[tbb-bugs] #19657 [Applications/Tor Browser]: ASan detects heap buffer overflow in Tor Browser 6.5a1 Hardened

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#19657: ASan detects heap buffer overflow in Tor Browser 6.5a1 Hardened
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 Reporter:  cypherpunks               |          Owner:  tbb-team
     Type:  defect                    |         Status:  new
 Priority:  High                      |      Milestone:
Component:  Applications/Tor Browser  |        Version:
 Severity:  Major                     |     Resolution:
 Keywords:  tbb-crash                 |  Actual Points:
Parent ID:                            |         Points:
 Reviewer:                            |        Sponsor:
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Comment (by cypherpunks):

 I've just seen #19417 (asm.js files are saved to disk and reloaded next
 launch/on new identity). Looking at the backtraces I attached, it seems
 Tor Browser is crashing whilst deserializing asm.js cache files.

 My hunch is that this crash is actually caused by #19417. Two
 observations:

 1. I upgraded to 6.5a1 "in place" allowing the builtin updater to run.
 This may have left asm.js cache files on disk.
 2. Because we don't change the Firefox build-id between versions of Tor
 Browser (as Georg noted in
 https://trac.torproject.org/projects/tor/ticket/19417#comment:11 ) the
 newly updated Tor Browser would try to load the old cache files, even
 though they were created by a previous Firefox version.

 Normally, Firefox would not load cache files from a previous version. If
 the cache file format has changed at all between the two Tor Browser
 versions then we could easily end up with a memory bug issue like this.
 I'll try to confirm this hunch with some experiments now.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/19657#comment:2>
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