From patchwork Fri Jul 15 05:49:58 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Tetsuo Handa X-Patchwork-Id: 12918744 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 DBC2FC433EF for ; Fri, 15 Jul 2022 05:51:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229468AbiGOFvy (ORCPT ); Fri, 15 Jul 2022 01:51:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43086 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229456AbiGOFvy (ORCPT ); Fri, 15 Jul 2022 01:51:54 -0400 Received: from www262.sakura.ne.jp (www262.sakura.ne.jp [202.181.97.72]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7AE82747A1 for ; Thu, 14 Jul 2022 22:51:53 -0700 (PDT) Received: from fsav115.sakura.ne.jp (fsav115.sakura.ne.jp [27.133.134.242]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id 26F5o0XU020229; Fri, 15 Jul 2022 14:50:00 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav115.sakura.ne.jp (F-Secure/fsigk_smtp/550/fsav115.sakura.ne.jp); Fri, 15 Jul 2022 14:50:00 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/fsav115.sakura.ne.jp) Received: from [192.168.1.9] (M106072142033.v4.enabler.ne.jp [106.72.142.33]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id 26F5nxg6020212 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NO); Fri, 15 Jul 2022 14:50:00 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Message-ID: <04278747-41fe-3a0a-81bf-2935efaafac0@I-love.SAKURA.ne.jp> Date: Fri, 15 Jul 2022 14:49:58 +0900 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 6.3; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Content-Language: en-US To: Greg KH , Oliver Neukum , Wedson Almeida Filho , "Rafael J. Wysocki" , Arjan van de Ven , Len Brown , Dmitry Vyukov Cc: linux-pm@vger.kernel.org, LKML From: Tetsuo Handa Subject: [PATCH v3] PM: hibernate: defer device probing when resuming from hibernation Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org syzbot is reporting hung task at misc_open() [1], for there is a race window of AB-BA deadlock which involves probe_count variable. Currently wait_for_device_probe() from snapshot_open() from misc_open() can sleep forever with misc_mtx held if probe_count cannot become 0. When a device is probed by hub_event() work function, probe_count is incremented before the probe function starts, and probe_count is decremented after the probe function completed. There are three cases that can prevent probe_count from dropping to 0. (a) A device being probed stopped responding (i.e. broken/malicious hardware). (b) A process emulating a USB device using /dev/raw-gadget interface stopped responding for some reason. (c) New device probe requests keeps coming in before existing device probe requests complete. The phenomenon syzbot is reporting is (b). A process which is holding system_transition_mutex and misc_mtx is waiting for probe_count to become 0 inside wait_for_device_probe(), but the probe function which is called from hub_event() work function is waiting for the processes which are blocked at mutex_lock(&misc_mtx) to respond via /dev/raw-gadget interface. This patch mitigates (b) by deferring wait_for_device_probe() from snapshot_open() to snapshot_write() and snapshot_ioctl(). Please note that the possibility of (b) remains as long as any thread which is emulating a USB device via /dev/raw-gadget interface can be blocked by uninterruptible blocking operations (e.g. mutex_lock()). Please also note that (a) and (c) are not addressed. Regarding (c), we should change the code to wait for only one device which contains the image for resuming from hibernation. I don't know how to address (a), for use of timeout for wait_for_device_probe() might result in loss of user data in the image. Maybe we should require the userland to wait for the image device before opening /dev/snapshot interface. Link: https://syzkaller.appspot.com/bug?extid=358c9ab4c93da7b7238c [1] Reported-by: syzbot Signed-off-by: Tetsuo Handa Tested-by: syzbot Cc: Greg KH Cc: Oliver Neukum Cc: Wedson Almeida Filho Cc: Rafael J. Wysocki Cc: Arjan van de Ven --- Changes in v3: Defer wait_for_device_probe() till first write()/ioctl() request. v2 is at https://lkml.kernel.org/r/03096156-3478-db03-c015-28643479116c@I-love.SAKURA.ne.jp . v1 is at https://lkml.kernel.org/r/72e74af9-f1b6-e383-a2c3-6ee8a0aea5e0@I-love.SAKURA.ne.jp . kernel/power/user.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/kernel/power/user.c b/kernel/power/user.c index ad241b4ff64c..d43c2aa583b2 100644 --- a/kernel/power/user.c +++ b/kernel/power/user.c @@ -26,6 +26,7 @@ #include "power.h" +static bool need_wait; static struct snapshot_data { struct snapshot_handle handle; @@ -78,7 +79,7 @@ static int snapshot_open(struct inode *inode, struct file *filp) * Resuming. We may need to wait for the image device to * appear. */ - wait_for_device_probe(); + need_wait = true; data->swap = -1; data->mode = O_WRONLY; @@ -168,6 +169,11 @@ static ssize_t snapshot_write(struct file *filp, const char __user *buf, ssize_t res; loff_t pg_offp = *offp & ~PAGE_MASK; + if (need_wait) { + wait_for_device_probe(); + need_wait = false; + } + lock_system_sleep(); data = filp->private_data; @@ -244,6 +250,11 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd, loff_t size; sector_t offset; + if (need_wait) { + wait_for_device_probe(); + need_wait = false; + } + if (_IOC_TYPE(cmd) != SNAPSHOT_IOC_MAGIC) return -ENOTTY; if (_IOC_NR(cmd) > SNAPSHOT_IOC_MAXNR)