GH-49614: [C++] Report an error instead of silent truncation in base64_decode on invalid input

cpp/src/arrow/flight/flight_test.cc

@@ -620,7 +620,8 @@ void ParseBasicHeader(const CallHeaders& incoming_headers, std::string& username
  std::string& password) {
  std::string encoded_credentials =
  FindKeyValPrefixInCallHeaders(incoming_headers, kAuthHeader, kBasicPrefix);
- std::stringstream decoded_stream(arrow::util::base64_decode(encoded_credentials));
+ ASSERT_OK_AND_ASSIGN(auto decoded, arrow::util::base64_decode(encoded_credentials));
+ std::stringstream decoded_stream(decoded);
  std::getline(decoded_stream, username, ':');
  std::getline(decoded_stream, password, ':');
 }

cpp/src/arrow/util/CMakeLists.txt

@@ -49,6 +49,7 @@ add_arrow_test(utility-test
  SOURCES
  align_util_test.cc
  atfork_test.cc
+ base64_test.cc
  byte_size_test.cc
  byte_stream_split_test.cc
  cache_test.cc

cpp/src/arrow/util/base64.h

@@ -20,6 +20,7 @@
 #include <string>
 #include <string_view>
 
+#include "arrow/result.h"
 #include "arrow/util/visibility.h"
 
 namespace arrow {
@@ -29,7 +30,7 @@ ARROW_EXPORT
 std::string base64_encode(std::string_view s);
 
 ARROW_EXPORT
-std::string base64_decode(std::string_view s);
+arrow::Result<std::string> base64_decode(std::string_view s);
 
 } // namespace util
 } // namespace arrow

cpp/src/arrow/util/base64_test.cc

@@ -0,0 +1,98 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements. See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership. The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License. You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied. See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#include "arrow/util/base64.h"
+#include "arrow/testing/gtest_util.h"
+
+namespace arrow {
+namespace util {
+
+TEST(Base64DecodeTest, ValidInputs) {
+ ASSERT_OK_AND_ASSIGN(auto empty, base64_decode(""));
+ EXPECT_EQ(empty, "");
+
+ ASSERT_OK_AND_ASSIGN(auto two_paddings, base64_decode("Zg=="));
+ EXPECT_EQ(two_paddings, "f");
+
+ ASSERT_OK_AND_ASSIGN(auto one_padding, base64_decode("Zm8="));
+ EXPECT_EQ(one_padding, "fo");
+
+ ASSERT_OK_AND_ASSIGN(auto no_padding, base64_decode("Zm9v"));
+ EXPECT_EQ(no_padding, "foo");
+
+ ASSERT_OK_AND_ASSIGN(auto multiblock, base64_decode("SGVsbG8gd29ybGQ="));
+ EXPECT_EQ(multiblock, "Hello world");
+}
+
+TEST(Base64DecodeTest, BinaryOutput) {
+ // 'A' maps to index 0 — same zero value used for padding slots
+ // verifies the 'A' bug is not present
+ ASSERT_OK_AND_ASSIGN(auto all_A, base64_decode("AAAA"));
+ EXPECT_EQ(all_A, std::string("\x00\x00\x00", 3));
+
+ // Arbitrary non-ASCII output bytes
+ ASSERT_OK_AND_ASSIGN(auto binary, base64_decode("AP8A"));
+ EXPECT_EQ(binary, std::string("\x00\xff\x00", 3));
+}
+
+TEST(Base64DecodeTest, InvalidLength) {
+ ASSERT_RAISES_WITH_MESSAGE(
+ Invalid, "Invalid: Invalid base64 input: length is not a multiple of 4",
+ base64_decode("abc"));
+}
+
+TEST(Base64DecodeTest, InvalidCharacters) {
+ ASSERT_RAISES_WITH_MESSAGE(
+ Invalid, "Invalid: Invalid base64 input: character is not valid base64 character",
+ base64_decode("ab$="));
+
+ // Non-ASCII byte
+ std::string non_ascii = std::string("abc") + static_cast<char>(0xFF);
+ ASSERT_RAISES_WITH_MESSAGE(
+ Invalid, "Invalid: Invalid base64 input: character is not valid base64 character",
+ base64_decode(non_ascii));
+
+ // Corruption mid-string across multiple blocks
+ ASSERT_RAISES_WITH_MESSAGE(
+ Invalid, "Invalid: Invalid base64 input: character is not valid base64 character",
+ base64_decode("aGVs$G8gd29ybGQ="));
+}
+
+TEST(Base64DecodeTest, InvalidPadding) {
+ // Padding in wrong position within block
+ ASSERT_RAISES_WITH_MESSAGE(Invalid,
+ "Invalid: Invalid base64 input: padding in wrong position",
+ base64_decode("ab=c"));
+
+ // 3 padding characters — exceeds maximum of 2
+ ASSERT_RAISES_WITH_MESSAGE(Invalid,
+ "Invalid: Invalid base64 input: too many padding characters",
+ base64_decode("a==="));
+
+ // 4 padding characters
+ ASSERT_RAISES_WITH_MESSAGE(Invalid,
+ "Invalid: Invalid base64 input: too many padding characters",
+ base64_decode("===="));
+
+ // Padding in non-final block across multiple blocks
+ ASSERT_RAISES_WITH_MESSAGE(Invalid,
+ "Invalid: Invalid base64 input: padding in wrong position",
+ base64_decode("Zm8=Zm8="));
+}
+
+} // namespace util
+} // namespace arrow

cpp/src/arrow/vendored/base64.cpp

@@ -40,11 +40,6 @@ static const std::string base64_chars =
  "abcdefghijklmnopqrstuvwxyz"
  "0123456789+/";
 
-
-static inline bool is_base64(unsigned char c) {
- return (isalnum(c) || (c == '+') || (c == '/'));
-}
-
 static std::string base64_encode(unsigned char const* bytes_to_encode, unsigned int in_len) {
  std::string ret;
  int i = 0;
@@ -93,38 +88,65 @@ std::string base64_encode(std::string_view string_to_encode) {
  return base64_encode(bytes_to_encode, in_len);
 }
 
-std::string base64_decode(std::string_view encoded_string) {
+Result<std::string> base64_decode(std::string_view encoded_string) {
  size_t in_len = encoded_string.size();
  int i = 0;
- int j = 0;
- int in_ = 0;
+ std::string_view::size_type in_ = 0;
+ int padding_count = 0;
+ int block_padding = 0;
+ bool padding_started = false;
  unsigned char char_array_4[4], char_array_3[3];
  std::string ret;
 
- while (in_len-- && ( encoded_string[in_] != '=') && is_base64(encoded_string[in_])) {
- char_array_4[i++] = encoded_string[in_]; in_++;
- if (i ==4) {
- for (i = 0; i <4; i++)
- char_array_4[i] = base64_chars.find(char_array_4[i]) & 0xff;
+ if (encoded_string.size() % 4 != 0) {
+ return Status::Invalid("Invalid base64 input: length is not a multiple of 4");
+ }
 
- char_array_3[0] = ( char_array_4[0] << 2 ) + ((char_array_4[1] & 0x30) >> 4);
- char_array_3[1] = ((char_array_4[1] & 0xf) << 4) + ((char_array_4[2] & 0x3c) >> 2);
- char_array_3[2] = ((char_array_4[2] & 0x3) << 6) + char_array_4[3];
+ while (in_len--) {
+ unsigned char c = encoded_string[in_];
 
- for (i = 0; (i < 3); i++)
- ret += char_array_3[i];
- i = 0;
+ if (c == '=') {
+ padding_started = true;
+ padding_count++;
+
+ if (padding_count > 2) {
+ return Status::Invalid("Invalid base64 input: too many padding characters");
+ }
+
+ char_array_4[i++] = 0;
+ } else {
+ if (padding_started) {
+ return Status::Invalid("Invalid base64 input: padding in wrong position");
+ }
+
+ if (base64_chars.find(c) == std::string::npos) {
+ return Status::Invalid("Invalid base64 input: character is not valid base64 character");
+ }
+
+ char_array_4[i++] = c;
  }
- }
 
- if (i) {
- for (j = 0; j < i; j++)
- char_array_4[j] = base64_chars.find(char_array_4[j]) & 0xff;
+ in_++;
+
+ if (i == 4) {
+ for (i = 0; i < 4; i++) {
+ if (char_array_4[i] != 0) {
+ char_array_4[i] = base64_chars.find(char_array_4[i]) & 0xff;
+ }
+ }
+
+ char_array_3[0] = (char_array_4[0] << 2) + ((char_array_4[1] & 0x30) >> 4);
+ char_array_3[1] = ((char_array_4[1] & 0xf) << 4) + ((char_array_4[2] & 0x3c) >> 2);
+ char_array_3[2] = ((char_array_4[2] & 0x3) << 6) + char_array_4[3];
+
+ block_padding = padding_count;
 
- char_array_3[0] = (char_array_4[0] << 2) + ((char_array_4[1] & 0x30) >> 4);
- char_array_3[1] = ((char_array_4[1] & 0xf) << 4) + ((char_array_4[2] & 0x3c) >> 2);
+ for (i = 0; i < 3 - block_padding; i++) {
+ ret += char_array_3[i];
+ }
 
- for (j = 0; (j < i - 1); j++) ret += char_array_3[j];
+ i = 0;
+ }
  }
 
  return ret;

cpp/src/gandiva/gdv_function_stubs.cc

@@ -269,7 +269,15 @@ const char* gdv_fn_base64_decode_utf8(int64_t context, const char* in, int32_t i
  return "";
  }
  // use arrow method to decode base64 string
- std::string decoded_str = arrow::util::base64_decode(std::string_view(in, in_len));
+ auto result = arrow::util::base64_decode(std::string_view(in, in_len));
+ if (!result.ok()) {
+ gdv_fn_context_set_error_msg(context, result.status().message().c_str());
+ *out_len = 0;
+ return "";
+ }
+
+ std::string decoded_str = *result;
+
  *out_len = static_cast<int32_t>(decoded_str.length());
  // allocate memory for response
  char* ret = reinterpret_cast<char*>(

cpp/src/parquet/arrow/fuzz_internal.cc

@@ -83,8 +83,11 @@ class FuzzDecryptionKeyRetriever : public DecryptionKeyRetriever {
  }
  // Is it a key generated by MakeEncryptionKey?
  if (key_id.starts_with(kInlineKeyPrefix)) {
- return SecureString(
+ PARQUET_ASSIGN_OR_THROW(
+ auto decoded_key,
  ::arrow::util::base64_decode(key_id.substr(kInlineKeyPrefix.length())));
+
+ return SecureString(std::move(decoded_key));
  }
  throw ParquetException("Unknown fuzz encryption key_id");
  }

cpp/src/parquet/arrow/schema.cc

@@ -953,7 +953,8 @@ Status GetOriginSchema(const std::shared_ptr<const KeyValueMetadata>& metadata,
  // The original Arrow schema was serialized using the store_schema option.
  // We deserialize it here and use it to inform read options such as
  // dictionary-encoded fields.
- auto decoded = ::arrow::util::base64_decode(metadata->value(schema_index));
+ ARROW_ASSIGN_OR_RAISE(auto decoded,
+ ::arrow::util::base64_decode(metadata->value(schema_index)));
  auto schema_buf = std::make_shared<Buffer>(decoded);
 
  ::arrow::ipc::DictionaryMemo dict_memo;

cpp/src/parquet/encryption/file_key_unwrapper.cc

@@ -19,6 +19,7 @@
 
 #include "arrow/util/utf8.h"
 
+#include "arrow/util/base64.h"
 #include "parquet/encryption/file_key_unwrapper.h"
 #include "parquet/encryption/key_metadata.h"
 
@@ -122,7 +123,10 @@ KeyWithMasterId FileKeyUnwrapper::GetDataEncryptionKey(const KeyMaterial& key_ma
  });
 
  // Decrypt the data key
- std::string aad = ::arrow::util::base64_decode(encoded_kek_id);
+ PARQUET_ASSIGN_OR_THROW(auto decoded_kek,
+ ::arrow::util::base64_decode(encoded_kek_id));
+
+ std::string aad = std::move(decoded_kek);
  data_key = internal::DecryptKeyLocally(encoded_wrapped_dek, kek_bytes, aad);
  }
 

cpp/src/parquet/encryption/key_toolkit_internal.cc

@@ -52,7 +52,8 @@ std::string EncryptKeyLocally(const SecureString& key_bytes,
 
 SecureString DecryptKeyLocally(const std::string& encoded_encrypted_key,
  const SecureString& master_key, const std::string& aad) {
- std::string encrypted_key = ::arrow::util::base64_decode(encoded_encrypted_key);
+ PARQUET_ASSIGN_OR_THROW(auto encrypted_key,
+ ::arrow::util::base64_decode(encoded_encrypted_key));
 
  AesDecryptor key_decryptor(ParquetCipher::AES_GCM_V1,
  static_cast<int>(master_key.size()), false,