Merge pull request #2884 from gavinandresen/canonicalsizes2

Reject non-canonically-encoded CompactSize

src/main.cpp

@@ -3677,7 +3677,6 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv)
     {
         vector<uint256> vWorkQueue;
         vector<uint256> vEraseQueue;
-        CDataStream vMsg(vRecv);
         CTransaction tx;
         vRecv >> tx;
 

src/serialize.h

@@ -216,18 +216,24 @@ uint64 ReadCompactSize(Stream& is)
         unsigned short xSize;
         READDATA(is, xSize);
         nSizeRet = xSize;
+        if (nSizeRet < 253)
+            throw std::ios_base::failure("non-canonical ReadCompactSize()");
     }
     else if (chSize == 254)
     {
         unsigned int xSize;
         READDATA(is, xSize);
         nSizeRet = xSize;
+        if (nSizeRet < 0x10000u)
+            throw std::ios_base::failure("non-canonical ReadCompactSize()");
     }
     else
     {
         uint64 xSize;
         READDATA(is, xSize);
         nSizeRet = xSize;
+        if (nSizeRet < 0x100000000LLu)
+            throw std::ios_base::failure("non-canonical ReadCompactSize()");
     }
     if (nSizeRet > (uint64)MAX_SIZE)
         throw std::ios_base::failure("ReadCompactSize() : size too large");

src/test/serialize_tests.cpp

@@ -39,7 +39,67 @@ BOOST_AUTO_TEST_CASE(varints)
         ss >> VARINT(j);
         BOOST_CHECK_MESSAGE(i == j, "decoded:" << j << " expected:" << i);
     }
+}
+
+BOOST_AUTO_TEST_CASE(compactsize)
+{
+    CDataStream ss(SER_DISK, 0);
+    vector<char>::size_type i, j;
+
+    for (i = 1; i <= MAX_SIZE; i *= 2)
+    {
+        WriteCompactSize(ss, i-1);
+        WriteCompactSize(ss, i);
+    }
+    for (i = 1; i <= MAX_SIZE; i *= 2)
+    {
+        j = ReadCompactSize(ss);
+        BOOST_CHECK_MESSAGE((i-1) == j, "decoded:" << j << " expected:" << (i-1));
+        j = ReadCompactSize(ss);
+        BOOST_CHECK_MESSAGE(i == j, "decoded:" << j << " expected:" << i);
+    }
+}
+
+static bool isCanonicalException(const std::ios_base::failure& ex)
+{
+    return std::string("non-canonical ReadCompactSize()") == ex.what();
+}
+
+BOOST_AUTO_TEST_CASE(noncanonical)
+{
+    // Write some non-canonical CompactSize encodings, and
+    // make sure an exception is thrown when read back.
+    CDataStream ss(SER_DISK, 0);
+    vector<char>::size_type n;
+
+    // zero encoded with three bytes:
+    ss.write("\xfd\x00\x00", 3);
+    BOOST_CHECK_EXCEPTION(ReadCompactSize(ss), std::ios_base::failure, isCanonicalException);
+
+    // 0xfc encoded with three bytes:
+    ss.write("\xfd\xfc\x00", 3);
+    BOOST_CHECK_EXCEPTION(ReadCompactSize(ss), std::ios_base::failure, isCanonicalException);
+
+    // 0xfd encoded with three bytes is OK:
+    ss.write("\xfd\xfd\x00", 3);
+    n = ReadCompactSize(ss);
+    BOOST_CHECK(n == 0xfd);
+
+    // zero encoded with five bytes:
+    ss.write("\xfe\x00\x00\x00\x00", 5);
+    BOOST_CHECK_EXCEPTION(ReadCompactSize(ss), std::ios_base::failure, isCanonicalException);
+
+    // 0xffff encoded with five bytes:
+    ss.write("\xfe\xff\xff\x00\x00", 5);
+    BOOST_CHECK_EXCEPTION(ReadCompactSize(ss), std::ios_base::failure, isCanonicalException);
+
+    // zero encoded with nine bytes:
+    ss.write("\xff\x00\x00\x00\x00\x00\x00\x00\x00", 9);
+    BOOST_CHECK_EXCEPTION(ReadCompactSize(ss), std::ios_base::failure, isCanonicalException);
 
+    // 0x01ffffff encoded with nine bytes:
+    ss.write("\xff\xff\xff\xff\x01\x00\x00\x00\x00", 9);
+    BOOST_CHECK_EXCEPTION(ReadCompactSize(ss), std::ios_base::failure, isCanonicalException);
 }
 
 BOOST_AUTO_TEST_SUITE_END()