Block domain labels made of Cyrillic letters that look alike Latin

components/url_formatter/url_formatter.cc

 // Copyright 2015 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 "components/url_formatter/url_formatter.h"
 
 #include <algorithm>
 #include <utility>
 
 #include "base/lazy_instance.h"
 #include "base/macros.h"
 #include "base/numerics/safe_conversions.h"
 #include "base/strings/string_piece.h"
 #include "base/strings/string_util.h"
 #include "base/strings/utf_offset_string_conversions.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/threading/thread_local_storage.h"
+#include "third_party/icu/source/common/unicode/schriter.h"
 #include "third_party/icu/source/common/unicode/uidna.h"
 #include "third_party/icu/source/common/unicode/uniset.h"
 #include "third_party/icu/source/common/unicode/uscript.h"
 #include "third_party/icu/source/common/unicode/uvernum.h"
 #include "third_party/icu/source/i18n/unicode/regex.h"
 #include "third_party/icu/source/i18n/unicode/uspoof.h"
 #include "url/gurl.h"
 #include "url/third_party/mozilla/url_parse.h"
 
 namespace url_formatter {
 
 namespace {
 
 base::string16 IDNToUnicodeWithAdjustments(
     base::StringPiece host,
     base::OffsetAdjuster::Adjustments* adjustments);
 bool IDNToUnicodeOneComponent(const base::char16* comp,
                               size_t comp_len,
+                              bool is_tld_ascii,
                               base::string16* out);
 
 class AppendComponentTransform {
  public:
   AppendComponentTransform() {}
   virtual ~AppendComponentTransform() {}
 
   virtual base::string16 Execute(
       const std::string& component_text,
       base::OffsetAdjuster::Adjustments* adjustments) const = 0;
@@ skipping 147 matching lines @@
 // allow unicode UNC hostnames regardless of encodings.
 base::string16 IDNToUnicodeWithAdjustments(
     base::StringPiece host, base::OffsetAdjuster::Adjustments* adjustments) {
   if (adjustments)
     adjustments->clear();
   // Convert the ASCII input to a base::string16 for ICU.
   base::string16 input16;
   input16.reserve(host.length());
   input16.insert(input16.end(), host.begin(), host.end());
 
+  bool is_tld_ascii = true;
+  size_t last_dot = host.rfind('.');
+  if (last_dot != base::StringPiece::npos &&
+      host.substr(last_dot).starts_with(".xn--")) {
+    is_tld_ascii = false;
+  }
+
   // Do each component of the host separately, since we enforce script matching
   // on a per-component basis.
   base::string16 out16;
   for (size_t component_start = 0, component_end;
        component_start < input16.length();
        component_start = component_end + 1) {
     // Find the end of the component.
     component_end = input16.find('.', component_start);
     if (component_end == base::string16::npos)
       component_end = input16.length();  // For getting the last component.
     size_t component_length = component_end - component_start;
     size_t new_component_start = out16.length();
     bool converted_idn = false;
     if (component_end > component_start) {
       // Add the substring that we just found.
       converted_idn =
           IDNToUnicodeOneComponent(input16.data() + component_start,
-                                   component_length, &out16);
+                                   component_length, is_tld_ascii, &out16);
     }
     size_t new_component_length = out16.length() - new_component_start;
 
     if (converted_idn && adjustments) {
       adjustments->push_back(base::OffsetAdjuster::Adjustment(
           component_start, component_length, new_component_length));
     }
 
     // Need to add the dot we just found (if we found one).
     if (component_end < input16.length())
       out16.push_back('.');
   }
   return out16;
 }
 
 // A helper class for IDN Spoof checking, used to ensure that no IDN input is
 // spoofable per Chromium's standard of spoofability. For a more thorough
 // explanation of how spoof checking works in Chromium, see
 // http://dev.chromium.org/developers/design-documents/idn-in-google-chrome .
 class IDNSpoofChecker {
  public:
   IDNSpoofChecker();
 
-  // Returns true if |label| is safe to display as Unicode. In the event of
-  // library failure, all IDN inputs will be treated as unsafe.
-  bool Check(base::StringPiece16 label);
+  // Returns true if |label| is safe to display as Unicode. When the TLD is
+  // ASCII, check if a label is entirely made of Cyrillic letters that look like
+  // Latin letters. In the event of library failure, all IDN inputs will be
+  // treated as unsafe.
+  bool Check(base::StringPiece16 label, bool is_tld_ascii);
 
  private:
   void SetAllowedUnicodeSet(UErrorCode* status);
+  bool IsMadeOfLatinAlikeCyrillic(const icu::UnicodeString& label_string);
 
   USpoofChecker* checker_;
   icu::UnicodeSet deviation_characters_;
   icu::UnicodeSet non_ascii_latin_letters_;
   icu::UnicodeSet kana_letters_exceptions_;
+  icu::UnicodeSet cyrillic_letters_;
+  icu::UnicodeSet cyrillic_letters_latin_alike_;
 
   DISALLOW_COPY_AND_ASSIGN(IDNSpoofChecker);
 };
 
 base::LazyInstance<IDNSpoofChecker>::Leaky g_idn_spoof_checker =
     LAZY_INSTANCE_INITIALIZER;
 base::ThreadLocalStorage::StaticSlot tls_index = TLS_INITIALIZER;
 
 void OnThreadTermination(void* regex_matcher) {
   delete reinterpret_cast<icu::RegexMatcher*>(regex_matcher);
@@ skipping 42 matching lines @@
   // the allowed set.
   non_ascii_latin_letters_ = icu::UnicodeSet(
       UNICODE_STRING_SIMPLE("[[:Latin:] - [a-zA-Z]]"), status);
   non_ascii_latin_letters_.freeze();
 
   // These letters are parts of |dangerous_patterns_|.
   kana_letters_exceptions_ = icu::UnicodeSet(UNICODE_STRING_SIMPLE(
       "[\\u3078-\\u307a\\u30d8-\\u30da\\u30fb\\u30fc]"), status);
   kana_letters_exceptions_.freeze();
 
+  // These Cyrillic letters look like Latin. A domain label entirely made of
+  // these letters is blocked as a simpliified whole-script-spoofable.
+  cyrillic_letters_latin_alike_ =
+      icu::UnicodeSet(icu::UnicodeString("[асԁеһіјӏорԛѕԝхуъЬҽпгѵѡ]"), status);
+  cyrillic_letters_latin_alike_.freeze();
+
+  cyrillic_letters_ =
+      icu::UnicodeSet(UNICODE_STRING_SIMPLE("[[:Cyrl:]]"), status);
+  cyrillic_letters_.freeze();
+
   DCHECK(U_SUCCESS(status));
 }
 
-bool IDNSpoofChecker::Check(base::StringPiece16 label) {
+bool IDNSpoofChecker::Check(base::StringPiece16 label, bool is_tld_ascii) {
   UErrorCode status = U_ZERO_ERROR;
   int32_t result = uspoof_check(checker_, label.data(),
                                 base::checked_cast<int32_t>(label.size()),
                                 NULL, &status);
   // If uspoof_check fails (due to library failure), or if any of the checks
   // fail, treat the IDN as unsafe.
   if (U_FAILURE(status) || (result & USPOOF_ALL_CHECKS))
     return false;
 
   icu::UnicodeString label_string(FALSE, label.data(),
                                   base::checked_cast<int32_t>(label.size()));
 
   // A punycode label with 'xn--' prefix is not subject to the URL
   // canonicalization and is stored as it is in GURL. If it encodes a deviation
   // character (UTS 46; e.g. U+00DF/sharp-s), it should be still shown in
   // punycode instead of Unicode. Without this check, xn--fu-hia for
   // 'fu<sharp-s>' would be converted to 'fu<sharp-s>' for display because
   // "UTS 46 section 4 Processing step 4" applies validity criteria for
   // non-transitional processing (i.e. do not map deviation characters) to any
   // punycode labels regardless of whether transitional or non-transitional is
   // chosen. On the other hand, 'fu<sharp-s>' typed or copy and pasted
   // as Unicode would be canonicalized to 'fuss' by GURL and is displayed as
   // such. See http://crbug.com/595263 .
   if (deviation_characters_.containsSome(label_string))
     return false;
 
   // If there's no script mixing, the input is regarded as safe without any
-  // extra check unless it contains Kana letter exceptions. Note that
-  // the following combinations of scripts are treated as a 'logical' single
-  // script.
+  // extra check unless it contains Kana letter exceptions or it's made entirely
+  // of Cyrillic letters that look like Latin letters. Note that the following
+  // combinations of scripts are treated as a 'logical' single script.
   //  - Chinese: Han, Bopomofo, Common
   //  - Japanese: Han, Hiragana, Katakana, Common
   //  - Korean: Hangul, Han, Common
   result &= USPOOF_RESTRICTION_LEVEL_MASK;
-  if (result == USPOOF_ASCII ||
-      (result == USPOOF_SINGLE_SCRIPT_RESTRICTIVE &&
-       kana_letters_exceptions_.containsNone(label_string)))
-    return true;
+  if (result == USPOOF_ASCII) return true;
+  if (result == USPOOF_SINGLE_SCRIPT_RESTRICTIVE &&
+      kana_letters_exceptions_.containsNone(label_string)) {
+    // Check Cyrillic confusable only for ASCII TLDs.
+    return !is_tld_ascii || !IsMadeOfLatinAlikeCyrillic(label_string);
+  }
 
   // Additional checks for |label| with multiple scripts, one of which is Latin.
   // Disallow non-ASCII Latin letters to mix with a non-Latin script.
   if (non_ascii_latin_letters_.containsSome(label_string))
     return false;
 
   if (!tls_index.initialized())
     tls_index.Initialize(&OnThreadTermination);
   icu::RegexMatcher* dangerous_pattern =
       reinterpret_cast<icu::RegexMatcher*>(tls_index.Get());
@@ skipping 31 matching lines @@
             "[a-z][\\u0585\\u0581]+[a-z]|"
             "^[og]+[\\p{scx=armn}]|[\\p{scx=armn}][og]+$|"
             "[\\p{scx=armn}][og]+[\\p{scx=armn}]", -1, US_INV),
         0, status);
     tls_index.Set(dangerous_pattern);
   }
   dangerous_pattern->reset(label_string);
   return !dangerous_pattern->find();
 }
 
+bool IDNSpoofChecker::IsMadeOfLatinAlikeCyrillic(
+    const icu::UnicodeString& label_string) {
+  // Collect all the Cyrillic letters in |label_string| and see if they're
+  // a subset of |cyrillic_letters_latin_alike_|.
+  // A shortcut of defining cyrillic_letters_latin_alike_ to include [0-9] and
+  // [_-] and checking if the set contains all letters of |label_string|
+  // would work in most cases, but not if a label has non-letters outside
+  // ASCII.
+  icu::UnicodeSet cyrillic_in_label;
+  icu::StringCharacterIterator it(label_string);
+  for (it.setToStart(); it.hasNext();) {
+    const UChar32 c = it.next32PostInc();
+    if (cyrillic_letters_.contains(c))
+      cyrillic_in_label.add(c);
+  }
+  return !cyrillic_in_label.isEmpty() &&
+         cyrillic_letters_latin_alike_.containsAll(cyrillic_in_label);
+}
+
 void IDNSpoofChecker::SetAllowedUnicodeSet(UErrorCode* status) {
   if (U_FAILURE(*status))
     return;
 
   // The recommended set is a set of characters for identifiers in a
   // security-sensitive environment taken from UTR 39
   // (http://unicode.org/reports/tr39/) and
   // http://www.unicode.org/Public/security/latest/xidmodifications.txt .
   // The inclusion set comes from "Candidate Characters for Inclusion
   // in idenfiers" of UTR 31 (http://www.unicode.org/reports/tr31). The list
@@ skipping 54 matching lines @@
   allowed_set.remove(0x2010u);  // Hyphen
   allowed_set.remove(0x2027u);  // Hyphenation Point
 
   uspoof_setAllowedUnicodeSet(checker_, &allowed_set, status);
 }
 
 // Returns true if the given Unicode host component is safe to display to the
 // user. Note that this function does not deal with pure ASCII domain labels at
 // all even though it's possible to make up look-alike labels with ASCII
 // characters alone.
-bool IsIDNComponentSafe(base::StringPiece16 label) {
-  return g_idn_spoof_checker.Get().Check(label);
+bool IsIDNComponentSafe(base::StringPiece16 label, bool is_tld_ascii) {
+  return g_idn_spoof_checker.Get().Check(label, is_tld_ascii);
 }
 
 // A wrapper to use LazyInstance<>::Leaky with ICU's UIDNA, a C pointer to
 // a UTS46/IDNA 2008 handling object opened with uidna_openUTS46().
 //
 // We use UTS46 with BiDiCheck to migrate from IDNA 2003 to IDNA 2008 with the
 // backward compatibility in mind. What it does:
 //
 // 1. Use the up-to-date Unicode data.
 // 2. Define a case folding/mapping with the up-to-date Unicode data as in
@@ skipping 24 matching lines @@
 
 base::LazyInstance<UIDNAWrapper>::Leaky g_uidna = LAZY_INSTANCE_INITIALIZER;
 
 // Converts one component (label) of a host (between dots) to Unicode if safe.
 // The result will be APPENDED to the given output string and will be the
 // same as the input if it is not IDN in ACE/punycode or the IDN is unsafe to
 // display.
 // Returns whether any conversion was performed.
 bool IDNToUnicodeOneComponent(const base::char16* comp,
                               size_t comp_len,
+                              bool is_tld_ascii,
                               base::string16* out) {
   DCHECK(out);
   if (comp_len == 0)
     return false;
 
   // Only transform if the input can be an IDN component.
   static const base::char16 kIdnPrefix[] = {'x', 'n', '-', '-'};
   if ((comp_len > arraysize(kIdnPrefix)) &&
       !memcmp(comp, kIdnPrefix, sizeof(kIdnPrefix))) {
     UIDNA* uidna = g_uidna.Get().value;
@@ skipping 11 matching lines @@
       output_length = uidna_labelToUnicode(
           uidna, comp, static_cast<int32_t>(comp_len), &(*out)[original_length],
           output_length, &info, &status);
     } while ((status == U_BUFFER_OVERFLOW_ERROR && info.errors == 0));
 
     if (U_SUCCESS(status) && info.errors == 0) {
       // Converted successfully. Ensure that the converted component
       // can be safely displayed to the user.
       out->resize(original_length + output_length);
       if (IsIDNComponentSafe(
-          base::StringPiece16(out->data() + original_length,
-                              base::checked_cast<size_t>(output_length))))
+              base::StringPiece16(out->data() + original_length,
+                                  base::checked_cast<size_t>(output_length)),
+              is_tld_ascii))
         return true;
     }
 
     // Something went wrong. Revert to original string.
     out->resize(original_length);
   }
 
   // We get here with no IDN or on error, in which case we just append the
   // literal input.
   out->append(comp, comp_len);
@@ skipping 226 matching lines @@
   return base::StartsWith(text, www, base::CompareCase::SENSITIVE)
       ? text.substr(www.length()) : text;
 }
 
 base::string16 StripWWWFromHost(const GURL& url) {
   DCHECK(url.is_valid());
   return StripWWW(base::ASCIIToUTF16(url.host_piece()));
 }
 
 }  // namespace url_formatter