This is trying to be an AIMD event-driven algorithm, but we ended up with
two different add paths with diverging behavior. This fix makes the AIMD
events more explicit, and it fixes an earlier behavior where the effort
could be decreased (by the add/recalculate branch) even when the pqueue
was not emptying at all. With this patch we shouldn't drop down to an
effort of zero as long as even low-effort attacks are flooding the
pqueue.
Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>
The goal of this patch is to add an additional mechanism for adjusting
PoW effort upwards, where clients rather than services can choose to
solve their puzzles at a higher effort than what was suggested in the
descriptor.
I wanted to use hs_cache's existing unreachability stats to drive this
effort bump, but this revealed some cases where a circuit (intro or
rend) closed early on can end up in hs_cache with an all zero intro
point key, where nobody will find it. This moves intro_auth_pk
initialization earlier in a couple places and adds nonfatal asserts to
catch the problem if it shows up elsewhere.
The actual effort adjustment method I chose is to multiply the suggested
effort by (1 + unresponsive_count), then ensure the result is at least
1. If a service has suggested effort of 0 but we fail to connect,
retries will all use an effort of 1. If the suggestion was 50, we'll try
50, 100, 150, 200, etc. This is bounded both by our client effort limit
and by the limit on unresponsive_count (currently 5).
Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>
Asan catches this pretty readily when ending a service gracefully while
a DoS is in progress and the queue is full of items that haven't yet
timed out.
The module boundaries in hs_circuit are quite fuzzy here, but I'm trying
to follow the vibe of the existing hs_pow code.
Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>
500 was quite low, but this limit was helpful when the suggested-effort
estimation algorithm was likely to give us large abrupt increases. Now
that this should be fixed, let's allow spending a bit more time on the
client puzzles if it's actually necessary.
Solving a puzzle with effort=10000 usually completes within a minute
on my old x86_64 machine. We may want to fine tune this further, and it
should probably be made into a config option.
Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>
I don't think the concept of "minimum effort" is really useful to us,
so this patch removes it entirely and consequentially changes the way
that "total" effort is calculated so that we don't rely on any minimum
and we instead ramp up effort no faster than necessary.
If at least some portion of the attack is conducted by clients that
avoid PoW or provide incorrect solutions, those (potentially very
cheap) attacks will end up keeping the pqueue full. Prior to this patch,
that would cause suggested efforts to be unnecessarily high, because
rounding these very cheap requests up to even a minimum of 1 will
overestimate how much actual attack effort is being spent.
The result is that this patch is a simplification and it also allows a
slower start, where PoW effort jumps up either by a single unit or by an
amount calculated from actual effort in the queue.
Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>
This patch is intended to clarify the points at which we convert
between the internal representation of an equix_solution and a portable
but opaque byte array representation.
Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>
This fixes a failure that was showing up on i386 Debian hosts
with sandboxing enabled, now that cpuworker is enabled on clients.
We already had allowances for creating threads and creating stacks
in the sandbox, but prot_none (probably used for a stack guard)
was not allowed so thread creation failed.
Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>
This leak was showing up in address sanitizer runs of test_hs_pow,
but it will also happen during normal operation as seeds are rotated.
Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>
This is more consistent with the specification, and it's much
less confusing with endianness. This resolves the underlying
cause of the earlier byte-swap. This patch itself does not
change the wire protocol at all, it's just tidying up the
types we use at the trunnel layer.
Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>
We were using a native uint128_t to represent the hs_pow nonce,
but as the comments note it's more portable and more flexible to
use a byte array. Indeed the uint128_t was a problem for 32-bit
platforms. This swaps in a new implementation that uses multiple
machine words to implement the nonce incrementation.
Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>
In proposal 327, "POW_SEED is the first 4 bytes of the seed used".
The proposal doesn't specifically mention the data type of this field,
and the code in hs_pow so far treats it as an integer but semantically
it's more like the first four bytes of an already-encoded little endian
blob. This leads to a byte swap, since the type confusion takes place
in a little-endian subsystem but the wire encoding of seed_head uses
tor's default of big endian.
This patch does not address the underlying type confusion, it's a
minimal change that only swaps the byte order and updates unit tests
accordingly. Further changes will clean up the data types.
Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>
Much faster per-hash, affects both verify and solve.
Only implemented on x86_64 and aarch64, other platforms
always use the interpreted version of hashx.
Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>
This adds test vectors for the overall client puzzle at the
hs_pow and hs_cell layers.
These are similar to the crypto/equix tests, but they also cover
particulars of our hs_pow format like the conversion to byte arrays,
the replay cache, the effort test, and the formatting of the equix
challenge string.
Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>
Fixes some type nitpicks that show up in Tor development builds,
which usually run with -Wall -Werror. Tested on x86_64 and aarch64
for clean build and passing equix-tests + hashx-tests.
Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>
This replaces the sketchy cmake invocation we had inside configure
The libs are always built and always used in unit tests, but only
included in libtor and tor when --enable-gpl is set.
Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>
This forgoes another external library dependency, and instead
introduces a compatibility header so that interested parties
(who already depend on equix, like hs_pow and unit tests) can
use the implementation of blake2b included in hashx.
Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>
This adds test vectors for the Equi-X proof of work algorithm and the
Hash-X function it's based on. The overall Equi-X test takes about
10 seconds to run on my machine, so it's in test_crypto_slow. The hashx
test still covers both the compiled and interpreted versions of the
hash function.
There aren't any official test vectors for Equi-X or for its particular
configuration of Hash-X, so I made some up based on the current
implementation.
Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>
I'm planning on swapping blake2b implementations, and this test
is intended to prevent regressions. Right now blake2b is only used by
hs_pow.
Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>
This adds a new "pow" module for the user-visible proof
of work support in ./configure, and this disables
src/feature/hs/hs_pow at compile-time.
Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>
This change on its own doesn't use the option for anything, but
it includes support for configure and a message in 'tor --version'
Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>
This was apparently misinterpreting "zero solutions" as an error
instead of just moving on to the next nonce. Additionally, equix
could have been returning up to 8 solutions and we would only
give one of those a chance to succeed.
Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>
We may want to choose something larger eventually, but 20 seemed
much too large. Very low nonzero efforts are still useful against
a script kiddie level DoS attack.
Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>
This adds a token bucket ratelimiter on the dequeue side
of hs_pow's priority queue. It adds config options and docs
for those options. (HiddenServicePoWQueueRate/Burst)
I'm testing this as a way to limit the overhead of circuit
creation when we're experiencing a flood of rendezvous requests.
Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>
Without this check, we never actually refetch the hs descriptor
when PoW parameters expire, because can_client_refetch_desc
deems the descriptor to be still good.
Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>
Adds two new metrics for hs_pow, and an internal parameter within
hs_metrics for implementing gauge parameters that reset before
every update.
Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>
We mark the intro circuit with a new flag saying that the pow is
in the cpuworker queue. When the cpuworker comes back, it either
has a solution, in which case we proceed with sending the intro1
cell, or it has no solution, in which case we unmark the intro
circuit and let the whole process restart on the next iteration of
connection_ap_handshake_attach_circuit().
into two parts:
* a "consider whether to send an intro2 cell" part (now called
consider_sending_introduce1()), and
* an "actually send it" (now called send_introduce1()).
prepares the way for client-side pow cpuworkers
also happens to resolve bug https://bugs.torproject.org/tpo/core/tor/40617
(which went into 0.4.7.4-alpha) because now we survive initing the
cpuworker subsystem when we're not a relay.
First (both client and service), make descriptor parsing not fail when
suggested_effort is 0.
Second (client side), if we get a descriptor with a pow_params section
but with suggested_effort of 0, treat it as not requiring a pow.
Third (service side), when deciding whether the suggested effort has
changed, don't treat "previous suggested effort 0, new suggested effort 0"
as a change.
An alternative design to resolve 'first' and 'second' above would be
to omit the pow_params from the descriptor when suggested_effort is 0,
so clients never see the pow_params so they don't compute a pow. But
I decided to include a pow_params with an explicit suggested_effort
of 0, since this way the client knows the seed etc so they can solve
a higher-effort pow if they want. The tradeoff is that the descriptor
reveals whether HiddenServicePoWDefensesEnabled is set to 1 for this onion
service, even if the AIMD calculation is currently requiring effort 0.
our pqueue implementation does bizarre unspecified things with
ordering of elements that are equal. it certainly doesn't do any
sort of "first in first out" property that i was expecting.
now make it explicit by saying that "equal-effort, added-earlier" is
higher priority.
specifically, if we have 16 in-flight rend circs, and the next
one at the top of the pqueue is lower than our suggested effort,
then don't launch it yet.
this way we always launch adequate-effort requests immediately, and
we always handle *some* low-effort requests, but we are ready at any
moment to handle a few new adequate-effort requests.
this change makes us reach the callback *after* each mainloop
run, rather than as the next event to run immediately after
activation.
with the old behavior, we were starving everything else to drain the
pqueue entirely, each time we got a new intro2 cell.
now we at least will get to other activities as well.
