bug#21913: sed/utils.c temporary file handling code review

[Stanislav Brabec]

Stanislav Brabec wrote:
> While trying to reproduce an obscure crash with temporary file experiencing
> file system error, I looked deeper into sed/utils.c. I found several strange
> things.
> 
Here is a detailed regression map:

commit 9c9919efe2166efd32409054005619062624226c (initial import in 2004)
imported the broken code vulnerable to double fclose() issue and leaving
orphan temporary files in some situations.

commit 9c9919efe2166efd32409054005619062624226c in 2004 introduced the
register_open_file() temporary file bug. No side effects yet.

commit 3a8e165ab02487c372df217c1989e287625ce0ae in 2006 started to really use
broken register_open_file() in ck_mkstemp() with third argument "true". It
caused a regression: keeping orphan files after even more errors than before,
but the regression hides the double fclose() vulnerability.

commit 768901548e280726f160a1da4434f3fde8f9921a in 2015 introduced
register_cleanup_file() that re-implements broken temporary removal feature
of register_open_file(). This change hides the register_open_file() temporary
file bug.

Both mentioned bugs are now present in the code, but probably cannot be
triggered.

-- 
Best Regards / S pozdravem,

Stanislav Brabec
software developer
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