[PATCH AUTOSEL 6.16-5.4] HID: hid-ntrig: fix unable to handle page fault in ntrig_report_version()

[Sasha Levin <sashal@kernel.org>]

From: Minjong Kim <minbell.kim@samsung.com>

[ Upstream commit 185c926283da67a72df20a63a5046b3b4631b7d9 ]

in ntrig_report_version(), hdev parameter passed from hid_probe().
sending descriptor to /dev/uhid can make hdev->dev.parent->parent to null
if hdev->dev.parent->parent is null, usb_dev has
invalid address(0xffffffffffffff58) that hid_to_usb_dev(hdev) returned
when usb_rcvctrlpipe() use usb_dev,it trigger
page fault error for address(0xffffffffffffff58)

add null check logic to ntrig_report_version()
before calling hid_to_usb_dev()

Signed-off-by: Minjong Kim <minbell.kim@samsung.com>
Link: https://patch.msgid.link/20250813-hid-ntrig-page-fault-fix-v2-1-f98581f35106@samsung.com
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

Now let me analyze what I've found to make a decision on backporting.

## Backport Status: YES

This commit should be backported to stable kernel trees for the
following reasons:

### 1. **Critical Bug Fix - Kernel Page Fault**
The commit fixes a kernel page fault (crash) that can occur when using
N-Trig HID devices with virtual HID interfaces (through /dev/uhid). The
commit message describes:
- When descriptors are sent through /dev/uhid,
  `hdev->dev.parent->parent` can be NULL
- This causes `hid_to_usb_dev(hdev)` to return an invalid address
  (0xffffffffffffff58)
- When `usb_rcvctrlpipe()` tries to use this invalid pointer, it
  triggers a page fault

### 2. **Simple and Contained Fix**
The fix is minimal and surgical:
```c
+       if (!hid_is_usb(hdev))
+               return;
```
This adds a single safety check before attempting USB-specific
operations. The `hid_is_usb()` function is a well-established pattern in
the kernel for determining if an HID device is actually backed by USB.

### 3. **Follows Established Pattern**
The fix follows an established pattern in the kernel. My analysis shows:
- The `hid_is_usb()` helper was introduced specifically for this purpose
  (commit f83baa0cb6cfc)
- Multiple other HID drivers already use this check pattern to avoid
  similar issues
- Greg KH's original commit adding `hid_is_usb()` was marked for stable
  (`Cc: stable@vger.kernel.org`)

### 4. **Security Implications**
This bug could potentially be triggered from userspace through
/dev/uhid, making it a potential denial-of-service vector. Any userspace
application with access to /dev/uhid could potentially trigger a kernel
crash.

### 5. **Minimal Risk of Regression**
The fix:
- Only adds a defensive check that returns early if the device is not
  USB
- Does not change any existing logic for actual USB devices
- Cannot break existing functionality as it only prevents invalid memory
  access
- The kmalloc() allocation is moved after the check, which is also a
  good practice (avoiding unnecessary allocation)

### 6. **Affects Real Hardware**
N-Trig devices are real touchscreen/digitizer hardware used in various
tablets and touch-enabled devices. Users of these devices could
experience kernel crashes when virtual HID tools interact with the
driver.

### 7. **Clear Root Cause**
The commit clearly identifies the root cause: the `hid_to_usb_dev()`
macro directly dereferences `hdev->dev.parent->parent` without checking
if it's valid. For non-USB HID devices (like those created through
uhid), this pointer chain may not be valid.

The fix is appropriate for stable backporting as it:
- Fixes a real crash that affects users
- Is minimal and well-understood
- Follows established kernel patterns
- Has low risk of introducing new issues
- Addresses a potential security concern (userspace-triggerable crash)

 drivers/hid/hid-ntrig.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/hid/hid-ntrig.c b/drivers/hid/hid-ntrig.c
index 2738ce947434f..0f76e241e0afb 100644
--- a/drivers/hid/hid-ntrig.c
+++ b/drivers/hid/hid-ntrig.c
@@ -144,6 +144,9 @@ static void ntrig_report_version(struct hid_device *hdev)
 	struct usb_device *usb_dev = hid_to_usb_dev(hdev);
 	unsigned char *data = kmalloc(8, GFP_KERNEL);
 
+	if (!hid_is_usb(hdev))
+		return;
+
 	if (!data)
 		goto err_free;
 
-- 
2.50.1