Implementation of subresource integrity attribute for secure origins.

Source/core/frame/SubresourceIntegrity.cpp

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "config.h"
+#include "core/frame/SubresourceIntegrity.h"
+
+#include "core/HTMLNames.h"
+#include "core/dom/Document.h"
+#include "core/dom/Element.h"
+#include "core/frame/UseCounter.h"
+#include "platform/Crypto.h"
+#include "platform/ParsingUtilities.h"
+#include "platform/RuntimeEnabledFeatures.h"
+#include "platform/weborigin/KURL.h"
+#include "platform/weborigin/SecurityOrigin.h"
+#include "public/platform/WebCrypto.h"
+#include "public/platform/WebCryptoAlgorithm.h"
+#include "wtf/ASCIICType.h"
+#include "wtf/text/Base64.h"
+#include "wtf/text/StringUTF8Adaptor.h"
+#include "wtf/text/WTFString.h"
+
+namespace blink {
+
+// FIXME: This should probably use common functions with ContentSecurityPolicy.
+static bool isIntegrityCharacter(UChar c)
+{
+    // Check if it's a base64 encoded value.
+    return isASCIIAlphanumeric(c) || c == '+' || c == '/' || c == '=';
+}
+
+static bool DigestsEqual(const DigestValue& digest1, const DigestValue& digest2)
+{
+    if (digest1.size() != digest2.size())
+        return false;
+
+    for (size_t i = 0; i < digest1.size(); i++) {
+        if (digest1[i] != digest2[i])
+            return false;
+    }
+
+    return true;
+}
+
+// FIXME: If CheckSubresourceIntegrity fails, Blink should create a console
+// message to alert the developer of the failure.
+bool SubresourceIntegrity::CheckSubresourceIntegrity(const Element& element, const String& source, const KURL& resourceUrl)
+{
+    if (!RuntimeEnabledFeatures::subresourceIntegrityEnabled())
+        return true;
+
+    if (!element.fastHasAttribute(HTMLNames::integrityAttr))
+        return true;
+
+    // FIXME: If insecureOriginMsg is not empty after the check, Blink
+    // should send a console message.
+    //
+    // Instead of just checking SecurityOrigin::isSecure on resourceUrl, this
+    // checks canAccessFeatureRequiringSecureOrigin so that file:// protocols
+    // and localhost resources can be allowed. These may be useful for testing
+    // and are allowed for features requiring authenticated origins, so Chrome
+    // allows them here.
+    String insecureOriginMsg = "";
+    RefPtr<SecurityOrigin> resourceSecurityOrigin = SecurityOrigin::create(resourceUrl);
+    if (!element.document().securityOrigin()->canAccessFeatureRequiringSecureOrigin(insecureOriginMsg)) {
+        UseCounter::count(element.document(), UseCounter::SRIElementWithIntegrityAttributeAndInsecureOrigin);
+        return false;
+    }
+    if (!resourceSecurityOrigin->canAccessFeatureRequiringSecureOrigin(insecureOriginMsg)) {
+        UseCounter::count(element.document(), UseCounter::SRIElementWithIntegrityAttributeAndInsecureResource);
+        return false;
+    }
+
+    String integrity;
+    HashAlgorithm algorithm;
+    if (!parseIntegrityAttribute(element.fastGetAttribute(HTMLNames::integrityAttr), integrity, algorithm)) {
+        UseCounter::count(element.document(), UseCounter::SRIElementWithUnparsableIntegrityAttribute);
+        return false;
+    }
+
+    Vector<char> hashVector;
+    base64Decode(integrity, hashVector);
+
+    StringUTF8Adaptor normalizedSource(source, StringUTF8Adaptor::Normalize, WTF::EntitiesForUnencodables);
+
+    DigestValue digest;
+    bool digestSuccess = computeDigest(algorithm, normalizedSource.data(), normalizedSource.length(), digest);
+
+    if (digestSuccess) {
+        DigestValue convertedHashVector;
+        convertedHashVector.append(reinterpret_cast<uint8_t*>(hashVector.data()), hashVector.size());
+        if (DigestsEqual(digest, convertedHashVector)) {
+            UseCounter::count(element.document(), UseCounter::SRIElementWithMatchingIntegrityAttribute);
+            return true;
+        }
+    }
+
+    UseCounter::count(element.document(), UseCounter::SRIElementWithNonMatchingIntegrityAttribute);
+    return false;
+}
+
+bool SubresourceIntegrity::parseIntegrityAttribute(const String& attribute, String& integrity, HashAlgorithm& algorithm)
+{
+    DEFINE_STATIC_LOCAL(const String, integrityPrefix, ("ni://"));
+    // Any additions or subtractions from this struct should also modify the
+    // respective entries in the kAlgorithmMap array in checkDigest().
+    static const struct {
+        const char* prefix;
+        HashAlgorithm algorithm;
+    } kSupportedPrefixes[] = {
+        { "sha256", HashAlgorithmSha256 },
+        { "sha384", HashAlgorithmSha384 },
+        { "sha512", HashAlgorithmSha512 }
+    };
+    Vector<UChar> characters;
+    attribute.stripWhiteSpace().appendTo(characters);
+    UChar* begin = characters.data();
+    UChar* end = characters.end();
+
+    if (characters.size() < 1)
+        return false;
+
+    if (!equalIgnoringCase(integrityPrefix.characters8(), begin, integrityPrefix.length()))
+        return false;
+
+    const UChar* algorithmStart = begin + integrityPrefix.length();
+    const UChar* algorithmEnd = algorithmStart;
+
+    skipUntil<UChar>(algorithmEnd, end, ';');
+
+    // Instead of this sizeof() calculation to get the length of this array,
+    // it would be preferable to use WTF_ARRAY_LENGTH for simplicity and to
+    // guarantee a compile time calculation. Unfortunately, on some
+    // compliers, the call to WTF_ARRAY_LENGTH fails on arrays of anonymous
+    // stucts, so, for now, it is necessary to resort to this sizeof
+    // calculation.
+    size_t i = 0;
+    size_t kSupportedPrefixesLength = sizeof(kSupportedPrefixes) / sizeof(kSupportedPrefixes[0]);
+    for (; i < kSupportedPrefixesLength; i++) {
+        if (equalIgnoringCase(kSupportedPrefixes[i].prefix, algorithmStart, strlen(kSupportedPrefixes[i].prefix))) {
+            algorithm = kSupportedPrefixes[i].algorithm;
+            break;
+        }
+    }
+
+    if (i == kSupportedPrefixesLength)
+        return false;
+
+    const UChar* integrityStart = algorithmEnd;
+    if (!skipExactly<UChar>(integrityStart, end, ';'))
+        return false;
+
+    const UChar* integrityEnd = integrityStart;
+    skipWhile<UChar, isIntegrityCharacter>(integrityEnd, end);
+    if (integrityEnd != end)
+        return false;
+
+    integrity = String(integrityStart, integrityEnd - integrityStart);
+    return true;
+}
+
+} // namespace blink