fix(net): Check if interface is valid first. (#2497)

Fixes #2496

include/adapters/net.hpp

@@ -37,6 +37,7 @@ class file_descriptor;
 namespace net {
   DEFINE_ERROR(network_error);
 
+  bool is_interface_valid(const string& ifname);
   bool is_wireless_interface(const string& ifname);
   std::string find_wireless_interface();
   std::string find_wired_interface();

src/adapters/net.cpp

@@ -12,8 +12,7 @@
 #include <sys/socket.h>
 #include <sys/types.h>
 
-#include <iomanip>
-
+#include <cassert>
 #include <iomanip>
 
 #include "common.hpp"
@@ -37,6 +36,11 @@ namespace net {
 
   static bool is_virtual(const std::string& ifname) {
     char* target = realpath((NET_PATH + ifname).c_str(), nullptr);
+
+    if (!target) {
+      throw system_error("realpath");
+    }
+
     const std::string real_path{target};
     free(target);
     return real_path.rfind(VIRTUAL_PATH, 0) == 0;
@@ -54,6 +58,10 @@ namespace net {
     return NetType::ETHERNET;
   }
 
+  bool is_interface_valid(const string& ifname) {
+    return if_nametoindex(ifname.c_str()) != 0;
+  }
+
   /**
    * Test if interface with given name is a wireless device
    */
@@ -91,9 +99,7 @@ namespace net {
    * Construct network interface
    */
   network::network(string interface) : m_log(logger::make()), m_interface(move(interface)) {
-    if (if_nametoindex(m_interface.c_str()) == 0) {
-      throw network_error("Invalid network interface \"" + m_interface + "\"");
-    }
+    assert(is_virtual(interface));
 
     m_socketfd = file_util::make_file_descriptor(socket(AF_INET, SOCK_DGRAM, 0));
     if (!*m_socketfd) {
@@ -294,8 +300,8 @@ namespace net {
       units.pop_back();
     }
 
-    return sstream() << std::setw(minwidth) << std::setfill(' ') << std::setprecision(precision) << std::fixed << speedrate
-                     << " " << suffix << unit;
+    return sstream() << std::setw(minwidth) << std::setfill(' ') << std::setprecision(precision) << std::fixed
+                     << speedrate << " " << suffix << unit;
   }
 
   // }}}

src/modules/network.cpp

@@ -38,7 +38,11 @@ namespace modules {
     }
 
     if (m_interface.empty()) {
-      throw module_error("missing 'interface' or 'interface-type'");
+      throw module_error("Missing 'interface' or 'interface-type'");
+    }
+
+    if (!net::is_interface_valid(m_interface)) {
+      throw module_error("Invalid network interface \"" + m_interface + "\"");
     }
 
     m_ping_nth_update = m_conf.get(name(), "ping-interval", m_ping_nth_update);