Pass a maximum output length to DecodeBase58 and DecodeBase58Check

Also remove a needless loop in DecodeBase58 to prune zeroes in the base256
output of the conversion. The number of zeroes is implied by keeping track
explicitly of the length during the loop.

3 files changed, 33 insertions, 13 deletions

diff --git a/src/base58.cpp b/src/base58.cpp
index e3d2853399..a0149fb641 100644
--- a/src/base58.cpp
+++ b/src/base58.cpp
@@ -11,6 +11,8 @@
 #include <assert.h>
 #include <string.h>
 
+#include <limits>
+
 /** All alphanumeric characters except for "0", "I", "O", and "l" */
 static const char* pszBase58 = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz";
 static const int8_t mapBase58[256] = {
@@ -32,7 +34,7 @@ static const int8_t mapBase58[256] = {
     -1,-1,-1,-1,-1,-1,-1,-1, -1,-1,-1,-1,-1,-1,-1,-1,
 };
 
-bool DecodeBase58(const char* psz, std::vector<unsigned char>& vch)
+bool DecodeBase58(const char* psz, std::vector<unsigned char>& vch, int max_ret_len)
 {
     // Skip leading spaces.
     while (*psz && IsSpace(*psz))
@@ -42,6 +44,7 @@ bool DecodeBase58(const char* psz, std::vector<unsigned char>& vch)
     int length = 0;
     while (*psz == '1') {
         zeroes++;
+        if (zeroes > max_ret_len) return false;
         psz++;
     }
     // Allocate enough space in big-endian base256 representation.
@@ -62,6 +65,7 @@ bool DecodeBase58(const char* psz, std::vector<unsigned char>& vch)
         }
         assert(carry == 0);
         length = i;
+        if (length + zeroes > max_ret_len) return false;
         psz++;
     }
     // Skip trailing spaces.
@@ -71,8 +75,6 @@ bool DecodeBase58(const char* psz, std::vector<unsigned char>& vch)
         return false;
     // Skip leading zeroes in b256.
     std::vector<unsigned char>::iterator it = b256.begin() + (size - length);
-    while (it != b256.end() && *it == 0)
-        it++;
     // Copy result into output vector.
     vch.reserve(zeroes + (b256.end() - it));
     vch.assign(zeroes, 0x00);
@@ -126,9 +128,9 @@ std::string EncodeBase58(const std::vector<unsigned char>& vch)
     return EncodeBase58(vch.data(), vch.data() + vch.size());
 }
 
-bool DecodeBase58(const std::string& str, std::vector<unsigned char>& vchRet)
+bool DecodeBase58(const std::string& str, std::vector<unsigned char>& vchRet, int max_ret_len)
 {
-    return DecodeBase58(str.c_str(), vchRet);
+    return DecodeBase58(str.c_str(), vchRet, max_ret_len);
 }
 
 std::string EncodeBase58Check(const std::vector<unsigned char>& vchIn)
@@ -140,9 +142,9 @@ std::string EncodeBase58Check(const std::vector<unsigned char>& vchIn)
     return EncodeBase58(vch);
 }
 
-bool DecodeBase58Check(const char* psz, std::vector<unsigned char>& vchRet)
+bool DecodeBase58Check(const char* psz, std::vector<unsigned char>& vchRet, int max_ret_len)
 {
-    if (!DecodeBase58(psz, vchRet) ||
+    if (!DecodeBase58(psz, vchRet, max_ret_len > std::numeric_limits<int>::max() - 4 ? std::numeric_limits<int>::max() : max_ret_len + 4) ||
         (vchRet.size() < 4)) {
         vchRet.clear();
         return false;
@@ -157,7 +159,7 @@ bool DecodeBase58Check(const char* psz, std::vector<unsigned char>& vchRet)
     return true;
 }
 
-bool DecodeBase58Check(const std::string& str, std::vector<unsigned char>& vchRet)
+bool DecodeBase58Check(const std::string& str, std::vector<unsigned char>& vchRet, int max_ret)
 {
-    return DecodeBase58Check(str.c_str(), vchRet);
+    return DecodeBase58Check(str.c_str(), vchRet, max_ret);
 }
diff --git a/src/base58.h b/src/base58.h
index d6e0299a1e..cfdab511b6 100644
--- a/src/base58.h
+++ b/src/base58.h
@@ -16,6 +16,7 @@
 
 #include <attributes.h>
 
+#include <limits>
 #include <string>
 #include <vector>
 
@@ -35,13 +36,13 @@ std::string EncodeBase58(const std::vector<unsigned char>& vch);
  * return true if decoding is successful.
  * psz cannot be nullptr.
  */
-NODISCARD bool DecodeBase58(const char* psz, std::vector<unsigned char>& vchRet);
+NODISCARD bool DecodeBase58(const char* psz, std::vector<unsigned char>& vchRet, int max_ret_len = std::numeric_limits<int>::max());
 
 /**
  * Decode a base58-encoded string (str) into a byte vector (vchRet).
  * return true if decoding is successful.
  */
-NODISCARD bool DecodeBase58(const std::string& str, std::vector<unsigned char>& vchRet);
+NODISCARD bool DecodeBase58(const std::string& str, std::vector<unsigned char>& vchRet, int max_ret_len = std::numeric_limits<int>::max());
 
 /**
  * Encode a byte vector into a base58-encoded string, including checksum
@@ -52,12 +53,12 @@ std::string EncodeBase58Check(const std::vector<unsigned char>& vchIn);
  * Decode a base58-encoded string (psz) that includes a checksum into a byte
  * vector (vchRet), return true if decoding is successful
  */
-NODISCARD bool DecodeBase58Check(const char* psz, std::vector<unsigned char>& vchRet);
+NODISCARD bool DecodeBase58Check(const char* psz, std::vector<unsigned char>& vchRet, int max_ret_len = std::numeric_limits<int>::max());
 
 /**
  * Decode a base58-encoded string (str) that includes a checksum into a byte
  * vector (vchRet), return true if decoding is successful
  */
-NODISCARD bool DecodeBase58Check(const std::string& str, std::vector<unsigned char>& vchRet);
+NODISCARD bool DecodeBase58Check(const std::string& str, std::vector<unsigned char>& vchRet, int max_ret_len = std::numeric_limits<int>::max());
 
 #endif // BITCOIN_BASE58_H
diff --git a/src/test/base58_tests.cpp b/src/test/base58_tests.cpp
index 52301f799a..5d53088cc6 100644
--- a/src/test/base58_tests.cpp
+++ b/src/test/base58_tests.cpp
@@ -7,6 +7,7 @@
 #include <base58.h>
 #include <test/util/setup_common.h>
 #include <util/strencodings.h>
+#include <util/vector.h>
 
 #include <univalue.h>
 
@@ -66,4 +67,20 @@ BOOST_AUTO_TEST_CASE(base58_DecodeBase58)
     BOOST_CHECK_EQUAL_COLLECTIONS(result.begin(), result.end(), expected.begin(), expected.end());
 }
 
+BOOST_AUTO_TEST_CASE(base58_random_encode_decode)
+{
+    for (int n = 0; n < 1000; ++n) {
+        unsigned int len = 1 + InsecureRandBits(8);
+        unsigned int zeroes = InsecureRandBool() ? InsecureRandRange(len + 1) : 0;
+        auto data = Cat(std::vector<unsigned char>(zeroes, '\000'), g_insecure_rand_ctx.randbytes(len - zeroes));
+        auto encoded = EncodeBase58Check(data);
+        std::vector<unsigned char> decoded;
+        auto ok_too_small = DecodeBase58Check(encoded, decoded, InsecureRandRange(len));
+        BOOST_CHECK(!ok_too_small);
+        auto ok = DecodeBase58Check(encoded, decoded, len + InsecureRandRange(257 - len));
+        BOOST_CHECK(ok);
+        BOOST_CHECK(data == decoded);
+    }
+}
+
 BOOST_AUTO_TEST_SUITE_END()