[PATCH v2] HID: haptic: fix use-after-free of devm haptic data in hid_haptic_destroy()

[Aldo Ariel Panzardo <qwe.aldo@gmail.com>]

mt_probe() allocates td->haptic with devm_kzalloc(), tying its
lifetime to the HID device's driver unbind.  hid_haptic_init() then
installs hid_haptic_destroy() as the force-feedback destroy callback,
which dereferences haptic->hdev on its very first line.

When the HID device is removed while a process still holds an evdev
fd, devres frees td->haptic at unbind time, but hid_haptic_destroy()
runs later from input_dev_release() when the last fd closes.  The
callback operates on freed memory.

The existing get_device()/put_device() pair in init/destroy pins the
struct hid_device but does not keep its devres allocations alive,
since devres runs at driver unbind, not at the final device kref put.

Replace devm_kzalloc() with plain kzalloc() for the haptic struct so
it outlives the driver.  Free it at the end of hid_haptic_destroy(),
which already tears down every sub-allocation manually and holds a
device reference that keeps hdev alive until the kfree.  On the
non-haptic path and the pre-hid_hw_start error paths in mt_probe(),
use kfree() instead of devm_kfree().

Fixes: 8d0bf7908b5a ("HID: multitouch: add haptic multitouch support")
Cc: stable@vger.kernel.org
Signed-off-by: Aldo Ariel Panzardo <qwe.aldo@gmail.com>
---
v2: do not free td->haptic on hid_hw_start() failure — if
    hid_haptic_init() ran inside hid_hw_start() and installed the
    FF destroy callback, the internal cleanup already frees the
    struct via hid_haptic_destroy().  Only free it on the error
    paths before hid_hw_start() (found by Sashiko AI review).

 drivers/hid/hid-haptic.c     |  2 ++
 drivers/hid/hid-multitouch.c | 16 +++++++++++-----
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/drivers/hid/hid-haptic.c b/drivers/hid/hid-haptic.c
index 8760eeb08..6c365dbf0 100644
--- a/drivers/hid/hid-haptic.c
+++ b/drivers/hid/hid-haptic.c
@@ -406,6 +406,8 @@ static void hid_haptic_destroy(struct ff_device *ff)
 	haptic->hid_usage_map = NULL;
 
 	module_put(THIS_MODULE);
+
+	kfree(haptic);
 }
 
 int hid_haptic_init(struct hid_device *hdev,
diff --git a/drivers/hid/hid-multitouch.c b/drivers/hid/hid-multitouch.c
index 4e19a0c4d..f4d8d640d 100644
--- a/drivers/hid/hid-multitouch.c
+++ b/drivers/hid/hid-multitouch.c
@@ -2132,7 +2132,7 @@ static int mt_probe(struct hid_device *hdev, const struct hid_device_id *id)
 		dev_err(&hdev->dev, "cannot allocate multitouch data\n");
 		return -ENOMEM;
 	}
-	td->haptic = devm_kzalloc(&hdev->dev, sizeof(*(td->haptic)), GFP_KERNEL);
+	td->haptic = kzalloc(sizeof(*(td->haptic)), GFP_KERNEL);
 	if (!td->haptic)
 		return -ENOMEM;
 
@@ -2181,12 +2181,14 @@ static int mt_probe(struct hid_device *hdev, const struct hid_device_id *id)
 
 	ret = hid_parse(hdev);
 	if (ret != 0)
-		return ret;
+		goto err_free_haptic;
 
 	if (mtclass->name == MT_CLS_APPLE_TOUCHBAR &&
 	    !hid_find_field(hdev, HID_INPUT_REPORT,
-			    HID_DG_TOUCHPAD, HID_DG_TRANSDUCER_INDEX))
-		return -ENODEV;
+			    HID_DG_TOUCHPAD, HID_DG_TRANSDUCER_INDEX)) {
+		ret = -ENODEV;
+		goto err_free_haptic;
+	}
 
 	if (mtclass->quirks & MT_QUIRK_FIX_CONST_CONTACT_ID)
 		mt_fix_const_fields(hdev, HID_DG_CONTACTID);
@@ -2206,9 +2208,13 @@ static int mt_probe(struct hid_device *hdev, const struct hid_device_id *id)
 	mt_set_modes(hdev, HID_LATENCY_NORMAL, TOUCHPAD_REPORT_ALL);
 
 	if (!td->is_haptic_touchpad)
-		devm_kfree(&hdev->dev, td->haptic);
+		kfree(td->haptic);
 
 	return 0;
+
+err_free_haptic:
+	kfree(td->haptic);
+	return ret;
 }
 
 static int mt_suspend(struct hid_device *hdev, pm_message_t state)
-- 
2.43.0