From nobody Sat Feb 7 11:31:24 2026 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 7FCB9C433EF for ; Mon, 23 May 2022 17:20:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240167AbiEWRUJ (ORCPT ); Mon, 23 May 2022 13:20:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37706 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240709AbiEWRQk (ORCPT ); Mon, 23 May 2022 13:16:40 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7F95012752; Mon, 23 May 2022 10:16:29 -0700 (PDT) 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 dfw.source.kernel.org (Postfix) with ESMTPS id 3A4FF608C3; Mon, 23 May 2022 17:16:06 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 39E39C385A9; Mon, 23 May 2022 17:16:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1653326165; bh=DhR6AeTKiLjq/3nWP2sq4FthZdkWvOrag8B25MAR0RQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=MFu5MH02Svij+sOyXikXt3+7cqbC2RqiM2C4Bf4+j7EZ/72z3DEcJdOWrAWNpJPEK 1ExcsIwVWUnlQxY7HtfmNcnmWKC9rf29SVHXUMcYKWQ3MJPdwiiMm7DswbZbCi6IPV r2iAJya3p1/jep5juDyXR5V3zBAuQbH6aTb0JQMs= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Tzung-Bi Shih , Guenter Roeck , Benson Leung , Sasha Levin Subject: [PATCH 5.10 27/97] platform/chrome: cros_ec_debugfs: detach log reader wq from devm Date: Mon, 23 May 2022 19:05:31 +0200 Message-Id: <20220523165816.495757072@linuxfoundation.org> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20220523165812.244140613@linuxfoundation.org> References: <20220523165812.244140613@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Tzung-Bi Shih [ Upstream commit 0e8eb5e8acbad19ac2e1856b2fb2320184299b33 ] Debugfs console_log uses devm memory (e.g. debug_info in cros_ec_console_log_poll()). However, lifecycles of device and debugfs are independent. An use-after-free issue is observed if userland program operates the debugfs after the memory has been freed. The call trace: do_raw_spin_lock _raw_spin_lock_irqsave remove_wait_queue ep_unregister_pollwait ep_remove do_epoll_ctl A Python example to reproduce the issue: ... import select ... p =3D select.epoll() ... f =3D open('/sys/kernel/debug/cros_scp/console_log') ... p.register(f, select.POLLIN) ... p.poll(1) [(4, 1)] # 4=3Dfd, 1=3Dselect.POLLIN [ shutdown cros_scp at the point ] ... p.poll(1) [(4, 16)] # 4=3Dfd, 16=3Dselect.POLLHUP ... p.unregister(f) An use-after-free issue raises here. It called epoll_ctl with EPOLL_CTL_DEL which in turn to use the workqueue in the devm (i.e. log_wq). Detaches log reader's workqueue from devm to make sure it is persistent even if the device has been removed. Signed-off-by: Tzung-Bi Shih Reviewed-by: Guenter Roeck Link: https://lore.kernel.org/r/20220209051130.386175-1-tzungbi@google.com Signed-off-by: Benson Leung Signed-off-by: Sasha Levin --- drivers/platform/chrome/cros_ec_debugfs.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/drivers/platform/chrome/cros_ec_debugfs.c b/drivers/platform/c= hrome/cros_ec_debugfs.c index 272c89837d74..0dbceee87a4b 100644 --- a/drivers/platform/chrome/cros_ec_debugfs.c +++ b/drivers/platform/chrome/cros_ec_debugfs.c @@ -25,6 +25,9 @@ =20 #define CIRC_ADD(idx, size, value) (((idx) + (value)) & ((size) - 1)) =20 +/* waitqueue for log readers */ +static DECLARE_WAIT_QUEUE_HEAD(cros_ec_debugfs_log_wq); + /** * struct cros_ec_debugfs - EC debugging information. * @@ -33,7 +36,6 @@ * @log_buffer: circular buffer for console log information * @read_msg: preallocated EC command and buffer to read console log * @log_mutex: mutex to protect circular buffer - * @log_wq: waitqueue for log readers * @log_poll_work: recurring task to poll EC for new console log data * @panicinfo_blob: panicinfo debugfs blob */ @@ -44,7 +46,6 @@ struct cros_ec_debugfs { struct circ_buf log_buffer; struct cros_ec_command *read_msg; struct mutex log_mutex; - wait_queue_head_t log_wq; struct delayed_work log_poll_work; /* EC panicinfo */ struct debugfs_blob_wrapper panicinfo_blob; @@ -107,7 +108,7 @@ static void cros_ec_console_log_work(struct work_struct= *__work) buf_space--; } =20 - wake_up(&debug_info->log_wq); + wake_up(&cros_ec_debugfs_log_wq); } =20 mutex_unlock(&debug_info->log_mutex); @@ -141,7 +142,7 @@ static ssize_t cros_ec_console_log_read(struct file *fi= le, char __user *buf, =20 mutex_unlock(&debug_info->log_mutex); =20 - ret =3D wait_event_interruptible(debug_info->log_wq, + ret =3D wait_event_interruptible(cros_ec_debugfs_log_wq, CIRC_CNT(cb->head, cb->tail, LOG_SIZE)); if (ret < 0) return ret; @@ -173,7 +174,7 @@ static __poll_t cros_ec_console_log_poll(struct file *f= ile, struct cros_ec_debugfs *debug_info =3D file->private_data; __poll_t mask =3D 0; =20 - poll_wait(file, &debug_info->log_wq, wait); + poll_wait(file, &cros_ec_debugfs_log_wq, wait); =20 mutex_lock(&debug_info->log_mutex); if (CIRC_CNT(debug_info->log_buffer.head, @@ -377,7 +378,6 @@ static int cros_ec_create_console_log(struct cros_ec_de= bugfs *debug_info) debug_info->log_buffer.tail =3D 0; =20 mutex_init(&debug_info->log_mutex); - init_waitqueue_head(&debug_info->log_wq); =20 debugfs_create_file("console_log", S_IFREG | 0444, debug_info->dir, debug_info, &cros_ec_console_log_fops); --=20 2.35.1