From 76579d21abb2ae22a7e19be1dd71af9cad10da4f Mon Sep 17 00:00:00 2001
From: Johann Fischer <johann.fischer@nordicsemi.no>
Date: Tue, 17 Jun 2025 10:20:46 +0200
Subject: [PATCH] usb: device_next: allow to limit number or digits in serial
 number

Add Kconfig option to limit the length requested from HWINFO to a
meaningful number of digits. Also, check the length returned by the
HWINFO driver and rename the variables to a more suitable name.

Signed-off-by: Johann Fischer <johann.fischer@nordicsemi.no>
---
 subsys/usb/device_next/Kconfig    | 10 ++++++++++
 subsys/usb/device_next/usbd_ch9.c | 25 +++++++++++++------------
 2 files changed, 23 insertions(+), 12 deletions(-)

diff --git a/subsys/usb/device_next/Kconfig b/subsys/usb/device_next/Kconfig
index b72de53f0b3..18b6860b0e6 100644
--- a/subsys/usb/device_next/Kconfig
+++ b/subsys/usb/device_next/Kconfig
@@ -96,6 +96,16 @@ config USBD_MSG_WORK_DELAY
 	  Message work may need to be delayed because the device stack is not
 	  yet ready to publish the message. The delay unit is milliseconds.
 
+config USBD_HWINFO_DEVID_LENGTH
+	int "The length of the device ID requested from HWINFO in bytes"
+	depends on HWINFO
+	range 8 128
+	default 16
+	help
+	  Each byte represents two digits in the serial number string
+	  descriptor. This option can be used to limit the length requested
+	  from HWINFO to a meaningful number of digits.
+
 rsource "class/Kconfig"
 rsource "app/Kconfig.cdc_acm_serial"
 
diff --git a/subsys/usb/device_next/usbd_ch9.c b/subsys/usb/device_next/usbd_ch9.c
index 3adb3574f0c..599eb161178 100644
--- a/subsys/usb/device_next/usbd_ch9.c
+++ b/subsys/usb/device_next/usbd_ch9.c
@@ -533,13 +533,13 @@ static int sreq_get_desc_cfg(struct usbd_context *const uds_ctx,
 	return 0;
 }
 
-#define USBD_HWID_SN_MAX 32U
+#define USBD_SN_ASCII7_LENGTH (CONFIG_USBD_HWINFO_DEVID_LENGTH * 2)
 
 /* Generate valid USB device serial number from hwid */
-static ssize_t get_sn_from_hwid(uint8_t sn[static USBD_HWID_SN_MAX])
+static ssize_t get_sn_from_hwid(uint8_t sn[static USBD_SN_ASCII7_LENGTH])
 {
 	static const char hex[] = "0123456789ABCDEF";
-	uint8_t hwid[USBD_HWID_SN_MAX / 2U];
+	uint8_t hwid[USBD_SN_ASCII7_LENGTH / 2U];
 	ssize_t hwid_len = -ENOSYS;
 
 	if (IS_ENABLED(CONFIG_HWINFO)) {
@@ -554,36 +554,37 @@ static ssize_t get_sn_from_hwid(uint8_t sn[static USBD_HWID_SN_MAX])
 		return hwid_len;
 	}
 
-	for (ssize_t i = 0; i < hwid_len; i++) {
+	for (ssize_t i = 0; i < MIN(hwid_len, sizeof(hwid)); i++) {
 		sn[i * 2] = hex[hwid[i] >> 4];
 		sn[i * 2 + 1] = hex[hwid[i] & 0xF];
 	}
 
-	return hwid_len * 2;
+	return MIN(hwid_len, sizeof(hwid)) * 2;
 }
 
 /* Copy and convert ASCII-7 string descriptor to UTF16-LE */
 static void string_ascii7_to_utf16le(struct usbd_desc_node *const dn,
 				     struct net_buf *const buf, const uint16_t wLength)
 {
-	uint8_t hwid_sn[USBD_HWID_SN_MAX];
+	uint8_t sn_ascii7_str[USBD_SN_ASCII7_LENGTH];
 	struct usb_desc_header head = {
 		.bDescriptorType = dn->bDescriptorType,
 	};
-	uint8_t *ascii7_str;
+	const uint8_t *ascii7_str;
 	size_t len;
 	size_t i;
 
-	if (dn->str.utype == USBD_DUT_STRING_SERIAL_NUMBER && dn->str.use_hwinfo) {
-		ssize_t hwid_len = get_sn_from_hwid(hwid_sn);
+	if (IS_ENABLED(CONFIG_HWINFO) &&
+	    dn->str.utype == USBD_DUT_STRING_SERIAL_NUMBER && dn->str.use_hwinfo) {
+		ssize_t sn_ascii7_str_len = get_sn_from_hwid(sn_ascii7_str);
 
-		if (hwid_len < 0) {
+		if (sn_ascii7_str_len < 0) {
 			errno = -ENOTSUP;
 			return;
 		}
 
-		head.bLength = sizeof(head) + hwid_len * 2;
-		ascii7_str = hwid_sn;
+		head.bLength = sizeof(head) + sn_ascii7_str_len * 2;
+		ascii7_str = sn_ascii7_str;
 	} else {
 		head.bLength = dn->bLength;
 		ascii7_str = (uint8_t *)dn->ptr;