Commit d316b8b1 authored by unknown's avatar unknown
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BUG#17917 - SELECT from compressed MyISAM table crashes MySQL server 

Retrieving data from compressed MyISAM table which is bigger than 4G on 32-bit box
with mmap() support results in server crash.

mmap() accepts length of bytes to be mapped in second param, which is 32-bit
size_t. But we pass data_file_length, which is 64-bit my_off_t. As a result only
first data_file_length % 4G were mapped.

This fix adds additional condition for mmap() usage, that is use mmap() for
compressed table which size is no more than 4G on 32-bit platform.


myisam/mi_packrec.c:
  Use mmap() for compressed table which size is no more than 4G on 32-bit platform.
parent 20270e43

myisam/mi_packrec.c

+10 −4
Original line number Diff line number Diff line
@@ -1158,16 +1158,22 @@ my_bool _mi_memmap_file(MI_INFO *info) 
  MYISAM_SHARE *share=info->s;

  DBUG_ENTER("mi_memmap_file");



  if (!info->s->file_map)

  if (!share->file_map)

  {

    my_off_t data_file_length= share->state.state.data_file_length;

    if (data_file_length > (my_off_t) (~((size_t) 0)) - MEMMAP_EXTRA_MARGIN)

    {

      DBUG_PRINT("warning", ("File is too large for mmap"));

      DBUG_RETURN(0);

    }

    if (my_seek(info->dfile,0L,MY_SEEK_END,MYF(0)) <

	share->state.state.data_file_length+MEMMAP_EXTRA_MARGIN)

        data_file_length + MEMMAP_EXTRA_MARGIN)

    {

      DBUG_PRINT("warning",("File isn't extended for memmap"));

      DBUG_RETURN(0);

    }

    file_map=(byte*)

      mmap(0,share->state.state.data_file_length+MEMMAP_EXTRA_MARGIN,PROT_READ,

      mmap(0, data_file_length + MEMMAP_EXTRA_MARGIN, PROT_READ,

	   MAP_SHARED | MAP_NORESERVE,info->dfile,0L);

    if (file_map == (byte*) MAP_FAILED)

    {
@@ -1175,7 +1181,7 @@ my_bool _mi_memmap_file(MI_INFO *info) 
      my_errno=errno;

      DBUG_RETURN(0);

    }

    info->s->file_map=file_map;

    share->file_map= file_map;

  }

  info->opt_flag|= MEMMAP_USED;

  info->read_record=share->read_record=_mi_read_mempack_record;