Re: [PATCH] libio: Eliminate _IO_stdin, _IO_stdout, _IO_stderr

["Dmitry V. Levin" <ldv at altlinux dot org>]

On Mon, Feb 18, 2019 at 10:58:47AM +0100, Florian Weimer wrote:
> * Dmitry V. Levin:
> 
> > Looks like _IO_legacy_file makes sense only when &_IO_stdin_used == NULL.
> > If the check was moved inside _IO_legacy_file, then ...
> 
> I'm not sure.  We have seen cases where new binaries do not define
> _IO_stdin_used, perhaps related to symbol visibility.
> 
> <https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=634261>
> <https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=816059>
> <https://bugs.launchpad.net/ubuntu/+source/lua5.3/+bug/1570055>

Yes, and we also have
https://sourceware.org/bugzilla/show_bug.cgi?id=17908

> So at least for the free call (in _IO_deallocate_file after the patch),
> I really want to check that the object isn't any of the preallocated
> ones, in case the crashes aren't immediate and we have the potential
> here for causing heap corruption.

Fair enough.

Why do we check
	(&_IO_stdin_used == NULL) && _IO_legacy_file (fp)
instead of just
	_IO_legacy_file (fp)
then?  Is it just an optimization?


-- 
ldv

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