Re: bugs when operating with closed file descriptors

[Gary V. Vaughan]

Hi Eric,

(Another!) Nice catch :-)

Even in the absence of any fixes, making these sorts of issues into  
tests
as we find them serves both to document known shortcomings and to  
prevent
future regressions when the problems have been fixed -- an excellent way
to make the source code robust...

Cheers,
        Gary.

On 18 Aug 2006, at 20:58, Eric Blake wrote:

> Eric Blake <ebb9 <at> byu.net> writes:
>
> > I'm still thinking about how best to patch this.  I know gnulib  
> > provides the
> > stdio-safer module (and friends) that guarantee that stdio  
> > functions like
> fopen
> > don't reuse fd's 0, 1, or 2 (and hence that stdin, stdout, and  
> > stderr remain
> > closed if they started life closed).  I also know that gnulib  
> > provides the
> > closeout module, which we should probably be using (and issue an  
> > error if any
> > output was attempted to stdout when it was already closed).
>
> Even with my earlier patches, I'm still finding issues.  For example:
>
> $ m4 | cat -s
> divert(-1)
> define(`f',`
> ')
> define(`f',defn(`f')defn(`f'))
> define(`f',defn(`f')defn(`f'))
> define(`f',defn(`f')defn(`f'))
> define(`f',defn(`f')defn(`f'))
> define(`f',defn(`f')defn(`f'))
> define(`f',defn(`f')defn(`f'))
> define(`f',defn(`f')defn(`f'))
> define(`f',defn(`f')defn(`f'))
> define(`f',defn(`f')defn(`f'))
> define(`f',defn(`f')defn(`f'))
> define(`f',defn(`f')defn(`f'))
> define(`f',defn(`f')defn(`f'))
> define(`f',defn(`f')defn(`f'))
> define(`f',defn(`f')defn(`f'))
> define(`f',defn(`f')defn(`f'))
> define(`f',defn(`f')defn(`f'))
> define(`f',defn(`f')defn(`f'))
> define(`f',defn(`f')defn(`f'))
> define(`f',defn(`f')defn(`f'))
> define(`f',defn(`f')defn(`f'))
> divert(1)
> f
> divert
> syscmd(echo hi >&3)
>
> hi
>
> $
>
> Oops - we didn't set the fd of our temporary file to close-on-exec,  
> so the
> child process inherited it and was able to pollute it.
>
> --
> Eric Blake
>
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--
Gary V. Vaughan      ())_.  gary@ 
{lilith.warpmail.net,gnu.org},address@hidden
Research Scientist   ( '/   http://blog.azazil.net
GNU Hacker           / )=   http://www.gnu.org/software/{libtool,m4}
Technical Author   `(_~)_   http://sources.redhat.com/autobook

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