[PATCH 1/3] hwmon: (coretemp) Check for NULL platform device in hotplug callbacks

[Guenter Roeck <linux@roeck-us.net>]

coretemp_get_pdev() returns NULL when topology_logical_die_id(cpu) is
negative (such as -ENODEV or -ERANGE from topology_get_logical_id() on a
firmware/hardware APIC ID mismatch) or exceeds max_zones (for example,
under asymmetric or anomalous ACPI die topologies where
topology_max_packages() * topology_max_dies_per_package() is smaller
than the logical die count).

Commit 6d03bbff456b ("hwmon: (coretemp) Simplify platform device
handling") pre-allocated zone_devices[0 .. max_zones - 1] during module
init and dropped the NULL checks on pdev in coretemp_cpu_online() and
coretemp_cpu_offline(), passing pdev unconditionally to
platform_get_drvdata(). When coretemp_get_pdev() returns NULL,
platform_get_drvdata(pdev) dereferences &pdev->dev and triggers a kernel
NULL pointer dereference.

Check for a NULL pdev and return 0 in both coretemp_cpu_online() and
coretemp_cpu_offline() before calling platform_get_drvdata(). Returning
0 in coretemp_cpu_online() ignores the unmapped CPU without blocking CPU
bringup or tearing down valid thermal zones on other dies.

Reported-by: Sashiko <sashiko-bot@kernel.org>
Fixes: 6d03bbff456b ("hwmon: (coretemp) Simplify platform device handling")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
 drivers/hwmon/coretemp.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/hwmon/coretemp.c b/drivers/hwmon/coretemp.c
index 3836beade59f..eb74ecd12310 100644
--- a/drivers/hwmon/coretemp.c
+++ b/drivers/hwmon/coretemp.c
@@ -695,6 +695,9 @@ static int coretemp_cpu_online(unsigned int cpu)
 	if (!housekeeping_cpu(cpu, HK_TYPE_MISC))
 		return 0;
 
+	if (!pdev)
+		return 0;
+
 	pdata = platform_get_drvdata(pdev);
 	if (!pdata->hwmon_dev) {
 		struct device *hwmon;
@@ -746,6 +749,9 @@ static int coretemp_cpu_offline(unsigned int cpu)
 		return 0;
 
 	/* If the physical CPU device does not exist, just return */
+	if (!pdev)
+		return 0;
+
 	pd = platform_get_drvdata(pdev);
 	if (!pd->hwmon_dev)
 		return 0;
-- 
2.45.2