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 2A9B6EE49A0 for ; Wed, 23 Aug 2023 14:55:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234555AbjHWOz0 (ORCPT ); Wed, 23 Aug 2023 10:55:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56670 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232387AbjHWOz0 (ORCPT ); Wed, 23 Aug 2023 10:55:26 -0400 Received: from mail-oi1-x231.google.com (mail-oi1-x231.google.com [IPv6:2607:f8b0:4864:20::231]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5A6CFFB; Wed, 23 Aug 2023 07:55:21 -0700 (PDT) Received: by mail-oi1-x231.google.com with SMTP id 5614622812f47-3a751d2e6ecso4113089b6e.0; Wed, 23 Aug 2023 07:55:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20221208; t=1692802520; x=1693407320; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=1fxfMEra2Sjwl937QWvjlw0hXe/ba4hRBNWPmSgSiUg=; b=sg1T+XYbtN3k37473p0YFIQlYXt+ZxKqcIaIfC0mNyww9OUCgtcIfrdIfFNftj6GHF LFjtSCcJGt46i+pCesBEGCx1uWKSFxQGh2DUlSyOJ+mc08MuIvxYqEiTxcpTpGT+k35y 43UZ1qEmbNdSZ7GHYmKaozVKUgI8idgm4qecvnl/dOFLD0kVJculm2x/VfnVcf54cIti 3YNxk8lb1WflUTV8CJW0sCCxgoZT15lXINYo5JsXHQ28N6IaC1vmtkmqhLQdg+mqUYXK AEc9rhalN6IIHDy0vDWOMopWSHd8rIhRKrGAhlSV74w5PxiKsfHmmyqzyrkm31w5APm7 apyQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1692802520; x=1693407320; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=1fxfMEra2Sjwl937QWvjlw0hXe/ba4hRBNWPmSgSiUg=; b=KgsiVt8DCz4uX6AjZ9swA7nnjqiWu95qXXF1WXNus4HFcGElqDBzitqKG3eIFFU8+A MDQ4gjj42QAd+Q26cx/h0tzTBfzWQihBz7UwjOgLWpYUGE+xHBOwt7dMvgCkeVpzF+FE /Hysw/lQX/ji4xvdfBa9fnykqnYXSKNjkMfqOigIbgGvvZUm2K2YfRWM8SCFpRxDSPlr /VEOFmchq4vDgFtvevAsjo/9atSHBVS/n4x3s0RRBFTTvyVHB0I1V5ew61yyAxgONE4d luuo7Lk1/rcfOQG/bYXUNd4pfUu8tPipGq01fzlj3a9j+2PlK/e/1DeV7iyB6huCWNK0 pv9w== X-Gm-Message-State: AOJu0YyceB1ydQc2BytNlyvFK2bIcZP/3W+z+wTJyeT3FruPQ447Vn0e cX43oD7Ds4m+VrWTHUuVPeM= X-Google-Smtp-Source: AGHT+IHeEPSVr0CzcelUNSAmqmL2k6GbVVmR1nmrrxKraJxivaEWuJAVX8rImt3Nypk+eJqiYXyIaQ== X-Received: by 2002:a05:6808:1788:b0:3a3:ed41:5ab with SMTP id bg8-20020a056808178800b003a3ed4105abmr18471883oib.9.1692802520553; Wed, 23 Aug 2023 07:55:20 -0700 (PDT) Received: from google.com ([2620:15c:9d:2:ee3c:9990:bc14:d56e]) by smtp.gmail.com with ESMTPSA id q11-20020a638c4b000000b005637030d00csm9899161pgn.30.2023.08.23.07.55.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 23 Aug 2023 07:55:20 -0700 (PDT) Date: Wed, 23 Aug 2023 07:55:17 -0700 From: Dmitry Torokhov To: Maxime Ripard Cc: Rahul Rameshbabu , syzbot , davidgow@google.com, gregkh@linuxfoundation.org, linux-input@vger.kernel.org, linux-kernel@vger.kernel.org, rydberg@bitmath.org, syzkaller-bugs@googlegroups.com, benjamin.tissoires@redhat.com Subject: Re: [syzbot] [input?] KASAN: slab-use-after-free Read in input_dev_uevent Message-ID: References: <00000000000035beba060371a468@google.com> <878ra3m5my.fsf@nvidia.com> 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-input@vger.kernel.org Hi Maxime, On Wed, Aug 23, 2023 at 03:16:02PM +0200, Maxime Ripard wrote: > Hi Dmitry, > > On Wed, Aug 23, 2023 at 05:51:00AM -0700, Dmitry Torokhov wrote: > > On Wed, Aug 23, 2023 at 09:44:22AM +0200, Maxime Ripard wrote: > > > On Tue, Aug 22, 2023 at 08:57:41AM -0700, Rahul Rameshbabu wrote: > > > > On Tue, 22 Aug, 2023 11:12:28 +0200 Maxime Ripard wrote: > > > > > Hi, > > > > > > > > > > So, we discussed it this morning with Benjamin, and I think the culprit > > > > > is that the uclogic driver will allocate a char array with devm_kzalloc > > > > > in uclogic_input_configured() > > > > > (https://elixir.bootlin.com/linux/latest/source/drivers/hid/hid-uclogic-core.c#L149), > > > > > and will assign input_dev->name to that pointer. > > > > > > > > > > When the device is removed, the devm-allocated array is freed, and the > > > > > input framework will send a uevent in input_dev_uevent() using the > > > > > input_dev->name field: > > > > > > > > > > https://elixir.bootlin.com/linux/latest/source/drivers/input/input.c#L1688 > > > > > > > > > > So it's a classic dangling pointer situation. > > > > > > > > > > And even though it was revealed by that patch, I think the issue is > > > > > unrelated. The fundamental issue seems to be that the usage of devm in > > > > > that situation is wrong. > > > > > > > > > > input_dev->name is accessed by input_dev_uevent, which for KOBJ_UNBIND > > > > > and KOBJ_REMOVE will be called after remove. > > > > > > > > > > For example, in __device_release_driver() (with the driver remove hook > > > > > being called in device_remove() and devres_release_all() being called in > > > > > device_unbind_cleanup()): > > > > > https://elixir.bootlin.com/linux/latest/source/drivers/base/dd.c#L1278 > > > > > > > > > > So, it looks to me that, with or without the patch we merged recently, > > > > > the core has always sent uevent after device-managed resources were > > > > > freed. Thus, the uclogic (and any other input driver) was wrong in > > > > > allocating its input_dev name with devm_kzalloc (or the phys and uniq > > > > > fields in that struct). > > > > > > > > > > Note that freeing input_dev->name in remove would have been just as bad. > > > > > > > > > > Looking at the code quickly, at least hid-playstation, > > > > > hid-nvidia-shield, hid-logitech-hidpp, mms114 and tsc200x seem to be > > > > > affected by the same issue. > > > > > > > > I agree with this analysis overall. At least in hid-nvidia-shield, I can > > > > not use devm for allocating the input name string and explicitly free it > > > > after calling input_unregister_device. In this scenario, the name string > > > > would have been freed explicitly after input_put_device was called > > > > (since the input device is not devres managed). input_put_device would > > > > drop the reference count to zero and the device would be cleaned up at > > > > that point triggering KOBJ_REMOVE and firing off that final > > > > input_dev_uevent. > > > > > > > > I think this can be done for a number of the drivers as a workaround > > > > till this issue is properly resolved. If this seems appropriate, I can > > > > send out a series later in the day. This is just a workaround till the > > > > discussion below converges (which I am interested in). > > > > > > I'm sorry, I don't know the input framework well enough to understand > > > what you had in mind exactly. Could you send a patch with your > > > suggestion for the hid-nvidia-shield so we can discuss this further? > > > > > > That being said, I think that the current design around name, phys and > > > uniq is fairly treacherous to drivers and we should aim for a solution > > > that prevents that issue from being possible at all. > > > > > > I was inclined to go for a char array for each to get rid of the pointer > > > entirely, but Benjamin raised some concerns over the structure size so > > > it's probably not a great solution. > > > > I think everything is much simpler, with uclogic driver being in the > > wrong here: devm resource needs to be attached to the right device > > (instance of HID) rather than to the input device itself (which should > > never have any driver resources attached since it never has a driver). > > Something like this: > > > > diff --git a/drivers/hid/hid-uclogic-core.c b/drivers/hid/hid-uclogic-core.c > > index f67835f9ed4c..f234a7c97360 100644 > > --- a/drivers/hid/hid-uclogic-core.c > > +++ b/drivers/hid/hid-uclogic-core.c > > @@ -148,7 +148,7 @@ static int uclogic_input_configured(struct hid_device *hdev, > > > > if (suffix) { > > len = strlen(hdev->name) + 2 + strlen(suffix); > > - name = devm_kzalloc(&hi->input->dev, len, GFP_KERNEL); > > + name = devm_kzalloc(&hdev->dev, len, GFP_KERNEL); > > if (name) { > > snprintf(name, len, "%s %s", hdev->name, suffix); > > hi->input->name = name; > > > > In general, drivers should attach devm resources they allocate to the > > instance of device they are binding to, and nothing else. > > I'm not sure that's enough unfortunately. The fundamental issue here > seems to be that input_dev_uevent follows a pointer that can be > allocated by the driver, and will be free'd before the last call to > input_dev_uevent. Yes, this is a fundamental property of C pointers - you should not free them before exiting last code section that may reference them. For input devices it means that pointers should not be freed until after input_unregister_device() is called. I.e. you have sequence like this: driver_data = kzalloc(...); driver_data->input_name = kstrdup(...); driver_data->input_phys = kstrdup(...); input = input_allocate_device(); input->name = driver_data->input_name; input->phys = driver_data->input_phys; input_register_device(input); ... input_unregister_device(input); kfree(driver_data->input_name); kfree(driver_data->input_phys); kfree(driver_data); devm typically helps with resources being freed at the right time, but for that the managed resources should be attached to the *correct device*, with correct device being one the driver is binding to, not any random device structure. > > And I think that's true for both devices here Yes, it looks like the shield is also using wrong device. Thanks. -- Dmitry