[tor-bugs] #20337 [Core Tor]: Support abstract namespace AF_UNIX sockets.

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#20337: Support abstract namespace AF_UNIX sockets.
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     Reporter:  yawning      |      Owner:
         Type:  enhancement  |     Status:  new
     Priority:  Low          |  Milestone:  Tor: unspecified
    Component:  Core Tor     |    Version:  Tor: unspecified
     Severity:  Normal       |   Keywords:
Actual Points:               |  Parent ID:
       Points:               |   Reviewer:
      Sponsor:               |
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 Linux has a notion of `abstract` AF_UNIX sockets.  This should be
 supported both for the control and socks port, as they are convenient and
 useful, as long as they are used correctly.

 Benefits:
  * Easier to bundle.  `sun_path` length limitations are dumb, being able
 to use an abstract identifier is simpler.
  * No need to mess around with creating a directory, arguing over what
 permissions the directory and the socket file has.
  * The socket goes away when the last reference to the socekt is closed,
 removing the need to unlink it.

 Downsides:
  * There is no access control, at all.  Primarily relevant for the
 ControlPort, but that has separate mechanisms for restricting access.
  * Not wildly useful for sandboxes, since most sandboxing approaches will
 unshare/create a new IPC namespace.
  * Non-portable.

 (0.2.0.3-alpha was the first time we supported AF_UNIX at all)

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/20337>
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