[tor-bugs] #13776 [Tor Browser]: Generation of incremental mar files is not reproducible (was: Generation of incremental mar files is not reproducbile)

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#13776: Generation of incremental mar files is not reproducible
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     Reporter:  gk          |      Owner:  tbb-team
         Type:  defect      |     Status:  needs_revision
     Priority:  normal      |  Milestone:
    Component:  Tor         |    Version:
  Browser                   |   Keywords:  tbb-gitian, TorBrowserTeam201412
   Resolution:              |  Parent ID:
Actual Points:              |
       Points:              |
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Comment (by mcs):

 Replying to [comment:7 gk]:
 > Setting `LC_ALL` to `C` solves the difference of the manifest files. But
 the resulting incremental .mar files are still different for some reason.
 The only differences I see on the attachment are `a4` -> `b0`.

 It looks all of the differences are in the bytes that immediately precede
 a file name within the MAR header.  Looking at the code in
 modules/libmar/src/mar_create.c, that byte is a flags field that is
 derived from the file mode bits, like this:
   st.st_mode & 0777
 The difference is really 1A4 vs. 1B0 (0644 vs. 0660).  So we probably just
 need to set the umask before running the make_incremental_update.sh
 script.  Or we could avoid these kinds of issues by generating the
 incremental MARs inside a VM.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/13776#comment:8>
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