Lodestar snappy decompression issue

Summary

### Impact Unintended permanent chain split affecting greater than or equal to 25% of the network, requiring hard fork (network partition requiring hard fork) ### Description Lodestar client may fail to decode snappy framing compressed messages. ### Vulnerability Details In Req/Resp protocol the message are encoded by using ssz_snappy encoding, which is basically snappy framing compression over ssz encoded message. It's mentioned here - https://github.com/ethereum/consensus-specs/blob/dev/specs/phase0/p2p-interface.md ``` The token of the negotiated protocol ID specifies the type of encoding to be used for the req/resp interaction. Only one value is possible at this time: ssz_snappy: The contents are first SSZ-encoded and then compressed with Snappy frames compression. For objects containing a single field, only the field is SSZ-encoded not a container with a single field. For example, the BeaconBlocksByRoot request is an SSZ-encoded list of Root's. This encoding type MUST be supported by all clients. ``` In snappy framing format there a few types of chunks. We are interested in so called reserved skippable chunks. These are chunks with chunk type in range [0x80, 0xfd] Let's see how rust snappy handles them https://github.com/BurntSushi/rust-snappy/blob/master/src/read.rs#L137 ``` impl<R: io::Read> io::Read for FrameDecoder<R> { fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> { ... ... let len = len64 as usize; match ty { Err(b) if 0x02 <= b && b <= 0x7F => { // Spec says that chunk types 0x02-0x7F are reserved and // conformant decoders must return an error. fail!(Error::UnsupportedChunkType { byte: b }); } Err(b) if 0x80 <= b && b <= 0xFD => { // Spec says that chunk types 0x80-0xFD are reserved but // skippable. self.r.read_exact(&mut self.src[0..len])?; } ``` Similar code can be found in golang implementation - https://github.com/golang/snappy/blob/master/decode.go#L221 ``` func (r *Reader) fill() error { ... if chunkType <= 0x7f { // Section 4.5. Reserved unskippable chunks (chunk types 0x02-0x7f). r.err = ErrUnsupported return r.err } // Section 4.4 Padding (chunk type 0xfe). // Section 4.6. Reserved skippable chunks (chunk types 0x80-0xfd). if !r.readFull(r.buf[:chunkLen], false) { return r.err } ``` Now let's see how lodestar handles such chunks https://github.com/ChainSafe/lodestar/blob/unstable/packages/reqresp/src/encodingStrategies/sszSnappy/snappyFrames/uncompress.ts#L17 ``` uncompress(chunk: Uint8ArrayList): Uint8ArrayList | null { this.buffer.append(chunk); const result = new Uint8ArrayList(); while (this.buffer.length > 0) { if (this.buffer.length < 4) break; const type = getChunkType(this.buffer.get(0)); const frameSize = getFrameSize(this.buffer, 1); if (this.buffer.length - 4 < frameSize) { break; } const data = this.buffer.subarray(4, 4 + frameSize); this.buffer.consume(4 + frameSize); if (!this.state.foundIdentifier && type !== ChunkType.IDENTIFIER) { throw "malformed input: must begin with an identifier"; } if (type === ChunkType.IDENTIFIER) { if (!Buffer.prototype.equals.call(data, IDENTIFIER)) { throw "malformed input: bad identifier"; } this.state.foundIdentifier = true; continue; } if (type === ChunkType.COMPRESSED) { result.append(uncompress(data.subarray(4))); } if (type === ChunkType.UNCOMPRESSED) { result.append(data.subarray(4)); } } if (result.length === 0) { return null; } return result; } function getChunkType(value: number): ChunkType { switch (value) { case ChunkType.IDENTIFIER: return ChunkType.IDENTIFIER; case ChunkType.COMPRESSED: return ChunkType.COMPRESSED; case ChunkType.UNCOMPRESSED: return ChunkType.UNCOMPRESSED; case ChunkType.PADDING: return ChunkType.PADDING; default: throw new Error("Unsupported snappy chunk type"); } ``` As you can see, lodestar does not recognize such chunks. If it sees such chunk, function getChunkType() throws an exception and decoding fails. ### Impact Details Faulty nodes may trigger chain stall by sending messages which lodestar fails to parse, while other clients will be able to handle. ### Proof of Concept How to reproduce: 1. get archive (via provided [gist link](https://gist.github.com/gln7/bdde7f4e0bdf9d47bf810a015796867a)), decode and unpack it: ``` $ base64 -d poc.txt > poc.tgz $ tar zxf poc.tgz ``` 2. run dec1.go to verify that our snappy file decompressed successfully ``` $ go run dec1.go reading 1.snappy... read 124 bytes, err <nil> ``` 3. run dec1.mjs to verify that lodestar fails to decode such file ``` checking chunk type=255 checking chunk type=1 got uncompressed chunk.. checking chunk type=129 file:///../poc/dec1.mjs:74 throw new Error("Unsupported snappy chunk type"); ```