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  1. Core Server
  2. SERVER-27240

ConnectBG must not close() while the background thread is active

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    Details

    • Type: Bug
    • Status: Closed
    • Priority: Major - P3
    • Resolution: Fixed
    • Affects Version/s: None
    • Fix Version/s: 3.0.15, 3.2.12, 3.4.1, 3.5.1
    • Component/s: Networking
    • Labels:
      None
    • Backwards Compatibility:
      Fully Compatible
    • Operating System:
      ALL
    • Backport Completed:
    • Backport Requested:
      v3.4, v3.2, v3.0
    • Sprint:
      Platforms 2017-01-23
    • Case:

      Description

      ConnectBG handles asynchronous connects by spinning up a background thread to call ::connect(). We kick that thread out of connect, after a timeout, by calling close. This isn't safe because:

      Thread A: Your call to Socket::connect()
      Thread B: BG connector for A
      Thread C: Unrelated thread calling Socket::connect()
      Thread D: BG connector for C
       
       
       
      Thread A                     Thread B                Thread C           Thread D
      Start Thread B
                                   connect(N)
      Wait 4.9999 seconds
                                   get EINTR
      Trigger timeout
      shutdown(N)
      close(N)
                                                           N = socket()
                                   connect(N)
                                                                              connect(N)
                                                                              errno == EISCONN
      

      Which can lead us to connect a fd to the wrong endpoint.

      We can work around this by only calling shutdown from the parent thread, waiting for the child to join, then calling close.

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                • Created:
                  Updated:
                  Resolved: