More generalized fix for #127855, overallocate in SvGROW and not just sv_grow()

If we overallocate in SvGROW() and not just sv_grow() we can ensure
we have more cases where we can COW. We need to ensure we always
have room for a null and a reference count.

1 files changed, 7 insertions, 4 deletions

diff --git a/sv.h b/sv.h
index bfda6bf6cb..0c6e6d49b1 100644
--- a/sv.h
+++ b/sv.h
@@ -2111,12 +2111,15 @@ See also C<L</PL_sv_yes>> and C<L</PL_sv_no>>.
 
 #ifdef PERL_ANY_COW
 # define SvGROW(sv,len) \
-	(SvIsCOW(sv) || SvLEN(sv) < (len) ? sv_grow(sv,len) : SvPVX(sv))
+        (SvIsCOW(sv) || SvLEN(sv) < ((len)+2) ? sv_grow(sv,(len)+2) : SvPVX(sv))
+# define SvGROW_mutable(sv,len) \
+    (SvLEN(sv) < ((len)+2) ? sv_grow(sv,(len)+2) : SvPVX_mutable(sv))
 #else
-# define SvGROW(sv,len) (SvLEN(sv) < (len) ? sv_grow(sv,len) : SvPVX(sv))
+# define SvGROW(sv,len) \
+    (SvLEN(sv) < ((len)+1) ? sv_grow(sv,(len)+1) : SvPVX(sv))
+# define SvGROW_mutable(sv,len) \
+    (SvLEN(sv) < ((len)+1) ? sv_grow(sv,(len)+1) : SvPVX_mutable(sv))
 #endif
-#define SvGROW_mutable(sv,len) \
-    (SvLEN(sv) < (len) ? sv_grow(sv,len) : SvPVX_mutable(sv))
 #define Sv_Grow sv_grow
 
 #define CLONEf_COPY_STACKS 1