User,Utils: move ConstantTimeEquals to CUtils and add tests (#2011)

test/UserTest.cpp

@@ -16,6 +16,7 @@
 
 #include <gtest/gtest.h>
 #include <znc/User.h>
+#include <znc/Utils.h>
 #include <znc/znc.h>
 
 class UserTest : public ::testing::Test {
@@ -149,3 +150,51 @@ TEST_F(UserTest, TestAuthOnlyViaModule) {
 
     CZNC::Get().SetAuthOnlyViaModule(bAuthOnlyViaModuleDefault);
 }
+
+// Functional regression for the constant-time CheckPass paths (#2011).
+// We can't measure timing in a unit test, but we verify the boolean
+// contract for each hash mode: correct password matches, wrong password
+// (including same-length and length-mismatch variants) does not.
+TEST_F(UserTest, CheckPassPlain) {
+    CUser user("user");
+    user.SetPass("plaintext", CUser::HASH_NONE);
+
+    EXPECT_FALSE(user.CheckPass(""));
+    EXPECT_FALSE(user.CheckPass("plaintex"));    // shorter
+    EXPECT_FALSE(user.CheckPass("plaintextX"));  // longer
+    EXPECT_FALSE(user.CheckPass("plaintexT"));   // case-sensitive
+    EXPECT_FALSE(user.CheckPass("Xlaintext"));   // first byte differs
+    EXPECT_FALSE(user.CheckPass("plaintexX"));   // last byte differs
+    EXPECT_TRUE(user.CheckPass("plaintext"));
+}
+
+TEST_F(UserTest, CheckPassMD5) {
+    CUser user("user");
+    CString sSalt = "the-salt";
+    CString sCorrect = "correct-password";
+    user.SetPass(CUtils::SaltedMD5Hash(sCorrect, sSalt), CUser::HASH_MD5,
+                 sSalt);
+
+    // Wrong inputs first; the success path may upgrade the stored hash
+    // to argon2id, after which the hash type is no longer MD5.
+    EXPECT_FALSE(user.CheckPass(""));
+    EXPECT_FALSE(user.CheckPass("wrong-password"));
+    EXPECT_FALSE(user.CheckPass("correct-passworX"));  // last byte differs
+    EXPECT_FALSE(user.CheckPass("Xorrect-password"));  // first byte differs
+    EXPECT_FALSE(user.CheckPass("Correct-password"));  // case-sensitive
+    EXPECT_TRUE(user.CheckPass(sCorrect));
+}
+
+TEST_F(UserTest, CheckPassSHA256) {
+    CUser user("user");
+    CString sSalt = "another-salt";
+    CString sCorrect = "another-password";
+    user.SetPass(CUtils::SaltedSHA256Hash(sCorrect, sSalt),
+                 CUser::HASH_SHA256, sSalt);
+
+    EXPECT_FALSE(user.CheckPass(""));
+    EXPECT_FALSE(user.CheckPass("wrong"));
+    EXPECT_FALSE(user.CheckPass("another-passworX"));
+    EXPECT_FALSE(user.CheckPass("Another-password"));
+    EXPECT_TRUE(user.CheckPass(sCorrect));
+}

test/UtilsTest.cpp

@@ -141,6 +141,34 @@ TEST(UtilsTest, ServerTime) {
     tzset();
 }
 
+TEST(UtilsTest, ConstantTimeEquals) {
+    // Functional correctness for the helper introduced for #2011.
+    // We can't measure timing in a unit test, so we verify the boolean
+    // contract: equal inputs match, any difference (length or content)
+    // does not.
+    EXPECT_TRUE(CUtils::ConstantTimeEquals("", ""));
+    EXPECT_TRUE(CUtils::ConstantTimeEquals("abc", "abc"));
+    EXPECT_TRUE(CUtils::ConstantTimeEquals(CString("\x00\x01\x02", 3),
+                                            CString("\x00\x01\x02", 3)));
+
+    // Differs in last byte (the hardest case for short-circuit compare).
+    EXPECT_FALSE(CUtils::ConstantTimeEquals("abc", "abd"));
+    // Differs in first byte.
+    EXPECT_FALSE(CUtils::ConstantTimeEquals("abc", "Xbc"));
+    // Length mismatch on either side.
+    EXPECT_FALSE(CUtils::ConstantTimeEquals("abc", "abcd"));
+    EXPECT_FALSE(CUtils::ConstantTimeEquals("abcd", "abc"));
+    EXPECT_FALSE(CUtils::ConstantTimeEquals("", "x"));
+    EXPECT_FALSE(CUtils::ConstantTimeEquals("x", ""));
+    // Case-sensitive (unlike CString::Equals default).
+    EXPECT_FALSE(CUtils::ConstantTimeEquals("abc", "ABC"));
+    // Embedded NUL is compared, not used as a terminator.
+    EXPECT_FALSE(CUtils::ConstantTimeEquals(CString("a\x00""c", 3),
+                                             CString("a\x00""d", 3)));
+    EXPECT_TRUE(CUtils::ConstantTimeEquals(CString("a\x00""c", 3),
+                                            CString("a\x00""c", 3)));
+}
+
 TEST(UtilsTest, ParseServerTime) {
     char* oldTZ = getenv("TZ");
     if (oldTZ) oldTZ = strdup(oldTZ);