From: Benjamin Tissoires <bentiss@kernel.org>
Date: Mon, 15 Dec 2025 11:57:21 +0000 (+0100)
Subject: HID: usbhid: paper over wrong bNumDescriptor field
X-Git-Tag: v6.19-rc5~30^2~20
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f28beb69c51517aec7067dfb2074e7c751542384;p=thirdparty%2Fkernel%2Fstable.git

HID: usbhid: paper over wrong bNumDescriptor field

Some faulty devices (ZWO EFWmini) have a wrong optional HID class
descriptor count compared to the provided length.

Given that we plainly ignore those optional descriptor, we can attempt
to fix the provided number so we do not lock out those devices.

Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
---

diff --git a/drivers/hid/usbhid/hid-core.c b/drivers/hid/usbhid/hid-core.c
index aac0051a2cf65..758eb21430cda 100644
--- a/drivers/hid/usbhid/hid-core.c
+++ b/drivers/hid/usbhid/hid-core.c
@@ -985,6 +985,7 @@ static int usbhid_parse(struct hid_device *hid)
 	struct usb_device *dev = interface_to_usbdev (intf);
 	struct hid_descriptor *hdesc;
 	struct hid_class_descriptor *hcdesc;
+	__u8 fixed_opt_descriptors_size;
 	u32 quirks = 0;
 	unsigned int rsize = 0;
 	char *rdesc;
@@ -1015,7 +1016,21 @@ static int usbhid_parse(struct hid_device *hid)
 			      (hdesc->bNumDescriptors - 1) * sizeof(*hcdesc)) {
 		dbg_hid("hid descriptor invalid, bLen=%hhu bNum=%hhu\n",
 			hdesc->bLength, hdesc->bNumDescriptors);
-		return -EINVAL;
+
+		/*
+		 * Some devices may expose a wrong number of descriptors compared
+		 * to the provided length.
+		 * However, we ignore the optional hid class descriptors entirely
+		 * so we can safely recompute the proper field.
+		 */
+		if (hdesc->bLength >= sizeof(*hdesc)) {
+			fixed_opt_descriptors_size = hdesc->bLength - sizeof(*hdesc);
+
+			hid_warn(intf, "fixing wrong optional hid class descriptors count\n");
+			hdesc->bNumDescriptors = fixed_opt_descriptors_size / sizeof(*hcdesc) + 1;
+		} else {
+			return -EINVAL;
+		}
 	}
 
 	hid->version = le16_to_cpu(hdesc->bcdHID);