usb: gadget: add WebUSB landing page support

There is a custom (non-USB IF) extension to the USB standard:

https://wicg.github.io/webusb/

This specification is published under the W3C Community Contributor
Agreement, which in particular allows to implement the specification
without any royalties.

The specification allows USB gadgets to announce an URL to landing
page and describes a Javascript interface for websites to interact
with the USB gadget, if the user allows it. It is currently
supported by Chromium-based browsers, such as Chrome, Edge and
Opera on all major operating systems including Linux.

This patch adds optional support for Linux-based USB gadgets
wishing to expose such a landing page.

During device enumeration, a host recognizes that the announced
USB version is at least 2.01, which means, that there are BOS
descriptors available. The device than announces WebUSB support
using a platform device capability. This includes a vendor code
under which the landing page URL can be retrieved using a
vendor-specific request.

Previously, the BOS descriptors would unconditionally include an
LPM related descriptor, as BOS descriptors were only ever sent
when the device was LPM capable. As this is no longer the case,
this patch puts this descriptor behind a lpm_capable condition.

Usage is modeled after os_desc descriptors:
echo 1 > webusb/use
echo "https://www.kernel.org" > webusb/landingPage

lsusb will report the device with the following lines:
  Platform Device Capability:
    bLength                24
    bDescriptorType        16
    bDevCapabilityType      5
    bReserved               0
    PlatformCapabilityUUID    {3408b638-09a9-47a0-8bfd-a0768815b665}
      WebUSB:
        bcdVersion    1.00
        bVendorCode      0
        iLandingPage     1 https://www.kernel.org

Signed-off-by: Jó Ágila Bitsch <jgilab@gmail.com>
Link: https://lore.kernel.org/r/Y8Crf8P2qAWuuk/F@jo-einhundert
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 166 insertions, 0 deletions

diff --git a/drivers/usb/gadget/configfs.c b/drivers/usb/gadget/configfs.c
index 96121d1c8df4..4a1236063c19 100644
--- a/drivers/usb/gadget/configfs.c
+++ b/drivers/usb/gadget/configfs.c
@@ -7,6 +7,7 @@
 #include <linux/nls.h>
 #include <linux/usb/composite.h>
 #include <linux/usb/gadget_configfs.h>
+#include <linux/usb/webusb.h>
 #include "configfs.h"
 #include "u_f.h"
 #include "u_os_desc.h"
@@ -39,6 +40,7 @@ struct gadget_info {
 	struct config_group configs_group;
 	struct config_group strings_group;
 	struct config_group os_desc_group;
+	struct config_group webusb_group;
 
 	struct mutex lock;
 	struct usb_gadget_strings *gstrings[MAX_USB_STRING_LANGS + 1];
@@ -50,6 +52,11 @@ struct gadget_info {
 	bool use_os_desc;
 	char b_vendor_code;
 	char qw_sign[OS_STRING_QW_SIGN_LEN];
+	bool use_webusb;
+	u16 bcd_webusb_version;
+	u8 b_webusb_vendor_code;
+	char landing_page[WEBUSB_URL_RAW_MAX_LENGTH];
+
 	spinlock_t spinlock;
 	bool unbind;
 };
@@ -780,6 +787,154 @@ static void gadget_strings_attr_release(struct config_item *item)
 USB_CONFIG_STRING_RW_OPS(gadget_strings);
 USB_CONFIG_STRINGS_LANG(gadget_strings, gadget_info);
 
+static inline struct gadget_info *webusb_item_to_gadget_info(
+		struct config_item *item)
+{
+	return container_of(to_config_group(item),
+			struct gadget_info, webusb_group);
+}
+
+static ssize_t webusb_use_show(struct config_item *item, char *page)
+{
+	return sysfs_emit(page, "%d\n",
+			webusb_item_to_gadget_info(item)->use_webusb);
+}
+
+static ssize_t webusb_use_store(struct config_item *item, const char *page,
+				 size_t len)
+{
+	struct gadget_info *gi = webusb_item_to_gadget_info(item);
+	int ret;
+	bool use;
+
+	mutex_lock(&gi->lock);
+	ret = kstrtobool(page, &use);
+	if (!ret) {
+		gi->use_webusb = use;
+		ret = len;
+	}
+	mutex_unlock(&gi->lock);
+
+	return ret;
+}
+
+static ssize_t webusb_bcdVersion_show(struct config_item *item, char *page)
+{
+	return sysfs_emit(page, "0x%04x\n",
+					webusb_item_to_gadget_info(item)->bcd_webusb_version);
+}
+
+static ssize_t webusb_bcdVersion_store(struct config_item *item,
+		const char *page, size_t len)
+{
+	struct gadget_info *gi = webusb_item_to_gadget_info(item);
+	u16 bcdVersion;
+	int ret;
+
+	mutex_lock(&gi->lock);
+	ret = kstrtou16(page, 0, &bcdVersion);
+	if (ret)
+		goto out;
+	ret = is_valid_bcd(bcdVersion);
+	if (ret)
+		goto out;
+
+	gi->bcd_webusb_version = bcdVersion;
+	ret = len;
+
+out:
+	mutex_unlock(&gi->lock);
+
+	return ret;
+}
+
+static ssize_t webusb_bVendorCode_show(struct config_item *item, char *page)
+{
+	return sysfs_emit(page, "0x%02x\n",
+			webusb_item_to_gadget_info(item)->b_webusb_vendor_code);
+}
+
+static ssize_t webusb_bVendorCode_store(struct config_item *item,
+					   const char *page, size_t len)
+{
+	struct gadget_info *gi = webusb_item_to_gadget_info(item);
+	int ret;
+	u8 b_vendor_code;
+
+	mutex_lock(&gi->lock);
+	ret = kstrtou8(page, 0, &b_vendor_code);
+	if (!ret) {
+		gi->b_webusb_vendor_code = b_vendor_code;
+		ret = len;
+	}
+	mutex_unlock(&gi->lock);
+
+	return ret;
+}
+
+static ssize_t webusb_landingPage_show(struct config_item *item, char *page)
+{
+	return sysfs_emit(page, "%s\n", webusb_item_to_gadget_info(item)->landing_page);
+}
+
+static ssize_t webusb_landingPage_store(struct config_item *item, const char *page,
+				     size_t len)
+{
+	struct gadget_info *gi = webusb_item_to_gadget_info(item);
+	unsigned int bytes_to_strip = 0;
+	int l = len;
+
+	if (page[l - 1] == '\n') {
+		--l;
+		++bytes_to_strip;
+	}
+
+	if (l > sizeof(gi->landing_page)) {
+		pr_err("webusb: landingPage URL too long\n");
+		return -EINVAL;
+	}
+
+	// validation
+	if (strncasecmp(page, "https://",  8) == 0)
+		bytes_to_strip = 8;
+	else if (strncasecmp(page, "http://", 7) == 0)
+		bytes_to_strip = 7;
+	else
+		bytes_to_strip = 0;
+
+	if (l > U8_MAX - WEBUSB_URL_DESCRIPTOR_HEADER_LENGTH + bytes_to_strip) {
+		pr_err("webusb: landingPage URL %d bytes too long for given URL scheme\n",
+			l - U8_MAX + WEBUSB_URL_DESCRIPTOR_HEADER_LENGTH - bytes_to_strip);
+		return -EINVAL;
+	}
+
+	mutex_lock(&gi->lock);
+	// ensure 0 bytes are set, in case the new landing page is shorter then the old one.
+	memset(gi->landing_page, 0, sizeof(gi->landing_page));
+	memcpy(gi->landing_page, page, l);
+	mutex_unlock(&gi->lock);
+
+	return len;
+}
+
+CONFIGFS_ATTR(webusb_, use);
+CONFIGFS_ATTR(webusb_, bVendorCode);
+CONFIGFS_ATTR(webusb_, bcdVersion);
+CONFIGFS_ATTR(webusb_, landingPage);
+
+static struct configfs_attribute *webusb_attrs[] = {
+	&webusb_attr_use,
+	&webusb_attr_bcdVersion,
+	&webusb_attr_bVendorCode,
+	&webusb_attr_landingPage,
+	NULL,
+};
+
+static struct config_item_type webusb_type = {
+	.ct_attrs	= webusb_attrs,
+	.ct_owner	= THIS_MODULE,
+};
+
 static inline struct gadget_info *os_desc_item_to_gadget_info(
 		struct config_item *item)
 {
@@ -1341,6 +1496,13 @@ static int configfs_composite_bind(struct usb_gadget *gadget,
 		gi->cdev.desc.iSerialNumber = s[USB_GADGET_SERIAL_IDX].id;
 	}
 
+	if (gi->use_webusb) {
+		cdev->use_webusb = true;
+		cdev->bcd_webusb_version = gi->bcd_webusb_version;
+		cdev->b_webusb_vendor_code = gi->b_webusb_vendor_code;
+		memcpy(cdev->landing_page, gi->landing_page, WEBUSB_URL_RAW_MAX_LENGTH);
+	}
+
 	if (gi->use_os_desc) {
 		cdev->use_os_string = true;
 		cdev->b_vendor_code = gi->b_vendor_code;
@@ -1605,6 +1767,10 @@ static struct config_group *gadgets_make(
 			&os_desc_type);
 	configfs_add_default_group(&gi->os_desc_group, &gi->group);
 
+	config_group_init_type_name(&gi->webusb_group, "webusb",
+			&webusb_type);
+	configfs_add_default_group(&gi->webusb_group, &gi->group);
+
 	gi->composite.bind = configfs_do_nothing;
 	gi->composite.unbind = configfs_do_nothing;
 	gi->composite.suspend = NULL;