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Merge #14685: fix a deserialization overflow edge case

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b08af10fb2 disallow oversized CBlockHeaderAndShortTxIDs (Kaz Wesley)
6bed4b374d fix a deserialization overflow edge case (Kaz Wesley)
051faf7e9d add a test demonstrating an overflow in a deserialization edge case (Kaz Wesley)

Pull request description:

  A specially-constructed BlockTransactionsRequest can cause `offset` to wrap in deserialization. In the current code, there is not any way this could be dangerous; but disallowing it reduces the potential for future surprises.

Tree-SHA512: 1aaf7636e0801a905ed8807d0d1762132ac8b4421a600c35fb6d5e5033c6bfb587d8668cd9f48c7a08a2ae793a677b7649661e3ae248ab4f8499ab7b6ede483c
This commit is contained in:
Wladimir J. van der Laan 2018-11-18 10:14:25 +01:00
commit 6d58a5c3b0
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GPG key ID: 1E4AED62986CD25D
2 changed files with 51 additions and 3 deletions
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9
src/blockencodings.h
View file

@ -52,12 +52,12 @@ public:
}
}
uint16_t offset = 0;
int32_t offset = 0;
for (size_t j = 0; j < indexes.size(); j++) {
if (uint64_t(indexes[j]) + uint64_t(offset) > std::numeric_limits<uint16_t>::max())
if (int32_t(indexes[j]) + offset > std::numeric_limits<uint16_t>::max())
throw std::ios_base::failure("indexes overflowed 16 bits");
indexes[j] = indexes[j] + offset;
offset = indexes[j] + 1;
offset = int32_t(indexes[j]) + 1;
}
} else {
for (size_t i = 0; i < indexes.size(); i++) {
@ -186,6 +186,9 @@ public:
READWRITE(prefilledtxn);
if (BlockTxCount() > std::numeric_limits<uint16_t>::max())
throw std::ios_base::failure("indexes overflowed 16 bits");
if (ser_action.ForRead())
FillShortTxIDSelector();
}

45
src/test/blockencodings_tests.cpp
View file

@ -344,4 +344,49 @@ BOOST_AUTO_TEST_CASE(TransactionsRequestSerializationTest) {
BOOST_CHECK_EQUAL(req1.indexes[3], req2.indexes[3]);
}
BOOST_AUTO_TEST_CASE(TransactionsRequestDeserializationMaxTest) {
// Check that the highest legal index is decoded correctly
BlockTransactionsRequest req0;
req0.blockhash = InsecureRand256();
req0.indexes.resize(1);
req0.indexes[0] = 0xffff;
CDataStream stream(SER_NETWORK, PROTOCOL_VERSION);
stream << req0;
BlockTransactionsRequest req1;
stream >> req1;
BOOST_CHECK_EQUAL(req0.indexes.size(), req1.indexes.size());
BOOST_CHECK_EQUAL(req0.indexes[0], req1.indexes[0]);
}
BOOST_AUTO_TEST_CASE(TransactionsRequestDeserializationOverflowTest) {
// Any set of index deltas that starts with N values that sum to (0x10000 - N)
// causes the edge-case overflow that was originally not checked for. Such
// a request cannot be created by serializing a real BlockTransactionsRequest
// due to the overflow, so here we'll serialize from raw deltas.
BlockTransactionsRequest req0;
req0.blockhash = InsecureRand256();
req0.indexes.resize(3);
req0.indexes[0] = 0x7000;
req0.indexes[1] = 0x10000 - 0x7000 - 2;
req0.indexes[2] = 0;
CDataStream stream(SER_NETWORK, PROTOCOL_VERSION);
stream << req0.blockhash;
WriteCompactSize(stream, req0.indexes.size());
WriteCompactSize(stream, req0.indexes[0]);
WriteCompactSize(stream, req0.indexes[1]);
WriteCompactSize(stream, req0.indexes[2]);
BlockTransactionsRequest req1;
try {
stream >> req1;
// before patch: deserialize above succeeds and this check fails, demonstrating the overflow
BOOST_CHECK(req1.indexes[1] < req1.indexes[2]);
// this shouldn't be reachable before or after patch
BOOST_CHECK(0);
} catch(std::ios_base::failure &) {
// deserialize should fail
}
}
BOOST_AUTO_TEST_SUITE_END()