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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0079AC433EF for ; Mon, 3 Jan 2022 14:06:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233259AbiACOGT (ORCPT ); Mon, 3 Jan 2022 09:06:19 -0500 Received: from ams.source.kernel.org ([145.40.68.75]:45760 "EHLO ams.source.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233264AbiACOGQ (ORCPT ); Mon, 3 Jan 2022 09:06:16 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id B750FB80EEA for ; Mon, 3 Jan 2022 14:06:15 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id CD0FBC36AEB; Mon, 3 Jan 2022 14:06:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1641218774; bh=sFpmXQ4D7WUWJn7Neb6X08knhaaOMyrWV937piA6e7U=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=TadLBHXMTPUflQ7tAyW8B1LYOMcjMSVO5VXRTFAqo7P/9pkrcuW+B21fbF86I/MfJ mSr4lL6S2fr4scGw7y62JI7Yk95lcJ/qBIjy5LwazD9GaNWDcoj7xc2Ffjjz39y/mQ wu70vjxNDgny+inQQMLd+L70VGRoDXNhNLTCvb1U= Date: Mon, 3 Jan 2022 15:06:11 +0100 From: Greg KH To: Daniel Xu Cc: arnd@arndb.de, giometti@enneenne.com, linux-kernel@vger.kernel.org, thesven73@gmail.com, ojeda@kernel.org Subject: Re: [RFC char-misc-next 2/2] pps: Fix use-after-free cdev bug on module unload Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Jan 02, 2022 at 09:01:40PM -0800, Daniel Xu wrote: > Previously, a use-after-free KASAN splat could be reliably triggered > with: > > # insmod ./pps-ktimer.ko > # rmmod pps-ktimer.ko > > > and CONFIG_DEBUG_KOBJECT_RELEASE=y. > > This commit moves the driver to use cdev_alloc() instead of cdev_init() > to decouple the lifetime of struct cdev from struct pps_device. > > We also make use of the previous commit's new cdev->private field to > store a pointer to the containing struct. We have to do this because > container_of() does not work when we store a pointer to struct cdev. > > Signed-off-by: Daniel Xu > --- > drivers/pps/pps.c | 20 +++++++++++--------- > include/linux/pps_kernel.h | 2 +- > 2 files changed, 12 insertions(+), 10 deletions(-) > > diff --git a/drivers/pps/pps.c b/drivers/pps/pps.c > index 22a65ad4e46e..97ce26f67806 100644 > --- a/drivers/pps/pps.c > +++ b/drivers/pps/pps.c > @@ -298,8 +298,7 @@ static long pps_cdev_compat_ioctl(struct file *file, > > static int pps_cdev_open(struct inode *inode, struct file *file) > { > - struct pps_device *pps = container_of(inode->i_cdev, > - struct pps_device, cdev); > + struct pps_device *pps = inode->i_cdev->private; Why is this pointer now valid while the original structure that the cdev lived in, not valid? I do not think this really solves your problem, only papers over the delay in removing the kobject that the config option you enabled is trying to tell you is a problem. > file->private_data = pps; > kobject_get(&pps->dev->kobj); > return 0; > @@ -307,8 +306,7 @@ static int pps_cdev_open(struct inode *inode, struct file *file) > > static int pps_cdev_release(struct inode *inode, struct file *file) > { > - struct pps_device *pps = container_of(inode->i_cdev, > - struct pps_device, cdev); > + struct pps_device *pps = inode->i_cdev->private; > kobject_put(&pps->dev->kobj); > return 0; > } > @@ -332,7 +330,7 @@ static void pps_device_destruct(struct device *dev) > { > struct pps_device *pps = dev_get_drvdata(dev); > > - cdev_del(&pps->cdev); > + cdev_del(pps->cdev); > > /* Now we can release the ID for re-use */ > pr_debug("deallocating pps%d\n", pps->id); > @@ -368,10 +366,14 @@ int pps_register_cdev(struct pps_device *pps) > > devt = MKDEV(MAJOR(pps_devt), pps->id); > > - cdev_init(&pps->cdev, &pps_cdev_fops); > - pps->cdev.owner = pps->info.owner; > + pps->cdev = cdev_alloc(); > + if (!pps->cdev) > + goto free_idr; > + pps->cdev->owner = pps->info.owner; > + pps->cdev->ops = &pps_cdev_fops; > + pps->cdev->private = pps; > > - err = cdev_add(&pps->cdev, devt, 1); > + err = cdev_add(pps->cdev, devt, 1); > if (err) { > pr_err("%s: failed to add char device %d:%d\n", > pps->info.name, MAJOR(pps_devt), pps->id); > @@ -393,7 +395,7 @@ int pps_register_cdev(struct pps_device *pps) > return 0; > > del_cdev: > - cdev_del(&pps->cdev); > + cdev_del(pps->cdev); > > free_idr: > mutex_lock(&pps_idr_lock); > diff --git a/include/linux/pps_kernel.h b/include/linux/pps_kernel.h > index 78c8ac4951b5..4e401793880f 100644 > --- a/include/linux/pps_kernel.h > +++ b/include/linux/pps_kernel.h > @@ -56,7 +56,7 @@ struct pps_device { > > unsigned int id; /* PPS source unique ID */ > void const *lookup_cookie; /* For pps_lookup_dev() only */ > - struct cdev cdev; > + struct cdev *cdev; So now who owns the lifecycle for the ppc_device structure? You just took it away from the cdev kobject, and replaced it with what? thanks, greg k-h