dnsproxy: Remove TCP receive path potential busy waits

When receiving a DNS over TCP request response back from the server,
ConnMan busy waits for the whole response to arrive, or if the server
closes the TCP connection.

Fixes BMC#9960

diff --git a/plugins/dnsproxy.c b/plugins/dnsproxy.c
index a241399..9deeb96 100644 (file)
--- a/plugins/dnsproxy.c
+++ b/plugins/dnsproxy.c
@@ -75,6 +75,12 @@ struct domain_hdr {
 #error "Unknown byte order"
 #endif
 
+struct partial_reply {
+       uint16_t len;
+       uint16_t received;
+       unsigned char buf[];
+};
+
 struct server_data {
        char *interface;
        char *domain;
@@ -85,6 +91,7 @@ struct server_data {
        guint timeout;
        gboolean enabled;
        gboolean connected;
+       struct partial_reply *incoming_reply;
 };
 
 struct request_data {
@@ -441,6 +448,7 @@ static void destroy_server(struct server_data *server)
        if (server->protocol == IPPROTO_UDP)
                connman_info("Removing DNS server %s", server->server);
 
+       g_free(server->incoming_reply);
        g_free(server->server);
        g_free(server->domain);
        g_free(server->interface);
@@ -484,9 +492,16 @@ static gboolean tcp_server_event(GIOChannel *channel, GIOCondition condition,
 
        if (condition & (G_IO_NVAL | G_IO_ERR | G_IO_HUP)) {
                GSList *list;
-
+       hangup:
                DBG("TCP server channel closed");
 
+               /*
+                * Discard any partial response which is buffered; better
+                * to get a proper response from a working server.
+                */
+               g_free(server->incoming_reply);
+               server->incoming_reply = NULL;
+
                for (list = request_list; list; list = list->next) {
                        struct request_data *req = list->data;
                        struct domain_hdr *hdr;
@@ -546,49 +561,62 @@ static gboolean tcp_server_event(GIOChannel *channel, GIOCondition condition,
                }
 
        } else if (condition & G_IO_IN) {
-               int len, bytes_recv, total_bytes_recv;
-               unsigned char reply_len_buf[2];
-               uint16_t reply_len;
-               unsigned char *reply;
+               struct partial_reply *reply = server->incoming_reply;
+               int bytes_recv;
 
-               len = recv(sk, reply_len_buf, 2, 0);
-               if (len < 2)
-                       return TRUE;
+               if (!reply) {
+                       unsigned char reply_len_buf[2];
+                       uint16_t reply_len;
+
+                       bytes_recv = recv(sk, reply_len_buf, 2, MSG_PEEK);
+                       if (!bytes_recv) {
+                               goto hangup;
+                       } else if (bytes_recv < 0) {
+                               if (errno == EAGAIN || errno == EWOULDBLOCK)
+                                       return TRUE;
+
+                               connman_error("DNS proxy error %s",
+                                               strerror(errno));
+                               goto hangup;
+                       } else if (bytes_recv < 2)
+                               return TRUE;
 
-               reply_len = reply_len_buf[1] | reply_len_buf[0] << 8;
+                       reply_len = reply_len_buf[1] | reply_len_buf[0] << 8;
+                       reply_len += 2;
 
-               DBG("TCP reply %d bytes", reply_len);
+                       DBG("TCP reply %d bytes", reply_len);
 
-               reply = g_try_malloc0(reply_len + 2);
-               if (reply == NULL)
-                       return TRUE;
+                       reply = g_try_malloc(sizeof(*reply) + reply_len + 2);
+                       if (!reply)
+                               return TRUE;
+
+                       reply->len = reply_len;
+                       reply->received = 0;
 
-               reply[0] = reply_len_buf[0];
-               reply[1] = reply_len_buf[1];
+                       server->incoming_reply = reply;
+               }
 
-               total_bytes_recv = bytes_recv = 0;
-               while (total_bytes_recv < reply_len) {
-                       bytes_recv = recv(sk, reply + 2 + total_bytes_recv,
-                                       reply_len - total_bytes_recv, 0);
-                       if (bytes_recv < 0) {
+               while (reply->received < reply->len) {
+                       bytes_recv = recv(sk, reply->buf + reply->received,
+                                       reply->len - reply->received, 0);
+                       if (!bytes_recv) {
+                               connman_error("DNS proxy TCP disconnect");
+                               break;
+                       } else if (bytes_recv < 0) {
                                if (errno == EAGAIN || errno == EWOULDBLOCK)
-                                       continue;
+                                       return TRUE;
 
                                connman_error("DNS proxy error %s",
-                                                       strerror(errno));
-
+                                               strerror(errno));
                                break;
                        }
-
-                       total_bytes_recv += bytes_recv;
+                       reply->received += bytes_recv;
                }
 
-               if (total_bytes_recv > reply_len)
-                       total_bytes_recv = reply_len;
-
-               forward_dns_reply(reply, total_bytes_recv + 2, IPPROTO_TCP);
+               forward_dns_reply(reply->buf, reply->received, IPPROTO_TCP);
 
                g_free(reply);
+               server->incoming_reply = NULL;
 
                destroy_server(server);