Allow read-only access to lists of certificates, CRL, CRL entries

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/include/mbedtls/x509_crl.h b/include/mbedtls/x509_crl.h
index f65e984..52bd43c 100644
--- a/include/mbedtls/x509_crl.h
+++ b/include/mbedtls/x509_crl.h
@@ -63,7 +63,10 @@
      * `entry_ext.p == NULL`. */
     mbedtls_x509_buf entry_ext;
 
-    struct mbedtls_x509_crl_entry *MBEDTLS_PRIVATE(next);
+    /** Next element in the linked list of entries.
+     * \p NULL indicates the end of the list.
+     * Do not modify this field directly. */
+    struct mbedtls_x509_crl_entry *next;
 }
 mbedtls_x509_crl_entry;
 
@@ -96,7 +99,10 @@
     mbedtls_pk_type_t MBEDTLS_PRIVATE(sig_pk);           /**< Internal representation of the Public Key algorithm of the signature algorithm, e.g. MBEDTLS_PK_RSA */
     void *MBEDTLS_PRIVATE(sig_opts);             /**< Signature options to be passed to mbedtls_pk_verify_ext(), e.g. for RSASSA-PSS */
 
-    struct mbedtls_x509_crl *MBEDTLS_PRIVATE(next);
+    /** Next element in the linked list of CRL.
+     * \p NULL indicates the end of the list.
+     * Do not modify this field directly. */
+    struct mbedtls_x509_crl *next;
 }
 mbedtls_x509_crl;
 
diff --git a/include/mbedtls/x509_crt.h b/include/mbedtls/x509_crt.h
index 6731100..3c11a99 100644
--- a/include/mbedtls/x509_crt.h
+++ b/include/mbedtls/x509_crt.h
@@ -95,7 +95,10 @@
     mbedtls_pk_type_t MBEDTLS_PRIVATE(sig_pk);           /**< Internal representation of the Public Key algorithm of the signature algorithm, e.g. MBEDTLS_PK_RSA */
     void *MBEDTLS_PRIVATE(sig_opts);             /**< Signature options to be passed to mbedtls_pk_verify_ext(), e.g. for RSASSA-PSS */
 
-    struct mbedtls_x509_crt *MBEDTLS_PRIVATE(next);     /**< Next certificate in the CA-chain. */
+    /** Next certificate in the linked list that constitutes the CA chain.
+     * \p NULL indicates the end of the list.
+     * Do not modify this field directly. */
+    struct mbedtls_x509_crt *next;
 }
 mbedtls_x509_crt;