From 8e103cb2d0d2710066e97d62a408c6ce7de49422 Mon Sep 17 00:00:00 2001
From: "teor (Tim Wilson-Brown)" <teor2345@gmail.com>
Date: Fri, 26 Feb 2016 10:53:57 +0100
Subject: [PATCH] Set EXCLUSIVEADDRUSE on Win32 to avoid a local port-stealing
 attack

---
 changes/bug18123    |  4 ++++
 src/or/connection.c | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)
 create mode 100644 changes/bug18123

diff --git a/changes/bug18123 b/changes/bug18123
new file mode 100644
index 0000000000..1359b4ef67
--- /dev/null
+++ b/changes/bug18123
@@ -0,0 +1,4 @@
+  o Minor bugfixes (security, win32):
+    - Set SO_EXCLUSIVEADDRUSE on Win32 to avoid a local port-stealing
+      attack.
+      Fixes bug 18123; bugfix on all tor versions. Patch by "teor".
diff --git a/src/or/connection.c b/src/or/connection.c
index 0f2b3e356e..c8fc662129 100644
--- a/src/or/connection.c
+++ b/src/or/connection.c
@@ -1061,6 +1061,31 @@ make_socket_reuseable(tor_socket_t sock)
 #endif
 }
 
+#ifdef _WIN32
+/** Tell the Windows TCP stack to prevent other applications from receiving
+ * traffic from tor's open ports. Return 0 on success, -1 on failure. */
+static int
+make_win32_socket_exclusive(tor_socket_t sock)
+{
+#ifdef SO_EXCLUSIVEADDRUSE
+  int one=1;
+
+  /* Any socket that sets REUSEADDR on win32 can bind to a port _even when
+   * somebody else already has it bound_, and _even if the original socket
+   * didn't set REUSEADDR_. Use EXCLUSIVEADDRUSE to prevent this port-stealing
+   * on win32. */
+  if (setsockopt(sock, SOL_SOCKET, SO_EXCLUSIVEADDRUSE, (void*) &one,
+                 (socklen_t)sizeof(one))) {
+    return -1;
+  }
+  return 0;
+#else
+  (void) sock;
+  return 0;
+#endif
+}
+#endif
+
 /** Max backlog to pass to listen.  We start at */
 static int listen_limit = INT_MAX;
 
@@ -1137,6 +1162,14 @@ connection_listener_new(const struct sockaddr *listensockaddr,
                tor_socket_strerror(errno));
     }
 
+#ifdef _WIN32
+    if (make_win32_socket_exclusive(s) < 0) {
+      log_warn(LD_NET, "Error setting SO_EXCLUSIVEADDRUSE flag on %s: %s",
+               conn_type_to_string(type),
+               tor_socket_strerror(errno));
+    }
+#endif
+
 #if defined(USE_TRANSPARENT) && defined(IP_TRANSPARENT)
     if (options->TransProxyType_parsed == TPT_TPROXY &&
         type == CONN_TYPE_AP_TRANS_LISTENER) {