From patchwork Mon Nov 9 12:54:56 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg KH X-Patchwork-Id: 322610 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=-9.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 68292C2D0A3 for ; Mon, 9 Nov 2020 13:38:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 15540206B2 for ; Mon, 9 Nov 2020 13:38:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604929102; bh=y7ZK+pDC5G/MNWFHAgykspgjpyRitgHR80fbbwpq6o0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=1ZXB0XB2NkVRSZWiP4OV5ICTogDQzixVaxKtpCjsLTy+zNlarQ8kr04mvdycwuovr XmS5VcrKp9iPvbhtSedhWxYa9Cc1dGTAM69mTz7nicpS7QH6V3sHOYujJmcB4jAuvq Q9Eag+k58Lx35sThvvKae7MSFBAPlxYTSknz473s= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730712AbgKINiS (ORCPT ); Mon, 9 Nov 2020 08:38:18 -0500 Received: from mail.kernel.org ([198.145.29.99]:56770 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730664AbgKINDl (ORCPT ); Mon, 9 Nov 2020 08:03:41 -0500 Received: from localhost (83-86-74-64.cable.dynamic.v4.ziggo.nl [83.86.74.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 7C16C2220B; Mon, 9 Nov 2020 13:03:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604926983; bh=y7ZK+pDC5G/MNWFHAgykspgjpyRitgHR80fbbwpq6o0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=nbWy9V4pRzCn0kFShOIU3FJZquufnKb51bEYfxhHVH/Dhc/IHtQOQfxBkylB8ogtr KqLCk6Pqkt1zjPC3rAz7+VJVbyG9mAlfLIInSMk1qKD1gsE1DYCOIACxXF80HKoj3G DOK5LwocPin+BThg7Oa9FMvWBVby1FKB91kGO6Z4= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Oliver OHalloran , Mahesh Salgaonkar , "Aneesh Kumar K.V" , Vasant Hegde , Michael Ellerman Subject: [PATCH 4.9 070/117] powerpc/powernv/elog: Fix race while processing OPAL error log event. Date: Mon, 9 Nov 2020 13:54:56 +0100 Message-Id: <20201109125029.002479558@linuxfoundation.org> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20201109125025.630721781@linuxfoundation.org> References: <20201109125025.630721781@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Mahesh Salgaonkar commit aea948bb80b478ddc2448f7359d574387521a52d upstream. Every error log reported by OPAL is exported to userspace through a sysfs interface and notified using kobject_uevent(). The userspace daemon (opal_errd) then reads the error log and acknowledges the error log is saved safely to disk. Once acknowledged the kernel removes the respective sysfs file entry causing respective resources to be released including kobject. However it's possible the userspace daemon may already be scanning elog entries when a new sysfs elog entry is created by the kernel. User daemon may read this new entry and ack it even before kernel can notify userspace about it through kobject_uevent() call. If that happens then we have a potential race between elog_ack_store->kobject_put() and kobject_uevent which can lead to use-after-free of a kernfs object resulting in a kernel crash. eg: BUG: Unable to handle kernel data access on read at 0x6b6b6b6b6b6b6bfb Faulting instruction address: 0xc0000000008ff2a0 Oops: Kernel access of bad area, sig: 11 [#1] LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA PowerNV CPU: 27 PID: 805 Comm: irq/29-opal-elo Not tainted 5.9.0-rc2-gcc-8.2.0-00214-g6f56a67bcbb5-dirty #363 ... NIP kobject_uevent_env+0xa0/0x910 LR elog_event+0x1f4/0x2d0 Call Trace: 0x5deadbeef0000122 (unreliable) elog_event+0x1f4/0x2d0 irq_thread_fn+0x4c/0xc0 irq_thread+0x1c0/0x2b0 kthread+0x1c4/0x1d0 ret_from_kernel_thread+0x5c/0x6c This patch fixes this race by protecting the sysfs file creation/notification by holding a reference count on kobject until we safely send kobject_uevent(). The function create_elog_obj() returns the elog object which if used by caller function will end up in use-after-free problem again. However, the return value of create_elog_obj() function isn't being used today and there is no need as well. Hence change it to return void to make this fix complete. Fixes: 774fea1a38c6 ("powerpc/powernv: Read OPAL error log and export it through sysfs") Cc: stable@vger.kernel.org # v3.15+ Reported-by: Oliver O'Halloran Signed-off-by: Mahesh Salgaonkar Signed-off-by: Aneesh Kumar K.V Reviewed-by: Oliver O'Halloran Reviewed-by: Vasant Hegde [mpe: Rework the logic to use a single return, reword comments, add oops] Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20201006122051.190176-1-mpe@ellerman.id.au Signed-off-by: Greg Kroah-Hartman --- arch/powerpc/platforms/powernv/opal-elog.c | 33 ++++++++++++++++++++++------- 1 file changed, 26 insertions(+), 7 deletions(-) --- a/arch/powerpc/platforms/powernv/opal-elog.c +++ b/arch/powerpc/platforms/powernv/opal-elog.c @@ -183,14 +183,14 @@ static ssize_t raw_attr_read(struct file return count; } -static struct elog_obj *create_elog_obj(uint64_t id, size_t size, uint64_t type) +static void create_elog_obj(uint64_t id, size_t size, uint64_t type) { struct elog_obj *elog; int rc; elog = kzalloc(sizeof(*elog), GFP_KERNEL); if (!elog) - return NULL; + return; elog->kobj.kset = elog_kset; @@ -223,18 +223,37 @@ static struct elog_obj *create_elog_obj( rc = kobject_add(&elog->kobj, NULL, "0x%llx", id); if (rc) { kobject_put(&elog->kobj); - return NULL; + return; } + /* + * As soon as the sysfs file for this elog is created/activated there is + * a chance the opal_errd daemon (or any userspace) might read and + * acknowledge the elog before kobject_uevent() is called. If that + * happens then there is a potential race between + * elog_ack_store->kobject_put() and kobject_uevent() which leads to a + * use-after-free of a kernfs object resulting in a kernel crash. + * + * To avoid that, we need to take a reference on behalf of the bin file, + * so that our reference remains valid while we call kobject_uevent(). + * We then drop our reference before exiting the function, leaving the + * bin file to drop the last reference (if it hasn't already). + */ + + /* Take a reference for the bin file */ + kobject_get(&elog->kobj); rc = sysfs_create_bin_file(&elog->kobj, &elog->raw_attr); - if (rc) { + if (rc == 0) { + kobject_uevent(&elog->kobj, KOBJ_ADD); + } else { + /* Drop the reference taken for the bin file */ kobject_put(&elog->kobj); - return NULL; } - kobject_uevent(&elog->kobj, KOBJ_ADD); + /* Drop our reference */ + kobject_put(&elog->kobj); - return elog; + return; } static irqreturn_t elog_event(int irq, void *data)