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

[Aleksa Savic <savicaleksa83@gmail.com>]

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@gmail.com>
---
 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);
-- 
2.44.0