[PATCH v2 1/2] soc: xilinx: Fix race condition in event registration

[Prasanna Kumar T S M <ptsm@linux.microsoft.com>]

The zynqmp_power driver registers handlers for suspend and subsystem
restart events using register_event(). However, the work structures
(zynqmp_pm_init_suspend_work and zynqmp_pm_init_restart_work) used by
these handlers were allocated and initialized after the registration
call.

This created a race window where, if the firmware triggered an event
immediately after registration but before allocation, the callback
(suspend_event_callback or subsystem_restart_event_callback) would
dereference a NULL pointer in work_pending(), leading to a crash.

Fix this by allocating and initializing the work structures before
registering the events.

Fixes: fcf544ac6439 ("soc: xilinx: Add cb event for subsystem restart")
Signed-off-by: Prasanna Kumar T S M <ptsm@linux.microsoft.com>
---
 drivers/soc/xilinx/zynqmp_power.c | 43 ++++++++++++-------------------
 1 file changed, 17 insertions(+), 26 deletions(-)

diff --git a/drivers/soc/xilinx/zynqmp_power.c b/drivers/soc/xilinx/zynqmp_power.c
index 9085db1b480a..9dd938bd01d8 100644
--- a/drivers/soc/xilinx/zynqmp_power.c
+++ b/drivers/soc/xilinx/zynqmp_power.c
@@ -303,18 +303,18 @@ static int zynqmp_pm_probe(struct platform_device *pdev)
 	 * is not available to use) or -ENODEV(Xilinx Event Manager not compiled),
 	 * then use ipi-mailbox or interrupt method.
 	 */
+	zynqmp_pm_init_suspend_work = devm_kzalloc(&pdev->dev,
+						   sizeof(struct zynqmp_pm_work_struct),
+						   GFP_KERNEL);
+	if (!zynqmp_pm_init_suspend_work)
+		return -ENOMEM;
+
+	INIT_WORK(&zynqmp_pm_init_suspend_work->callback_work,
+		  zynqmp_pm_init_suspend_work_fn);
+
 	ret = register_event(&pdev->dev, PM_INIT_SUSPEND_CB, 0, 0, false,
 			     suspend_event_callback);
 	if (!ret) {
-		zynqmp_pm_init_suspend_work = devm_kzalloc(&pdev->dev,
-							   sizeof(struct zynqmp_pm_work_struct),
-							   GFP_KERNEL);
-		if (!zynqmp_pm_init_suspend_work)
-			return -ENOMEM;
-
-		INIT_WORK(&zynqmp_pm_init_suspend_work->callback_work,
-			  zynqmp_pm_init_suspend_work_fn);
-
 		ret = zynqmp_pm_get_family_info(&pm_family_code);
 		if (ret < 0)
 			return ret;
@@ -326,14 +326,6 @@ static int zynqmp_pm_probe(struct platform_device *pdev)
 		else
 			return -ENODEV;
 
-		ret = register_event(&pdev->dev, PM_NOTIFY_CB, node_id, EVENT_SUBSYSTEM_RESTART,
-				     false, subsystem_restart_event_callback);
-		if (ret) {
-			dev_err(&pdev->dev, "Failed to Register with Xilinx Event manager %d\n",
-				ret);
-			return ret;
-		}
-
 		zynqmp_pm_init_restart_work = devm_kzalloc(&pdev->dev,
 							   sizeof(struct zynqmp_pm_work_struct),
 							   GFP_KERNEL);
@@ -342,19 +334,18 @@ static int zynqmp_pm_probe(struct platform_device *pdev)
 
 		INIT_WORK(&zynqmp_pm_init_restart_work->callback_work,
 			  zynqmp_pm_subsystem_restart_work_fn);
+
+		ret = register_event(&pdev->dev, PM_NOTIFY_CB, node_id, EVENT_SUBSYSTEM_RESTART,
+				     false, subsystem_restart_event_callback);
+		if (ret) {
+			dev_err(&pdev->dev, "Failed to Register with Xilinx Event manager %d\n",
+				ret);
+			return ret;
+		}
 	} else if (ret != -EACCES && ret != -ENODEV) {
 		dev_err(&pdev->dev, "Failed to Register with Xilinx Event manager %d\n", ret);
 		return ret;
 	} else if (of_property_present(pdev->dev.of_node, "mboxes")) {
-		zynqmp_pm_init_suspend_work =
-			devm_kzalloc(&pdev->dev,
-				     sizeof(struct zynqmp_pm_work_struct),
-				     GFP_KERNEL);
-		if (!zynqmp_pm_init_suspend_work)
-			return -ENOMEM;
-
-		INIT_WORK(&zynqmp_pm_init_suspend_work->callback_work,
-			  zynqmp_pm_init_suspend_work_fn);
 		client = devm_kzalloc(&pdev->dev, sizeof(*client), GFP_KERNEL);
 		if (!client)
 			return -ENOMEM;
-- 
2.49.0