binding STDIN to scalar hides fd 0 forever

[p5pRT]

Migrated from rt.perl.org#34981 (status was 'open')

Searchable as RT34981$

[p5pRT]

From Steffen_Ullrich@genua.de

Created by Steffen_Ullrich@genua.de

Binding STDIN to a scalar, e.g. "open(STDIN,'<',\$x)" makes fd 0
inaccessable in the future. with lsof from perl it looks like that
the fd 0 is then bound to PerlIO.pm forever.
Even forking does not help.
The side effect is that children startet with IPC​::Open2 or
"open(X,'|prog')" cannot read from stdin, e.g. they try to read
from fd 0 which is bound to something else.

The following script shows the problem and a possible workaround
(line 9​: closing the fd 0 manually using POSIX​::close).

The problem exists at least with perl5.8.6 on OpenBSD3.7 and
perl5.8.4 an Linux (Kubuntu 5.04).

  1 use strict;
  2 use POSIX;
  3
  4 open( STDIN,'</dev/null') || die $!;
  5 p();
  6 my $content = 'bla';
  7 close(STDIN);
  8 open( STDIN,'<',\$content ) || die $!;
  9 ##### POSIX​::close(0); <<<<< workaround
  10 p();
  11 close(STDIN);
  12 open( STDIN,'</dev/null' ) || die $!;
  13 p();
  14 system( "fstat -p$$" );
  15
  16 sub p() { print "XXX fileno=".fileno(STDIN)."\n" }

Perl Info

Flags:
    category=core
    severity=medium

Site configuration information for perl v5.8.6:

Configured by root at Thu Jan  1  0:00:00 UTC 1970.

Summary of my perl5 (revision 5 version 8 subversion 6) configuration:
  Platform:
    osname=openbsd, osvers=3.7, archname=i386-openbsd
    uname='openbsd'
    config_args='-dsE -Dopenbsd_distribution=defined'
    hint=recommended, useposix=true, d_sigaction=define
    usethreads=undef use5005threads=undef useithreads=undef usemultiplicity=undef
    useperlio=define d_sfio=undef uselargefiles=define usesocks=undef
    use64bitint=undef use64bitall=undef uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-fno-strict-aliasing -fno-delete-null-pointer-checks -pipe -I/usr/local/include',
    optimize='-O2',
    cppflags='-fno-strict-aliasing -fno-delete-null-pointer-checks -pipe -I/usr/local/include'
    ccversion='', gccversion='3.3.5 (propolice)', gccosandvers='openbsd3.7'
    intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
    ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
    alignbytes=4, prototype=define
  Linker and Libraries:
    ld='cc', ldflags ='-Wl,-E '
    libpth=/usr/lib
    libs=-lm -lutil -lc
    perllibs=-lm -lutil -lc
    libc=/usr/lib/libc.so.34.2, so=so, useshrplib=true, libperl=libperl.so.10.0
    gnulibc_version=''
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-R/usr/libdata/perl5/i386-openbsd/5.8.6/CORE'
    cccdlflags='-DPIC -fPIC ', lddlflags='-shared -fPIC '

Locally applied patches:
    SUIDPERLIO1 - fix PERLIO_DEBUG buffer overflow (CAN-2005-0156)


@INC for perl v5.8.6:
    /usr/libdata/perl5/i386-openbsd/5.8.6
    /usr/local/libdata/perl5/i386-openbsd/5.8.6
    /usr/libdata/perl5
    /usr/local/libdata/perl5
    /usr/local/libdata/perl5/site_perl/i386-openbsd
    /usr/libdata/perl5/site_perl/i386-openbsd
    /usr/local/libdata/perl5/site_perl
    /usr/libdata/perl5/site_perl
    /usr/local/lib/perl5/site_perl
    .


Environment for perl v5.8.6:
    HOME=/home/steffen
    LANG (unset)
    LANGUAGE (unset)
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/home/steffen/bin:/home/steffen/bin/OpenBSD.bin:/mount/share/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/X11R6/bin:/usr/local/bin:/usr/local/bin
    PERL_BADLANG (unset)
    SHELL=/usr/local/bin/bash

[p5pRT]

From guest@guest.guest.xxxxxxxx

still unresolved in perl5.8.7

[p5pRT]

The RT System itself - Status changed from 'new' to 'open'

[jkeenan]

The following is a slight reworking of the program originally submitted in this ticket back in 2005.

$ cat gh-7879-fd.pl 
use strict;
use warnings;
use POSIX;
# https://github.com/Perl/perl5/issues/7879
# Originally: https://rt-archive.perl.org/perl5/Ticket/Display.html?id=34981

sub p() { print "XXX fileno=".fileno(STDIN)."\n" }

open( STDIN,'</dev/null') || die $!;
p();
my $content = 'bla';
close(STDIN);

open( STDIN,'<',\$content ) || die $!;
##### POSIX​::close(0); <<<<< workaround
p();
close(STDIN);

open( STDIN,'</dev/null' ) || die $!;
p();
system( "fstat -p$$" );

Running this program on Linux with perl-5.38.0, I get:

$ perl gh-7879-fd.pl
XXX fileno=0
XXX fileno=-1
XXX fileno=0
Can't exec "fstat": No such file or directory at gh-7879-fd.pl line 21.

The OP didn't post explicit output. Can someone comment on the output above and whether it remains a problem needing fixing?