MDEV-32397 join_read_first, keyread SEGV crash

Queries having the following form may cause a crash SELECT t1.a FROM ( SELECT a AS a1 FROM t1 ) dt JOIN t1 ON a1 LIKE EXISTS ( SELECT a + RAND () FROM t1 UNION SELECT a FROM t1); because the table t1 has some cleanup operations performed prematurely during the subselect, before the outer query has finished with the table. In this particular case, the presence of RAND() makes the subquery uncacheable, necessitating the need to execute the subquery multiple times during join record evaluation. Each time the subquery runs, it creates its own JOIN structure which has references to the table t1. When the subquery completes, JOIN::cleanup and functions called by it result in ha_end_keyread() being called on table t1. However, we are not done with table t1 because the upper level `select t1.a from...` query requires table t1 to be open. To solve this, we make the executor aware of when we're in subqueries like this and delay when we call ha_end_keyread() until the end of the parent query.
MariaDB · Mar 28, 2024 · b68a2b9 · b68a2b9
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diff --git a/mysql-test/main/subselect_like_exists.result b/mysql-test/main/subselect_like_exists.result
@@ -0,0 +1,116 @@
+CREATE TABLE t0 ( c38 DOUBLE ( 87 , 18 ) ) ;
+INSERT INTO t0 VALUES ( DEFAULT ) , ( DEFAULT ) ;
+CREATE INDEX i0 ON t0 ( c38 ) ;
+INSERT INTO t0 VALUES ( 34 ) , ( -14 ) ;
+SELECT t0 . c38 AS c5 FROM ( SELECT c38 AS c27 FROM t0 ) AS t1 JOIN t0 ON t0 . c38 >= LN ( c27 IS TRUE ) LIKE EXISTS ( SELECT SPACE ( c24 ) - UNHEX ( c38 ) + STD( ORD ( -26 ) & RADIANS ( 62 ) / TRIM( LEADING 110 FROM 'a4~mq;A825}$&%(C
+{!}
+
+.!
+{S&pATQJb%F}
+
+qU@UH?VHFyU4%))Gx' ) AND -19.704435 | ACOS ( -69 IS TRUE ) ) % + RAND ( CONVERT ( -75 , UNSIGNED ) IN ( -64 , 10 , -118 ) XOR -85 = MAKE_SET ( 11 , ROUND ( -89 , -20 ) SOUNDS LIKE TRIM( TRAILING FROM 34 ) AND RAND ( ) ) ) AS c17 FROM ( SELECT t2 . c38 AS c24 FROM t0 LEFT OUTER JOIN t0 AS t2 USING ( c38 ) ) AS t3 JOIN t0 ON t3 . c24 = t0 . c38 GROUP BY c38 , c24 UNION SELECT c38 + 35 AS c48 FROM t0 WHERE c38 IN ( SELECT c38 AS c12 FROM t0 ) ) ;
+c5
+34.000000000000000000
+34.000000000000000000
+Warnings:
+Warning	1292	Truncated incorrect DOUBLE value: 'a4~mq;A825}$&%(C
+{!}
+
+.!
+{S&pATQJb%F}
+
+qU@UH?VHFyU4%))Gx'
+Warning	1365	Division by 0
+Warning	1365	Division by 0
+Warning	1365	Division by 0
+Warning	1292	Truncated incorrect DOUBLE value: 'a4~mq;A825}$&%(C
+{!}
+
+.!
+{S&pATQJb%F}
+
+qU@UH?VHFyU4%))Gx'
+Warning	1365	Division by 0
+Note	1105	Cast to unsigned converted negative integer to it's positive complement
+Warning	1292	Truncated incorrect DOUBLE value: ''
+Warning	1292	Truncated incorrect DOUBLE value: 'a4~mq;A825}$&%(C
+{!}
+
+.!
+{S&pATQJb%F}
+
+qU@UH?VHFyU4%))Gx'
+Warning	1365	Division by 0
+Note	1105	Cast to unsigned converted negative integer to it's positive complement
+Warning	1292	Truncated incorrect DOUBLE value: '                                  '
+Warning	1292	Truncated incorrect DOUBLE value: 'a4~mq;A825}$&%(C
+{!}
+
+.!
+{S&pATQJb%F}
+
+qU@UH?VHFyU4%))Gx'
+Warning	1365	Division by 0
+Note	1105	Cast to unsigned converted negative integer to it's positive complement
+Warning	1292	Truncated incorrect DOUBLE value: ''
+Warning	1292	Truncated incorrect DOUBLE value: 'a4~mq;A825}$&%(C
+{!}
+
+.!
+{S&pATQJb%F}
+
+qU@UH?VHFyU4%))Gx'
+Warning	1365	Division by 0
+Note	1105	Cast to unsigned converted negative integer to it's positive complement
+Warning	1292	Truncated incorrect DOUBLE value: '                                  '
+Warning	1365	Division by 0
+Warning	1365	Division by 0
+Warning	1292	Truncated incorrect DOUBLE value: 'a4~mq;A825}$&%(C
+{!}
+
+.!
+{S&pATQJb%F}
+
+qU@UH?VHFyU4%))Gx'
+Warning	1365	Division by 0
+Note	1105	Cast to unsigned converted negative integer to it's positive complement
+Warning	1292	Truncated incorrect DOUBLE value: ''
+Warning	1292	Truncated incorrect DOUBLE value: 'a4~mq;A825}$&%(C
+{!}
+
+.!
+{S&pATQJb%F}
+
+qU@UH?VHFyU4%))Gx'
+Warning	1365	Division by 0
+Note	1105	Cast to unsigned converted negative integer to it's positive complement
+Warning	1292	Truncated incorrect DOUBLE value: '                                  '
+Warning	1292	Truncated incorrect DOUBLE value: 'a4~mq;A825}$&%(C
+{!}
+
+.!
+{S&pATQJb%F}
+
+qU@UH?VHFyU4%))Gx'
+Warning	1365	Division by 0
+Note	1105	Cast to unsigned converted negative integer to it's positive complement
+Warning	1292	Truncated incorrect DOUBLE value: ''
+Warning	1292	Truncated incorrect DOUBLE value: 'a4~mq;A825}$&%(C
+{!}
+
+.!
+{S&pATQJb%F}
+
+qU@UH?VHFyU4%))Gx'
+Warning	1365	Division by 0
+Note	1105	Cast to unsigned converted negative integer to it's positive complement
+Warning	1292	Truncated incorrect DOUBLE value: '                                  '
+CREATE TABLE t1 ( a double, key (a)) ;
+INSERT INTO t1 VALUES (1),(2),(-3);
+SELECT t1.a FROM ( SELECT a AS a1 FROM t1 ) dt 
+JOIN t1 ON a1  LIKE EXISTS ( SELECT a + RAND () FROM t1 UNION SELECT a FROM t1) ;
+a
+-3
+1
+2
+drop table t0, t1;
diff --git a/mysql-test/main/subselect_like_exists.test b/mysql-test/main/subselect_like_exists.test
@@ -0,0 +1,23 @@
+#
+# MDEV-32397 join_read_first, keyread SEGV crash
+#
+
+CREATE TABLE t0 ( c38 DOUBLE ( 87 , 18 ) ) ;
+INSERT INTO t0 VALUES ( DEFAULT ) , ( DEFAULT ) ;
+CREATE INDEX i0 ON t0 ( c38 ) ;
+INSERT INTO t0 VALUES ( 34 ) , ( -14 ) ;
+SELECT t0 . c38 AS c5 FROM ( SELECT c38 AS c27 FROM t0 ) AS t1 JOIN t0 ON t0 . c38 >= LN ( c27 IS TRUE ) LIKE EXISTS ( SELECT SPACE ( c24 ) - UNHEX ( c38 ) + STD( ORD ( -26 ) & RADIANS ( 62 ) / TRIM( LEADING 110 FROM 'a4~mq;A825}$&%(C
+{!}
+
+.!
+{S&pATQJb%F}
+
+qU@UH?VHFyU4%))Gx' ) AND -19.704435 | ACOS ( -69 IS TRUE ) ) % + RAND ( CONVERT ( -75 , UNSIGNED ) IN ( -64 , 10 , -118 ) XOR -85 = MAKE_SET ( 11 , ROUND ( -89 , -20 ) SOUNDS LIKE TRIM( TRAILING FROM 34 ) AND RAND ( ) ) ) AS c17 FROM ( SELECT t2 . c38 AS c24 FROM t0 LEFT OUTER JOIN t0 AS t2 USING ( c38 ) ) AS t3 JOIN t0 ON t3 . c24 = t0 . c38 GROUP BY c38 , c24 UNION SELECT c38 + 35 AS c48 FROM t0 WHERE c38 IN ( SELECT c38 AS c12 FROM t0 ) ) ;
+
+
+CREATE TABLE t1 ( a double, key (a)) ;
+INSERT INTO t1 VALUES (1),(2),(-3);
+SELECT t1.a FROM ( SELECT a AS a1 FROM t1 ) dt 
+JOIN t1 ON a1  LIKE EXISTS ( SELECT a + RAND () FROM t1 UNION SELECT a FROM t1) ;
+
+drop table t0, t1;
diff --git a/sql/item_subselect.cc b/sql/item_subselect.cc
@@ -4096,7 +4096,9 @@ int subselect_single_select_engine::exec()
 int subselect_union_engine::exec()
 {
   char const *save_where= thd->where;
+  unit->in_subselect= true;
   int res= unit->exec();
+  unit->in_subselect= false;
   thd->where= save_where;
   return res;
 }

diff --git a/sql/sql_lex.cc b/sql/sql_lex.cc
@@ -9957,15 +9957,42 @@ void st_select_lex_unit::fix_distinct()
 }
 
 
+/*
+  If the table list of previous_sel has any tables found in the table
+  list of sel, then mark both previous_sel and sel such that the call
+  to ha_end_keyread() during JOIN cleanup may be delayed.  However,
+  delaying the call to ha_end_keyread() only be be considered when
+  we're executing within the context of a subquery.  The call will
+  be delayed until the end of the parent query and its corresponding
+  JOIN cleanup.
+*/
+static void mark_for_delayed_end_keyread(SELECT_LEX *previous_sel,
+                                         SELECT_LEX *sel)
+{
+  if (!previous_sel)
+    return;
+  DBUG_ASSERT(previous_sel && sel);
+  for (auto tlm= previous_sel->table_list.first; tlm; tlm= tlm->next_local)
+    for (auto tlm2= sel->table_list.first; tlm2; tlm2= tlm2->next_local)
+      if (!cmp(tlm2->db, tlm->db) && !cmp(tlm2->table_name, tlm->table_name)) {
+        previous_sel->delay_keyread_end= true;
+        sel->delay_keyread_end= true;
+      }
+}
+
+
 void st_select_lex_unit::register_select_chain(SELECT_LEX *first_sel)
 {
   DBUG_ASSERT(first_sel != 0);
   slave= first_sel;
   first_sel->prev= &slave;
+  SELECT_LEX *previous_sel= nullptr;
   for(SELECT_LEX *sel=first_sel; sel; sel= sel->next_select())
   {
     sel->master= (st_select_lex_node *)this;
     uncacheable|= sel->uncacheable;
+    mark_for_delayed_end_keyread(previous_sel, sel);
+    previous_sel= sel;
   }
 }
 

diff --git a/sql/sql_lex.h b/sql/sql_lex.h
@@ -878,6 +878,14 @@ class st_select_lex_unit: public st_select_lex_node {
 public:
   bool join_union_item_types(THD *thd, List<Item> &types, uint count);
 public:
+  /*
+    This value is true whenever we're withing the
+    subselect_union_engine::exec() method call, to
+    indicate that the current execution context for
+    this unit is a subselect.
+  */
+  bool in_subselect{false};
+
   // Ensures that at least all members used during cleanup() are initialized.
   st_select_lex_unit()
     : union_result(NULL), table(NULL), result(NULL),
@@ -1081,6 +1089,17 @@ Field_pair *find_matching_field_pair(Item *item, List<Field_pair> pair_list);
 class st_select_lex: public st_select_lex_node
 {
 public:
+  /*
+    When true, don't invoke ha_end_keyread for a given table
+    during JOIN cleanup (but only when that cleanup happens
+    during a subselect), avoiding a premature reset of the
+    corresponding handler's keyread value.  Other parts of
+    the query may not yet be done reading from the table
+    and we don't want to call ha_end_keyread until all parts
+    of the query have finished executing.
+  */
+  bool delay_keyread_end{false};
+
   /*
     Currently the field first_nested is used only by parser.
     It containa either a reference to the first select

diff --git a/sql/sql_select.cc b/sql/sql_select.cc
@@ -13803,6 +13803,28 @@ bool JOIN_TAB::build_range_rowid_filter_if_needed()
 }
 
 
+static bool should_invoke_end_keyread(JOIN *join)
+{
+  DBUG_ASSERT(join);
+  /*
+    - If there's no unit associated with the join, then we
+    cannot be within a subselect, so it's okay to call
+    ha_end_keyread().
+    - If we have a unit but we're not within a subselect,
+    then it's okay to call ha_end_keyread().
+    - If we have a unit and we're within a subselect and
+    delay_keyread_end is false, then it's okay to call
+    ha_end_keyread().
+
+    Put another way, do not call ha_end_keyread() when
+    we're in a subselect and delay_keyread_end is true.
+  */
+  return !join->unit ||
+         !join->unit->in_subselect ||
+         !join->select_lex->delay_keyread_end;
+}
+
+
 /**
   cleanup JOIN_TAB.
 
@@ -13842,12 +13864,14 @@ void JOIN_TAB::cleanup()
   if (table &&
       (table->s->tmp_table != INTERNAL_TMP_TABLE || table->is_created()))
   {
-    table->file->ha_end_keyread();
+    if (should_invoke_end_keyread(join))
+      table->file->ha_end_keyread();
     table->file->ha_index_or_rnd_end();
   }
   if (table)
   {
-    table->file->ha_end_keyread();
+    if (should_invoke_end_keyread(join))
+      table->file->ha_end_keyread();
     if (type == JT_FT)
       table->file->ha_ft_end();
     else