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Sun, 13 Jul 2025 16:31:02 -0700 (PDT) Received: from qasdev.Home ([2a02:c7c:f4f0:900:20f4:6eb9:1d8b:99cc]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3b5e8dc21e7sm10865512f8f.36.2025.07.13.16.31.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 13 Jul 2025 16:31:02 -0700 (PDT) From: Qasim Ijaz To: jikos@kernel.org, bentiss@kernel.org Cc: gargaditya08@live.com, orlandoch.dev@gmail.com, linux-input@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: [PATCH] HID: apple: validate feature-report field count to prevent NULL pointer dereference Date: Mon, 14 Jul 2025 00:30:08 +0100 Message-Id: <20250713233008.15131-1-qasdev00@gmail.com> X-Mailer: git-send-email 2.39.5 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" A malicious HID device with quirk APPLE_MAGIC_BACKLIGHT can trigger a NULL pointer dereference whilst the power feature-report is toggled and sent to the device in apple_magic_backlight_report_set(). The power feature-report is expected to have two data fields, but if the descriptor declares one field then accessing field[1] and dereferencing it in apple_magic_backlight_report_set() becomes invalid since field[1] will be NULL. An example of a minimal descriptor which can cause the crash is something like the following where the report with ID 3 (power report) only references a single 1-byte field. When hid core parses the descriptor it will encounter the final feature tag, allocate a hid_report (all members of field[] will be zeroed out), create field structure and populate it, increasing the maxfield to 1. The subsequent field[1] access and dereference causes the crash. Usage Page (Vendor Defined 0xFF00) Usage (0x0F) Collection (Application) Report ID (1) Usage (0x01) Logical Minimum (0) Logical Maximum (255) Report Size (8) Report Count (1) Feature (Data,Var,Abs) Usage (0x02) Logical Maximum (32767) Report Size (16) Report Count (1) Feature (Data,Var,Abs) Report ID (3) Usage (0x03) Logical Minimum (0) Logical Maximum (1) Report Size (8) Report Count (1) Feature (Data,Var,Abs) End Collection Here we see the KASAN splat when the kernel dereferences the NULL pointer and crashes: [ 15.164723] Oops: general protection fault, probably for non-canonical= address 0xdffffc0000000006: 0000 [#1] SMP KASAN NOPTI [ 15.165691] KASAN: null-ptr-deref in range [0x0000000000000030-0x00000= 00000000037] [ 15.165691] CPU: 0 UID: 0 PID: 10 Comm: kworker/0:1 Not tainted 6.15.0= #31 PREEMPT(voluntary)=20 [ 15.165691] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIO= S 1.16.2-debian-1.16.2-1 04/01/2014 [ 15.165691] RIP: 0010:apple_magic_backlight_report_set+0xbf/0x210 [ 15.165691] Call Trace: [ 15.165691] [ 15.165691] apple_probe+0x571/0xa20 [ 15.165691] hid_device_probe+0x2e2/0x6f0 [ 15.165691] really_probe+0x1ca/0x5c0 [ 15.165691] __driver_probe_device+0x24f/0x310 [ 15.165691] driver_probe_device+0x4a/0xd0 [ 15.165691] __device_attach_driver+0x169/0x220 [ 15.165691] bus_for_each_drv+0x118/0x1b0 [ 15.165691] __device_attach+0x1d5/0x380 [ 15.165691] device_initial_probe+0x12/0x20 [ 15.165691] bus_probe_device+0x13d/0x180 [ 15.165691] device_add+0xd87/0x1510 [...] To fix this issue we should validate the number of fields that the backlight and power reports have and if they do not have the required number of fields then bail. Fixes: 394ba612f941 ("HID: apple: Add support for magic keyboard backlight = on T2 Macs") Cc: stable@vger.kernel.org Signed-off-by: Qasim Ijaz Reviewed-by: Orlando Chamberlain --- drivers/hid/hid-apple.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/hid/hid-apple.c b/drivers/hid/hid-apple.c index ed34f5cd5a91..183229ae5f02 100644 --- a/drivers/hid/hid-apple.c +++ b/drivers/hid/hid-apple.c @@ -890,7 +890,8 @@ static int apple_magic_backlight_init(struct hid_device= *hdev) backlight->brightness =3D report_enum->report_id_hash[APPLE_MAGIC_REPORT_= ID_BRIGHTNESS]; backlight->power =3D report_enum->report_id_hash[APPLE_MAGIC_REPORT_ID_PO= WER]; =20 - if (!backlight->brightness || !backlight->power) + if (!backlight->brightness || backlight->brightness->maxfield < 2 || + !backlight->power || backlight->power->maxfield < 2) return -ENODEV; =20 backlight->cdev.name =3D ":white:" LED_FUNCTION_KBD_BACKLIGHT; --=20 2.39.5