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Message-ID: <62b09eee-553a-a3d1-e2e0-59dee7289019@gmail.com>
Date: Sun, 27 Oct 2024 15:20:19 +0100
From: Jacek Anaszewski <jacek.anaszewski@...il.com>
To: Mukesh Ojha <quic_mojha@...cinc.com>, Pavel Machek <pavel@....cz>,
Lee Jones <lee@...nel.org>
Cc: linux-leds@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] leds: class: Protect brightness_show() with
led_cdev->led_access mutex
Hi Mukesh,
On 10/25/24 19:11, 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.
>
> Use mutex led_cdev->led_access to protect access to led->cdev and its
> attribute inside brightness_show() and max_brightness_show() and also
> update the comment for mutex that it should be used to protect the led
> class device fields.
>
> 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 <quic_mojha@...cinc.com>
> ---
> Changes in v2:
> - Updated the comment for led_access mutex lock.
> - Also added mutex protection for max_brightness_show().
>
> drivers/leds/led-class.c | 14 +++++++++++---
> include/linux/leds.h | 2 +-
> 2 files changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
> index 06b97fd49ad9..f69f4e928d61 100644
> --- a/drivers/leds/led-class.c
> +++ b/drivers/leds/led-class.c
> @@ -29,11 +29,14 @@ static ssize_t brightness_show(struct device *dev,
> struct device_attribute *attr, char *buf)
> {
> struct led_classdev *led_cdev = dev_get_drvdata(dev);
> + unsigned int brightness;
>
> - /* no lock needed for this */
> + mutex_lock(&led_cdev->led_access);
> led_update_brightness(led_cdev);
> + brightness = led_cdev->brightness;
> + mutex_unlock(&led_cdev->led_access);
>
> - return sprintf(buf, "%u\n", led_cdev->brightness);
> + return sprintf(buf, "%u\n", brightness);
> }
>
> static ssize_t brightness_store(struct device *dev,
> @@ -70,8 +73,13 @@ static ssize_t max_brightness_show(struct device *dev,
> struct device_attribute *attr, char *buf)
> {
> struct led_classdev *led_cdev = dev_get_drvdata(dev);
> + unsigned int max_brightness;
> +
> + mutex_lock(&led_cdev->led_access);
> + max_brightness = led_cdev->max_brightness;
> + mutex_unlock(&led_cdev->led_access);
>
> - return sprintf(buf, "%u\n", led_cdev->max_brightness);
> + return sprintf(buf, "%u\n", max_brightness);
> }
> static DEVICE_ATTR_RO(max_brightness);
>
> diff --git a/include/linux/leds.h b/include/linux/leds.h
> index e5968c3ed4ae..3524634fcc47 100644
> --- a/include/linux/leds.h
> +++ b/include/linux/leds.h
> @@ -238,7 +238,7 @@ struct led_classdev {
> struct kernfs_node *brightness_hw_changed_kn;
> #endif
>
> - /* Ensures consistent access to the LED Flash Class device */
> + /* Ensures consistent access to the LED Class device */
Nit: It was improper in the original comment as well:
s/Class/class/
> struct mutex led_access;
> };
>
Reviewed-by: Jacek Anaszewski <jacek.anaszewski@...il.com>
--
Best regards,
Jacek Anaszewski
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