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fix(chain): Validate header versions when serializing blocks #6475

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merged 4 commits into from
Apr 12, 2023
Merged

fix(chain): Validate header versions when serializing blocks #6475

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6bf2e28
checks block header version when serializing
arya2 Apr 7, 2023
86ec19b
fixes test panic
arya2 Apr 11, 2023
7d7594f
adds docs
arya2 Apr 11, 2023
6b4ec1b
test block header (de)serialization
arya2 Apr 12, 2023
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68 changes: 33 additions & 35 deletions zebra-chain/src/block/serialize.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -22,9 +22,40 @@ use crate::{
/// transaction in the chain is approximately 1.5 kB smaller.)
pub const MAX_BLOCK_BYTES: u64 = 2_000_000;

/// Checks if a block header version is valid
fn check_version(version: u32) -> Result<(), &'static str> {
match version {
// The Zcash specification says that:
// "The current and only defined block version number for Zcash is 4."
// but this is not actually part of the consensus rules, and in fact
// broken mining software created blocks that do not have version 4.
// There are approximately 4,000 blocks with version 536870912; this
// is the bit-reversal of the value 4, indicating that that mining pool
// reversed bit-ordering of the version field. Because the version field
// was not properly validated, these blocks were added to the chain.
//
// The only possible way to work around this is to do a similar hack
// as the overwintered field in transaction parsing, which we do here:
// treat the high bit (which zcashd interprets as a sign bit) as an
// indicator that the version field is meaningful.
version if version >> 31 != 0 => Err("high bit was set in version field"),

// # Consensus
//
// > The block version number MUST be greater than or equal to 4.
//
// https://zips.z.cash/protocol/protocol.pdf#blockheader
version if version < ZCASH_BLOCK_VERSION => Err("version must be at least 4"),

_ => Ok(()),
}
}

impl ZcashSerialize for Header {
#[allow(clippy::unwrap_in_result)]
fn zcash_serialize<W: io::Write>(&self, mut writer: W) -> Result<(), io::Error> {
check_version(self.version).map_err(|msg| io::Error::new(io::ErrorKind::Other, msg))?;

writer.write_u32::<LittleEndian>(self.version)?;
self.previous_block_hash.zcash_serialize(&mut writer)?;
writer.write_all(&self.merkle_root.0[..])?;
Expand All @@ -44,41 +75,8 @@ impl ZcashSerialize for Header {

impl ZcashDeserialize for Header {
fn zcash_deserialize<R: io::Read>(mut reader: R) -> Result<Self, SerializationError> {
// The Zcash specification says that
// "The current and only defined block version number for Zcash is 4."
// but this is not actually part of the consensus rules, and in fact
// broken mining software created blocks that do not have version 4.
// There are approximately 4,000 blocks with version 536870912; this
// is the bit-reversal of the value 4, indicating that that mining pool
// reversed bit-ordering of the version field. Because the version field
// was not properly validated, these blocks were added to the chain.
//
// The only possible way to work around this is to do a similar hack
// as the overwintered field in transaction parsing, which we do here:
// treat the high bit (which zcashd interprets as a sign bit) as an
// indicator that the version field is meaningful.
//
//
let (version, future_version_flag) = {
const LOW_31_BITS: u32 = (1 << 31) - 1;
let raw_version = reader.read_u32::<LittleEndian>()?;
(raw_version & LOW_31_BITS, raw_version >> 31 != 0)
};

if future_version_flag {
return Err(SerializationError::Parse(
"high bit was set in version field",
));
}

// # Consensus
//
// > The block version number MUST be greater than or equal to 4.
//
// https://zips.z.cash/protocol/protocol.pdf#blockheader
if version < ZCASH_BLOCK_VERSION {
return Err(SerializationError::Parse("version must be at least 4"));
}
let version = reader.read_u32::<LittleEndian>()?;
check_version(version).map_err(SerializationError::Parse)?;

Ok(Header {
version,
Expand Down