Re: [musl] [PATCH] fix avoidable segfault in catclose

[Markus Wichmann <nullplan@gmx.net>]

Am Thu, Jan 25, 2024 at 08:09:49AM +0100 schrieb Ismael Luceno:
> catclose may be called with an invalid argument, particularly -1 may be
> returned by catopen if there's an error.
>

May it, though? My copy of POSIX does not say so. Whenever a function
description does not say that you can call a function with invalid
arguments, you cannot do so. And it has been musl policy to crash on
invalid args since the beginning.

The problem you describe sounds like your app has control flow being
approximately:

nl_catd cat = catopen(...);
if (cat != (nl_catd)-1) {
    use_cat(cat);
}
catclose(cat);

and that is just wrong control flow and can be remedied by just moving
one line:

nl_catd cat = catopen(...);
if (cat != (nl_catd)-1) {
    use_cat(cat);
    catclose(cat);
}

BTW, POSIX does not say catclose() is required (or even allowed) to
accept (nl_catd)-1 as argument, its description of the return value of
catopen() also says that it is only suitable for use with catclose()
when successful.

Ciao,
Markus