From patchwork Fri Dec 17 02:13:56 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Lin Ma X-Patchwork-Id: 12683567 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 1E596C433EF for ; Fri, 17 Dec 2021 02:14:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229982AbhLQCOH (ORCPT ); Thu, 16 Dec 2021 21:14:07 -0500 Received: from spam.zju.edu.cn ([61.164.42.155]:47158 "EHLO zju.edu.cn" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S229449AbhLQCOG (ORCPT ); Thu, 16 Dec 2021 21:14:06 -0500 Received: from localhost.localdomain (unknown [222.205.0.213]) by mail-app2 (Coremail) with SMTP id by_KCgB3fMBm8rthNrdgAA--.6886S4; Fri, 17 Dec 2021 10:14:00 +0800 (CST) From: Lin Ma To: netdev@vger.kernel.org Cc: davem@davemloft.net, kuba@kernel.org, jirislaby@kernel.org, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, Lin Ma Subject: [PATCH v0] hamradio: improve the incomplete fix to avoid NPD Date: Fri, 17 Dec 2021 10:13:56 +0800 Message-Id: <20211217021356.27322-1-linma@zju.edu.cn> X-Mailer: git-send-email 2.33.1 MIME-Version: 1.0 X-CM-TRANSID: by_KCgB3fMBm8rthNrdgAA--.6886S4 X-Coremail-Antispam: 1UD129KBjvJXoW7uF15Ary7AFWDGF47Cr1Dtrb_yoW8CFWkpF 45Ka4akF4kJr1kAw4DAFWkZFyDXFsrtayUur4I934q9w4qyr1UZr10ga4j9r1UurZ3Arya vF15A3yIqF1Fy3DanT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUkF1xkIjI8I6I8E6xAIw20EY4v20xvaj40_Wr0E3s1l1IIY67AE w4v_Jr0_Jr4l8cAvFVAK0II2c7xJM28CjxkF64kEwVA0rcxSw2x7M28EF7xvwVC0I7IYx2 IY67AKxVWDJVCq3wA2z4x0Y4vE2Ix0cI8IcVCY1x0267AKxVW0oVCq3wA2z4x0Y4vEx4A2 jsIE14v26rxl6s0DM28EF7xvwVC2z280aVCY1x0267AKxVW0oVCq3wAS0I0E0xvYzxvE52 x082IY62kv0487Mc02F40EFcxC0VAKzVAqx4xG6I80ewAv7VC0I7IYx2IY67AKxVWUJVWU GwAv7VC2z280aVAFwI0_Jr0_Gr1lOx8S6xCaFVCjc4AY6r1j6r4UM4x0Y48IcxkI7VAKI4 8JM4x0x7Aq67IIx4CEVc8vx2IErcIFxwCF04k20xvY0x0EwIxGrwCF04k20xvE74AGY7Cv 6cx26r4fKr1UJr1l4I8I3I0E4IkC6x0Yz7v_Jr0_Gr1lx2IqxVAqx4xG67AKxVWUJVWUGw C20s026x8GjcxK67AKxVWUGVWUWwC2zVAF1VAY17CE14v26r126r1DMIIYrxkI7VAKI48J MIIF0xvE2Ix0cI8IcVAFwI0_Jr0_JF4lIxAIcVC0I7IYx2IY6xkF7I0E14v26r1j6r4UMI IF0xvE42xK8VAvwI8IcIk0rVWUJVWUCwCI42IY6I8E87Iv67AKxVWUJVW8JwCI42IY6I8E 87Iv6xkF7I0E14v26r1j6r4UYxBIdaVFxhVjvjDU0xZFpf9x0JUdHUDUUUUU= X-CM-SenderInfo: qtrwiiyqvtljo62m3hxhgxhubq/ Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org X-Patchwork-Delegate: kuba@kernel.org The previous commit 3e0588c291d6 ("hamradio: defer ax25 kfree after unregister_netdev") reorder the kfree operations and unregister_netdev operation to prevent UAF. This commit improves the previous one by also deferring the nullify of the ax->tty pointer. Otherwise, a NULL pointer dereference bug occurs. Partial of the stack trace is shown below. BUG: kernel NULL pointer dereference, address: 0000000000000538 RIP: 0010:ax_xmit+0x1f9/0x400 ... Call Trace: dev_hard_start_xmit+0xec/0x320 sch_direct_xmit+0xea/0x240 __qdisc_run+0x166/0x5c0 __dev_queue_xmit+0x2c7/0xaf0 ax25_std_establish_data_link+0x59/0x60 ax25_connect+0x3a0/0x500 ? security_socket_connect+0x2b/0x40 __sys_connect+0x96/0xc0 ? __hrtimer_init+0xc0/0xc0 ? common_nsleep+0x2e/0x50 ? switch_fpu_return+0x139/0x1a0 __x64_sys_connect+0x11/0x20 do_syscall_64+0x33/0x40 entry_SYSCALL_64_after_hwframe+0x44/0xa9 The crash point is shown as below static void ax_encaps(...) { ... set_bit(TTY_DO_WRITE_WAKEUP, &ax->tty->flags); // ax->tty = NULL! ... } By placing the nullify action after the unregister_netdev, the ax->tty pointer won't be assigned as NULL net_device framework layer is well synchronized. Signed-off-by: Lin Ma --- drivers/net/hamradio/mkiss.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/net/hamradio/mkiss.c b/drivers/net/hamradio/mkiss.c index 7da2bb8a443c..edde9c3ae12b 100644 --- a/drivers/net/hamradio/mkiss.c +++ b/drivers/net/hamradio/mkiss.c @@ -794,14 +794,14 @@ static void mkiss_close(struct tty_struct *tty) */ netif_stop_queue(ax->dev); - ax->tty = NULL; - unregister_netdev(ax->dev); /* Free all AX25 frame buffers after unreg. */ kfree(ax->rbuff); kfree(ax->xbuff); + ax->tty = NULL; + free_netdev(ax->dev); }