From 369daf56bca1cf56ceddfc5808b8e91a67d4a7ef Mon Sep 17 00:00:00 2001
From: Marcus Eriksson <marcuse@apache.org>
Date: Mon, 3 Mar 2025 08:41:34 +0100
Subject: [PATCH] Fix PartitionUpdate.isEmpty deserialization issue to avoid
 potential EOFException

Patch by marcuse; reviewed by Sam Tunnicliffe for CASSANDRA-20345
---
 CHANGES.txt                                   |  1 +
 .../db/partitions/PartitionUpdate.java        |  2 +-
 .../distributed/test/PaxosRepairTest.java     | 33 +++++++++++++++++++
 .../paxos/uncommitted/PaxosRowsTest.java      |  5 +--
 4 files changed, 38 insertions(+), 3 deletions(-)

diff --git a/CHANGES.txt b/CHANGES.txt
index 76e6fc4872..f6cbace4f0 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -1,4 +1,5 @@
 5.1
+ * Fix PartitionUpdate.isEmpty deserialization issue to avoid potential EOFException (CASSANDRA-20345)
  * Avoid adding LEFT nodes to tokenMap on upgrade from gossip (CASSANDRA-20344)
  * Allow empty placements when deserializing cluster metadata (CASSANDRA-20343)
  * Reduce heap pressure when initializing CMS (CASSANDRA-20267)
diff --git a/src/java/org/apache/cassandra/db/partitions/PartitionUpdate.java b/src/java/org/apache/cassandra/db/partitions/PartitionUpdate.java
index c20a8490a4..ff5d0f9035 100644
--- a/src/java/org/apache/cassandra/db/partitions/PartitionUpdate.java
+++ b/src/java/org/apache/cassandra/db/partitions/PartitionUpdate.java
@@ -800,7 +800,7 @@ public class PartitionUpdate extends AbstractBTreePartition
             if (version >= MessagingService.VERSION_51)
             {
                 long epoch = VIntCoding.getUnsignedVInt(in, position);
-                position += VIntCoding.computeVIntSize(epoch);
+                position += VIntCoding.computeUnsignedVIntSize(epoch);
             }
 
             // DecoratedKey key = metadata.decorateKey(ByteBufferUtil.readWithVIntLength(in));
diff --git a/test/distributed/org/apache/cassandra/distributed/test/PaxosRepairTest.java b/test/distributed/org/apache/cassandra/distributed/test/PaxosRepairTest.java
index e22a6be3ea..0197106bc6 100644
--- a/test/distributed/org/apache/cassandra/distributed/test/PaxosRepairTest.java
+++ b/test/distributed/org/apache/cassandra/distributed/test/PaxosRepairTest.java
@@ -74,6 +74,7 @@ import org.apache.cassandra.tcm.ClusterMetadata;
 import org.apache.cassandra.tcm.ClusterMetadataService;
 import org.apache.cassandra.tcm.membership.Directory;
 import org.apache.cassandra.tcm.membership.NodeVersion;
+import org.apache.cassandra.tcm.transformations.CustomTransformation;
 import org.apache.cassandra.tcm.transformations.ForceSnapshot;
 import org.apache.cassandra.utils.*;
 
@@ -271,6 +272,38 @@ public class PaxosRepairTest extends TestBaseImpl
         }
     }
 
+    @Test
+    public void epochBadDeserializationTest() throws Throwable
+    {
+        try (Cluster cluster = init(Cluster.build(3).withConfig(WITH_NETWORK).withoutVNodes().start()))
+        {
+            cluster.schemaChange("CREATE TABLE " + KEYSPACE + '.' + TABLE + " (pk text primary key, v int)");
+            cluster.get(1).runOnInstance(() -> {
+                // just execute transformations to get epoch bumped enough for the bug to occur
+                for (int i = 0; i < 75; i++)
+                    ClusterMetadataService.instance().commit(CustomTransformation.make("x"+i));
+            });
+            // and bump the epoch in the tablemetadata:
+            cluster.schemaChange("ALTER TABLE " + KEYSPACE + '.' + TABLE + " WITH comment='abc'");
+
+            cluster.verbs(PAXOS_COMMIT_REQ).drop();
+            try
+            {
+                cluster.coordinator(1).execute("INSERT INTO " + KEYSPACE + '.' + TABLE + " (pk, v) VALUES ('xyzxyzxyzxyzxyzxyzxyzxyz', 1) IF NOT EXISTS", ConsistencyLevel.QUORUM);
+                Assert.fail("expected write timeout");
+            }
+            catch (RuntimeException e)
+            {
+                // exception expected
+            }
+
+            cluster.filters().reset();
+            cluster.get(1).shutdown().get();
+            cluster.get(1).startup();
+        }
+    }
+
+
     @Ignore
     @Test
     public void topologyChangePaxosTest() throws Throwable
diff --git a/test/unit/org/apache/cassandra/service/paxos/uncommitted/PaxosRowsTest.java b/test/unit/org/apache/cassandra/service/paxos/uncommitted/PaxosRowsTest.java
index 911ac72d82..529a2cf0a8 100644
--- a/test/unit/org/apache/cassandra/service/paxos/uncommitted/PaxosRowsTest.java
+++ b/test/unit/org/apache/cassandra/service/paxos/uncommitted/PaxosRowsTest.java
@@ -43,6 +43,7 @@ import org.apache.cassandra.schema.TableId;
 import org.apache.cassandra.schema.TableMetadata;
 import org.apache.cassandra.service.paxos.Ballot;
 import org.apache.cassandra.service.paxos.Commit;
+import org.apache.cassandra.tcm.Epoch;
 import org.apache.cassandra.utils.ByteBufferUtil;
 import org.apache.cassandra.utils.CloseableIterator;
 import org.apache.cassandra.utils.FBUtilities;
@@ -96,7 +97,7 @@ public class PaxosRowsTest
         SchemaLoader.prepareServer();
 
         ks = "coordinatorsessiontest";
-        metadata = CreateTableStatement.parse("CREATE TABLE tbl (k INT PRIMARY KEY, v INT)", ks).build();
+        metadata = CreateTableStatement.parse("CREATE TABLE tbl (k INT PRIMARY KEY, v INT)", ks).epoch(Epoch.create(100)).build();
         tableId = metadata.id;
     }
 
@@ -109,7 +110,7 @@ public class PaxosRowsTest
     @Test
     public void testRowInterpretation()
     {
-        DecoratedKey key = dk(5);
+        DecoratedKey key = dk(Integer.MAX_VALUE);
         Ballot[] ballots = createBallots(3);
 
         SystemKeyspace.savePaxosWritePromise(key, metadata, ballots[0]);