wg-quick: fsync the temporary file before renaming

This ensures that on an unclean shutdown, we either see the old content
or the new content, but not empty content.

Suggested-by: Ka Ho Ng <ngkaho1234@gmail.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

src/wg-quick.bash

@@ -197,6 +197,7 @@ save_config() {
 	current_config="$(cmd wg showconf "$INTERFACE")"
 	trap 'rm -f "$CONFIG_FILE.tmp"; exit' INT TERM EXIT
 	echo "${current_config/\[Interface\]$'\n'/$new_config}" > "$CONFIG_FILE.tmp" || die "Could not write configuration file"
+	sync "$CONFIG_FILE.tmp"
 	mv "$CONFIG_FILE.tmp" "$CONFIG_FILE" || die "Could not move configuration file"
 	trap - INT TERM EXIT
 	umask "$old_umask"