-l treats globref as filename #16248

p5pRT · 2017-11-15T08:41:15Z

Migrated from rt.perl.org#132449 (status was 'open')

Searchable as RT132449$

p5pRT · 2017-11-15T08:41:16Z

From zefram@fysh.org

Created by zefram@fysh.org

The -l file test operation is not valid to perform on a file handle,
because a file handle can't be opened on a symlink per se, so one could
never get a true result. So if we try to apply it to a file handle, we
see this warning and error result, produced without performing any lstat:

$ strace -qqelstat perl -lwe 'print -l STDIN // "undef"'
Use of -l on filehandle STDIN at -e line 1.
undef

But if we try to apply it to a file handle the *other* way, the behaviour
is different:

$ strace -qqelstat perl -lwe 'print -l \*STDIN // "undef"'
Use of -l on filehandle STDIN at -e line 1.
lstat("GLOB(0x14bbc90)", 0x1495228) = -1 ENOENT (No such file or directory)
undef

The warning claims that the argument is still being treated as a file
handle, but an lstat was actually performed, using the stringification
of the globref as a filename. One can even contrive for this lstat to
succeed and make -l return a true result, ostensibly on a file handle:

$ strace -qqelstat perl -lwe 'symlink "z", \*STDIN or die $!; print -l \*STDIN // "undef"'
Use of -l on filehandle STDIN at -e line 1.
lstat("GLOB(0x1bbfcc0)", {st_mode=S_IFLNK|0777, st_size=1, ...}) = 0
1

The documentation doesn't mention -l being any different in its
interpretation of arguments from the other file test operators. I reckon
\*STDIN should be treated consistently as a file handle, and should
yield a failure without performing any lstat syscall.

Perl Info


Flags:
    category=core
    severity=low

Site configuration information for perl 5.27.5:

Configured by zefram at Fri Oct 20 23:24:00 BST 2017.

Summary of my perl5 (revision 5 version 27 subversion 5) configuration:
   
  Platform:
    osname=linux
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    archname=x86_64-linux-thread-multi
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    config_args='-des -Dprefix=/home/zefram/usr/perl/perl_install/perl-5.27.5-i64-f52 -Duselargefiles -Dusethreads -Uafs -Ud_csh -Uusesfio -Uusenm -Duseshrplib -Dusedevel -Uversiononly -Ui_db'
    hint=recommended
    useposix=true
    d_sigaction=define
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    uselongdouble=undef
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  Compiler:
    cc='cc'
    ccflags ='-D_REENTRANT -D_GNU_SOURCE -fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -D_FORTIFY_SOURCE=2'
    optimize='-O2'
    cppflags='-D_REENTRANT -D_GNU_SOURCE -fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include'
    ccversion=''
    gccversion='4.9.2'
    gccosandvers=''
    intsize=4
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    doublekind=3
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    longlongsize=8
    d_longdbl=define
    longdblsize=16
    longdblkind=3
    ivtype='long'
    ivsize=8
    nvtype='double'
    nvsize=8
    Off_t='off_t'
    lseeksize=8
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    prototype=define
  Linker and Libraries:
    ld='cc'
    ldflags =' -fstack-protector-strong -L/usr/local/lib'
    libpth=/usr/local/lib /usr/lib/gcc/x86_64-linux-gnu/4.9/include-fixed /usr/include/x86_64-linux-gnu /usr/lib /lib/x86_64-linux-gnu /lib/../lib /usr/lib/x86_64-linux-gnu /usr/lib/../lib /lib
    libs=-lpthread -lnsl -ldb -ldl -lm -lcrypt -lutil -lc
    perllibs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc
    libc=libc-2.19.so
    so=so
    useshrplib=true
    libperl=libperl.so
    gnulibc_version='2.19'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs
    dlext=so
    d_dlsymun=undef
    ccdlflags='-Wl,-E -Wl,-rpath,/home/zefram/usr/perl/perl_install/perl-5.27.5-i64-f52/lib/5.27.5/x86_64-linux-thread-multi/CORE'
    cccdlflags='-fPIC'
    lddlflags='-shared -O2 -L/usr/local/lib -fstack-protector-strong'



@INC for perl 5.27.5:
    /home/zefram/usr/perl/perl_install/perl-5.27.5-i64-f52/lib/site_perl/5.27.5/x86_64-linux-thread-multi
    /home/zefram/usr/perl/perl_install/perl-5.27.5-i64-f52/lib/site_perl/5.27.5
    /home/zefram/usr/perl/perl_install/perl-5.27.5-i64-f52/lib/5.27.5/x86_64-linux-thread-multi
    /home/zefram/usr/perl/perl_install/perl-5.27.5-i64-f52/lib/5.27.5


Environment for perl 5.27.5:
    HOME=/home/zefram
    LANG (unset)
    LANGUAGE (unset)
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/home/zefram/usr/perl/perl_install/perl-5.27.5-i64-f52/bin:/home/zefram/usr/perl/util:/home/zefram/pub/x86_64-unknown-linux-gnu/bin:/home/zefram/pub/common/bin:/usr/bin:/bin:/usr/local/bin:/usr/games
    PERLDOC=-oman
    PERL_BADLANG (unset)
    SHELL=/usr/bin/zsh

p5pRT · 2017-11-17T01:23:40Z

From blgl@stacken.kth.se

Quoth Zefram:

because a file handle can't be opened on a symlink per se

False. Darwin has the O_SYMLINK mode which lets you do exactly that.
The resulting file descriptor can't be used for i/o, but it can be passed
to fstat, fchmod, fchown, etc.

{
use Fcntl
qw(S_ISLNK);

my $fn = "/etc/localtime";
sysopen(my $fh, $fn, 0x200000)
or die "open: $!\n";
my @fstat = stat($fh)
or die "fstat: $!\n";
close($fh);
print $fn, " is ", S_ISLNK($fstat[2]) ? "" : "not ", "a symlink\n";
}

/Bo Lindbergh

p5pRT · 2017-11-17T01:23:40Z

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

p5pRT added Severity Low type-core labels Oct 19, 2019

xenu removed the affects-5.27 label Nov 19, 2021

xenu removed the Severity Low label Dec 29, 2021

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-l treats globref as filename #16248

-l treats globref as filename #16248

p5pRT commented Nov 15, 2017

p5pRT commented Nov 15, 2017

p5pRT commented Nov 17, 2017

p5pRT commented Nov 17, 2017

-l treats globref as filename #16248

-l treats globref as filename #16248

Comments

p5pRT commented Nov 15, 2017

p5pRT commented Nov 15, 2017

From zefram@fysh.org

Created by zefram@fysh.org

p5pRT commented Nov 17, 2017

From blgl@stacken.kth.se

p5pRT commented Nov 17, 2017