[tor-bugs] #18123 [Tor]: Avoid a local port-stealing attack on Windows

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#18123: Avoid a local port-stealing attack on Windows
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     Reporter:  teor    |      Owner:
         Type:  defect  |     Status:  new
     Priority:  Medium  |  Milestone:  Tor: 0.2.8.x-final
    Component:  Tor     |    Version:
     Severity:  Normal  |   Keywords:  security 027-backport 026-backport
Actual Points:          |  Parent ID:
       Points:          |    Sponsor:
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 On Windows, Tor is vulnerable to a port-stealing attack described on this
 StackOverflow post under the "Windows" heading:
 https://stackoverflow.com/questions/14388706/socket-options-so-reuseaddr-
 and-so-reuseport-how-do-they-differ-do-they-mean-t

 In short, another app can set SO_REUSEADDR, then bind to a port that Tor
 is already bound to, stealing all future connections to Tor.

 Therefore, I think we should set SO_EXCLUSIVEADDRUSE on all listener
 sockets on Windows, which prevents this attack.

 We could do this near make_socket_reusable in connection_listener_new.
 make_socket_reusable already has a comment about this issue.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/18123>
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