Fix printing of PROXY_CERT_INFO_EXTENSION to not assume NUL terminate…

…d strings

ASN.1 strings may not be NUL terminated. Don't assume they are.

CVE-2021-3712

Reviewed-by: Viktor Dukhovni <viktor@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>

crypto/x509v3/v3_pci.c

@@ -77,7 +77,8 @@ static int i2r_pci(X509V3_EXT_METHOD *method, PROXY_CERT_INFO_EXTENSION *pci,
     i2a_ASN1_OBJECT(out, pci->proxyPolicy->policyLanguage);
     BIO_puts(out, "\n");
     if (pci->proxyPolicy->policy && pci->proxyPolicy->policy->data)
-        BIO_printf(out, "%*sPolicy Text: %s\n", indent, "",
+        BIO_printf(out, "%*sPolicy Text: %.*s\n", indent, "",
+                   pci->proxyPolicy->policy->length,
                    pci->proxyPolicy->policy->data);
     return 1;
 }