sanghyeok An created KAFKA-21238:
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Summary: Mutating nested sets in consumer assignor input can
corrupt coordinator target assignment state
Key: KAFKA-21238
URL: https://issues.apache.org/jira/browse/KAFKA-21238
Project: Kafka
Issue Type: Bug
Reporter: sanghyeok An
Assignee: sanghyeok An
*Description*
{{MemberSubscriptionAndAssignmentImpl}} retains an {{Assignment}} that
references the coordinator’s existing target assignment. Although
{{Assignment}} wraps the outer map with {{{}Collections.unmodifiableMap(){}}},
the nested partition sets remain mutable.
If a custom assignor uses the input assignment as a working data structure and
modifies a nested set, it also modifies the coordinator’s existing target
assignment before returning the assignment result.
KS also had similar issue https://issues.apache.org/jira/browse/KAFKA-20846 and
it had been resolved.
*Actual Behavior*
A local reproduction of the Consumer path demonstrated the following:
* The existing target assignment changes from {{{0, 1}}} to {{{1}}} during
assignor execution.
* {{TargetAssignmentBuilder}} considers the existing assignment and the
returned result equal, so it does not generate a target assignment change
record for the member.
* The reverse index still retains the ownership information for partition 0.
* Rolling back to the snapshot does not restore partition 0 in the nested set.
This can leave the coordinator’s in-memory state, reverse index, and logged
state inconsistent.
*Expected Behavior*
The input assignment provided to the assignor should be immutable and isolated
from coordinator state. Attempts to modify nested partition sets should be
rejected without affecting the coordinator’s existing target assignment.
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