protect CvSTASH weakref with backrefs

Each CV usually has a pointer, CvSTASH, back to the stash that it was
complied in. This pointer isn't reference counted, to avoid loops. Which
can leave it dangling if the stash is deleted.

There is already protection for the similar GvSTASH field in GVs: the
stash has an array of backrefs, xhv_backreferences, pointing to the GVs
whose GvSTASHes point to it, and which is used to zero all the GvSTASH
fields should the stash be deleted.

All this patch does is also add the CVs with CvSTASH to that stash's
backref list too.

1 files changed, 2 insertions, 0 deletions

diff --git a/pad.c b/pad.c
index e8ba139434..92f4041398 100644
--- a/pad.c
+++ b/pad.c
@@ -1573,6 +1573,8 @@ Perl_cv_clone(pTHX_ CV *proto)
 #endif
     CvGV(cv)		= CvGV(proto);
     CvSTASH(cv)		= CvSTASH(proto);
+    if (CvSTASH(cv))
+	Perl_sv_add_backref(aTHX_ MUTABLE_SV(CvSTASH(cv)), MUTABLE_SV(cv));
     OP_REFCNT_LOCK;
     CvROOT(cv)		= OpREFCNT_inc(CvROOT(proto));
     OP_REFCNT_UNLOCK;