[PATCH v2] ACPI: PCI: Clear driver_data on all paths that free the acpi_pci_root

acpi_pci_root_add() assigns the freshly allocated root to
device->driver_data before dmar_device_add() and pci_acpi_scan_root().
Both failure paths reach the end: label where root is kfree()'d, but
only the pci_acpi_scan_root() path clears driver_data first.

When dmar_device_add() fails during a hot-add, root is freed while
device->driver_data still points at it.  The ACPI core does not clear
driver_data on attach failure, so a later acpi_pci_find_root() call may
dereference this dangling pointer.

acpi_pci_root_remove() has the same problem: it frees root without
clearing device->driver_data, leaving a dangling pointer behind after
the root bridge is removed.

Move the NULL assignment to the shared end: label so every error path in
acpi_pci_root_add() clears driver_data before freeing root, and clear it
in acpi_pci_root_remove() as well, so the object is never left reachable
through driver_data after being freed.

Fixes: db89b4f0dbab ("ACPI: catch calls of acpi_driver_data on pointer of wrong type")
Reported-by: Sashiko AI review <[email protected]>
Link: https://sashiko.dev/#/patchset/[email protected]
Link: https://sashiko.dev/#/patchset/[email protected]
Signed-off-by: Chen Pei <[email protected]>
---
Changes in v2:
 - Also clear device->driver_data in acpi_pci_root_remove() before
   kfree(root), so the remove path no longer leaves a dangling pointer
   (Sashiko AI review).

 drivers/acpi/pci_root.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
index 4c06c3ffd0cb..408ba12362a7 100644
--- a/drivers/acpi/pci_root.c
+++ b/drivers/acpi/pci_root.c
@@ -725,7 +725,6 @@ static int acpi_pci_root_add(struct acpi_device *device,
 		dev_err(&device->dev,
 			"Bus %04x:%02x not present in PCI namespace\n",
 			root->segment, (unsigned int)root->secondary.start);
-		device->driver_data = NULL;
 		result = -ENODEV;
 		goto remove_dmar;
 	}
@@ -765,6 +764,7 @@ static int acpi_pci_root_add(struct acpi_device *device,
 	if (hotadd)
 		dmar_device_remove(handle);
 end:
+	device->driver_data = NULL;
 	kfree(root);
 	return result;
 }
@@ -788,6 +788,7 @@ static void acpi_pci_root_remove(struct acpi_device *device)
 
 	pci_unlock_rescan_remove();
 
+	device->driver_data = NULL;
 	kfree(root);
 }
 
-- 
2.50.1