Audit log hangs when trying to write log record of length audit_log_buffer_size

[Sergei Glushchenko]

It is a bug in audit_log_buffer_write:

loop:
  if (log->write_pos + len < log->flush_pos + log->size)
  {
    size_t wrlen= min(len, log->size -
                              (log->write_pos % log->size));
    memcpy(log->buf + (log->write_pos % log->size), buf, wrlen);
    if (wrlen < len)
      memcpy(log->buf, buf + wrlen, len - wrlen);
    log->write_pos= log->write_pos + len;
    DBUG_ASSERT(log->write_pos >= log->flush_pos);
  }
  else
  {
    if (!log->drop_if_full)
    {
      mysql_cond_wait(&log->flushed_cond, &log->mutex);
      goto loop;
    }
  }

When len equals to log->size and both log->flush_pos == log->write_pos == 0 (buffer is fully flushed) this is going to be infinite loop.

[Sergei Glushchenko (sergei.glushchenko)]

Nobody has probably seen it because minimum value for audit_log_buffer_size is 4K, when log record was limited to 1K and even less (see Bug 1557293).

[Sergei Glushchenko (sergei.glushchenko)]

https://github.com/percona/percona-server/pull/572

[Sergei Glushchenko (sergei.glushchenko)]

https://github.com/percona/percona-server/pull/925

[Shahriyar Rzayev (rzayev-sehriyar)]

Percona now uses JIRA for bug reports so this bug report is migrated to: https://jira.percona.com/browse/PS-987