Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7347FC433FE for ; Mon, 27 Dec 2021 15:54:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241025AbhL0PyR (ORCPT ); Mon, 27 Dec 2021 10:54:17 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39520 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238713AbhL0PvP (ORCPT ); Mon, 27 Dec 2021 10:51:15 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1F946C08EB2E; Mon, 27 Dec 2021 07:46:13 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id D3F31B810CF; Mon, 27 Dec 2021 15:46:11 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0F60FC36AE7; Mon, 27 Dec 2021 15:46:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1640619970; bh=3za8ShKFypf2gtjUMw0RZPcP1wQ3ppYpJLRO0U8bkv0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=C3Whb9eI3xbTdSvpQ4A3xLlS9vUggksL7j9XguwptZnwmZy2IRL0skTai3XgTLRCA X8vCe+WhXxVu+EPUhraCjPlU1q+I0osqcEZpn4pShWxUdqj6u0234R1LyTuusHSAv+ RM9dwplQOme0Uumq9lTIv0eP/HGxvDji+9DB1jOY= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Lin Ma , "David S. Miller" Subject: [PATCH 5.15 125/128] hamradio: defer ax25 kfree after unregister_netdev Date: Mon, 27 Dec 2021 16:31:40 +0100 Message-Id: <20211227151335.694624615@linuxfoundation.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20211227151331.502501367@linuxfoundation.org> References: <20211227151331.502501367@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Lin Ma commit 3e0588c291d6ce225f2b891753ca41d45ba42469 upstream. There is a possible race condition (use-after-free) like below (USE) | (FREE) ax25_sendmsg | ax25_queue_xmit | dev_queue_xmit | __dev_queue_xmit | __dev_xmit_skb | sch_direct_xmit | ... xmit_one | netdev_start_xmit | tty_ldisc_kill __netdev_start_xmit | mkiss_close ax_xmit | kfree ax_encaps | | Even though there are two synchronization primitives before the kfree: 1. wait_for_completion(&ax->dead). This can prevent the race with routines from mkiss_ioctl. However, it cannot stop the routine coming from upper layer, i.e., the ax25_sendmsg. 2. netif_stop_queue(ax->dev). It seems that this line of code aims to halt the transmit queue but it fails to stop the routine that already being xmit. This patch reorder the kfree after the unregister_netdev to avoid the possible UAF as the unregister_netdev() is well synchronized and won't return if there is a running routine. Signed-off-by: Lin Ma Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- drivers/net/hamradio/mkiss.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) --- a/drivers/net/hamradio/mkiss.c +++ b/drivers/net/hamradio/mkiss.c @@ -792,13 +792,14 @@ static void mkiss_close(struct tty_struc */ netif_stop_queue(ax->dev); - /* Free all AX25 frame buffers. */ - kfree(ax->rbuff); - kfree(ax->xbuff); - ax->tty = NULL; unregister_netdev(ax->dev); + + /* Free all AX25 frame buffers after unreg. */ + kfree(ax->rbuff); + kfree(ax->xbuff); + free_netdev(ax->dev); }