gtpu: fix gtpu segfault

This was occuring due to the io_broker thread trying to access the map
to get the right executor, while the tunnel was being removed from the
map by the UE executor.

Author: alvasMan

lib/gtpu/gtpu_demux_impl.cpp

@@ -24,6 +24,7 @@ bool gtpu_demux_impl::add_tunnel(gtpu_teid_t                           teid,
                                  task_executor&                        tunnel_exec,
                                  gtpu_tunnel_rx_upper_layer_interface* tunnel)
 {
+  std::lock_guard<std::mutex> guard(map_mutex);
   if (teid_to_tunnel.find(teid) != teid_to_tunnel.end()) {
     logger.error("Tunnel already exists. teid={}", teid);
     return false;
@@ -35,6 +36,7 @@ bool gtpu_demux_impl::add_tunnel(gtpu_teid_t                           teid,
 
 bool gtpu_demux_impl::remove_tunnel(gtpu_teid_t teid)
 {
+  std::lock_guard<std::mutex> guard(map_mutex);
   if (teid_to_tunnel.find(teid) == teid_to_tunnel.end()) {
     logger.error("Tunnel not found. teid={}", teid);
     return false;
@@ -53,7 +55,8 @@ void gtpu_demux_impl::handle_pdu(byte_buffer pdu, const sockaddr_storage& src_ad
   }
   gtpu_teid_t teid{read_teid};
 
-  const auto& it = teid_to_tunnel.find(teid);
+  std::lock_guard<std::mutex> guard(map_mutex);
+  const auto&                 it = teid_to_tunnel.find(teid);
   if (it == teid_to_tunnel.end()) {
     logger.info("Dropped GTP-U PDU, tunnel not found. teid={}", teid);
     return;

lib/gtpu/gtpu_demux_impl.h

@@ -15,6 +15,7 @@
 #include "srsran/support/executors/task_executor.h"
 #include "fmt/format.h"
 #include <memory>
+#include <mutex>
 #include <unordered_map>
 
 namespace srsran {
@@ -47,6 +48,9 @@ class gtpu_demux_impl final : public gtpu_demux
   const gtpu_demux_cfg_t cfg;
   dlt_pcap&              gtpu_pcap;
 
+  // The map is modified by accessed the io_broker (to get the right executor)
+  // and the modified by UE executors when setting up/tearing down.
+  std::mutex                                                                   map_mutex;
   std::unordered_map<gtpu_teid_t, gtpu_demux_tunnel_ctx_t, gtpu_teid_hasher_t> teid_to_tunnel;
 
   srslog::basic_logger& logger;