[PATCH] Do not leave random talloc magic in free()'ed memory

[Andrew Bartlett]

G'Day,

I've been thinking about ways that our talloc magic protection might be
avoided and reading the magic from memory that has recently been
free()ed would be a good attack.

So this patch marks this memory with a fixed magic.  All valid use of
memory still uses the random magic.

This passed a full autobuild.

Please carefully review!  

On my re-look it might need to tweak talloc_chunk_from_ptr() a little
(when other flags could be set), but I would like other thoughts too!

Andrew Bartlett
-- 
Andrew Bartlett                       http://samba.org/~abartlet/
Authentication Developer, Samba Team  http://samba.org
Samba Developer, Catalyst IT          http://catalyst.net.nz/services/samba
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