Bug #108317 clone_os_copy_file_to_buf partial read handling completely broken

Description:
clone_os_copy_file_to_buf appears to try to handle partial reads in a completely broken way:

  auto len_left = length;

  while (len_left > 0) {
    uint ret_length = 0;
    auto error =  read_from_file(from_file, to_buffer, length, src_name, ret_length);

    if (error != 0) {
       ...
    }

    len_left -= ret_length;
  }

If a partial read happens:
- file position is advanced
- len_left is reduced
- buffer stays the same
- length stays the same

So the second loop iteration would try to read into the same buffer position the same number of bytes, but from advanced file position, overwriting the read bytes from the first loop iteration partial read.

How to repeat:
Code analysis

Suggested fix:
Pass len_length not length to read_from_file
Add to_buffer += ret_length;

Hello Laurynas,

Thank you for the report and feedback!

regards,
Umesh

Bug 108317 fix for 8.0.30

(*) I confirm the code being submitted is offered under the terms of the OCA, and that I am authorized to contribute it.

Contribution: bug108317.patch (application/octet-stream, text), 2.67 KiB.

Documented fix as follows in the MySQL 8.0.32 changelog:

    The internal function clone_os_copy_file_to_buf() did not
    advance the buffer position in the event of a partial read.

    Our thanks to Laurynas Biveinis for the contribution.

Closed.