[TCLCORE] a comment with regard to the fix of bug 2494093

[Matthias K. <ma...@us...>]

Hi everybody,

I want to give two points to your attention that concern me with the fix
of bug 2494093 (buffer overflow in AppendUnicodeToUnicode() ->
SEGFAULT). But first thank you very much for helping to find the problem
and then fixing it promptly!

1) The fix as now implemented restricts the content of variables to
  INT_MAX/4 which is 512MB! To my mind this is comparatively small and
  should be documented somewhere. Please notice that this is also half
  the size, of what was possible in 8.4.19 / 8.5.6.

2) In tclStringObj.c is a lengthy documentation of the memory allocation
  algorithm for strings. This is now obsolete in the case when more than
  INT_MAX/4 memory is free and could be allocated. As in this case we
  panic() before even coming to the attemptckalloc().

What you should make with this information? Well, I don't know. I just
wanted to make sure it doesn't get lost and someone has to learn it the
hard way. I can live with the fix now.

Where is the use case that needs so much memory? Consider vfs::memchan.
This is where I stumbled over the issue. I thought I use vfs::memchan to
be able to transparently uncompress and evaluate the crc of archives...

kind regards
-- Matthias Kraft