Padding, Keepalive and Drop cells should have random payloads
tor-spec says:
Link padding can be created by sending PADDING or VPADDING cells
along the connection; relay cells of type "DROP" can be used for
long-range padding. The contents of a PADDING, VPADDING, or DROP
cell SHOULD be chosen randomly, and MUST be ignored.https://gitweb.torproject.org/torspec.git/tree/tor-spec.txt#n1534
But padding cells sent by channelpadding_send_padding_cell_for_callback() and keepalive cells sent by run_connection_housekeeping() have a payload of all zero bytes.
I don't know if this is a security issue or not. It is probably ok, unless Tor has compression enabled on its TLS connections. If compression is enabled, all the padding data size calculations will be wrong.
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