scores, ptrdiff_t count);
 
 static _Noreturn void
@@ -122,18 +122,19 @@
 }
 
 static const char *
-get_prefix (bool running_suid, const char *user_prefix)
+get_prefix (bool privileged, const char *user_prefix)
 {
-  if (!running_suid && user_prefix == NULL)
-    lose ("Not using a shared game directory, and no prefix given.");
-  if (running_suid)
+  if (privileged)
     {
 #ifdef HAVE_SHARED_GAME_DIR
       return HAVE_SHARED_GAME_DIR;
 #else
-      lose ("This program was compiled without HAVE_SHARED_GAME_DIR,\n and should not be suid.");
+      lose ("This program was compiled without HAVE_SHARED_GAME_DIR,\n"
+	    "and should not run with elevated privileges.");
 #endif
     }
+  if (user_prefix == NULL)
+    lose ("Not using a shared game directory, and no prefix given.");
   return user_prefix;
 }
 
@@ -141,7 +142,7 @@
 main (int argc, char **argv)
 {
   int c;
-  bool running_suid;
+  bool running_suid, running_sgid;
   void *lockstate;
   char *scorefile;
   char *nl;
@@ -183,8 +184,11 @@
     usage (EXIT_FAILURE);
 
   running_suid = (getuid () != geteuid ());
+  running_sgid = (getgid () != getegid ());
+  if (running_suid && running_sgid)
+    lose ("This program can run either suid or sgid, but not both.");
 
-  prefix = get_prefix (running_suid, user_prefix);
+  prefix = get_prefix (running_suid || running_sgid, user_prefix);
 
   scorefile = malloc (strlen (prefix) + strlen (argv[optind]) + 2);
   if (!scorefile)
@@ -234,7 +238,8 @@
 	scores += scorecount - max_scores;
       scorecount = max_scores;
     }
-  if (write_scores (scorefile, scores, scorecount) < 0)
+  if (write_scores (scorefile, running_sgid ? 0664 : 0644,
+		    scores, scorecount) < 0)
     {
       unlock_file (scorefile, lockstate);
       lose_syserr ("Failed to write scores file");
@@ -429,8 +434,8 @@
 }
 
 static int
-write_scores (const char *filename, const struct score_entry *scores,
-	      ptrdiff_t count)
+write_scores (const char *filename, mode_t mode,
+	      const struct score_entry *scores, ptrdiff_t count)
 {
   int fd;
   FILE *f;
@@ -444,7 +449,7 @@
   if (fd < 0)
     return -1;
 #ifndef DOS_NT
-  if (fchmod (fd, 0644) != 0)
+  if (fchmod (fd, mode) != 0)
     return -1;
 #endif
   f = fdopen (fd, "w");
@@ -460,7 +465,7 @@
   if (rename (tempfile, filename) != 0)
     return -1;
 #ifdef DOS_NT
-  if (chmod (filename, 0644) < 0)
+  if (chmod (filename, mode) < 0)
     return -1;
 #endif
   return 0;
--- emacs-24.4-orig/lisp/play/gamegrid.el
+++ emacs-24.4/lisp/play/gamegrid.el
@@ -462,22 +462,22 @@
 ;;        `gamegrid-add-score' was supposed to be used in the past and
 ;;        is covered here for backward-compatibility.
 ;;
-;;     2. The helper program "update-game-score" is setuid and the
-;;        file FILE does already exist in a system wide shared game
-;;        directory.  This should be the normal case on POSIX systems,
-;;        if the game was installed system wide.  Use
+;;     2. The helper program "update-game-score" is setgid or setuid
+;;        and the file FILE does already exist in a system wide shared
+;;        game directory.  This should be the normal case on POSIX
+;;        systems, if the game was installed system wide.  Use
 ;;        "update-game-score" to add the score to the file in the
 ;;        shared game directory.
 ;;
-;;     3. "update-game-score" is setuid, but the file FILE does *not*
-;;        exist in the system wide shared game directory.  Use
+;;     3. "update-game-score" is setgid/setuid, but the file FILE does
+;;        *not* exist in the system wide shared game directory.  Use
 ;;        `gamegrid-add-score-insecure' to create--if necessary--and
 ;;        update FILE.  This is for the case that a user has installed
 ;;        a game on her own.
 ;;
-;;     4. "update-game-score" is not setuid.  Use it to create/update
-;;        FILE in the user's home directory.  There is presumably no
-;;        shared game directory.
+;;     4. "update-game-score" is not setgid/setuid.  Use it to
+;;        create/update FILE in the user's home directory.  There is
+;;        presumably no shared game directory.
 
 (defvar gamegrid-shared-game-dir)
 
@@ -486,13 +486,13 @@
 	 (not (zerop (logand (file-modes
 			      (expand-file-name "update-game-score"
 						exec-directory))
-			     #o4000)))))
+			     #o6000)))))
     (cond ((file-name-absolute-p file)
 	   (gamegrid-add-score-insecure file score))
 	  ((and gamegrid-shared-game-dir
 		(file-exists-p (expand-file-name file shared-game-score-directory)))
-	   ;; Use the setuid "update-game-score" program to update a
-	   ;; system-wide score file.
+	   ;; Use the setgid (or setuid) "update-game-score" program
+	   ;; to update a system-wide score file.
 	   (gamegrid-add-score-with-update-game-score-1 file
 	    (expand-file-name file shared-game-score-directory) score))
 	  ;; Else: Add the score to a score file in the user's home