Revert of Mitigate spoofing attempt using Latin letters.

components/url_formatter/idn_spoof_checker.cc

Index: components/url_formatter/idn_spoof_checker.cc
diff --git a/components/url_formatter/idn_spoof_checker.cc b/components/url_formatter/idn_spoof_checker.cc
index d90442c84cf64b6f052a919984042e6151367796..156f0cd65ac81acc0907a01936837326926ef061 100644
--- a/components/url_formatter/idn_spoof_checker.cc
+++ b/components/url_formatter/idn_spoof_checker.cc
@@ -8,11 +8,9 @@
 #include "base/strings/string_split.h"
 #include "base/strings/string_util.h"
 #include "base/threading/thread_local_storage.h"
-#include "net/base/lookup_string_in_fixed_set.h"
 #include "third_party/icu/source/common/unicode/schriter.h"
 #include "third_party/icu/source/common/unicode/unistr.h"
 #include "third_party/icu/source/i18n/unicode/regex.h"
-#include "third_party/icu/source/i18n/unicode/translit.h"
 #include "third_party/icu/source/i18n/unicode/uspoof.h"
 
 namespace url_formatter {
@@ -22,31 +20,6 @@
 
 void OnThreadTermination(void* regex_matcher) {
   delete reinterpret_cast<icu::RegexMatcher*>(regex_matcher);
-}
-
-#include "components/url_formatter/top_domains/alexa_skeletons-inc.cc"
-// All the domains in the above file have 3 or fewer labels.
-const size_t kNumberOfLabelsToCheck = 3;
-
-bool LookupMatchInTopDomains(base::StringPiece skeleton) {
-  DCHECK_NE(skeleton.back(), '.');
-  auto labels = base::SplitStringPiece(skeleton, ".", base::KEEP_WHITESPACE,
-                                       base::SPLIT_WANT_ALL);
-
-  if (labels.size() > kNumberOfLabelsToCheck) {
-    labels.erase(labels.begin(),
-                 labels.begin() + labels.size() - kNumberOfLabelsToCheck);
-  }
-
-  while (labels.size() > 1) {
-    std::string partial_skeleton = base::JoinString(labels, ".");
-    if (net::LookupStringInFixedSet(
-            kDafsa, arraysize(kDafsa), partial_skeleton.data(),
-            partial_skeleton.length()) != net::kDafsaNotFound)
-      return true;
-    labels.erase(labels.begin());
-  }
-  return false;
 }
 
 }  // namespace
@@ -95,14 +68,11 @@
       icu::UnicodeSet(UNICODE_STRING_SIMPLE("[[:Latin:] - [a-zA-Z]]"), status);
   non_ascii_latin_letters_.freeze();
 
-  // The following two sets are parts of |dangerous_patterns_|.
+  // These letters are parts of |dangerous_patterns_|.
   kana_letters_exceptions_ = icu::UnicodeSet(
       UNICODE_STRING_SIMPLE("[\\u3078-\\u307a\\u30d8-\\u30da\\u30fb-\\u30fe]"),
       status);
   kana_letters_exceptions_.freeze();
-  combining_diacritics_exceptions_ =
-      icu::UnicodeSet(UNICODE_STRING_SIMPLE("[\\u0300-\\u0339]"), status);
-  combining_diacritics_exceptions_.freeze();
 
   // These Cyrillic letters look like Latin. A domain label entirely made of
   // these letters is blocked as a simplified whole-script-spoofable.
@@ -115,36 +85,6 @@
   cyrillic_letters_.freeze();
 
   DCHECK(U_SUCCESS(status));
-  // This set is used to determine whether or not to apply a slow
-  // transliteration to remove diacritics to a given hostname before the
-  // confusable skeleton calculation for comparison with top domain names. If
-  // it has any character outside the set, the expensive step will be skipped
-  // because it cannot match any of top domain names.
-  // The last ([\u0300-\u0339] is a shorthand for "[:Identifier_Status=Allowed:]
-  // & [:Script_Extensions=Inherited:] - [\\u200C\\u200D]". The latter is a
-  // subset of the former but it does not matter because hostnames with
-  // characters outside the latter set would be rejected in an earlier step.
-  lgc_letters_n_ascii_ = icu::UnicodeSet(
-      UNICODE_STRING_SIMPLE("[[:Latin:][:Greek:][:Cyrillic:][0-9\\u002e_"
-                            "\\u002d][\\u0300-\\u0339]]"),
-      status);
-  lgc_letters_n_ascii_.freeze();
-
-  // Used for diacritics-removal before the skeleton calculation. Add
-  // "ł > l; ø > o; đ > d" that are not handled by "NFD; Nonspacing mark
-  // removal; NFC". On top of that, supplement the Unicode confusable list by
-  // replacing {U+043A (к), U+0138(ĸ), U+03BA(κ)}, U+04CF (ӏ) and U+043F(п) by
-  // 'k', 'l' and 'n', respectively.
-  // TODO(jshin): Revisit "ł > l; ø > o" mapping.
-  UParseError parse_error;
-  transliterator_.reset(icu::Transliterator::createFromRules(
-      UNICODE_STRING_SIMPLE("DropAcc"),
-      icu::UnicodeString("::NFD; ::[:Nonspacing Mark:] Remove; ::NFC;"
-                         " ł > l; ø > o; đ > d; ӏ > l; [кĸκ] > k; п > n;"),
-      UTRANS_FORWARD, parse_error, status));
-  DCHECK(U_SUCCESS(status))
-      << "Spoofchecker initalization failed due to an error: "
-      << u_errorName(status);
 }
 
 IDNSpoofChecker::~IDNSpoofChecker() {
@@ -180,13 +120,9 @@
     return false;
 
   // If there's no script mixing, the input is regarded as safe without any
-  // extra check unless it falls into one of three categories:
-  //   - contains Kana letter exceptions
-  //   - the TLD is ASCII and the input is made entirely of Cyrillic letters
-  //     that look like Latin letters.
-  //   - it has combining diacritic marks.
-  // 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
@@ -194,19 +130,14 @@
   if (result == USPOOF_ASCII)
     return true;
   if (result == USPOOF_SINGLE_SCRIPT_RESTRICTIVE &&
-      kana_letters_exceptions_.containsNone(label_string) &&
-      combining_diacritics_exceptions_.containsNone(label_string)) {
+      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.
-  // Note that the non-ASCII Latin check should not be applied when the entire
-  // label is made of Latin. Checking with lgc_letters set here should be fine
-  // because script mixing of LGC is already rejected.
-  if (non_ascii_latin_letters_.containsSome(label_string) &&
-      !lgc_letters_n_ascii_.containsAll(label_string))
+  if (non_ascii_latin_letters_.containsSome(label_string))
     return false;
 
   if (!tls_index.initialized())
@@ -236,9 +167,6 @@
     //   Letter Co) to be next to Latin.
     // - Disallow Latin 'o' and 'g' next to Armenian.
     // - Disalow mixing of Latin and Canadian Syllabary.
-    // - Disallow combining diacritical mark (U+0300-U+0339) after a non-LGC
-    //   character. Other combining diacritical marks are not in the allowed
-    //   character set.
     dangerous_pattern = new icu::RegexMatcher(
         icu::UnicodeString(
             R"([^\p{scx=kana}\p{scx=hira}\p{scx=hani}])"
@@ -253,8 +181,7 @@
             R"([a-z][\u0585\u0581]+[a-z]|)"
             R"(^[og]+[\p{scx=armn}]|[\p{scx=armn}][og]+$|)"
             R"([\p{scx=armn}][og]+[\p{scx=armn}]|)"
-            R"([\p{sc=cans}].*[a-z]|[a-z].*[\p{sc=cans}]|)"
-            R"([^\p{scx=latn}\p{scx=grek}\p{scx=cyrl}][\u0300-\u0339])",
+            R"([\p{sc=cans}].*[a-z]|[a-z].*[\p{sc=cans}])",
             -1, US_INV),
         0, status);
     tls_index.Set(dangerous_pattern);
@@ -263,33 +190,10 @@
   return !dangerous_pattern->find();
 }
 
-bool IDNSpoofChecker::SimilarToTopDomains(base::StringPiece16 hostname) {
-  size_t hostname_length = hostname.length() - (hostname.back() == '.' ? 1 : 0);
-  icu::UnicodeString ustr_host(FALSE, hostname.data(), hostname_length);
-  // If input has any characters outside Latin-Greek-Cyrillic and [0-9._-],
-  // there is no point in getting rid of diacritics because combining marks
-  // attached to non-LGC characters are already blocked.
-  if (lgc_letters_n_ascii_.span(ustr_host, 0, USET_SPAN_CONTAINED) ==
-      ustr_host.length())
-    transliterator_.get()->transliterate(ustr_host);
-
-  UErrorCode status = U_ZERO_ERROR;
-  icu::UnicodeString ustr_skeleton;
-  uspoof_getSkeletonUnicodeString(checker_, 0, ustr_host, ustr_skeleton,
-                                  &status);
-  if (U_FAILURE(status))
-    return false;
-  std::string skeleton;
-  ustr_skeleton.toUTF8String(skeleton);
-  return LookupMatchInTopDomains(skeleton);
-}
-
 bool IDNSpoofChecker::IsMadeOfLatinAlikeCyrillic(
     const icu::UnicodeString& label) {
-  // 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|
+  // [_-] 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;