From patchwork Wed Feb 16 15:56:04 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Duoming Zhou X-Patchwork-Id: 12748711 X-Patchwork-Delegate: kuba@kernel.org 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 613C7C433F5 for ; Wed, 16 Feb 2022 15:56:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235503AbiBPP5D (ORCPT ); Wed, 16 Feb 2022 10:57:03 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:55226 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234100AbiBPP5D (ORCPT ); Wed, 16 Feb 2022 10:57:03 -0500 Received: from zju.edu.cn (mail.zju.edu.cn [61.164.42.155]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 632C11A1323; Wed, 16 Feb 2022 07:56:44 -0800 (PST) Received: from ubuntu.localdomain (unknown [10.15.192.164]) by mail-app3 (Coremail) with SMTP id cC_KCgAHz_CsHg1iQGxcDQ--.13121S2; Wed, 16 Feb 2022 23:56:34 +0800 (CST) From: Duoming Zhou To: linux-hams@vger.kernel.org Cc: kuba@kernel.org, ajk@comnets.uni-bremen.de, davem@davemloft.net, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Duoming Zhou Subject: [PATCH V2] drivers: hamradio: 6pack: fix UAF bug caused by mod_timer() Date: Wed, 16 Feb 2022 23:56:04 +0800 Message-Id: <20220216155604.92827-1-duoming@zju.edu.cn> X-Mailer: git-send-email 2.17.1 X-CM-TRANSID: cC_KCgAHz_CsHg1iQGxcDQ--.13121S2 X-Coremail-Antispam: 1UD129KBjvJXoWxGw4rZw1fuw1xGFy3GryrCrg_yoW5GryrpF Z8GryfJw48trZ8JrsrJa1kWr95uFsYyay8Crs3u3sI9FsxZr1j9F1UKFWvvF4UCrs3Aay7 AF1rJry7AF15A3DanT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUkI1xkIjI8I6I8E6xAIw20EY4v20xvaj40_Wr0E3s1l1IIY67AE w4v_Jr0_Jr4l8cAvFVAK0II2c7xJM28CjxkF64kEwVA0rcxSw2x7M28EF7xvwVC0I7IYx2 IY67AKxVW7JVWDJwA2z4x0Y4vE2Ix0cI8IcVCY1x0267AKxVWxJVW8Jr1l84ACjcxK6I8E 87Iv67AKxVW0oVCq3wA2z4x0Y4vEx4A2jsIEc7CjxVAFwI0_GcCE3s1le2I262IYc4CY6c 8Ij28IcVAaY2xG8wAqx4xG64xvF2IEw4CE5I8CrVC2j2WlYx0E2Ix0cI8IcVAFwI0_Jr0_ Jr4lYx0Ex4A2jsIE14v26r1j6r4UMcvjeVCFs4IE7xkEbVWUJVW8JwACjcxG0xvY0x0EwI xGrwACjI8F5VA0II8E6IAqYI8I648v4I1l42xK82IYc2Ij64vIr41l42xK82IY6x8ErcxF aVAv8VW8uw4UJr1UMxC20s026xCaFVCjc4AY6r1j6r4UMI8I3I0E5I8CrVAFwI0_Jr0_Jr 4lx2IqxVCjr7xvwVAFwI0_JrI_JrWlx4CE17CEb7AF67AKxVWUAVWUtwCIc40Y0x0EwIxG rwCI42IY6xIIjxv20xvE14v26r1j6r1xMIIF0xvE2Ix0cI8IcVCY1x0267AKxVWUJVW8Jw CI42IY6xAIw20EY4v20xvaj40_Jr0_JF4lIxAIcVC2z280aVAFwI0_Jr0_Gr1lIxAIcVC2 z280aVCY1x0267AKxVW8JVW8JrUvcSsGvfC2KfnxnUUI43ZEXa7VUbXdbUUUUUU== X-CM-SenderInfo: qssqjiasttq6lmxovvfxof0/1tbiAgIDAVZdtYL+yAAFsN Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org X-Patchwork-Delegate: kuba@kernel.org Although del_timer_sync() in sixpack_close() won't return if there is an active timer, we could use mod_timer() in sp_xmit_on_air() to wake up timer again by calling userspace syscall such as ax25_sendmsg(), ax25_connect() and ax25_ioctl(). If sp_xmit_on_air() registered as a callback function in timer_setup() calls pty_write() to use tty resources that already released by tty_release(), the UAF bug will happen. One of the possible race conditions is shown below: (USE) | (FREE) ax25_sendmsg() | ax25_queue_xmit() | ... | sp_xmit() | sp_encaps() | sixpack_close() sp_xmit_on_air() | del_timer_sync(&sp->tx_t) mod_timer(&sp->tx_t,...) | ... | unregister_netdev() | ... (wait a while) | tty_release() | tty_release_struct() | release_tty() sp_xmit_on_air() | tty_kref_put(tty_struct) //FREE pty_write(tty_struct) //USE | ... The corresponding fail log is shown below: =============================================================== BUG: KASAN: use-after-free in __run_timers.part.0+0x170/0x470 Write of size 8 at addr ffff88800a652ab8 by task swapper/2/0 ... Call Trace: ... queue_work_on+0x3f/0x50 pty_write+0xcd/0xe0pty_write+0xcd/0xe0 sp_xmit_on_air+0xb2/0x1f0 call_timer_fn+0x28/0x150 __run_timers.part.0+0x3c2/0x470 run_timer_softirq+0x3b/0x80 __do_softirq+0xf1/0x380 ... This patch reorders the del_timer_sync() after the unregister_netdev() to avoid UAF bugs. Because the unregister_netdev() is well synchronized, it flushs out any pending queues, waits the refcount of net_device decreases to zero and removes net_device from kernel. There is not any running routines after executing unregister_netdev(). Therefore, we could not arouse timer from userspace again. Signed-off-by: Duoming Zhou --- Changes in V2: - Make the commit message more clearer. - Modify the patch code. --- drivers/net/hamradio/6pack.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/net/hamradio/6pack.c b/drivers/net/hamradio/6pack.c index b1fc153125d..45c3c4a1101 100644 --- a/drivers/net/hamradio/6pack.c +++ b/drivers/net/hamradio/6pack.c @@ -668,11 +668,11 @@ static void sixpack_close(struct tty_struct *tty) */ netif_stop_queue(sp->dev); + unregister_netdev(sp->dev); + del_timer_sync(&sp->tx_t); del_timer_sync(&sp->resync_t); - unregister_netdev(sp->dev); - /* Free all 6pack frame buffers after unreg. */ kfree(sp->rbuff); kfree(sp->xbuff);