From 51c89057a00cb2be187eb069db4b770f07d5ccb3 Mon Sep 17 00:00:00 2001
From: Anway Durge <durgeanway@gmail.com>
Date: Mon, 19 Oct 2026 23:09:32 +0530
Subject: [PATCH] MDEV-40868: Do not let C++ exceptions leave send_data

Catch DuckDB conversion exceptions in send_data, raise a MariaDB error, and return -1.
---
 .../mysql-test/duckdb/r/mdev_40868.result     | 11 +++++
 .../mysql-test/duckdb/t/mdev_40868.test       | 25 ++++++++++
 storage/duckdb/runtime/fiber_scan.cc          | 48 ++++++++++++-------
 3 files changed, 67 insertions(+), 17 deletions(-)
 create mode 100644 storage/duckdb/mysql-test/duckdb/r/mdev_40868.result
 create mode 100644 storage/duckdb/mysql-test/duckdb/t/mdev_40868.test

diff --git a/storage/duckdb/mysql-test/duckdb/r/mdev_40868.result b/storage/duckdb/mysql-test/duckdb/r/mdev_40868.result
new file mode 100644
index 0000000000000..8d3526aca37b3
--- /dev/null
+++ b/storage/duckdb/mysql-test/duckdb/r/mdev_40868.result
@@ -0,0 +1,11 @@
+call mtr.add_suppression("FIBER: execution error");
+CREATE TABLE t1 (c2 DATETIME);
+INSERT INTO t1 VALUES ('0000-00-00');
+CREATE TABLE t2 (c1 INT PRIMARY KEY) ENGINE=DuckDB;
+SELECT * FROM t2 UNION SELECT * FROM t1;
+c1
+SELECT 1 AS still_alive;
+still_alive
+1
+DROP TABLE t2;
+DROP TABLE t1;
diff --git a/storage/duckdb/mysql-test/duckdb/t/mdev_40868.test b/storage/duckdb/mysql-test/duckdb/t/mdev_40868.test
new file mode 100644
index 0000000000000..2950944a7e0a5
--- /dev/null
+++ b/storage/duckdb/mysql-test/duckdb/t/mdev_40868.test
@@ -0,0 +1,25 @@
+--source ../include/have_duckdb.inc
+--source include/not_msan.inc
+--disable_warnings
+
+#
+# MDEV-40868 SIGABRT in duckdb::Value::CastAs on UNION of DuckDB
+# and InnoDB table.  Invalid DATETIME '0000-00-00' used to throw
+# out of select_to_duckdb::send_data and abort the server.
+# send_data now converts the exception into a THD error and returns
+# -1; the fiber scan finishes without crashing.
+#
+
+call mtr.add_suppression("FIBER: execution error");
+
+CREATE TABLE t1 (c2 DATETIME);
+INSERT INTO t1 VALUES ('0000-00-00');
+CREATE TABLE t2 (c1 INT PRIMARY KEY) ENGINE=DuckDB;
+
+SELECT * FROM t2 UNION SELECT * FROM t1;
+
+# Server must still be usable after the conversion error.
+SELECT 1 AS still_alive;
+
+DROP TABLE t2;
+DROP TABLE t1;
diff --git a/storage/duckdb/runtime/fiber_scan.cc b/storage/duckdb/runtime/fiber_scan.cc
index 588786f2feef7..cfdf4d9147e37 100644
--- a/storage/duckdb/runtime/fiber_scan.cc
+++ b/storage/duckdb/runtime/fiber_scan.cc
@@ -102,29 +102,43 @@ select_to_duckdb::select_to_duckdb(THD *thd_arg,
 
 int select_to_duckdb::send_data(List<Item> &items)
 {
-  List_iterator_fast<Item> it(items);
-  Item *item;
-  duckdb::idx_t col= 0;
-
-  while ((item= it++))
+  try
   {
-    if (col < types_->size())
+    List_iterator_fast<Item> it(items);
+    Item *item;
+    duckdb::idx_t col= 0;
+
+    while ((item= it++))
     {
-      duckdb::Value val= item_to_duckdb_value(item, (*types_)[col]);
-      buffer_->data[col].SetValue(row_count_, val);
+      if (col < types_->size())
+      {
+        duckdb::Value val= item_to_duckdb_value(item, (*types_)[col]);
+        buffer_->data[col].SetValue(row_count_, val);
+      }
+      col++;
+    }
+    row_count_++;
+
+    if (row_count_ >= STANDARD_VECTOR_SIZE)
+    {
+      buffer_->SetCardinality(row_count_);
+      row_count_= 0;
+      fiber_context_yield(ctx_);
     }
-    col++;
-  }
-  row_count_++;
 
-  if (row_count_ >= STANDARD_VECTOR_SIZE)
+    return thd->killed ? -1 : 0;
+  }
+  catch (const std::exception &ex)
   {
-    buffer_->SetCardinality(row_count_);
-    row_count_= 0;
-    fiber_context_yield(ctx_);
+    my_error(ER_GET_ERRMSG, MYF(0), HA_ERR_GENERIC, ex.what(), "DuckDB");
+    return -1;
+  }
+  catch (...)
+  {
+    my_error(ER_GET_ERRMSG, MYF(0), HA_ERR_GENERIC,
+             "Unknown error converting row to DuckDB", "DuckDB");
+    return -1;
   }
-
-  return thd->killed ? -1 : 0;
 }
 
 bool select_to_duckdb::send_eof()