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authorGavin Andresen <gavinandresen@gmail.com>2013-08-07 12:21:34 +1000
committerGavin Andresen <gavinandresen@gmail.com>2013-08-09 10:01:35 +1000
commit8dc206a1e2715be83912e039465a049b708b94c1 (patch)
treec5f8682aeca86134da42cea9dae729faf03ef73a /src/serialize.h
parentddd0e2f616be82fb57d68298be796c34268c6ae9 (diff)
Reject non-canonically-encoded sizes
The length of vectors, maps, sets, etc are serialized using Write/ReadCompactSize -- which, unfortunately, do not use a unique encoding. So deserializing and then re-serializing a transaction (for example) can give you different bits than you started with. That doesn't cause any problems that we are aware of, but it is exactly the type of subtle mismatch that can lead to exploits. With this pull, reading a non-canonical CompactSize throws an exception, which means nodes will ignore 'tx' or 'block' or other messages that are not properly encoded. Please check my logic... but this change is safe with respect to causing a network split. Old clients that receive non-canonically-encoded transactions or blocks deserialize them into CTransaction/CBlock structures in memory, and then re-serialize them before relaying them to peers. And please check my logic with respect to causing a blockchain split: there are no CompactSize fields in the block header, so the block hash is always canonical. The merkle root in the block header is computed on a vector<CTransaction>, so any non-canonical encoding of the transactions in 'tx' or 'block' messages is erased as they are read into memory by old clients, and does not affect the block hash. And, as noted above, old clients re-serialize (with canonical encoding) 'tx' and 'block' messages before relaying to peers.
Diffstat (limited to 'src/serialize.h')
-rw-r--r--src/serialize.h6
1 files changed, 6 insertions, 0 deletions
diff --git a/src/serialize.h b/src/serialize.h
index e3d9939bcc..ca3c962240 100644
--- a/src/serialize.h
+++ b/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");