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Handle overflow when applying offset 

If an overflow occurs, the reported `last_seen` times are either very
wrong or malicious, so reject all addresses gossiped by that peer.
This commit is contained in:
Janito Vaqueiro Ferreira Filho 2021-05-25 23:31:52 +00:00
parent 5b8f33390c
commit f3419b7baf
1 changed files with 27 additions and 14 deletions
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41
zebra-network/src/peer_set/candidate_set.rs
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@ -336,6 +336,10 @@ where
/// Adjusts untrusted last seen times so they are not in the future. This stops
/// malicious peers keeping all their addresses at the front of the connection
/// queue. Honest peers with future clock skew also get adjusted.
///
/// Rejects all addresses if there are at least two that have reported
/// last_seen` times where one is so far in the future and another is so far in
/// the past that they cause an overflow when offsetting the times.
fn validate_addrs(
addrs: impl IntoIterator<Item = MetaAddr>,
last_seen_limit: DateTime32,
@ -362,25 +366,34 @@ fn validate_addrs(
/// Ensure all reported `last_seen` times are less than or equal to `last_seen_limit`.
///
/// # Panics
///
/// If the `addrs` list is empty.
/// This will consider all addresses as invalid if trying to offset their
/// `last_seen` times to be before the limit causes an overflow.
fn limit_last_seen_times(addrs: &mut Vec<MetaAddr>, last_seen_limit: DateTime32) {
let most_recent_reported_seen_timestamp = addrs
.iter()
.map(|addr| addr.get_last_seen().timestamp())
.max()
.expect("unexpected empty address list");
let (oldest_reported_seen_timestamp, newest_reported_seen_timestamp) =
addrs
.iter()
.fold((u32::MAX, u32::MIN), |(oldest, newest), addr| {
let last_seen = addr.get_last_seen().timestamp();
(oldest.min(last_seen), newest.max(last_seen))
});
// If any time is in the future, adjust all times, to compensate for clock skew on honest peers
if most_recent_reported_seen_timestamp > last_seen_limit.timestamp() {
let offset = most_recent_reported_seen_timestamp - last_seen_limit.timestamp();
if newest_reported_seen_timestamp > last_seen_limit.timestamp() {
let offset = newest_reported_seen_timestamp - last_seen_limit.timestamp();
for addr in addrs {
let old_last_seen = addr.get_last_seen().timestamp();
let new_last_seen = old_last_seen - offset;
// Apply offset to oldest timestamp to check for underflow
let oldest_resulting_timestamp = oldest_reported_seen_timestamp as i64 - offset as i64;
if oldest_resulting_timestamp >= 0 {
// No overflow is possible, so apply offset to all addresses
for addr in addrs {
let old_last_seen = addr.get_last_seen().timestamp();
let new_last_seen = old_last_seen - offset;
addr.set_last_seen(new_last_seen.into());
addr.set_last_seen(new_last_seen.into());
}
} else {
// An overflow will occur, so reject all gossiped peers
addrs.clear();
}
}
}