MDEV-23867: insert... select crash in compute_window_func

There are 2 issues here:

Issue #1: memory allocation.
An IO_CACHE that uses encryption uses a larger buffer (it needs space for the encrypted data,
decrypted data, IO_CACHE_CRYPT struct to describe encryption parameters etc).

Issue #2: IO_CACHE::seek_not_done
When IO_CACHE objects are cloned, they still share the file descriptor.
This means, operation on one IO_CACHE may change the file read position
which will confuse other IO_CACHEs using it.

The fix of these issues would be:
Allocate the buffer to also include the extra size needed for encryption.
Perform seek again after one IO_CACHE reads the file.

include/my_sys.h

@@ -476,18 +476,19 @@ typedef struct st_io_cache		/* Used when cacheing files */
     partial.
   */
   int	seek_not_done,error;
-  /* buffer_length is memory size allocated for buffer or write_buffer */
+  /* length of the buffer used for storing un-encrypted data */
   size_t	buffer_length;
   /* read_length is the same as buffer_length except when we use async io */
   size_t  read_length;
   myf	myflags;			/* Flags used to my_read/my_write */
   /*
-    alloced_buffer is 1 if the buffer was allocated by init_io_cache() and
-    0 if it was supplied by the user.
+    alloced_buffer is set to the size of the buffer allocated for the IO_CACHE.
+    Includes the overhead(storing key to ecnrypt and decrypt) for encryption.
+    Set to 0 if nothing is allocated.
     Currently READ_NET is the only one that will use a buffer allocated
     somewhere else
   */
-  my_bool alloced_buffer;
+  size_t alloced_buffer;
 #ifdef HAVE_AIOWAIT
   /*
     As inidicated by ifdef, this is for async I/O, which is not currently

mysql-test/suite/encryption/t/tempfiles_encrypted.opt

+--encrypt-tmp_files=ON

mysql-test/suite/encryption/t/tempfiles_encrypted.test

+--echo #
+--echo # Tests when the temporary files are encrypted
+--echo #
+
+source include/have_file_key_management_plugin.inc;
+source include/have_sequence.inc;
+source include/have_innodb.inc;
+
+select @@encrypt_tmp_files;
+
+--source t/win.test
+
+--echo #
+--echo # MDEV-23867: select crash in compute_window_func
+--echo #
+
+set @save_sort_buffer_size=@@sort_buffer_size;
+
+set sort_buffer_size= 2000;
+CREATE TABLE t1( a INT, b INT, c INT);
+INSERT INTO t1 select seq, seq, seq from seq_1_to_5000;
+CREATE TABLE t2( a INT, b INT, c INT);
+INSERT INTO t2 SELECT a, b, ROW_NUMBER() OVER (PARTITION BY b) FROM t1;
+SELECT COUNT(*), MAX(c) FROM t2;
+CREATE TABLE t3( a INT, b INT, c INT);
+INSERT INTO t3 SELECT a, b, SUM(a) OVER () FROM t1;
+SELECT COUNT(*), MAX(c) FROM t3;
+set @@sort_buffer_size=@save_sort_buffer_size;
+DROP TABLE t1,t2,t3;
+
+--echo # end of 10.2 test

mysys/mf_iocache.c

@@ -250,7 +250,7 @@ int init_io_cache(IO_CACHE *info, File file, size_t cachesize,
 	  info->write_buffer= info->buffer + cachesize;
         else
           info->write_buffer= info->buffer;
-	info->alloced_buffer= 1;
+	info->alloced_buffer= buffer_block;
 	break;					/* Enough memory found */
       }
       if (cachesize == min_cache)
@@ -324,14 +324,14 @@ int init_slave_io_cache(IO_CACHE *master, IO_CACHE *slave)
   DBUG_ASSERT(!master->share);
   DBUG_ASSERT(master->alloced_buffer);
 
-  if (!(slave_buf= (uchar*)my_malloc(master->buffer_length, MYF(0))))
+  if (!(slave_buf= (uchar*)my_malloc(master->alloced_buffer, MYF(0))))
   {
     return 1;
   }
   memcpy(slave, master, sizeof(IO_CACHE));
   slave->buffer= slave_buf;
 
-  memcpy(slave->buffer, master->buffer, master->buffer_length);
+  memcpy(slave->buffer, master->buffer, master->alloced_buffer);
   slave->read_pos= slave->buffer + (master->read_pos - master->buffer);
   slave->read_end= slave->buffer + (master->read_end - master->buffer);
 

sql/mf_iocache_encr.cc

@@ -71,6 +71,16 @@ static int my_b_encr_read(IO_CACHE *info, uchar *Buffer, size_t Count)
       DBUG_RETURN(1);
     }
     info->seek_not_done= 0;
+    if (info->next_file_user)
+    {
+      IO_CACHE *c;
+      for (c= info->next_file_user;
+           c!= info;
+           c= c->next_file_user)
+      {
+        c->seek_not_done= 1;
+      }
+    }
   }
 
   do