Merge bitcoin#17721: util: Don't allow Base58 decoding of non-Base58 strings. Add Base58 tests.

d945c6f util: Don't allow base58-decoding of std::string:s containing non-base58 characters (practicalswift)
ff7a999 tests: Add tests for base58-decoding of std::string:s containing non-base58 characters (practicalswift)

Pull request description:

  Don't allow Base58 decoding of non-Base58 strings. Add Base58 tests.

  Fixes bitcoin#17718.

  Added tests before the Base58 decoding patch:

  ```
  $ make check
  …
  test/base58_tests.cpp(62): error: in "base58_tests/base58_DecodeBase58":
      check !DecodeBase58(std::string("\0invalid", 8), result) has failed
  test/base58_tests.cpp(67): error: in "base58_tests/base58_DecodeBase58":
      check !DecodeBase58(std::string("good\0bad0IOl", 12), result) has failed
  test/base58_tests.cpp(76): error: in "base58_tests/base58_DecodeBase58":
      check !DecodeBase58Check(std::string("3vQB7B6MrGQZaxCuFg4oh\00IOl", 26), result) has failed
  *** 3 failures are detected in the test module "Bitcoin Core Test Suite"
  …
  $ echo $?
  1
  ```

  Added tests before the Base58 decoding patch:

  ```
  $ make check
  …
  OK
  …
  $ echo $?
  0
  ```

ACKs for top commit:
  MarcoFalke:
    ACK d945c6f 🚓
  laanwj:
    ACK d945c6f

Tree-SHA512: 78fee3a18718c9cfbf2e4b26daaf8f24b4deca00475b7b254fec7f8be740f8898c696d9cd0eaa7c50bca55909b9dff3b516b6fe4db92dc132dcc0a1c5e3d61af

Author: laanwj

src/base58.cpp

@@ -7,6 +7,7 @@
 #include <hash.h>
 #include <uint256.h>
 #include <util/strencodings.h>
+#include <util/string.h>
 
 #include <assert.h>
 #include <string.h>
@@ -130,6 +131,9 @@ std::string EncodeBase58(const std::vector<unsigned char>& vch)
 
 bool DecodeBase58(const std::string& str, std::vector<unsigned char>& vchRet, int max_ret_len)
 {
+    if (!ValidAsCString(str)) {
+        return false;
+    }
     return DecodeBase58(str.c_str(), vchRet, max_ret_len);
 }
 
@@ -161,5 +165,8 @@ bool DecodeBase58Check(const char* psz, std::vector<unsigned char>& vchRet, int
 
 bool DecodeBase58Check(const std::string& str, std::vector<unsigned char>& vchRet, int max_ret)
 {
+    if (!ValidAsCString(str)) {
+        return false;
+    }
     return DecodeBase58Check(str.c_str(), vchRet, max_ret);
 }

src/test/base58_tests.cpp

@@ -59,12 +59,24 @@ BOOST_AUTO_TEST_CASE(base58_DecodeBase58)
     }
 
     BOOST_CHECK(!DecodeBase58("invalid", result, 100));
+    BOOST_CHECK(!DecodeBase58(std::string("invalid"), result, 100));
+    BOOST_CHECK(!DecodeBase58(std::string("\0invalid", 8), result, 100));
+
+    BOOST_CHECK(DecodeBase58(std::string("good", 4), result, 100));
+    BOOST_CHECK(!DecodeBase58(std::string("bad0IOl", 7), result, 100));
+    BOOST_CHECK(!DecodeBase58(std::string("goodbad0IOl", 11), result, 100));
+    BOOST_CHECK(!DecodeBase58(std::string("good\0bad0IOl", 12), result, 100));
 
     // check that DecodeBase58 skips whitespace, but still fails with unexpected non-whitespace at the end.
     BOOST_CHECK(!DecodeBase58(" \t\n\v\f\r skip \r\f\v\n\t a", result, 3));
     BOOST_CHECK( DecodeBase58(" \t\n\v\f\r skip \r\f\v\n\t ", result, 3));
     std::vector<unsigned char> expected = ParseHex("971a55");
     BOOST_CHECK_EQUAL_COLLECTIONS(result.begin(), result.end(), expected.begin(), expected.end());
+
+    BOOST_CHECK(DecodeBase58Check(std::string("3vQB7B6MrGQZaxCuFg4oh", 21), result, 100));
+    BOOST_CHECK(!DecodeBase58Check(std::string("3vQB7B6MrGQZaxCuFg4oi", 21), result, 100));
+    BOOST_CHECK(!DecodeBase58Check(std::string("3vQB7B6MrGQZaxCuFg4oh0IOl", 25), result, 100));
+    BOOST_CHECK(!DecodeBase58Check(std::string("3vQB7B6MrGQZaxCuFg4oh\00IOl", 26), result, 100));
 }
 
 BOOST_AUTO_TEST_CASE(base58_random_encode_decode)

src/util/strencodings.cpp

@@ -4,6 +4,7 @@
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include <util/strencodings.h>
+#include <util/string.h>
 
 #include <tinyformat.h>
 
@@ -269,7 +270,7 @@ NODISCARD static bool ParsePrechecks(const std::string& str)
         return false;
     if (str.size() >= 1 && (IsSpace(str[0]) || IsSpace(str[str.size()-1]))) // No padding allowed
         return false;
-    if (str.size() != strlen(str.c_str())) // No embedded NUL characters allowed
+    if (!ValidAsCString(str)) // No embedded NUL characters allowed
         return false;
     return true;
 }

src/util/string.h

@@ -5,6 +5,9 @@
 #ifndef BITCOIN_UTIL_STRING_H
 #define BITCOIN_UTIL_STRING_H
 
+#include <attributes.h>
+
+#include <cstring>
 #include <string>
 #include <vector>
 
@@ -31,4 +34,12 @@ inline std::string Join(const std::vector<std::string>& list, const std::string&
     return Join(list, separator, [](const std::string& i) { return i; });
 }
 
+/**
+ * Check if a string does not contain any embedded NUL (\0) characters
+ */
+NODISCARD inline bool ValidAsCString(const std::string& str) noexcept
+{
+    return str.size() == strlen(str.c_str());
+}
+
 #endif // BITCOIN_UTIL_STRENCODINGS_H