Since commit e2ffcda16290 ("ACPI: OSL: Allow Notify () handlers to run on
all CPUs") ACPI notify handlers like the intel-hid notify_handler() may
run on multiple CPU cores racing with themselves.

On convertibles and detachables (matched by DMI chassis-type 31 and 32 in
dmi_auto_add_switch[]) the SW_TABLET_MODE input device is registered
lazily from notify_handler() on the first tablet-mode event, via
intel_hid_switches_setup(). When two such events race on different CPUs
both can pass the !priv->switches check and register the priv->switches
input device twice, resulting in a duplicate sysfs entry and a subsequent
NULL pointer dereference.

This is the same class of bug fixed by commit e075c3b13a0a ("platform/x86:
intel-vbtn: Protect ACPI notify handler against recursion") for the
sibling intel-vbtn driver.

Protect intel-hid notify_handler() from racing with itself with a mutex
to fix this.

Fixes: e2ffcda16290 ("ACPI: OSL: Allow Notify () handlers to run on all CPUs")
Cc: stable@vger.kernel.org
Signed-off-by: HyeongJun An <sammiee5311@gmail.com>
---
 drivers/platform/x86/intel/hid.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/platform/x86/intel/hid.c b/drivers/platform/x86/intel/hid.c
index 085093506dda..6b4bac5f7051 100644
--- a/drivers/platform/x86/intel/hid.c
+++ b/drivers/platform/x86/intel/hid.c
@@ -7,11 +7,13 @@
  */
 
 #include <linux/acpi.h>
+#include <linux/cleanup.h>
 #include <linux/dmi.h>
 #include <linux/input.h>
 #include <linux/input/sparse-keymap.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
+#include <linux/mutex.h>
 #include <linux/platform_device.h>
 #include <linux/string_choices.h>
 #include <linux/suspend.h>
@@ -230,6 +232,7 @@ static const struct dmi_system_id dmi_auto_add_switch[] = {
 };
 
 struct intel_hid_priv {
+	struct mutex mutex; /* Avoid notify_handler() racing with itself */
 	struct input_dev *input_dev;
 	struct input_dev *array;
 	struct input_dev *switches;
@@ -565,6 +568,8 @@ static void notify_handler(acpi_handle handle, u32 event, void *context)
 	struct key_entry *ke;
 	int err;
 
+	guard(mutex)(&priv->mutex);
+
 	/*
 	 * Some convertible have unreliable VGBS return which could cause incorrect
 	 * SW_TABLET_MODE report, in these cases we enable support when receiving
@@ -720,6 +725,10 @@ static int intel_hid_probe(struct platform_device *device)
 		return -ENOMEM;
 	dev_set_drvdata(&device->dev, priv);
 
+	err = devm_mutex_init(&device->dev, &priv->mutex);
+	if (err)
+		return err;
+
 	/* See dual_accel_detect.h for more info on the dual_accel check. */
 	if (enable_sw_tablet_mode == TABLET_SW_AUTO) {
 		if (dmi_check_system(dmi_vgbs_allow_list))
-- 
2.43.0