Fix: unprivilieged sessiond agent port clashes with root sessiond

[lttng-tools.git] / src / bin / lttng-sessiond / agent-thread.c

diff --git a/src/bin/lttng-sessiond/agent-thread.c b/src/bin/lttng-sessiond/agent-thread.c
index d53e0b1c749e9c8291e5b6630ec4f55dde718257..f8456b428d49882945c2089bf12e3c4121c7420b 100644 (file)
--- a/src/bin/lttng-sessiond/agent-thread.c
+++ b/src/bin/lttng-sessiond/agent-thread.c
@@ -83,6 +83,8 @@ static struct lttcomm_sock *init_tcp_socket(void)
        int ret;
        struct lttng_uri *uri = NULL;
        struct lttcomm_sock *sock = NULL;
+       unsigned int port;
+       bool bind_succeeded = false;
 
        /*
         * This should never fail since the URI is hardcoded and the port is set
@@ -90,8 +92,8 @@ static struct lttcomm_sock *init_tcp_socket(void)
         */
        ret = uri_parse(default_reg_uri, &uri);
        assert(ret);
-       assert(config.agent_tcp_port);
-       uri->port = config.agent_tcp_port;
+       assert(config.agent_tcp_port.begin > 0);
+       uri->port = config.agent_tcp_port.begin;
 
        sock = lttcomm_alloc_sock_from_uri(uri);
        uri_free(uri);
@@ -105,11 +107,43 @@ static struct lttcomm_sock *init_tcp_socket(void)
                goto error;
        }
 
-       ret = sock->ops->bind(sock);
-       if (ret < 0) {
-               WARN("Another session daemon is using this agent port. Agent support "
-                               "will be deactivated to prevent interfering with the tracing.");
-               goto error;
+       for (port = config.agent_tcp_port.begin;
+                       port <= config.agent_tcp_port.end; port++) {
+               ret = lttcomm_sock_set_port(sock, (uint16_t) port);
+               if (ret) {
+                       ERR("[agent-thread] Failed to set port %u on socket",
+                                       port);
+                       goto error;
+               }
+               DBG3("[agent-thread] Trying to bind on port %u", port);
+               ret = sock->ops->bind(sock);
+               if (!ret) {
+                       bind_succeeded = true;
+                       break;
+               }
+
+               if (errno == EADDRINUSE) {
+                       DBG("Failed to bind to port %u since it is already in use",
+                                       port);
+               } else {
+                       PERROR("Failed to bind to port %u", port);
+                       goto error;
+               }
+       }
+
+       if (!bind_succeeded) {
+               if (config.agent_tcp_port.begin == config.agent_tcp_port.end) {
+                       WARN("Another process is already using the agent port %i. "
+                                       "Agent support will be deactivated.",
+                                       config.agent_tcp_port.begin);
+                       goto error;
+               } else {
+                       WARN("All ports in the range [%i, %i] are already in use. "
+                                       "Agent support will be deactivated.",
+                                       config.agent_tcp_port.begin,
+                                       config.agent_tcp_port.end);
+                       goto error;
+               }
        }
 
        ret = sock->ops->listen(sock, -1);
@@ -118,7 +152,7 @@ static struct lttcomm_sock *init_tcp_socket(void)
        }
 
        DBG("[agent-thread] Listening on TCP port %u and socket %d",
-                       config.agent_tcp_port, sock->fd);
+                       port, sock->fd);
 
        return sock;
 
@@ -134,9 +168,19 @@ error:
  */
 static void destroy_tcp_socket(struct lttcomm_sock *sock)
 {
+       int ret;
+       uint16_t port;
+
        assert(sock);
 
-       DBG3("[agent-thread] Destroy TCP socket on port %u", config.agent_tcp_port);
+       ret = lttcomm_sock_get_port(sock, &port);
+       if (ret) {
+               ERR("[agent-thread] Failed to get port of agent TCP socket");
+               port = 0;
+       }
+
+       DBG3("[agent-thread] Destroy TCP socket on port %" PRIu16,
+                       port);
 
        /* This will return gracefully if fd is invalid. */
        sock->ops->close(sock);
@@ -234,6 +278,15 @@ bool agent_tracing_is_enabled(void)
        return enabled == 1;
 }
 
+/*
+ * Write agent TCP port using the rundir.
+ */
+static int write_agent_port(uint16_t port)
+{
+       return utils_create_pid_file((pid_t) port,
+                       config.agent_port_file_path.value);
+}
+
 /*
  * This thread manage application notify communication.
  */
@@ -259,16 +312,30 @@ void *agent_thread_manage_registration(void *data)
        }
 
        reg_sock = init_tcp_socket();
-       uatomic_set(&agent_tracing_enabled, !!reg_sock);
+       if (reg_sock) {
+               uint16_t port;
+
+               assert(lttcomm_sock_get_port(reg_sock, &port) == 0);
+
+               ret = write_agent_port(port);
+               if (ret) {
+                       ERR("[agent-thread] Failed to create agent port file: agent tracing will be unavailable");
+                       /* Don't prevent the launch of the sessiond on error. */
+                       sessiond_notify_ready();
+                       goto error;
+               }
+       } else {
+               /* Don't prevent the launch of the sessiond on error. */
+               sessiond_notify_ready();
+               goto error_tcp_socket;
+       }
 
        /*
         * Signal that the agent thread is ready. The command thread
         * may start to query whether or not agent tracing is enabled.
         */
+       uatomic_set(&agent_tracing_enabled, 1);
        sessiond_notify_ready();
-       if (!reg_sock) {
-               goto error_tcp_socket;
-       }
 
        /* Add TCP socket to poll set. */
        ret = lttng_poll_add(&events, reg_sock->fd,
@@ -365,7 +432,6 @@ restart:
        }
 
 exit:
-       uatomic_set(&agent_tracing_enabled, 0);
        /* Whatever happens, try to delete it and exit. */
        (void) lttng_poll_del(&events, reg_sock->fd);
 error:
@@ -373,6 +439,7 @@ error:
 error_tcp_socket:
        lttng_poll_clean(&events);
 error_poll_create:
+       uatomic_set(&agent_tracing_enabled, 0);
        DBG("[agent-thread] is cleaning up and stopping.");
 
        rcu_thread_offline();