[tor-bugs] #18292 [Tor Browser]: staged updates fail on Windows

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#18292: staged updates fail on Windows
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     Reporter:  mcs          |      Owner:  mcs
         Type:  defect       |     Status:  new
     Priority:  Medium       |  Milestone:
    Component:  Tor Browser  |    Version:
     Severity:  Normal       |   Keywords:
Actual Points:               |  Parent ID:
       Points:               |    Sponsor:
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 On Windows, staged updates currently fail (I am not sure if they ever
 worked correctly, but I think they have not been working at least since
 MAR signing was introduced). The good news is that typically users do not
 notice the failure because the updater silently falls back to doing an in-
 place update. The failure occurs after the user restarts their browser to
 apply the update: switching to the staged copy that is under
 Browser/updated fails because files are in use under the Browser
 directory, and Windows does not allow a directory to be renamed if any
 open handles point to files within the directory or if any DLLs located in
 the directory are in use (at least that is my understanding based on my
 limited knowledge of system behavior on Windows).

 To fix this we will need to do two things:
 1) Copy updater.exe and the DLLs it uses into a temporary directory and
 run it from there.
 2) Modify the updater.exe code to not open and hold onto a handle for a
 log file that is located under Browser/TorBrowser.

 Because these changes will not be trivial to implement and test, I propose
 that for the stable branch of Tor Browser (5.5) we disable staged updates
 on Windows. That is a safe thing to do and it will speed up updates since
 currently updates are applied twice (one time to stage the update, which
 then fails, and a second time to do an in-place update, which succeeds).
 Of course we should fix this correctly for TB 6.0 and test it during one
 or more of our alpha cycles.

 One challenge is knowing which of our bundled DLLs the updater depends on.
 The set of DLLs might change over time, and some components such as NSS
 load DLLs at runtime (so it is not just a matter of checking DLL
 dependencies by dumping linker info from updater.exe).

 This ticket was split off from #18170.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/18292>
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