[tor-bugs] #31683 [Core Tor/Tor]: md: Bad family line in cached-microdescs.new

Tor Bug Tracker & Wiki blackhole at torproject.org
Thu Oct 10 14:04:44 UTC 2019


#31683: md: Bad family line in cached-microdescs.new
-----------------------------------+------------------------------------
 Reporter:  dgoulet                |          Owner:  nickm
     Type:  defect                 |         Status:  assigned
 Priority:  Medium                 |      Milestone:  Tor: 0.4.2.x-final
Component:  Core Tor/Tor           |        Version:
 Severity:  Normal                 |     Resolution:
 Keywords:  microdesc, 042-should  |  Actual Points:
Parent ID:                         |         Points:
 Reviewer:                         |        Sponsor:
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Comment (by nickm):

 Musing aloud:

 I'm trying to make sense of this and of #31364, which I strongly suspect
 have the same underlying cause.

 In both cases, it's microdescriptors, and it's the journal, not the cache.

 In both cases, it looks like we have started writing at the wrong point in
 the file: here, it seems we've started in the middle of another
 microdescriptor, and in #31364, it looks like we've seeked to a point
 after the end of the file.

 This makes me kind of suspect that our fake O_APPEND implementation in
 start_writing_to_file() might have something to do with this.  Or maybe
 something is doing concurrent modifications on the microdescriptors
 journal.

 Next to investigate: why do we not observe this with routerdescs?  Are we
 more tolerant of errors in cached_descriptors.new, or is there an
 important difference in the code?  If this is a concurrent modification
 problem, what could be causing it?

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/31683#comment:4>
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