PerlIOStdio_dup: survive empty fh

Fixes [perl #63244], which is broken from 5.8.8 to blead.

Author: Reini Urban

perlio.c

@@ -3122,26 +3122,30 @@ PerlIOStdio_dup(pTHX_ PerlIO *f, PerlIO *o, CLONE_PARAMS *param, int flags)
      */
     if ((f = PerlIOBase_dup(aTHX_ f, o, param, flags))) {
 	FILE *stdio = PerlIOSelf(o, PerlIOStdio)->stdio;
-	const int fd = fileno(stdio);
-	char mode[8];
-	if (flags & PERLIO_DUP_FD) {
-	    const int dfd = PerlLIO_dup(fileno(stdio));
-	    if (dfd >= 0) {
-		stdio = PerlSIO_fdopen(dfd, PerlIO_modestr(o,mode));
-		goto set_this;
-	    }
-	    else {
-		NOOP;
-		/* FIXME: To avoid messy error recovery if dup fails
-		   re-use the existing stdio as though flag was not set
-		 */
-	    }
-	}
-    	stdio = PerlSIO_fdopen(fd, PerlIO_modestr(o,mode));
-    set_this:
-	PerlIOSelf(f, PerlIOStdio)->stdio = stdio;
-        if(stdio) {
-	    PerlIOUnix_refcnt_inc(fileno(stdio));
+        if (!stdio) {
+            return f;
+        } else {
+            const int fd = fileno(stdio);
+            char mode[8];
+            if (flags & PERLIO_DUP_FD) {
+                const int dfd = PerlLIO_dup(fd);
+                if (dfd >= 0) {
+                    stdio = PerlSIO_fdopen(dfd, PerlIO_modestr(o,mode));
+                    goto set_this;
+                }
+                else {
+                    NOOP;
+                    /* FIXME: To avoid messy error recovery if dup fails
+                       re-use the existing stdio as though flag was not set
+                    */
+                }
+            }
+            stdio = PerlSIO_fdopen(fd, PerlIO_modestr(o,mode));
+        set_this:
+            PerlIOSelf(f, PerlIOStdio)->stdio = stdio;
+            if (stdio) {
+                PerlIOUnix_refcnt_inc(fileno(stdio));
+            }
         }
     }
     return f;

pod/perlcdelta.pod

@@ -751,6 +751,11 @@ See L<RT #128204|https://rt.perl.org/Public/Bug/Display.html?id=128204>
 
 See L<RT #128313|https://rt.perl.org/Public/Bug/Display.html?id=128313>
 
+=item Fix PERLIO=stdio dup on empty filehandle
+
+See L<RT #63244|https://rt.perl.org/Public/Bug/Display.html?id=63244>
+or L<http://bugs.debian.org/164615>, crashes from 5.8.8 to blead.
+
 =back
 
 =head1 Acknowledgements

t/io/open.t

@@ -10,7 +10,7 @@ $|  = 1;
 use warnings;
 use Config;
 
-plan tests => 156;
+plan tests => 157;
 
 my $Perl = which_perl();
 
@@ -485,5 +485,14 @@ pass("no crash when open autovivifies glob in freed package");
     unlink "$fh";
 }
 
+# [perl #63244] Survive dup of empty filehandle
+{
+    local $ENV{PERLIO} = 'stdio';
+    my $runperl = _create_runperl(prog => 'open(F, q{<&STDOUT});',
+                                  stdin => undef);
+    $runperl =~ s/ </ 1</;
+    ok(system($runperl)==0, 'stdio dup on empty filehandle [perl #63244]');
+}
+
 package OverloadTest;
 use overload '""' => sub { ${$_[0]} };