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Fri, 25 Oct 2024 10:01:26 +0000 (GMT) Received: from nasanex01c.na.qualcomm.com (nasanex01c.na.qualcomm.com [10.45.79.139]) by NASANPPMTA02.qualcomm.com (8.18.1.2/8.18.1.2) with ESMTPS id 49PA1Q5E004401 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 25 Oct 2024 10:01:26 GMT Received: from hu-mojha-hyd.qualcomm.com (10.80.80.8) by nasanex01c.na.qualcomm.com (10.45.79.139) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.9; Fri, 25 Oct 2024 03:01:23 -0700 Date: Fri, 25 Oct 2024 15:31:20 +0530 From: Mukesh Ojha To: Jacek Anaszewski CC: anish kumar , Pavel Machek , Lee Jones , , Subject: Re: [PATCH] leds: class: Protect brightness_show() with led_cdev->led_access mutex Message-ID: References: <385b7baa-8027-c4cf-948f-a1dff570befc@gmail.com> <70817d8a-4736-c788-77df-28b01517d6a7@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <70817d8a-4736-c788-77df-28b01517d6a7@gmail.com> X-ClientProxiedBy: nasanex01a.na.qualcomm.com (10.52.223.231) To nasanex01c.na.qualcomm.com (10.45.79.139) X-QCInternal: smtphost X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=5800 signatures=585085 X-Proofpoint-GUID: NqGQejd0iV5yVjUhqSBptXmidjK4ntDM X-Proofpoint-ORIG-GUID: NqGQejd0iV5yVjUhqSBptXmidjK4ntDM X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1039,Hydra:6.0.680,FMLib:17.12.60.29 definitions=2024-09-06_09,2024-09-06_01,2024-09-02_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 phishscore=0 impostorscore=0 mlxscore=0 bulkscore=0 spamscore=0 lowpriorityscore=0 mlxlogscore=999 malwarescore=0 priorityscore=1501 adultscore=0 clxscore=1011 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2409260000 definitions=main-2410250076 On Fri, Oct 18, 2024 at 10:10:39PM +0200, Jacek Anaszewski wrote: > On 10/17/24 22:30, anish kumar wrote: > > On Thu, Oct 17, 2024 at 10:59 AM Jacek Anaszewski > > wrote: > > > > > > > > > > > > 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? > > > > Based on the comment from mukesh, he confirmed that. > > > > Relevant comment from him: > > " > > 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); > > " > > Ah, right, I missed that. So yes, this change in general is justified, > but as you mentioned we need to adjust the comment next to the > led_access mutex definition. > > Probably just change s/LED Flash Class/LED class/. > > And also add the locking to max_brightness_show() to be consistent. Yes, max_brightness_show() would also need one. Will send v2. -Mukesh > > -- > Best regards, > Jacek Anaszewski