[perl #92258] <$fh> hangs on a glob copy

Opening a file handle to \$glob causes assertion failures
(under debugging) or hangs or other erratic behaviour without
debugging. This might even crash in some cases.

It never really worked properly, but it didn’t start hanging
apparently until 5.12.2 and 5.14.0.

2 files changed, 17 insertions, 4 deletions

diff --git a/ext/PerlIO-scalar/scalar.xs b/ext/PerlIO-scalar/scalar.xs
index de9873829c..e0f75acf1a 100644
--- a/ext/PerlIO-scalar/scalar.xs
+++ b/ext/PerlIO-scalar/scalar.xs
@@ -240,9 +240,13 @@ PerlIOScalar_get_cnt(pTHX_ PerlIO * f)
 {
     if (PerlIOBase(f)->flags & PERLIO_F_CANREAD) {
 	PerlIOScalar *s = PerlIOSelf(f, PerlIOScalar);
+	STRLEN len;
 	SvGETMAGIC(s->var);
-	if (SvCUR(s->var) > (STRLEN) s->posn)
-	    return SvCUR(s->var) - (STRLEN)s->posn;
+	if (isGV_with_GP(s->var))
+	    (void)SvPV(s->var,len);
+	else len = SvCUR(s->var);
+	if (len > (STRLEN) s->posn)
+	    return len - (STRLEN)s->posn;
 	else
 	    return 0;
     }
@@ -264,9 +268,12 @@ void
 PerlIOScalar_set_ptrcnt(pTHX_ PerlIO * f, STDCHAR * ptr, SSize_t cnt)
 {
     PerlIOScalar *s = PerlIOSelf(f, PerlIOScalar);
+    STRLEN len;
     PERL_UNUSED_ARG(ptr);
     SvGETMAGIC(s->var);
-    s->posn = SvCUR(s->var) - cnt;
+    if (isGV_with_GP(s->var)) (void)SvPV(s->var,len);
+    else len = SvCUR(s->var);
+    s->posn = len - cnt;
 }
 
 PerlIO *
diff --git a/t/io/perlio.t b/t/io/perlio.t
index 1a330f4367..a65b0d3eb9 100644
--- a/t/io/perlio.t
+++ b/t/io/perlio.t
@@ -6,7 +6,7 @@ BEGIN {
 	skip_all_without_perlio();
 }
 
-plan tests => 42;
+plan tests => 44;
 
 use_ok('PerlIO');
 
@@ -191,6 +191,12 @@ close ($perlio);
 close ($no_perlio);
 }
 
+{ # [perl #92258]
+    open my $fh, "<", \(my $f = *f);
+    is join("", <$fh>), '*main::f', 'reading from a glob copy';
+    is ref \$f, 'GLOB', 'the glob copy is unaffected';
+}
+
 }