Date: Tue, 7 Dec 2010 22:52:14 -0500 (EST) From: Daniel Eischen <deischen@freebsd.org> To: David Xu <davidxu@freebsd.org> Cc: freebsd-threads@freebsd.org Subject: Re: threads/79887: [patch] freopen() isn't thread-safe Message-ID: <Pine.GSO.4.64.1012072245570.20951@sea.ntplx.net> In-Reply-To: <201012080250.oB82o6X5072936@freefall.freebsd.org> References: <201012080250.oB82o6X5072936@freefall.freebsd.org>
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On Wed, 8 Dec 2010, David Xu wrote:
> John Baldwin wrote:
> > David,
> >
> > I think the submitter's analysis is correct that the only place that can set
> > the close function pointer is funopen() and that for that case (and any other
> > "fake" files), the file descriptor will be -1. If the fd is >= 0, then it
> > must be a file-descriptor-backed FILE, and relying on dup2() to close the fd
> > is ok.
> >
> > As the manpage notes, the most common usage is to redirect stderr or stdout by
> > doing 'freopen("/dev/null", "w", stderr)'. The bug allows some other random
> > code that is calling open() in another thread to have that open() return 2
> > during the window where fd '2' is closed during freopen(). That other file
> > descriptor then gets trounced by the dup2() call in freopen() to point to
> > something else.
> >
> > The code likely uses _close() rather than close() directly to be cleaner.
> > Given that this is stdio, I don't think we are really worried about the
> > performance impact of one extra wrapper function.
> >
> > I think the original patch is most likely correct.
> >
>
> The patch works, I just don't like the design of the
> (*fp->_close)(fp->_cookie)
> it seems the patch make freopen bypass it.
> I think the patch can be committed, but I am busy and have
> no time to do it by myself.
I can do it, but will be away on vacation until later next
week. If you want to wait, I can commit it.
Would you like to replace the (*fp->_close)(fp->_cookie)
with just _close(fp->_file) as you suggest in one of your
followups?
--
DE
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