From patchwork Thu Feb 17 01:43:03 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Duoming Zhou X-Patchwork-Id: 12749232 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 B1BB4C433EF for ; Thu, 17 Feb 2022 01:43:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231216AbiBQBng (ORCPT ); Wed, 16 Feb 2022 20:43:36 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:53620 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230501AbiBQBng (ORCPT ); Wed, 16 Feb 2022 20:43:36 -0500 Received: from zju.edu.cn (spam.zju.edu.cn [61.164.42.155]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id A126D214884; Wed, 16 Feb 2022 17:43:21 -0800 (PST) Received: from ubuntu.localdomain (unknown [10.15.192.164]) by mail-app3 (Coremail) with SMTP id cC_KCgCnj_IqqA1iK4ViDQ--.6490S2; Thu, 17 Feb 2022 09:43:09 +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, linma@zju.edu.cn, Duoming Zhou Subject: [PATCH V3] drivers: hamradio: 6pack: fix UAF bug caused by mod_timer() Date: Thu, 17 Feb 2022 09:43:03 +0800 Message-Id: <20220217014303.102986-1-duoming@zju.edu.cn> X-Mailer: git-send-email 2.17.1 X-CM-TRANSID: cC_KCgCnj_IqqA1iK4ViDQ--.6490S2 X-Coremail-Antispam: 1UD129KBjvJXoWxWr1rCFWrGF4xuFyktr4fZrb_yoW5XrWUpF Z8Kryftw48trZxGr4DXa1kWr95Za1kAay0krsak3sIvFs3Zr1j9F1jka4kZF4UCrZ3Aay7 ZF1rXry7AF15A3DanT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUkI1xkIjI8I6I8E6xAIw20EY4v20xvaj40_Wr0E3s1l1IIY67AE w4v_Jr0_Jr4l8cAvFVAK0II2c7xJM28CjxkF64kEwVA0rcxSw2x7M28EF7xvwVC0I7IYx2 IY67AKxVWDJVCq3wA2z4x0Y4vE2Ix0cI8IcVCY1x0267AKxVW8Jr0_Cr1UM28EF7xvwVC2 z280aVAFwI0_GcCE3s1l84ACjcxK6I8E87Iv6xkF7I0E14v26rxl6s0DM2AIxVAIcxkEcV Aq07x20xvEncxIr21l5I8CrVACY4xI64kE6c02F40Ex7xfMcIj6xIIjxv20xvE14v26r1j 6r18McIj6I8E87Iv67AKxVWUJVW8JwAm72CE4IkC6x0Yz7v_Jr0_Gr1lF7xvr2IYc2Ij64 vIr41lF7I21c0EjII2zVCS5cI20VAGYxC7MxAIw28IcxkI7VAKI48JMxAIw28IcVCjz48v 1sIEY20_GFWkJr1UJwCFx2IqxVCFs4IE7xkEbVWUJVW8JwC20s026c02F40E14v26r1j6r 18MI8I3I0E7480Y4vE14v26r106r1rMI8E67AF67kF1VAFwI0_Jw0_GFylIxkGc2Ij64vI r41lIxAIcVC0I7IYx2IY67AKxVWUJVWUCwCI42IY6xIIjxv20xvEc7CjxVAFwI0_Jr0_Gr 1lIxAIcVCF04k26cxKx2IYs7xG6r1j6r1xMIIF0xvEx4A2jsIE14v26r1j6r4UMIIF0xvE x4A2jsIEc7CjxVAFwI0_Jr0_GrUvcSsGvfC2KfnxnUUI43ZEXa7VUbXdbUUUUUU== X-CM-SenderInfo: qssqjiasttq6lmxovvfxof0/1tbiAgQDAVZdtYL++gAGs6 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org X-Patchwork-Delegate: kuba@kernel.org When a 6pack device is detaching, the sixpack_close() will act to cleanup necessary resources. Although del_timer_sync() in sixpack_close() won't return if there is an active timer, one 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(). This unexpected waked handler, sp_xmit_on_air(), realizes nothing about the undergoing cleanup and may still call pty_write() to use driver layer resources that have already been released. 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 Reviewed-by: Lin Ma --- Changes in V3: - Make the commit message more clearer. 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);