From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-ej1-f49.google.com (mail-ej1-f49.google.com [209.85.218.49]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 06E0D1D95BE; Thu, 17 Oct 2024 17:59:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.218.49 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729187949; cv=none; b=vEmojqU4ARJhFXMZilpawsHJebM6/Ux2K8pMCjz9juUAOH08McQiRcHilxwAJvgF5QCAajy7aOygVUSfmCVd+fwGlOV+Ic2bIyR8EU9CGy4fIyqg6yEiVNVFOYDDgtxSObVy/itKDb2GkFKF+OdKjNHUe/kEV2WHhBeZ1GxwVUQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729187949; c=relaxed/simple; bh=7SqJC9pFiwbpf0LX/JQifbtAyBNyeDs3+hWmcbAqqTg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=LMjUy87h6UstuHaxGfRlsKcvdia4NyolAoCu+jU8H69QIzJr/yeYRX+9SHhlQhuLcg64YJhIs1M89tPlDDZSknQw6nmvkKworRAzbvnPiW3gwxbnN5pv7YFflm5zKludwEAk9tMY5NFNBBl/diHvPgZixU9nO7QTvjo7eXXIp34= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=KDYsDxXc; arc=none smtp.client-ip=209.85.218.49 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="KDYsDxXc" Received: by mail-ej1-f49.google.com with SMTP id a640c23a62f3a-a86e9db75b9so165194866b.1; Thu, 17 Oct 2024 10:59:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1729187942; x=1729792742; darn=vger.kernel.org; h=content-transfer-encoding:in-reply-to:from:content-language :references:cc:to:subject:user-agent:mime-version:date:message-id :from:to:cc:subject:date:message-id:reply-to; bh=uvQrgOjAHlZRrBrPvACIpKwOIht0Nu1NboFA+g925w0=; b=KDYsDxXcPHxNxYN/W5yTvqi0zhXjIrwyFJyq6li985aMmU2b/wBerstaykJ2tTO4hW 4vv/MKaWRkP/4aRs1nsfkZKTQvEoXWG1FNbwnHcVyF0I1hbEAFcaeOgnNXQ+mvS6LUbp TvN8+XyS39MPKaHb/bwZx4ABhEe3yLho2W1IyvK3TlKZrTnFSAYQyFKpsjqFXkvc720c CZuFl2bASYPQzraOZsvspF1PEAkIJo2M/nSmujKzxjixKam7tXxbJenIpDl8ozq9SvaH R01ySzmB9CEKa7wM/zfR8V/45tyD20jHfdAmE8IRTmAFR5u5J1XjwO+Iiy9MMdY05c4S 3zlw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1729187942; x=1729792742; h=content-transfer-encoding:in-reply-to:from:content-language :references:cc:to:subject:user-agent:mime-version:date:message-id :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=uvQrgOjAHlZRrBrPvACIpKwOIht0Nu1NboFA+g925w0=; b=aMKhnDGCi8JQf4Koonwpj+Ek9u6SiIm/whB0edBXhbFLoL59L5Y8mwFs/iTqocSjSk 7kt50orgLLIipuh1UG2r8m26iiH4XEnS4o+4JbPbn+QALosU3QfYv5fZvC4yWIRJYBt/ yHRGV9DKnLrjNjksJtOXqcOqquiRLfDhWez0nzd8Vf7y10/Vm6djjbEjr0CE9mA/Bwjb aPTe00z92YdOfqHtV3vcVkVVqMEXRXu5xddcMvZouvMm12jcQEsjPC0szuIGKlKslFGm eIpe1PjbQcKMcKcZyE5xWX5vLJIn1fs/S7wdw5VJsAtwsA6ikxWskXLDBUXlDlvgydnF +h4Q== X-Forwarded-Encrypted: i=1; AJvYcCUHecwuzBiMFhgxeBIrDwkX+cyryfeLVIqBJeZU4duRtqRNeMKvXO5qw9Z6DS3qDImcpJQtcD51tYZC5w==@vger.kernel.org, AJvYcCVomYW6LZYNjkUPo5CR2DddIC164AFqV0Z99Pb/nZU9YfvtSw9XB4Ik7Z8A8gAwpm73zhnhxBYRnJQuXPo=@vger.kernel.org X-Gm-Message-State: AOJu0YyPvxfGDPSnIETs4ZYFC40gamFwu+atmBphhpZLPl7z8hvexrRP 4TtJL8/T9G1eyYTdraIf2Xx7/1hu3lKd3bvqQWTlMUD95W9KYFUl X-Google-Smtp-Source: AGHT+IFM4ZPg3CHF2owqATI8AWOFfLVcMwgoTw/hnRbe9m/y27yBkr44haiyBLrYw93gkjmPWS4vYg== X-Received: by 2002:a17:907:9489:b0:a99:e98f:e73d with SMTP id a640c23a62f3a-a99e9900010mr1382684066b.37.1729187941808; Thu, 17 Oct 2024 10:59:01 -0700 (PDT) Received: from [192.168.0.131] ([194.183.54.57]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a9a2981765esm319154366b.129.2024.10.17.10.59.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 17 Oct 2024 10:59:01 -0700 (PDT) Message-ID: Date: Thu, 17 Oct 2024 19:58:59 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.11.0 Subject: Re: [PATCH] leds: class: Protect brightness_show() with led_cdev->led_access mutex To: anish kumar Cc: Mukesh Ojha , Pavel Machek , Lee Jones , linux-leds@vger.kernel.org, linux-kernel@vger.kernel.org References: <20241015162532.2292871-1-quic_mojha@quicinc.com> <385b7baa-8027-c4cf-948f-a1dff570befc@gmail.com> Content-Language: en-US From: Jacek Anaszewski In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 10/17/24 18:41, anish kumar wrote: > On Thu, Oct 17, 2024 at 5:12 AM Jacek Anaszewski > wrote: >> >> Hi Anish and Mukesh, >> >> On 10/16/24 18:37, anish kumar wrote: >>> On Tue, Oct 15, 2024 at 10:45 PM Mukesh Ojha wrote: >>>> >>>> On Tue, Oct 15, 2024 at 03:28:08PM -0700, anish kumar wrote: >>>>> On Tue, Oct 15, 2024 at 12:28 PM Mukesh Ojha wrote: >>>>>> >>>>>> On Tue, Oct 15, 2024 at 10:59:12AM -0700, anish kumar wrote: >>>>>>> On Tue, Oct 15, 2024 at 9:26 AM Mukesh Ojha wrote: >>>>>>>> >>>>>>>> There is NULL pointer issue observed if from Process A where hid device >>>>>>>> being added which results in adding a led_cdev addition and later a >>>>>>>> another call to access of led_cdev attribute from Process B can result >>>>>>>> in NULL pointer issue. >>>>>>> >>>>>>> Which pointer is NULL? Call stack shows that dualshock4_led_get_brightness >>>>>>> function could be culprit? >>>>>> >>>>>> in dualshock4_led_get_brightness()[1], led->dev is NULL here, as [2] >>>>>> is not yet completed. >>>>>> >>>>>> [1] >>>>>> struct hid_device *hdev = to_hid_device(led->dev->parent); >>>>>> >>>>>> [2] >>>>>> led_cdev->dev = device_create_with_groups(&leds_class, parent, 0, >>>>>> led_cdev, led_cdev->groups, "%s", final_name); >>>>>> >>>>>>> >>>>>>>> >>>>>>>> Use mutex led_cdev->led_access to protect access to led->cdev and its >>>>>>>> attribute inside brightness_show(). >>>>>>> >>>>>>> I don't think it is needed here because it is just calling the led driver >>>>>>> callback and updating the brightness. So, why would we need to serialize >>>>>>> that using mutex? Maybe the callback needs some debugging. >>>>>>> I'm curious if it is ready by the time the callback is invoked. >>>>>> >>>>>> Because, we should not be allowed to access led_cdev->dev as it is not >>>>>> completed and since, brightness_store() has this lock brightness_show() >>>>>> should also have this as we are seeing the issue without it. >>>>>> >>>>>> I hope, above might have answered your question. >>>>>> >>>>>> -Mukesh >>>>>>> >>>>>>>> >>>>>>>> Process A Process B >>>>>>>> >>>>>>>> kthread+0x114 >>>>>>>> worker_thread+0x244 >>>>>>>> process_scheduled_works+0x248 >>>>>>>> uhid_device_add_worker+0x24 >>>>>>>> hid_add_device+0x120 >>>>>>>> device_add+0x268 >>>>>>>> bus_probe_device+0x94 >>>>>>>> device_initial_probe+0x14 >>>>>>>> __device_attach+0xfc >>>>>>>> bus_for_each_drv+0x10c >>>>>>>> __device_attach_driver+0x14c >>>>>>>> driver_probe_device+0x3c >>>>>>>> __driver_probe_device+0xa0 >>>>>>>> really_probe+0x190 >>>>>>>> hid_device_probe+0x130 >>>>>>>> ps_probe+0x990 >>>>>>>> ps_led_register+0x94 >>>>>>>> devm_led_classdev_register_ext+0x58 >>>>>>>> led_classdev_register_ext+0x1f8 >>>>>>>> device_create_with_groups+0x48 >>>>>>>> device_create_groups_vargs+0xc8 >>>>>>>> device_add+0x244 >>>>>>>> kobject_uevent+0x14 >>>>>>>> kobject_uevent_env[jt]+0x224 >>>>>>>> mutex_unlock[jt]+0xc4 >>>>>>>> __mutex_unlock_slowpath+0xd4 >>>>>>>> wake_up_q+0x70 >>>>>>>> try_to_wake_up[jt]+0x48c >>>>>>>> preempt_schedule_common+0x28 >>>>>>>> __schedule+0x628 >>>>>>>> __switch_to+0x174 >>>>>>>> el0t_64_sync+0x1a8/0x1ac >>>>>>>> el0t_64_sync_handler+0x68/0xbc >>>>>>>> el0_svc+0x38/0x68 >>>>>>>> do_el0_svc+0x1c/0x28 >>>>>>>> el0_svc_common+0x80/0xe0 >>>>>>>> invoke_syscall+0x58/0x114 >>>>>>>> __arm64_sys_read+0x1c/0x2c >>>>>>>> ksys_read+0x78/0xe8 >>>>>>>> vfs_read+0x1e0/0x2c8 >>>>>>>> kernfs_fop_read_iter+0x68/0x1b4 >>>>>>>> seq_read_iter+0x158/0x4ec >>>>>>>> kernfs_seq_show+0x44/0x54 >>>>>>>> sysfs_kf_seq_show+0xb4/0x130 >>>>>>>> dev_attr_show+0x38/0x74 >>>>>>>> brightness_show+0x20/0x4c >>>>>>>> dualshock4_led_get_brightness+0xc/0x74 >>>>>>>> >>>>>>>> [ 3313.874295][ T4013] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000060 >>>>>>>> [ 3313.874301][ T4013] Mem abort info: >>>>>>>> [ 3313.874303][ T4013] ESR = 0x0000000096000006 >>>>>>>> [ 3313.874305][ T4013] EC = 0x25: DABT (current EL), IL = 32 bits >>>>>>>> [ 3313.874307][ T4013] SET = 0, FnV = 0 >>>>>>>> [ 3313.874309][ T4013] EA = 0, S1PTW = 0 >>>>>>>> [ 3313.874311][ T4013] FSC = 0x06: level 2 translation fault >>>>>>>> [ 3313.874313][ T4013] Data abort info: >>>>>>>> [ 3313.874314][ T4013] ISV = 0, ISS = 0x00000006, ISS2 = 0x00000000 >>>>>>>> [ 3313.874316][ T4013] CM = 0, WnR = 0, TnD = 0, TagAccess = 0 >>>>>>>> [ 3313.874318][ T4013] GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0 >>>>>>>> [ 3313.874320][ T4013] user pgtable: 4k pages, 39-bit VAs, pgdp=00000008f2b0a000 >>>>>>>> .. >>>>>>>> >>>>>>>> [ 3313.874332][ T4013] Dumping ftrace buffer: >>>>>>>> [ 3313.874334][ T4013] (ftrace buffer empty) >>>>>>>> .. >>>>>>>> .. >>>>>>>> [ dd3313.874639][ T4013] CPU: 6 PID: 4013 Comm: InputReader >>>>>>>> [ 3313.874648][ T4013] pc : dualshock4_led_get_brightness+0xc/0x74 >>>>>>>> [ 3313.874653][ T4013] lr : led_update_brightness+0x38/0x60 >>>>>>>> [ 3313.874656][ T4013] sp : ffffffc0b910bbd0 >>>>>>>> .. >>>>>>>> .. >>>>>>>> [ 3313.874685][ T4013] Call trace: >>>>>>>> [ 3313.874687][ T4013] dualshock4_led_get_brightness+0xc/0x74 >>>>>>>> [ 3313.874690][ T4013] brightness_show+0x20/0x4c >>>>>>>> [ 3313.874692][ T4013] dev_attr_show+0x38/0x74 >>>>>>>> [ 3313.874696][ T4013] sysfs_kf_seq_show+0xb4/0x130 >>>>>>>> [ 3313.874700][ T4013] kernfs_seq_show+0x44/0x54 >>>>>>>> [ 3313.874703][ T4013] seq_read_iter+0x158/0x4ec >>>>>>>> [ 3313.874705][ T4013] kernfs_fop_read_iter+0x68/0x1b4 >>>>>>>> [ 3313.874708][ T4013] vfs_read+0x1e0/0x2c8 >>>>>>>> [ 3313.874711][ T4013] ksys_read+0x78/0xe8 >>>>>>>> [ 3313.874714][ T4013] __arm64_sys_read+0x1c/0x2c >>>>>>>> [ 3313.874718][ T4013] invoke_syscall+0x58/0x114 >>>>>>>> [ 3313.874721][ T4013] el0_svc_common+0x80/0xe0 >>>>>>>> [ 3313.874724][ T4013] do_el0_svc+0x1c/0x28 >>>>>>>> [ 3313.874727][ T4013] el0_svc+0x38/0x68 >>>>>>>> [ 3313.874730][ T4013] el0t_64_sync_handler+0x68/0xbc >>>>>>>> [ 3313.874732][ T4013] el0t_64_sync+0x1a8/0x1ac >>>>>>>> >>>>>>>> Signed-off-by: Mukesh Ojha >>>>>>>> --- >>>>>>>> drivers/leds/led-class.c | 3 ++- >>>>>>>> 1 file changed, 2 insertions(+), 1 deletion(-) >>>>>>>> >>>>>>>> diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c >>>>>>>> index 06b97fd49ad9..e3cb93f19c06 100644 >>>>>>>> --- a/drivers/leds/led-class.c >>>>>>>> +++ b/drivers/leds/led-class.c >>>>>>>> @@ -30,8 +30,9 @@ static ssize_t brightness_show(struct device *dev, >>>>>>>> { >>>>>>>> struct led_classdev *led_cdev = dev_get_drvdata(dev); >>>>>>>> >>>>>>>> - /* no lock needed for this */ >>>>> >>>>> just get rid of the above comment then. >>>> >>>> If you notice, it is already removed (-) . >>>> >>>>> >>>>> Also, the comment below in file leds.h >>>>> needs an update as originally the idea for this mutex lock was to >>>>> provide quick feedback to userspace based on this commit >>>>> https://github.com/torvalds/linux/commit/acd899e4f3066b6662f6047da5b795cc762093cb >>>>> >>>>> Basically a comment somewhere so that when a new attribute >>>>> gets added, it doesn't make the same mistake of not using the mutex >>>>> and run into the same issue. >>>>> >>>>> /* Ensures consistent access to the LED Flash Class device */ >>>>> struct mutex led_access; >>>> >>>> Thanks for accepting that it is an issue. >>>> I think, comment is very obvious actually the patch you mentioned should >>>> be in fixes tag as it introduced the lock but did not protect the show >>>> while it does it for store. >>> >>> Yes, but that patch was added for supporting flash class >>> device and wasn't explicitly to take care of the scenario that you >>> are trying to handle and the above comment in leds.h states the same. >> >> Correct. led_access mutex was introduced to add support for preventing >> any LED class device state changes originating from sysfs while >> v4l2_flash wrapper owns the device. >> >> Since the inception of LED subsystem all the locking was deemed to be >> the responsibility of every single LED class driver and initially sysfs >> attr callbacks didn't have any locking. After some time when LED core >> started to grow it turned out that it was required to lock the LED class >> initialization sequence, so as not to give the userspace an opportunity >> to set LED brightness on not fully initialized device, which was >> introduced in [0]. led_access mutex was already in place so it was used. >> However as you noticed, it is not used consistently across all LED class >> sysfs attrs callbacks. >> >> Since brightness_show() does not acquire led_access mutex it is still >> possible to call brightness_get op when LED class initialization >> sequence is not yet finished. >> >> Still, I'd propose to first narrow down the issue and figure out what >> actually causes NULL pointer dereference, as it apparently >> originates from dualshock4_led_get_brightness and not from LED core. > > Mukesh already explained the issue in earlier emails but here is the gist > anyway. > > led_cdev->dev = device_create_with_groups(&leds_class, parent, 0, > led_cdev, led_cdev->groups, "%s", final_name); > > If you look at the above code, device_create_with_groups function > can create all the sysfs and before it returns and assigns led_cdev->dev > pointer, those sysfs callback can get triggered and if the callback > accesses led_cdev->dev this variable, it will crash as it is not yet > assigned. Your trace ends in dualshock4_led_get_brightness(). Did you confirm that NULL pointer dereference is caused by accessing led_cdev->dev there? -- Best regards, Jacek Anaszewski