Fix flaky corrupted padding tests

It's possible that corrupted ciphertext decrypts just fine. e.g. the
output ends with "0x01".

However, the chances of this happening are relatively low
(roughly 1/256). Corrupt the ciphertext up to 8 times, ensuring that
the likelihood of multiple successful decryptions is so miniscule that
it's effectively impossible.

Test: Ran *PaddingCorrupted tests 50000 times
Change-Id: If40ecd7817819921c020ea9b86ada18c4c77ea55

1 files changed, 54 insertions, 14 deletions

diff --git a/security/keymint/aidl/vts/functional/KeyMintTest.cpp b/security/keymint/aidl/vts/functional/KeyMintTest.cpp
index d41d270764..caac3465b4 100644
--- a/security/keymint/aidl/vts/functional/KeyMintTest.cpp
+++ b/security/keymint/aidl/vts/functional/KeyMintTest.cpp
@@ -71,6 +71,12 @@ namespace {
 
 bool check_patchLevels = false;
 
+// The maximum number of times we'll attempt to verify that corruption
+// of an ecrypted blob results in an error. Retries are necessary as there
+// is a small (roughly 1/256) chance that corrupting ciphertext still results
+// in valid PKCS7 padding.
+constexpr size_t kMaxPaddingCorruptionRetries = 8;
+
 template <TagType tag_type, Tag tag, typename ValueT>
 bool contains(const vector<KeyParameter>& set, TypedTag<tag_type, tag> ttag,
               ValueT expected_value) {
@@ -4376,11 +4382,22 @@ TEST_P(EncryptionOperationsTest, AesEcbPkcs7PaddingCorrupted) {
     string ciphertext = EncryptMessage(message, params);
     EXPECT_EQ(16U, ciphertext.size());
     EXPECT_NE(ciphertext, message);
-    ++ciphertext[ciphertext.size() / 2];
 
-    EXPECT_EQ(ErrorCode::OK, Begin(KeyPurpose::DECRYPT, params));
-    string plaintext;
-    EXPECT_EQ(ErrorCode::INVALID_INPUT_LENGTH, Finish(message, &plaintext));
+    for (size_t i = 0; i < kMaxPaddingCorruptionRetries; ++i) {
+        ++ciphertext[ciphertext.size() / 2];
+
+        EXPECT_EQ(ErrorCode::OK, Begin(KeyPurpose::DECRYPT, params));
+        string plaintext;
+        ErrorCode error = Finish(message, &plaintext);
+        if (error == ErrorCode::INVALID_INPUT_LENGTH) {
+            // This is the expected error, we can exit the test now.
+            return;
+        } else {
+            // Very small chance we got valid decryption, so try again.
+            ASSERT_EQ(error, ErrorCode::OK);
+        }
+    }
+    FAIL() << "Corrupt ciphertext should have failed to decrypt by now.";
 }
 
 vector<uint8_t> CopyIv(const AuthorizationSet& set) {
@@ -5343,15 +5360,27 @@ TEST_P(EncryptionOperationsTest, TripleDesEcbPkcs7PaddingCorrupted) {
     string ciphertext = EncryptMessage(message, BlockMode::ECB, PaddingMode::PKCS7);
     EXPECT_EQ(8U, ciphertext.size());
     EXPECT_NE(ciphertext, message);
-    ++ciphertext[ciphertext.size() / 2];
 
     AuthorizationSetBuilder begin_params;
     begin_params.push_back(TAG_BLOCK_MODE, BlockMode::ECB);
     begin_params.push_back(TAG_PADDING, PaddingMode::PKCS7);
-    EXPECT_EQ(ErrorCode::OK, Begin(KeyPurpose::DECRYPT, begin_params));
-    string plaintext;
-    EXPECT_EQ(ErrorCode::OK, Update(ciphertext, &plaintext));
-    EXPECT_EQ(ErrorCode::INVALID_ARGUMENT, Finish(&plaintext));
+
+    for (size_t i = 0; i < kMaxPaddingCorruptionRetries; ++i) {
+        ++ciphertext[ciphertext.size() / 2];
+
+        EXPECT_EQ(ErrorCode::OK, Begin(KeyPurpose::DECRYPT, begin_params));
+        string plaintext;
+        EXPECT_EQ(ErrorCode::OK, Update(ciphertext, &plaintext));
+        ErrorCode error = Finish(&plaintext);
+        if (error == ErrorCode::INVALID_ARGUMENT) {
+            // This is the expected error, we can exit the test now.
+            return;
+        } else {
+            // Very small chance we got valid decryption, so try again.
+            ASSERT_EQ(error, ErrorCode::OK);
+        }
+    }
+    FAIL() << "Corrupt ciphertext should have failed to decrypt by now.";
 }
 
 struct TripleDesTestVector {
@@ -5679,16 +5708,27 @@ TEST_P(EncryptionOperationsTest, TripleDesCbcPkcs7PaddingCorrupted) {
     string ciphertext = EncryptMessage(message, BlockMode::CBC, PaddingMode::PKCS7, &iv);
     EXPECT_EQ(8U, ciphertext.size());
     EXPECT_NE(ciphertext, message);
-    ++ciphertext[ciphertext.size() / 2];
 
     auto begin_params = AuthorizationSetBuilder()
                                 .BlockMode(BlockMode::CBC)
                                 .Padding(PaddingMode::PKCS7)
                                 .Authorization(TAG_NONCE, iv);
-    EXPECT_EQ(ErrorCode::OK, Begin(KeyPurpose::DECRYPT, begin_params));
-    string plaintext;
-    EXPECT_EQ(ErrorCode::OK, Update(ciphertext, &plaintext));
-    EXPECT_EQ(ErrorCode::INVALID_ARGUMENT, Finish(&plaintext));
+
+    for (size_t i = 0; i < kMaxPaddingCorruptionRetries; ++i) {
+        ++ciphertext[ciphertext.size() / 2];
+        EXPECT_EQ(ErrorCode::OK, Begin(KeyPurpose::DECRYPT, begin_params));
+        string plaintext;
+        EXPECT_EQ(ErrorCode::OK, Update(ciphertext, &plaintext));
+        ErrorCode error = Finish(&plaintext);
+        if (error == ErrorCode::INVALID_ARGUMENT) {
+            // This is the expected error, we can exit the test now.
+            return;
+        } else {
+            // Very small chance we got valid decryption, so try again.
+            ASSERT_EQ(error, ErrorCode::OK);
+        }
+    }
+    FAIL() << "Corrupt ciphertext should have failed to decrypt by now.";
 }
 
 /*