[tor-bugs] #22926 [Core Tor/Tor]: The Tor compression code can call functions that are NULL

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#22926: The Tor compression code can call functions that are NULL
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     Reporter:  teor          |      Owner:
         Type:  defect        |     Status:  new
     Priority:  Medium        |  Milestone:  Tor: 0.3.1.x-final
    Component:  Core Tor/Tor  |    Version:  Tor: 0.3.1.1-alpha
     Severity:  Normal        |   Keywords:
Actual Points:                |  Parent ID:
       Points:  1             |   Reviewer:
      Sponsor:                |
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 The new Tor compression code in 0.3.1 assumes that all the compression
 functions are bound at runtime.

 For example, tor_lzma_method_supported() returns 1 when HAVE_LZMA is
 defined, but that doesn't mean that lzma_version_string() has actually
 been bound to a non-NULL address in the binary.

 This is more likely to happens when tor is used as a shared library rather
 than linked as an executable (shadow, iOS), and when using weak, lazy
 symbol binding.

 This might not be an issue we can solve unless we check for all the
 symbols being NULL at runtime. Maybe the responsibility for proper linking
 is on people who are compiling tor with weak, lazy symbol binding.

 This bug was discovered by Rob Jansen when running shadow.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/22926>
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