regexec.c - harden internals against missing logical_nparens

We can default a 0 rx->logical_nparens to rx->nparens. If rx->logical_nparens
is zero then either rx->nparens is also zero, or it can be defaulted. This
will fix most re::engine::XXX modules that do not know about the new field,
provided they zero the rx structure during construction. If they don't then
this patch won't hurt anything and we will have to patch them directly.

Also mark re_op_compile() as available to extensions. Marking it as hidden
means that re::engine::PCRE2 and others cannot build.

This patch should go a long way towards fixing issue #20710.

1 files changed, 13 insertions, 6 deletions

diff --git a/mg.c b/mg.c
index 83ae360527..5366f5767a 100644
--- a/mg.c
+++ b/mg.c
@@ -638,7 +638,7 @@ Perl_magic_regdata_cnt(pTHX_ SV *sv, MAGIC *mg)
             const SSize_t n = (SSize_t)mg->mg_obj;
             if (n == '+') {          /* @+ */
                 /* return the number possible */
-                return RX_LOGICAL_NPARENS(rx);
+                return RX_LOGICAL_NPARENS(rx) ? RX_LOGICAL_NPARENS(rx) : RX_NPARENS(rx);
             } else {   /* @- @^CAPTURE  @{^CAPTURE} */
                 I32 paren = RX_LASTPAREN(rx);
 
@@ -674,15 +674,22 @@ Perl_magic_regdatum_get(pTHX_ SV *sv, MAGIC *mg)
         /* @{^CAPTURE} does not contain $&, so we need to increment by 1 */
         const I32 paren = mg->mg_len
                         + (n == '\003' ? 1 : 0);
-        SSize_t s;
-        SSize_t t;
+        
         if (paren < 0)
             return 0;
+
+        SSize_t s;
+        SSize_t t;
+        I32 logical_nparens = (I32)RX_LOGICAL_NPARENS(rx);
+
+        if (!logical_nparens) 
+            logical_nparens = (I32)RX_NPARENS(rx);
+
         if (n != '+' && n != '-') {
             CALLREG_NUMBUF_FETCH(rx,paren,sv);
             return 0;
         }
-        if (paren <= (I32)RX_LOGICAL_NPARENS(rx)) {
+        if (paren <= (I32)logical_nparens) {
             I32 true_paren = RX_LOGICAL_TO_PARNO(rx)
                              ? RX_LOGICAL_TO_PARNO(rx)[paren]
                              : paren;
@@ -692,9 +699,9 @@ Perl_magic_regdatum_get(pTHX_ SV *sv, MAGIC *mg)
                 {
                     SSize_t i;
 
-                    if (n == '+')                /* @+ */
+                    if (n == '+')               /* @+ */
                         i = t;
-                    else if (n == '-')           /* @- */
+                    else                        /* @- */
                         i = s;
 
                     if (RX_MATCH_UTF8(rx)) {