[tls] Generalise mechanism for duplicating a TLS cursor

Generalise the mechanism used for storing a session ticket to allow
for storing copies of arbitrary TLS cursors.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/tls.h

@@ -382,14 +382,6 @@ struct tls_session_id {
 	uint8_t len;
 };
 
-/** A TLS session ticket */
-struct tls_session_ticket {
-	/** Ticket data */
-	void *data;
-	/** Length of ticket data */
-	size_t len;
-};
-
 /** A TLS session */
 struct tls_session {
 	/** Reference counter */
@@ -411,7 +403,7 @@ struct tls_session {
 	/** Session ID */
 	struct tls_session_id id;
 	/** Session ticket */
-	struct tls_session_ticket ticket;
+	struct tls_cursor ticket;
 
 	/** List of connections */
 	struct list_head conn;
@@ -489,7 +481,7 @@ struct tls_connection {
 	/** New session ID (if any) */
 	struct tls_session_id new_id;
 	/** New session ticket (if any) */
-	struct tls_session_ticket new_ticket;
+	struct tls_cursor new_ticket;
 
 	/** Plaintext stream */
 	struct interface plainstream;

src/net/tls.c

@@ -295,6 +295,49 @@ tls_has_inner ( struct tls_connection *tls, struct cipher_algorithm *cipher ) {
 		 ( cipher != &cipher_null ) );
 }
 
+/**
+ * Duplicate content of a TLS cursor
+ *
+ * @v src		Source cursor
+ * @v dst		Destination cursor
+ *
+ * The content of the source cursor (if any) will be copied.
+ *
+ * If the source cursor is not present (e.g. because it represents an
+ * extension that was not present, rather than being present but
+ * empty) then the destination cursor will also become not present.
+ *
+ * If the source cursor is present but empty (e.g. because it
+ * represents an extension that was present but empty) then the
+ * destination cursor will also become present but empty (with its
+ * pointer being the sentinel value as returned by malloc(0)).
+ *
+ * If the source cursor is either empty or not present, then this
+ * function is guaranteed to succeed.
+ */
+static int tls_copy ( const struct tls_cursor *src, struct tls_cursor *dst ) {
+
+	/* Free any existing content */
+	zfree ( dst->data );
+	dst->data = NULL;
+	dst->len = 0;
+
+	/* Do nothing if source cursor is not present */
+	if ( ! src->data ) {
+		assert ( src->len == 0 );
+		return 0;
+	}
+
+	/* Duplicate cursor */
+	dst->data = malloc ( src->len );
+	if ( ! dst->data )
+		return -ENOMEM;
+	memcpy ( dst->data, src->data, src->len );
+	dst->len = src->len;
+
+	return 0;
+}
+
 /**
  * Get pipe name (for debugging)
  *
@@ -2782,17 +2825,9 @@ static int tls_new_session_ticket ( struct tls_connection *tls,
 		return 0;
 	}
 
-	/* Free any unapplied new session ticket */
-	zfree ( tls->new_ticket.data );
-	tls->new_ticket.data = NULL;
-	tls->new_ticket.len = 0;
-
 	/* Record ticket */
-	tls->new_ticket.data = malloc ( ticket.ticket.len );
-	if ( ! tls->new_ticket.data )
-		return -ENOMEM;
-	memcpy ( tls->new_ticket.data, ticket.ticket.data, ticket.ticket.len );
-	tls->new_ticket.len = ticket.ticket.len;
+	if ( ( rc = tls_copy ( &ticket.ticket, &tls->new_ticket ) ) != 0 )
+		return rc;
 
 	return 0;
 }