From: Qasim Ijaz qasdev00@gmail.com

commit 1bb3363da862e0464ec050eea2fb5472a36ad86b upstream.

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 [0x0000000000000030-0x0000000000000037] [ 15.165691] CPU: 0 UID: 0 PID: 10 Comm: kworker/0:1 Not tainted 6.15.0 #31 PREEMPT(voluntary) [ 15.165691] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 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] <TASK> [ 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 qasdev00@gmail.com Reviewed-by: Orlando Chamberlain orlandoch.dev@gmail.com Tested-by: Aditya Garg gargaditya08@live.com Link: https://patch.msgid.link/20250713233008.15131-1-qasdev00@gmail.com Signed-off-by: Benjamin Tissoires bentiss@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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 d900dd05c335..c00ce5bfec4a 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 = report_enum->report_id_hash[APPLE_MAGIC_REPORT_ID_BRIGHTNESS]; backlight->power = report_enum->report_id_hash[APPLE_MAGIC_REPORT_ID_POWER];

- if (!backlight->brightness || !backlight->power) + if (!backlight->brightness || backlight->brightness->maxfield < 2 || + !backlight->power || backlight->power->maxfield < 2) return -ENODEV;

backlight->cdev.name = ":white:" LED_FUNCTION_KBD_BACKLIGHT;