[ID 20000904.004] perlsec Manual Page Incorrect Doing"Safe Backticks"

This is a bug report for perl from garry@zvolve.com,
generated with the help of perlbug 1.28 running under perl v5.6.0.


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[Please enter your report here]

The perlsec manual page suggests a safe way to fork/exec an external
program.  From the manual page:

         use English;
         die "Can't fork: $!" unless defined $pid = open(KID, "-|");
         if ($pid) {           # parent
             while (<KID>) {
                 # do something
             }
             close KID;
         } else {
             my @temp = ($EUID, $EGID);
             $EUID = $UID;
             $EGID = $GID;    #      initgroups() also called!
             # Make sure privs are really gone
             ($EUID, $EGID) = @temp;
             die "Can't drop privileges"
                     unless $UID == $EUID  && $GID eq $EGID;
             $ENV{PATH} = "/bin:/usr/bin";
             exec 'myprog', 'arg1', 'arg2'
                 or die "can't exec myprog: $!";
         }

This does *not* relinquish root privileges on this system.  I don't 
think that it would work on any SVR4 system.  Aside from the syntax 
error in line 2, the script will die printing "Can't drop privileges".  

The code should be:

        use English;
        die "Can't fork: $!" unless defined($pid = open(KID, "-|"));
        if ($pid) {           # parent
            while (<KID>) {
                # do something
            }
            close KID;
        } else {
            my @temp     = ($EUID, $EGID);
            my $orig_uid = $UID;
            my $orig_gid = $GID;
            $EUID = $UID;
            $EGID = $GID;
            # Drop privileges
            $UID  = $orig_uid;
            $GID  = $orig_gid;
            # Make sure privs are really gone
            ($EUID, $EGID) = @temp;
            die "Can't drop privileges"
                unless $UID == $EUID  && $GID eq $EGID;
            $ENV{PATH} = "/bin:/usr/bin";
            exec 'myprog', 'arg1', 'arg2'
                or die "can't exec myprog: $!";
        }

-Garry Williams

[Please do not change anything below this line]
-----------------------------------------------------------------
---
Flags:
    category=docs
    severity=low
---
Site configuration information for perl v5.6.0:

Configured by garry at Tue Aug  1 07:40:52 EDT 2000.

Summary of my perl5 (revision 5.0 version 6 subversion 0) configuration:
  Platform:
    osname=solaris, osvers=2.7, archname=sun4-solaris
    uname='sunos repos 5.7 generic_106541-11 sun4u sparc sunw,ultra-60 '
    config_args=''
    hint=recommended, useposix=true, d_sigaction=define
    usethreads=undef use5005threads=undef useithreads=undef usemultiplicity=undef
    useperlio=undef d_sfio=undef uselargefiles=define 
    use64bitint=undef use64bitall=undef uselongdouble=undef usesocks=undef
  Compiler:
    cc='cc', optimize='-O', gccversion=
    cppflags='-I/usr/local/include'
    ccflags ='-I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64'
    stdchar='char', d_stdstdio=define, usevfork=false
    intsize=4, longsize=4, ptrsize=4, doublesize=8
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16
    ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
    alignbytes=8, usemymalloc=y, prototype=define
  Linker and Libraries:
    ld='cc', ldflags ='-L/usr/local/lib '
    libpth=/usr/local/lib /opt/SUNWspro/SC5.0/lib /lib /usr/lib /usr/ccs/lib
    libs=-lsocket -lnsl -ldb -ldl -lm -lc -lcrypt -lsec
    libc=/lib/libc.so, so=so, useshrplib=false, libperl=libperl.a
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags=' '
    cccdlflags='-KPIC', lddlflags='-G -L/usr/local/lib'

Locally applied patches:
    

---
@INC for perl v5.6.0:
    /usr/local/lib/perl5/5.6.0/sun4-solaris
    /usr/local/lib/perl5/5.6.0
    /usr/local/lib/perl5/site_perl/5.6.0/sun4-solaris
    /usr/local/lib/perl5/site_perl/5.6.0
    /usr/local/lib/perl5/site_perl
    .

---
Environment for perl v5.6.0:
    HOME=/home/garry
    LANG (unset)
    LANGUAGE (unset)
    LC_COLLATE=C
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/home/garry/bin:/bin:/sbin:/usr/sbin:/opt/SUNWspro/bin:/usr/ccs/bin:/usr/local/bin:/usr/openwin/bin:/usr/java1.1/bin
    PERL_BADLANG (unset)
    SHELL=/bin/ksh

• [ID 20000904.004] perlsec Manual Page Incorrect Doing"Safe Backticks" by Garry T. Williams
• Re: [ID 20000904.004] perlsec Manual Page Incorrect Doing "Safe Backticks" by Jarkko Hietaniemi
• Re: [ID 20000904.004] perlsec Manual Page Incorrect Doing "Safe Backticks" by Jarkko Hietaniemi