FAILED: patch "[PATCH] hwmon: (coretemp) Check for NULL platform device in hotplug callbacks" failed to apply to 5.15-stable tree

[Sasha Levin <sashal@kernel.org>]

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 0f9c7ed3b5009a037e5533eac03a0d4d45ecf1f0
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '20261109202142-failed-5.15-0f9c7ed3b500@kernel.org' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From 0f9c7ed3b5009a037e5533eac03a0d4d45ecf1f0 Mon Sep 17 00:00:00 2001
From: Guenter Roeck <linux@roeck-us.net>
Date: Sat, 31 Oct 2026 03:08:08 +0000
Subject: [PATCH] hwmon: (coretemp) Check for NULL platform device in hotplug
 callbacks
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

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")
Cc: stable@vger.kernel.org
Tested-by: Asaf Nuri Bertizlioğlu <ycistak@gmail.com>
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 3836beade59f4..eb74ecd12310a 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;
-- 
2.53.0