Parse USB interface association descriptors.

USB interface association descriptors are used to combine multiple
interfaces into a single functional group. This patch adds support for
parsing them out of the |extra_data| field left by libusb's parsing of
configuration, interface and endpoint descriptors. The resulting
association is then represented by setting the |first_interface| field
of each interface in a function to the |interface_number| of the first
interface in the function.

WebUSB will use these associations to set permissions for an entire
function with a single descriptor.

BUG=492204

Review URL: https://codereview.chromium.org/1568673002

Cr-Commit-Position: refs/heads/master@{#375324}

1 files changed, 80 insertions, 1 deletions

diff --git a/device/usb/usb_descriptors.cc b/device/usb/usb_descriptors.cc
index 6defda8..22414d7 100644
--- a/device/usb/usb_descriptors.cc
+++ b/device/usb/usb_descriptors.cc
@@ -7,6 +7,7 @@
 #include <stddef.h>
 
 #include <algorithm>
+#include <vector>
 
 #include "base/barrier_closure.h"
 #include "base/bind.h"
@@ -26,6 +27,42 @@ const uint8_t kStringDescriptorType = 0x03;
 
 const int kControlTransferTimeout = 60000;  // 1 minute
 
+struct UsbInterfaceAssociationDescriptor {
+  UsbInterfaceAssociationDescriptor(uint8_t first_interface,
+                                    uint8_t interface_count)
+      : first_interface(first_interface), interface_count(interface_count) {}
+
+  bool operator<(const UsbInterfaceAssociationDescriptor& other) const {
+    return first_interface < other.first_interface;
+  }
+
+  uint8_t first_interface;
+  uint8_t interface_count;
+};
+
+void ParseInterfaceAssociationDescriptors(
+    const std::vector<uint8_t>& buffer,
+    std::vector<UsbInterfaceAssociationDescriptor>* functions) {
+  const uint8_t kInterfaceAssociationDescriptorType = 11;
+  const uint8_t kInterfaceAssociationDescriptorLength = 8;
+  std::vector<uint8_t>::const_iterator it = buffer.begin();
+
+  while (it != buffer.end()) {
+    // All descriptors must be at least 2 byte which means the length and type
+    // are safe to read.
+    if (std::distance(it, buffer.end()) < 2)
+      return;
+    uint8_t length = it[0];
+    if (length > std::distance(it, buffer.end()))
+      return;
+    if (it[1] == kInterfaceAssociationDescriptorType &&
+        length == kInterfaceAssociationDescriptorLength) {
+      functions->push_back(UsbInterfaceAssociationDescriptor(it[2], it[3]));
+    }
+    std::advance(it, length);
+  }
+}
+
 void StoreStringDescriptor(IndexMap::iterator it,
                            const base::Closure& callback,
                            const base::string16& string) {
@@ -113,7 +150,8 @@ UsbInterfaceDescriptor::UsbInterfaceDescriptor(uint8_t interface_number,
       alternate_setting(alternate_setting),
       interface_class(interface_class),
       interface_subclass(interface_subclass),
-      interface_protocol(interface_protocol) {}
+      interface_protocol(interface_protocol),
+      first_interface(interface_number) {}
 
 UsbInterfaceDescriptor::~UsbInterfaceDescriptor() = default;
 
@@ -128,6 +166,47 @@ UsbConfigDescriptor::UsbConfigDescriptor(uint8_t configuration_value,
 
 UsbConfigDescriptor::~UsbConfigDescriptor() = default;
 
+void UsbConfigDescriptor::AssignFirstInterfaceNumbers() {
+  std::vector<UsbInterfaceAssociationDescriptor> functions;
+  ParseInterfaceAssociationDescriptors(extra_data, &functions);
+  for (const auto& interface : interfaces) {
+    ParseInterfaceAssociationDescriptors(interface.extra_data, &functions);
+    for (const auto& endpoint : interface.endpoints)
+      ParseInterfaceAssociationDescriptors(endpoint.extra_data, &functions);
+  }
+
+  // libusb has collected interface association descriptors in the |extra_data|
+  // fields of other descriptor types. This may have disturbed their order
+  // but sorting by the bFirstInterface should fix it.
+  std::sort(functions.begin(), functions.end());
+
+  uint8_t remaining_interfaces = 0;
+  auto function_it = functions.cbegin();
+  for (auto interface_it = interfaces.begin(); interface_it != interfaces.end();
+       ++interface_it) {
+    if (remaining_interfaces > 0) {
+      // Continuation of a previous function. Tag all alternate interfaces
+      // (which are guaranteed to be contiguous).
+      for (uint8_t interface_number = interface_it->interface_number;
+           interface_it != interfaces.end() &&
+           interface_it->interface_number == interface_number;
+           ++interface_it) {
+        interface_it->first_interface = function_it->first_interface;
+      }
+      if (--remaining_interfaces == 0)
+        ++function_it;
+    } else if (function_it != functions.end() &&
+               interface_it->interface_number == function_it->first_interface) {
+      // Start of a new function.
+      interface_it->first_interface = function_it->first_interface;
+      remaining_interfaces = function_it->interface_count - 1;
+    } else {
+      // Unassociated interfaces already have |first_interface| set to
+      // |interface_number|.
+    }
+  }
+}
+
 bool ParseUsbStringDescriptor(const std::vector<uint8_t>& descriptor,
                               base::string16* output) {
   if (descriptor.size() < 2 || descriptor[1] != kStringDescriptorType)