From 6868ed9ccd918ef642df5d8f6a50eb7f53b1ae86 Mon Sep 17 00:00:00 2001
From: emanuele-f <black.silver@hotmail.it>
Date: Sun, 22 Sep 2019 19:45:51 +0200
Subject: [PATCH] Ensure that the TAP interface is up and running

---
 edge.c         |  2 +-
 tuntap_linux.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 66 insertions(+), 1 deletion(-)

diff --git a/edge.c b/edge.c
index 6d786ef..ac0b0b9 100644
--- a/edge.c
+++ b/edge.c
@@ -707,7 +707,7 @@ int main(int argc, char* argv[]) {
 
 #ifndef WIN32
   if((ec.userid != 0) || (ec.groupid != 0)) {
-    traceEvent(TRACE_NORMAL, "Interface up. Dropping privileges to uid=%d, gid=%d",
+    traceEvent(TRACE_NORMAL, "Dropping privileges to uid=%d, gid=%d",
 	       (signed int)ec.userid, (signed int)ec.groupid);
 
     /* Finished with the need for root privileges. Drop to unprivileged user. */
diff --git a/tuntap_linux.c b/tuntap_linux.c
index 66ea454..740c289 100644
--- a/tuntap_linux.c
+++ b/tuntap_linux.c
@@ -21,6 +21,8 @@
 #ifdef __linux__
 
 #include <net/if_arp.h>
+#include <linux/netlink.h>
+#include <linux/rtnetlink.h>
 
 /* *************************************************** */
 
@@ -138,6 +140,12 @@ int tuntap_open(tuntap_dev *device,
   int ioctl_fd;
   struct ifreq ifr;
   int rc;
+  int nl_fd;
+  char nl_buf[8192]; /* >= 8192 to avoid truncation, see "man 7 netlink" */
+  struct iovec iov;
+  struct sockaddr_nl sa;
+  int up_and_running = 0;
+  struct msghdr msg;
 
   device->fd = open(tuntap_device, O_RDWR);
   if(device->fd < 0) {
@@ -160,12 +168,38 @@ int tuntap_open(tuntap_dev *device,
   /* Store the device name for later reuse */
   strncpy(device->dev_name, ifr.ifr_name, MIN(IFNAMSIZ, N2N_IFNAMSIZ) );
 
+  if((nl_fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE)) == -1) {
+    traceEvent(TRACE_ERROR, "netlink socket creation failed [%d]: %s", errno, strerror(errno));
+    return -1;
+  }
+
+  iov.iov_base = nl_buf;
+  iov.iov_len = sizeof(nl_buf);
+
+  memset(&sa, 0, sizeof(sa));
+  sa.nl_family = PF_NETLINK;
+  sa.nl_groups = RTMGRP_LINK;
+  sa.nl_pid = getpid();
+
+  msg.msg_name = &sa;
+  msg.msg_namelen = sizeof(sa);
+  msg.msg_iov = &iov;
+  msg.msg_iovlen = 1;
+
+  /* Subscribe to interface events */
+  if(bind(nl_fd, (struct sockaddr*)&sa, sizeof(sa)) == -1) {
+    traceEvent(TRACE_ERROR, "netlink socket bind failed [%d]: %s", errno, strerror(errno));
+    return -1;
+  }
+
   if((ioctl_fd = socket(PF_INET, SOCK_DGRAM, IPPROTO_IP)) < 0) {
     traceEvent(TRACE_ERROR, "socket creation failed [%d]: %s", errno, strerror(errno));
+    close(nl_fd);
     return -1;
   }
 
   if(setup_ifname(ioctl_fd, device->dev_name, device_ip, device_mask, device_mac, mtu) < 0) {
+    close(nl_fd);
     close(ioctl_fd);
     close(device->fd);
     return -1;
@@ -173,6 +207,37 @@ int tuntap_open(tuntap_dev *device,
 
   close(ioctl_fd);
 
+  /* Wait for the up and running notification */
+  traceEvent(TRACE_INFO, "Waiting for TAP interface to be up and running...");
+
+  while(!up_and_running) {
+    ssize_t len = recvmsg(nl_fd, &msg, 0);
+    struct nlmsghdr *nh;
+
+    for(nh = (struct nlmsghdr *)nl_buf; NLMSG_OK(nh, len); nh = NLMSG_NEXT(nh, len)) {
+      if(nh->nlmsg_type == NLMSG_ERROR) {
+        traceEvent(TRACE_DEBUG, "nh->nlmsg_type == NLMSG_ERROR");
+        break;
+      }
+
+      if(nh->nlmsg_type == NLMSG_DONE)
+        break;
+
+      if(nh->nlmsg_type == NETLINK_GENERIC) {
+        struct ifinfomsg *ifi = NLMSG_DATA(nh);
+
+        /* NOTE: skipping interface name check, assuming it's our TAP */
+        if((ifi->ifi_flags & IFF_UP) && (ifi->ifi_flags & IFF_RUNNING)) {
+          up_and_running = 1;
+          traceEvent(TRACE_INFO, "Interface is up and running");
+          break;
+        }
+      }
+    }
+  }
+
+  close(nl_fd);
+
   device->ip_addr = inet_addr(device_ip);
   device->device_mask = inet_addr(device_mask);
   read_mac(dev, device->mac_addr);