Ensure that EXFLAG_INVALID_POLICY is checked even in leaf certs

Even though we check the leaf cert to confirm it is valid, we
later ignored the invalid flag and did not notice that the leaf
cert was bad.

Fixes: CVE-2023-0465

Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from #20588)

crypto/x509/x509_vfy.c

@@ -1649,18 +1649,25 @@ static int check_policy(X509_STORE_CTX *ctx)
     }
     /* Invalid or inconsistent extensions */
     if (ret == X509_PCY_TREE_INVALID) {
-        int i;
+        int i, cbcalled = 0;
 
         /* Locate certificates with bad extensions and notify callback. */
-        for (i = 1; i < sk_X509_num(ctx->chain); i++) {
+        for (i = 0; i < sk_X509_num(ctx->chain); i++) {
             X509 *x = sk_X509_value(ctx->chain, i);
 
             if (!(x->ex_flags & EXFLAG_INVALID_POLICY))
                 continue;
+            cbcalled = 1;
             if (!verify_cb_cert(ctx, x, i,
                                 X509_V_ERR_INVALID_POLICY_EXTENSION))
                 return 0;
         }
+        if (!cbcalled) {
+            /* Should not be able to get here */
+            X509err(X509_F_CHECK_POLICY, ERR_R_INTERNAL_ERROR);
+            return 0;
+        }
+        /* The callback ignored the error so we return success */
         return 1;
     }
     if (ret == X509_PCY_TREE_FAILURE) {