From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3DEFDC28CC0 for ; Thu, 30 May 2019 19:38:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0ADFE260D8 for ; Thu, 30 May 2019 19:38:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726574AbfE3Tif (ORCPT ); Thu, 30 May 2019 15:38:35 -0400 Received: from shards.monkeyblade.net ([23.128.96.9]:58966 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726045AbfE3Tif (ORCPT ); Thu, 30 May 2019 15:38:35 -0400 Received: from localhost (unknown [IPv6:2601:601:9f80:35cd::3d5]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) (Authenticated sender: davem-davemloft) by shards.monkeyblade.net (Postfix) with ESMTPSA id 3509214DA8954; Thu, 30 May 2019 12:38:34 -0700 (PDT) Date: Thu, 30 May 2019 12:38:33 -0700 (PDT) Message-Id: <20190530.123833.494901093768074533.davem@davemloft.net> To: 92siuyang@gmail.com Cc: isdn@linux-pingi.de, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] isdn: hisax: isac: fix a possible concurrency use-after-free bug in ISAC_l1hw() From: David Miller In-Reply-To: <1559119739-27588-1-git-send-email-92siuyang@gmail.com> References: <1559119739-27588-1-git-send-email-92siuyang@gmail.com> X-Mailer: Mew version 6.8 on Emacs 26.1 Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.5.12 (shards.monkeyblade.net [149.20.54.216]); Thu, 30 May 2019 12:38:34 -0700 (PDT) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Young Xiao <92siuyang@gmail.com> Date: Wed, 29 May 2019 16:48:59 +0800 > In drivers/isdn/hisax/isac.c, the function isac_interrupt() and > ISAC_l1hw() may be concurrently executed. > > ISAC_l1hw() > line 499: if (!cs->tx_skb) > > isac_interrupt() > line 250: dev_kfree_skb_irq(cs->tx_skb); > > Thus, a possible concurrency use-after-free bug may occur in ISAC_l1hw(). ... > + spin_lock_irqsave(&cs->lock, flags); > if (!cs->tx_skb) { > test_and_clear_bit(FLG_L1_PULL_REQ, &st->l1.Flags); > st->l1.l1l2(st, PH_PULL | CONFIRM, NULL); > } else > test_and_set_bit(FLG_L1_PULL_REQ, &st->l1.Flags); > + spin_unlock_irqrestore(&cs->lock, flags); Nothing in this code accesses the cs->tx_skb object. It is just a logic test upon whether it is NULL or not. I'm not applying stuff like this, sorry. You have to show how something can actually go wrong when fixing a bug.