fallback to file editing in case file is locked

sshuttle/firewall.py

@@ -1,4 +1,5 @@
 import errno
+import shutil
 import socket
 import signal
 import sys
@@ -30,7 +31,10 @@ def rewrite_etc_hosts(hostmap, port):
         else:
             raise
     if old_content.strip() and not os.path.exists(BAKFILE):
+        try:
             os.link(HOSTSFILE, BAKFILE)
+        except OSError:
+            shutil.copyfile(HOSTSFILE, BAKFILE)
     tmpname = "%s.%d.tmp" % (HOSTSFILE, port)
     f = open(tmpname, 'w')
     for line in old_content.rstrip().split('\n'):
@@ -47,7 +51,10 @@ def rewrite_etc_hosts(hostmap, port):
     else:
         os.chown(tmpname, 0, 0)
         os.chmod(tmpname, 0o600)
+    try:
         os.rename(tmpname, HOSTSFILE)
+    except OSError:
+        shutil.move(tmpname, HOSTSFILE)
 
 
 def restore_etc_hosts(hostmap, port):

tests/client/test_firewall.py

@@ -1,7 +1,11 @@
 import io
+import os
 from socket import AF_INET, AF_INET6
 
 from unittest.mock import Mock, patch, call
+
+import pytest
+
 import sshuttle.firewall
 
 
@@ -59,6 +63,21 @@ def test_rewrite_etc_hosts(tmpdir):
     assert orig_hosts.computehash() == new_hosts.computehash()
 
 
+@patch('os.link')
+@patch('os.rename')
+def test_rewrite_etc_hosts_no_overwrite(mock_link, mock_rename, tmpdir):
+    mock_link.side_effect = OSError
+    mock_rename.side_effect = OSError
+
+    with pytest.raises(OSError):
+        os.link('/test_from', '/test_to')
+
+    with pytest.raises(OSError):
+        os.rename('/test_from', '/test_to')
+
+    test_rewrite_etc_hosts(tmpdir)
+
+
 def test_subnet_weight():
     subnets = [
         (AF_INET, 16, 0, '192.168.0.0', 0, 0),