[tor-bugs] #22934 [Core Tor/Tor]: PADDING cells can't be sent immediately after a VERSIONS cell

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#22934: PADDING cells can't be sent immediately after a VERSIONS cell
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 Reporter:  teor                 |          Owner:  nickm
     Type:  defect               |         Status:  accepted
 Priority:  Medium               |      Milestone:  Tor: 0.3.1.x-final
Component:  Core Tor/Tor         |        Version:  Tor: 0.3.1.1-alpha
 Severity:  Normal               |     Resolution:
 Keywords:  tor-spec, tor-relay  |  Actual Points:
Parent ID:  #18856               |         Points:  0.5
 Reviewer:                       |        Sponsor:
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Changes (by nickm):

 * owner:  (none) => nickm
 * status:  new => accepted


Comment:

 So, two issues here: "can this happen on clients that are doing padding"
 and "what behavior should we allow"?

 I am fairly confident that the answer to the first question is "no".  The
 function `channelpadding_send_padding_cell_for_callback()` is where the
 code sends its cells, and it is always checks whether the channel state is
 CHAN_STATE_OPEN.  We only set the channel to that state when the OR
 connection enters OR_CONN_STATE_OPEN.  The same check is performed in
 channelpadding_decide_to_pad_channel().

 So we won't trigger this today from the channel padding code.  Hooray!

 So, what _should_ we be doing?  It's sure desirable to allow PADDING and
 VPADDING after the VERSIONS cell, but we can't actually do that until some
 Tors allow it, and we need some means to signal that they will.

 I suggest that for 0.3.2, we just fix the spec to note that this doesn't
 work, and for 0.3.3 we write a proposal and implement it.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/22934#comment:4>
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