MDEV-6878: Use of uninitialized saved_primary_key in Mrr_ordered_index_reader::resume_read()

(Backport to 5.3)
(variant #2, with fixed coding style)
- Make Mrr_ordered_index_reader::resume_read() restore index position 
  only if it was saved before with Mrr_ordered_index_reader::interrupt_read().

2 files changed, 14 insertions, 2 deletions

diff --git a/sql/multi_range_read.cc b/sql/multi_range_read.cc
index 727ebc29032..6dfd8bec980 100644
--- a/sql/multi_range_read.cc
+++ b/sql/multi_range_read.cc
@@ -410,6 +410,7 @@ bool Mrr_ordered_index_reader::set_interruption_temp_buffer(uint rowid_length,
   *space_start += key_len;
 
   have_saved_rowid= FALSE;
+  read_was_interrupted= FALSE;
   return FALSE;
 }
 
@@ -418,6 +419,7 @@ void Mrr_ordered_index_reader::set_no_interruption_temp_buffer()
   support_scan_interruptions= FALSE;
   saved_key_tuple= saved_rowid= saved_primary_key= NULL; /* safety */
   have_saved_rowid= FALSE;
+  read_was_interrupted= FALSE;
 }
 
 void Mrr_ordered_index_reader::interrupt_read()
@@ -435,6 +437,7 @@ void Mrr_ordered_index_reader::interrupt_read()
              &table->key_info[table->s->primary_key],
              table->key_info[table->s->primary_key].key_length);
   }
+  read_was_interrupted= TRUE;
 
   /* Save the last rowid */
   memcpy(saved_rowid, file->ref, file->ref_length);
@@ -452,6 +455,10 @@ void Mrr_ordered_index_reader::position()
 void Mrr_ordered_index_reader::resume_read()
 {
   TABLE *table= file->get_table();
+
+  if (!read_was_interrupted)
+    return;
+
   KEY *used_index= &table->key_info[file->active_index];
   key_restore(table->record[0], saved_key_tuple, 
               used_index, used_index->key_length);
@@ -541,8 +548,7 @@ int Mrr_ordered_index_reader::init(handler *h_arg, RANGE_SEQ_IF *seq_funcs,
   is_mrr_assoc=    !test(mode & HA_MRR_NO_ASSOCIATION);
   mrr_funcs= *seq_funcs;
   source_exhausted= FALSE;
-  if (support_scan_interruptions)
-    bzero(saved_key_tuple, key_info->key_length);
+  read_was_interrupted= false;
   have_saved_rowid= FALSE;
   return 0;
 }
diff --git a/sql/multi_range_read.h b/sql/multi_range_read.h
index 1b72e71944d..0ad61142b12 100644
--- a/sql/multi_range_read.h
+++ b/sql/multi_range_read.h
@@ -324,6 +324,12 @@ private:
   uchar *saved_key_tuple; /* Saved current key tuple */
   uchar *saved_primary_key; /* Saved current primary key tuple */
 
+  /*
+    TRUE<=> saved_key_tuple (and saved_primary_key when applicable) have
+    valid values.
+  */
+  bool read_was_interrupted;
+
   static int compare_keys(void* arg, uchar* key1, uchar* key2);
   static int compare_keys_reverse(void* arg, uchar* key1, uchar* key2);