From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-113.freemail.mail.aliyun.com (out30-113.freemail.mail.aliyun.com [115.124.30.113]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4C49B1FF7C8 for ; Fri, 24 Apr 2026 05:57:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.113 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777010228; cv=none; b=sQdrBxYXha6kpBJQIAXfp9Vb3OyNBhkBXwxz4K8B3/zx1rih/Uap6VQYPs56TJuSaunIqAAbv/jnaZGsEupt+3dgrJAlOxsCCwmnlnQTjyz2E+gmn3MafWUBNB47Cv/njXQMMq1XJBrArdxdfST+C4hLfXURh8fNJtNnRIvQibQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777010228; c=relaxed/simple; bh=yDOGpiIAEXFkPtg7R2CrjT64RsPMeFZEjFMxwgIvhS0=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=RmmxgqYib1GYA7Or1GHTcS2caqnJ7XFiTRwH3IOlwob0DbSLH6lBhepY2wqMHGVn/W+vPhYIARIn9Gv7BoKv8e4PpLSNBS+KbLydEa6jY6teNqM1/cJulamrArDHImpD0aG8TzQvKAs+qliOTMVh0tGVl/b3bFPJWhryfpb82ok= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=hRNGHMed; arc=none smtp.client-ip=115.124.30.113 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="hRNGHMed" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1777010212; h=Message-ID:Date:MIME-Version:Subject:From:To:Content-Type; bh=t4KwzDc+LzT8WbIyCmSIRus/6I530z/unHWf9vaxdyc=; b=hRNGHMedSp/xrltIlQ/oG+17+7hVLVMyRvaY4SXNfC82BCLgUZUOi1TFx2TviFlU5IJz+T1vp4lSGQmvGmirEEiIvjn2pQ26yhVwd44HG9Tv7ou7VnJiv+gqKrpWQsBRHPoiEwjGT22KW1DI1snOvTH0uIM7xfAGNt6dGjrPotc= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R201e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033032089153;MF=kanie@linux.alibaba.com;NM=1;PH=DS;RN=7;SR=0;TI=SMTPD_---0X1bYVIq_1777010211; Received: from 30.178.82.182(mailfrom:kanie@linux.alibaba.com fp:SMTPD_---0X1bYVIq_1777010211 cluster:ay36) by smtp.aliyun-inc.com; Fri, 24 Apr 2026 13:56:51 +0800 Message-ID: <3847a039-bdab-478d-be57-c46c7665f92c@linux.alibaba.com> Date: Fri, 24 Apr 2026 13:56:50 +0800 Precedence: bulk X-Mailing-List: dmaengine@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] dmaengine: idxd: Fix use-after-free of idxd_wq From: Guixin Liu To: Vinicius Costa Gomes Cc: Dave Jiang , Vinod Koul , Frank Li , dmaengine@vger.kernel.org, Xunlei Pang , oliver.yang@linux.alibaba.com References: <20260415095030.42183-1-kanie@linux.alibaba.com> <177689364254.530433.11713441936347707463.b4-review@b4> <968e2a4f-7613-4ef2-8cf4-68710ec55163@linux.alibaba.com> <87cxzp1p9o.fsf@intel.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 在 2026/4/24 13:43, Guixin Liu 写道: > > > 在 2026/4/24 02:54, Vinicius Costa Gomes 写道: >> Guixin Liu writes: >> >>> 在 2026/4/23 05:34, Vinicius Costa Gomes 写道: >>>> On Wed, 15 Apr 2026 17:50:30 +0800, Guixin Liu >>>> wrote: >>>>> diff --git a/drivers/dma/idxd/init.c b/drivers/dma/idxd/init.c >>>>> index fb80803d5b57..c3cfd96074c9 100644 >>>>> --- a/drivers/dma/idxd/init.c >>>>> +++ b/drivers/dma/idxd/init.c >>>>> @@ -1293,13 +1293,30 @@ static void idxd_remove(struct pci_dev *pdev) >>>>> [ ... skip 14 lines ... ] >>>>> +     * >>>>> +     * Use device_release_driver() to only unbind the driver >>>>> (triggering >>>>> +     * idxd_device_drv_remove()) without touching sysfs. Then safely >>>>> +     * unregister children before the parent. >>>>> +     */ >>>>> +    device_release_driver(idxd_confdev(idxd)); >>> Thanks for the reply. >>>> Below are sashiko comments verbatim, some notes: >>>> >>>>    - I do believe the race condition that it points out is real (but >>>>      very narrow), but not sure that we don't have a similar one in >>>>      current code (i.e. it wasn't introduced by your patch); >>>>    - The possible wq leak was definitely not introduced by this patch; >>>>    - The question about what happens with the file references after a >>>>      device is removed is a separate issue; >>>> >>>> The patch looks good, not opposed to it at all, the only one I am a >>>> bit concerned, about this patch, to be sure, is the race condition, >>>> and the two "paths" to reach it. (the others we can fix separately) >>>> >>>> sashiko.dev : >>>> >>>> Does this introduce a race condition with sysfs? >>>> >>>> Since the driver's sysfs nodes remain active after >>>> device_release_driver() >>>> is called, a user with sysfs privileges could write to the bind >>>> attribute >>>> to re-probe the driver before the device unregistration completes. >>>> >>>> If idxd_device_drv_probe()->idxd_wqs_setup() runs concurrently with >>>> idxd_unregister_devices(), does it cause a use-after-free when it >>>> iterates over the idxd->wqs[] objects being freed, since >>>> suppress_bind_attrs is not set? >>> I think re-probe will call idxd_pci_probe() to allocate an new idxd >>> device, >>> this avoids accessing stale data. >> Yeah, I missed the (now obvious) that a new 'probe' also means a new >> device. So this "path" is not valid. Thank you. >> >>>> Also, does this code leak the workqueue? >>>> >>>> The workqueue idxd->wq is dynamically allocated using >>>> create_workqueue() >>>> during device initialization, but destroy_workqueue(idxd->wq) does not >>>> appear to be called in idxd_remove() or the sysfs device release >>>> callback. >>> Looks like it's b7cb9a034305 ("dmaengine: idxd: Fix refcount underflow >>> on module unload") >>> overlooked this, destory_workqueue(idxd->wq) is called in >>> idxd_cleanup() >>> -> idxd_cleanup_internals(). >>> >>> If so, I can send another patch to fix this. >> Yes, please do. > Will be added in v3. Well, the idxd->wq is freed in idxd_conf_device_release(), so there is no problem, no need to fix. >>>>> idxd_unregister_devices(idxd); >>>> sashiko.dev : >>>> >>>> If idxd_unregister_devices() drops the last reference to the child wq >>>> objects and frees them, can idxd_shutdown() trigger a use-after-free >>>> when called shortly after? >>>> >>>> For example, if a hardware error interrupt fired during teardown, >>>> idxd_shutdown()->flush_workqueue() could execute an error handler that >>>> iterates over the freed idxd->wqs[] memory. >>>> >>>> Additionally, if the hardware is wedged, >>>> idxd_shutdown()->idxd_device_disable()->idxd_device_clear_state() >>>> iterates over idxd->wqs[] and attempts to acquire >>>> mutex_lock(&wq->wq_lock) >>>> on the freed memory. >>> I took a look — idxd_shutdown() is only invoked by idxd_remove() and >>> during system shutdown/reboot. >>> Is idxd_shutdown() ever reached from the idxd hardware error interrupt >>> path? >> The bot's suggestion that this code path could be hit by a hardware >> error is false, but the shutdown path (like the user pressing a button) >> could be valid. >> >> A crash during that could cause the machine to not poweroff, which is >> not good. Worth thinking about this, if there's something we could do >> while we are here. > > Both idxd_remove() and idxd_shutdown() are called under > device_lock(dev) — > the lock is acquired by the driver core before invoking any bus callback: > > 1. > >    Remove path: device_release_driver_internal() → >    __device_driver_lock(dev, parent) → device_lock(dev) → ... → >    pci_device_remove() → idxd_remove() > > 2. > >    Shutdown path: device_shutdown() → device_lock(dev) → >    dev->bus->shutdown(dev) → pci_device_shutdown() → idxd_shutdown() > > Since both paths acquire the same dev->mutex on the same PCI device, > > idxd_remove() and idxd_shutdown() are mutually exclusive. > > Best Regards, > > Guixin Liu > >>>> Is there also a missing reference count for the cdev open path? >>>> >>>> Since idxd_unregister_devices() frees the wq structure, if user space >>>> holds an open file descriptor, cdev_device_del() won't revoke it. >>>> Can file operations like mmap or poll subsequently access the freed >>>> ctx->wq pointer? Should idxd_cdev_open() take a kobject reference on >>>> the parent wq device? >>> To be honest, I'm not very familiar with the idxd driver. At this >>> point, >>> it looks like the idxd driver needs a state machine to ensure mutual >>> exclusion >>> across the various concurrent paths. >> Don't worry about this one, it's a separate issue. >> >>> Best Regards, >>> Guixin Liu >>>> via: >>>> https://sashiko.dev/#/message/20260415095030.42183-1-kanie@linux.alibaba.com >>>> via: >>>> https://sashiko.dev/#/message/20260415095030.42183-1-kanie@linux.alibaba.com >>>> >>>> via: >>>> https://sashiko.dev/#/message/20260415095030.42183-1-kanie@linux.alibaba.com >>>> via: >>>> https://sashiko.dev/#/message/20260415095030.42183-1-kanie@linux.alibaba.com >>>> >> >> Cheers, >