Now, every cached_resolve_t can remember an IPv4 result *and* an IPv6
result. As a light protection against timing-based distinguishers for
IPv6 users (and against complexity!), every forward request generates
an IPv4 *and* an IPv6 request, assuming that we're an IPv6 exit. Once
we have answers or errors for both, we act accordingly.
This patch additionally makes some useful refactorings in the dns.c
code, though there is quite a bit more of useful refactoring that could
be done.
Additionally, have a new interface for the argument passed to the
evdns_callback function. Previously, it was just the original address
we were resolving. But it turns out that, on error, evdns doesn't
tell you the type of the query, so on a failure we didn't know whether
IPv4 or IPv6 queries were failing.
The new convention is to have the first byte of that argument include
the query type. I've refactored the code a bit to make that simpler.
This makes it so we can handle getting an IPv6 in the 3 different
formats we specified it for in RESOLVED cells,
END_STREAM_REASON_EXITPOLICY cells, and CONNECTED cells.
We don't cache IPv6 addresses yet, since proposal 205 isn't
implemented.
There's a refactored function for parsing connected cells; it has unit
tests.
These options are for telling the SOCKSPort that it should allow or
not allow connections to IPv4/IPv6 addresses.
These aren't implemented yet; this is just the code to read the
options and get them into the entrey_connection_t.
Also, count ipv6 timeouts vs others. If we have too many ipv6
requests time out, then we could be degrading performance because of a
broken DNS server that ignores AAAA requests. Other cases in which
we never learn an AAAA address aren't so bad, since they don't slow
A (ipv4) answers down very much.
This is a relatively simple set of changes: we mostly need to
remove a few "but not for IPv6" changes. We also needed to tweak
the handling of DNS code to generate RESOLVED cells that could get
an IPv6 answer in return.
Now, "accept *:80" means "accept all addresses on port 80", and not
just IPv4. For just v4, say "accept *4:80"; for just v6 say "accept
*6:80".
We can parse these policies from torrc just fine, and we should be
successfully keeping them out of descriptors for now.
We also now include appropriate IPv6 addresses in "reject private:*"
By default, "*" means "All IPv4 addresses" with
tor_addr_parse_mask_ports, so I won't break anything. But if the new
EXTENDED_STAR flag is provided, then * means "any address", *4 means
"any IPv4 address" (that is, 0.0.0.0/0), and "*6" means "any IPv6
address" (that is, [::]/0).
This is going to let us have a syntax for specifying exit policies in
torrc that won't drive people mad.
Also, add a bunch of unit tests for tor_addr_parse_mask_ports to test
these new features, and to increase coverage.
We'd like these functions to be circuit-relative so that we can
implement a per-circuit DNS cache and per-circuit DNS cache rules for
proposal 205 or its successors. I'm doing this now, as a part of the
IPv6 exits code, since there are about to be a few more instances
of code using this.
This is the simplest possible workaround: make it safe to call
circuit_cell_queue_clear() on a non-attached circuit, and make it
safe-but-a-LD_BUG-warning to call update_circuit_on_cmux() on a
non-attached circuit.
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