Oops -- have to call setgroups() before giving up root.

Doc some of the peculiarities about starting rsyncd as root vs
non-root.

clientserver.c

@@ -282,6 +282,26 @@ static int rsync_module(int fd, int i)
 	}
 
 	if (am_root) {
+#ifdef HAVE_SETGROUPS
+		/* Get rid of any supplementary groups this process
+		 * might have inheristed. */
+		if (setgroups(0, NULL)) {
+			rsyserr(FERROR, errno, "setgroups failed");
+			io_printf(fd, "@ERROR: setgroups failed\n");
+			return -1;
+		}
+#endif
+
+		/* XXXX: You could argue that if the daemon is started
+		 * by a non-root user and they explicitly specify a
+		 * gid, then we should try to change to that gid --
+		 * this could be possible if it's already in their
+		 * supplementary groups. */
+
+		/* TODO: Perhaps we need to document that if rsyncd is
+		 * started by somebody other than root it will inherit
+		 * all their supplementary groups. */
+
 		if (setgid(gid)) {
 			rsyserr(FERROR, errno, "setgid %d failed", (int) gid);
 			io_printf(fd,"@ERROR: setgid failed\n");
@@ -294,16 +314,6 @@ static int rsync_module(int fd, int i)
 			return -1;
 		}
 
-#ifdef HAVE_SETGROUPS
-		/* Get rid of any supplementary groups this process
-		 * might have inheristed. */
-		if (setgroups(0, NULL)) {
-			rsyserr(FERROR, errno, "setgroups failed");
-			io_printf(fd, "@ERROR: setgroups failed\n");
-			return -1;
-		}
-#endif
-
 		am_root = (getuid() == 0);
 	}