Re: [PATCH 3/3] hwmon: (corsair-cpro) Protect ccp->wait_input_report with a spinlock

[Marius Zachmann]

On 04.05.24 at 11:25:03 MESZ, Aleksa Savic wrote
> Through hidraw, userspace can cause a status report to be sent
> from the device. The parsing in ccp_raw_event() may happen in
> parallel to a send_usb_cmd() call (which resets the completion
> for tracking the report) if it's running on a different CPU where
> bottom half interrupts are not disabled.
> 
> Add a spinlock around the complete_all() in ccp_raw_event() and
> reinit_completion() in send_usb_cmd() to prevent race issues.
> 
> Fixes: 40c3a4454225 ("hwmon: add Corsair Commander Pro driver")
> Signed-off-by: Aleksa Savic <savicaleksa83@xxxxxxxxx>
> ---
>  drivers/hwmon/corsair-cpro.c | 24 +++++++++++++++++++-----
>  1 file changed, 19 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/hwmon/corsair-cpro.c b/drivers/hwmon/corsair-cpro.c
> index 6ab4d2478b1f..3e63666a61bd 100644
> --- a/drivers/hwmon/corsair-cpro.c
> +++ b/drivers/hwmon/corsair-cpro.c
> @@ -16,6 +16,7 @@
>  #include <linux/module.h>
>  #include <linux/mutex.h>
>  #include <linux/slab.h>
> +#include <linux/spinlock.h>
>  #include <linux/types.h>
>  
>  #define USB_VENDOR_ID_CORSAIR			0x1b1c
> @@ -77,6 +78,8 @@
>  struct ccp_device {
>  	struct hid_device *hdev;
>  	struct device *hwmon_dev;
> +	/* For reinitializing the completion below */
> +	spinlock_t wait_input_report_lock;
>  	struct completion wait_input_report;
>  	struct mutex mutex; /* whenever buffer is used, lock before send_usb_cmd */
>  	u8 *cmd_buffer;
> @@ -118,7 +121,15 @@ static int send_usb_cmd(struct ccp_device *ccp, u8 command, u8 byte1, u8 byte2,
>  	ccp->cmd_buffer[2] = byte2;
>  	ccp->cmd_buffer[3] = byte3;
>  
> +	/*
> +	 * Disable raw event parsing for a moment to safely reinitialize the
> +	 * completion. Reinit is done because hidraw could have triggered
> +	 * the raw event parsing and marked the ccp->wait_input_report
> +	 * completion as done.
> +	 */
> +	spin_lock_bh(&ccp->wait_input_report_lock);
>  	reinit_completion(&ccp->wait_input_report);
> +	spin_unlock_bh(&ccp->wait_input_report_lock);
>  
>  	ret = hid_hw_output_report(ccp->hdev, ccp->cmd_buffer, OUT_BUFFER_SIZE);
>  	if (ret < 0)
> @@ -136,11 +147,12 @@ static int ccp_raw_event(struct hid_device *hdev, struct hid_report *report, u8
>  	struct ccp_device *ccp = hid_get_drvdata(hdev);
>  
>  	/* only copy buffer when requested */
> -	if (completion_done(&ccp->wait_input_report))
> -		return 0;
> -
> -	memcpy(ccp->buffer, data, min(IN_BUFFER_SIZE, size));
> -	complete_all(&ccp->wait_input_report);
> +	spin_lock(&ccp->wait_input_report_lock);
> +	if (!completion_done(&ccp->wait_input_report)) {
> +		memcpy(ccp->buffer, data, min(IN_BUFFER_SIZE, size));
> +		complete_all(&ccp->wait_input_report);
> +	}
> +	spin_unlock(&ccp->wait_input_report_lock);
>  
>  	return 0;
>  }
> @@ -515,7 +527,9 @@ static int ccp_probe(struct hid_device *hdev, const struct hid_device_id *id)
>  
>  	ccp->hdev = hdev;
>  	hid_set_drvdata(hdev, ccp);
> +
>  	mutex_init(&ccp->mutex);
> +	spin_lock_init(&ccp->wait_input_report_lock);
>  	init_completion(&ccp->wait_input_report);
>  
>  	hid_device_io_start(hdev);
> 

Acked-by: Marius Zachmann <mail@xxxxxxxxxxxxxxxxx>