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=-16.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,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 4EF29C43460 for ; Mon, 10 May 2021 14:39:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2F2FB61260 for ; Mon, 10 May 2021 14:39:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233122AbhEJOkW (ORCPT ); Mon, 10 May 2021 10:40:22 -0400 Received: from mail.kernel.org ([198.145.29.99]:54258 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231159AbhEJOht (ORCPT ); Mon, 10 May 2021 10:37:49 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id CA3AC61278; Mon, 10 May 2021 14:36:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1620657403; bh=mf8DFzyfgaOH7v8vx3Q7uibWS6woT6FrAkjhvPqyz58=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=toBIj0XzYalOJTP3F0ClgNxp84aoAgoeX2n0tkp0z3ZYQ6CA07V3HpYCynOIhFqk3 SrxQDMDp+yo4Q3bpDJ2EKdeYC3mIe488HPU+XGGKbjUggOy/5yXx+vq0OehZbarvLX MpselLlCHJ3neQnFistSgYFIAPsMM+DFCbUqjfDw= Date: Mon, 10 May 2021 16:36:41 +0200 From: Greg Kroah-Hartman To: Tong Zhang Cc: Arnd Bergmann , linux-kernel@vger.kernel.org Subject: Re: [PATCH] misc: alcor_pci: fix null-ptr-deref when there is no PCI bridge Message-ID: References: <20210426220728.1230340-1-ztong0001@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210426220728.1230340-1-ztong0001@gmail.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 26, 2021 at 06:07:27PM -0400, Tong Zhang wrote: > the PCI bridge might be NULL, so we'd better check before use it > > [ 1.246492] BUG: kernel NULL pointer dereference, address: 00000000000000c0 > [ 1.248731] RIP: 0010:pci_read_config_byte+0x5/0x40 > [ 1.253998] Call Trace: > [ 1.254131] ? alcor_pci_find_cap_offset.isra.0+0x3a/0x100 [alcor_pci] > [ 1.254476] alcor_pci_probe+0x169/0x2d5 [alcor_pci] > > Signed-off-by: Tong Zhang > --- > drivers/misc/cardreader/alcor_pci.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/drivers/misc/cardreader/alcor_pci.c b/drivers/misc/cardreader/alcor_pci.c > index cd402c89189e..1c33453fd5c7 100644 > --- a/drivers/misc/cardreader/alcor_pci.c > +++ b/drivers/misc/cardreader/alcor_pci.c > @@ -102,6 +102,9 @@ static int alcor_pci_find_cap_offset(struct alcor_pci_priv *priv, > u8 val8; > u32 val32; > > + if (!pci) > + return 0; > + > where = ALCOR_CAP_START_OFFSET; > pci_read_config_byte(pci, where, &val8); > if (!val8) > -- > 2.25.1 > I do not understand, how can pci ever be NULL? There is only 1 way this function can be called, and it's through the alcor_pci_probe() call, which should have always set up the parent and pci pointers that get passed to this function. How can that not happen? If it can happen, then something earlier than this should be fixed instead of papering over the root problem here. How did you duplicate the crash you list above? thanks, greg k-h