[NCC-E005955-VM7] zebra-network: Off-by-One Error in zebra-network Retry Parameter

[mpguerra]

Impact

The parameter MAX_SINGLE_PEER_RETRIES may not behave as expected due to an off-by-one error.

Description

Finding Off-by-One Errors and Inconsistent Usage of PARAMETER_DOWNLOAD_MAX_RETRIES documented an off-by-one issue with retry behavior in zebra-consensus. This finding documents a similar issue in zebra-network. Note that this does not represent a security issue or vulnerability, outside of potential user error during configuration.

The following code is part of peer DNS resolution, where each peer is resolved individually, and the complete process is repeated if no resolution is successful. The parameter MAX_SINGLE_PEER_RETRIES implies that it dictates the number of retry attempts for a given peer.

zebra/zebra-network/src/config.rs

Lines 25 to 27 in 5a88fe7

	/// The number of times Zebra will retry each initial peer's DNS resolution,
	/// before checking if any other initial peers have returned addresses.
	const MAX_SINGLE_PEER_RETRIES: usize = 1;

zebra/zebra-network/src/config.rs

Lines 161 to 170 in 5a88fe7

	// We retry each peer individually, as well as retrying if there are
	// no peers in the combined list. DNS failures are correlated, so all
	// peers can fail DNS, leaving Zebra with a small list of custom IP
	// address peers. Individual retries avoid this issue.
	let peer_addresses = peers
	.iter()
	.map(|s| Config::resolve_host(s, MAX_SINGLE_PEER_RETRIES))
	.collect::<futures::stream::FuturesUnordered<_>>()
	.concat()
	.await;

The retry function loops using for retry_count in 1..=max_retries, meaning that the value MAX_SINGLE_PEER_RETRIES will result in 1 single attempt and not 1 retry. Therefore, this parameter may be better named as MAX_SINGLE_PEER_ATTEMPTS or the behavior could be updated to loop one additional time.

Recommendation

Ensure the naming of the parameter accurately reflects its usage. Either rename the parameter to reflect the maximum number of connection attempts or revise the behavior to reflect its current name.

Location

zebra-network/src/config.rs