linux-kernel - Re: [PATCH] HID: logitech-hidpp: fix NULL pointer dereference in hidpp_get_report

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Message-ID: <CALEuBakRd8W-FvOiuih-CsEQH-CL_S1MBVVsOUj9g22zjxPEdQ@mail.gmail.com>
Date: Thu, 15 Jan 2026 22:17:23 +0800
From: 齐柯宇 <qikeyu2017@...il.com>
To: Bastien Nocera <hadess@...ess.net>
Cc: jikos@...nel.org, bentiss@...nel.org, lains@...eup.net, hansg@...nel.org, 
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] HID: logitech-hidpp: fix NULL pointer dereference in hidpp_get_report_length()

Hello,

Thank you for the review. I apologize for the format issue and will
resend the patch as plain text following the documentation guidelines.

Best regards,

Kery

Bastien Nocera <hadess@...ess.net> 于2026年1月15日周四 20:03写道：
>
> Hello,
>
> Patch looks good, but you will need to resend it as plain text, as per
> the submitting patches documentation:
> https://www.kernel.org/doc/html/v6.17/process/submitting-patches.html#no-mime-no-links-no-compression-no-attachments-just-plain-text
>
> Regards
>
> On Thu, 2026-01-15 at 01:48 +0800, 齐柯宇 wrote:
> > Add validation for report->maxfield and report->field[0] before
> > dereferencing to prevent NULL pointer dereference.
> >
> > The HID report descriptor is provided by the USB device firmware via
> > USB control transfer (GET_DESCRIPTOR). A malicious device can craft
> > a descriptor that defines an OUTPUT report without any usages
> > (padding fields). When the HID subsystem parses such a descriptor:
> >
> > 1. hid_add_field() calls hid_register_report() to create the report
> >    object and stores it in report_id_hash[id]
> > 2. Since parser->local.usage_index is 0, hid_add_field() returns
> > early
> >    without calling hid_register_field() to add any fields
> > 3. Result: report exists with maxfield=0 and field[0]=NULL
> >
> > When hidpp_probe() is called for a device matching this driver:
> >   - hidpp_validate_device() calls hidpp_get_report_length()
> >   - hidpp_get_report_length() retrieves the report from hash (not
> > NULL)
> >   - It then dereferences report->field[0]->report_count
> >   - Since field[0] is NULL, this triggers a kernel NULL pointer
> >     dereference
> >
> > Data flow from attacker to crash:
> >   Malicious USB Device
> >        |
> >        v (USB GET_DESCRIPTOR control transfer)
> >   hid_get_class_descriptor() -- reads HID report descriptor from
> > device
> >        |
> >        v
> >   hid_parse_report() -- stores descriptor in hid->dev_rdesc
> >        |
> >        v
> >   hid_open_report() -> hid_add_field()
> >        |                    |
> >        |                    v
> >        |              hid_register_report() -- creates report,
> > maxfield=0
> >        |                    |
> >        |                    v
> >        |              returns early if usage_index==0, no field added
> >        |
> >        v
> >   hidpp_validate_device() -> hidpp_get_report_length()
> >        |
> >        v
> >   report->field[0]->report_count -- NULL pointer dereference!
> >
> > This is triggerable by an attacker with physical access using a
> > malicious USB device (e.g., BadUSB, programmable USB development
> > boards).
> >
> > Fixes: d71b18f7c7999 ("HID: logitech-hidpp: do not hardcode very long
> > report length")
> > Signed-off-by: Kery Qi <qikeyu2017@...il.com>
> > ---
> >  drivers/hid/hid-logitech-hidpp.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/hid/hid-logitech-hidpp.c b/drivers/hid/hid-
> > logitech-hidpp.c
> > index d5011a5d0890..02ddbd658e89 100644
> > --- a/drivers/hid/hid-logitech-hidpp.c
> > +++ b/drivers/hid/hid-logitech-hidpp.c
> > @@ -4314,7 +4314,7 @@ static int hidpp_get_report_length(struct
> > hid_device *hdev, int id)
> >
> >         re = &(hdev->report_enum[HID_OUTPUT_REPORT]);
> >         report = re->report_id_hash[id];
> > -       if (!report)
> > +       if (!report || report->maxfield < 1 || !report->field[0])
> >                 return 0;
> >
> >         return report->field[0]->report_count + 1;
> > --
> > 2.34.1