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Add a getutxos command to the p2p protocol #4

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Add a getutxos command to the p2p protocol #4

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Introduction

The getutxo command allows querying of the UTXO set given a set of of outpoints. It has a simple implementation and the results are not authenticated in any way. Despite this, there are times when it is a useful capability to have. I believe @jgarzik also has a use case for this, though I don't know what it is.

As a motivating example I present Lighthouse, an app I'm writing that implements assurance contracts:

http://blog.vinumeris.com/2014/05/17/lighthouse/

Lighthouse works by collecting pledges, which contain an invalid transaction signed with SIGHASH_ANYONECANPAY. Once sufficient pledges are collected to make the combination valid, we say the contract is complete and it can be broadcast onto the network, spending the pledged outputs. Before that occurs however, a pledge can be revoked and the pledged money redeemed by double spending the pledged output. For instance you might want to do this if it becomes clear not enough people care about the assurance contract for it to reach its goal in a timely manner, or if you simply need the money back due to some kind of cashflow crunch.

It is convenient to be able to see when a pledge has been revoked, so the user interface can be updated, and so when the final contract is created revoked pledges can be left out. For this purpose "getutxos" is used.

Protocol

The getutxos message takes a boolean which controls whether outputs in the memory pool are considered, and a vector of COutPoint structures. It returns a bitmap with the same number of bits as outputs specified rounded up to the nearest 8 bits, and then a list of CTxOut structures, one for each set bit in the bitmap. The bitmap encodes whether the UTXO was found (i.e. is indeed unspent).

Authentication

The results of getutxos is not authenticated. This is because the obvious way to do this requires the work maaku has been doing on UTXO commitments to be merged, activated by default, miners to upgrade and a forking change made to enforce their accuracy. All this is a big project that may or may not ever come to fruition.

For the Lighthouse security model however, this doesn't matter much. The reason is that the pledge transactions you're getting (which may be malicious) don't come from the P2P network. They come in the form of files either from a simple rendezvous server, or e.g. a shared folder or email attachments. The people sending these files have no way to influence the choice of peers made by the app. Once the outputs are returned, they are used to check the signatures on the pledge, thus verifying that the pledge spends the UTXO returned by the P2P network.

So we can be attacked in the following ways:

  • The pledge may be attempting to pledge non-existent outputs, but this will be detected if the majority of peers are honest.
  • The peers may be malicious and return a wrong or bogus output, but this will be detected when the signature is checked, except for the value (!) but we want to fix this by including the value into the sighash at some point anyway because we need it to make the TREZOR efficient/faster.
  • The peers may bogusly claim no such UTXO exists when it does, but this would result in the pledge being seen as invalid. When the project creator asks the pledgor why they revoked their money, and learns that in fact they never did, the bogus peers will be detected. No money is at risk as the pledges cannot be spent.
  • If the pledgor AND all the peers collaborate (i.e. the pledgor controls your internet connection) then they can make you believe you have a valid pledge when you don't. This would result in the app getting "jammed" and attempting to close an uncloseable contract. No money is at risk and the user will eventually wonder why their contract is not confirming. Once they get to a working internet connection the subterfuge will be discovered.

There is a final issue: the answer to getutxos can of course change the instant the result is generated, thus leading you to construct an uncloseable transaction if the process of revocation races with the construction. The app can detect this by watching for either a reject message, or an inv requesting one of the inputs that is supposed to be in the UTXO set (i.e. the remote peer thinks it's an orphan). This can then cause the app to re-request the UTXO set and drop the raced pledge.

In practice I do not anticipate such attacks are likely to occur, as they're complicated to pull off and it's not obvious what the gain is.

There may be other apps that wish to use getutxos, with different security models. They may find this useful despite the lack of UTXO commitments, and the fact that the answer can change a moment later, if:

  • They are connecting to a trusted peer, i.e. localhost.
  • They trust their internet connection and peer selection, i.e. because they don't believe their datacenter or ISP will commit financial fraud against them, or they are tunnelling via endpoints they trust like a randomly chosen Tor exit.
  • They are not using the response for anything important or worth attacking, like some kind of visualisation.

Upgrade

If enforced UTXO commitments are added to the block chain in future, it would make sense to rev the P2P protocol to add the proofs (merkle branches) to the response.

Testing

I attempted to write unit tests for this, but Core has no infrastructure for building test chains .... the miner_tests.cpp code does it but at the cost of not allowing any other unit test to do so, as it doesn't reset or clean up the global state afterwards! I tried to fix this and ended up down a giant rabbit hole.

So instead I've tested it with a local test app I wrote, which also exercises the client side part in bitcoinj.

BIP

If the code is ACKd then I will write a short BIP explaining the new message.

Philosophy

On IRC I have discussed this patch a little bit before. One objection that was raised is that we shouldn't add anything to the P2P protocol unless it's unattackable, because otherwise it's a sharp knife that people might use to cut themselves.

I personally disagree with this notion for the following reasons.

Firstly, many parts of the P2P protocol are not completely unattackable: malicious remote nodes can withhold broadcast transactions, invent fictional ones (you'd think they're orphans), miss out Bloom filter responses, send addr messages for IP's that were never announced, etc. We shouldn't hold new messages to a standard existing messages don't meet.

Secondly, even with UTXO commitments in the block chain, given the sick state of mining this only requires a collaboration of two people to undo, although that failure would be publicly detectable which is at least something. But anyway, there's a clean upgrade path if/when UTXO authentication becomes available.

Thirdly, we have a valid use case that's actually implemented. This isn't some academic pie in the sky project.

Finally, Bitcoin is already the sharpest knife imaginable. I don't think we should start rejecting useful features on the grounds that someone else might screw up with them.

If the above analysis ends up not holding for some reason, and people do get attacked due to the lack of authentication, then Lighthouse and other apps can always fall back to connecting to trusted nodes (perhaps over SSL). But I would like to optimistically assume success up front and see what happens, than pessimistically assume the worst and centralise things up front.

adamjonas pushed a commit that referenced this pull request Mar 15, 2024
@fanquake
Merge bitcoin#28966: test: Add missing CBlockPolicyEstimator::process…
453c9ca 
…BlockTx suppression

fa9dc92 test: Add missing CBlockPolicyEstimator::processBlockTx suppression (MarcoFalke)

Pull request description:

  Fixes bitcoin#28865 (comment)

  ```
  # FUZZ=policy_estimator UBSAN_OPTIONS="suppressions=/root/fuzz_dir/scratch/fuzz_gen/code/test/sanitizer_suppressions/ubsan:print_stacktrace=1:halt_on_error=1:report_error_type=1" ./src/test/fuzz/fuzz /tmp/crash-154b42214e70781a9c1ad72d3f2693913dcf8c06

  ...

  policy/fees.cpp:632:27: runtime error: implicit conversion from type 'unsigned int' of value 4294574080 (32-bit, unsigned) to type 'int' changed the value to -393216 (32-bit, signed)
      #0 0x55cbbe10daee in CBlockPolicyEstimator::processBlockTx(unsigned int, CTxMemPoolEntry const*) src/policy/fees.cpp:632:27
      bitcoin#1 0x55cbbe10e361 in CBlockPolicyEstimator::processBlock(unsigned int, std::vector<CTxMemPoolEntry const*, std::allocator<CTxMemPoolEntry const*>>&) src/policy/fees.cpp:680:13
      #2 0x55cbbd84af48 in policy_estimator_fuzz_target(Span<unsigned char const>)::$_1::operator()() const src/test/fuzz/policy_estimator.cpp:69:40
      #3 0x55cbbd84af48 in unsigned long CallOneOf<policy_estimator_fuzz_target(Span<unsigned char const>)::$_0, policy_estimator_fuzz_target(Span<unsigned char const>)::$_1, policy_estimator_fuzz_target(Span<unsigned char const>)::$_2, policy_estimator_fuzz_target(Span<unsigned char const>)::$_3>(FuzzedDataProvider&, policy_estimator_fuzz_target(Span<unsigned char const>)::$_0, policy_estimator_fuzz_target(Span<unsigned char const>)::$_1, policy_estimator_fuzz_target(Span<unsigned char const>)::$_2, policy_estimator_fuzz_target(Span<unsigned char const>)::$_3) src/./test/fuzz/util.h:43:27
      #4 0x55cbbd84af48 in policy_estimator_fuzz_target(Span<unsigned char const>) src/test/fuzz/policy_estimator.cpp:38:9
      #5 0x55cbbda1cc18 in std::function<void (Span<unsigned char const>)>::operator()(Span<unsigned char const>) const /usr/bin/../lib/gcc/x86_64-linux-gnu/13/../../../../include/c++/13/bits/std_function.h:591:9
      #6 0x55cbbda1cc18 in LLVMFuzzerTestOneInput src/test/fuzz/fuzz.cpp:178:5
      #7 0x55cbbd26a944 in fuzzer::Fuzzer::ExecuteCallback(unsigned char const*, unsigned long) (/root/fuzz_dir/scratch/fuzz_gen/code/src/test/fuzz/fuzz+0x190e944) (BuildId: ffb89e0b86c093ca3bdeae6f85537737a4e3b42d)
      #8 0x55cbbd253916 in fuzzer::RunOneTest(fuzzer::Fuzzer*, char const*, unsigned long) (/root/fuzz_dir/scratch/fuzz_gen/code/src/test/fuzz/fuzz+0x18f7916) (BuildId: ffb89e0b86c093ca3bdeae6f85537737a4e3b42d)
      #9 0x55cbbd25945a in fuzzer::FuzzerDriver(int*, char***, int (*)(unsigned char const*, unsigned long)) (/root/fuzz_dir/scratch/fuzz_gen/code/src/test/fuzz/fuzz+0x18fd45a) (BuildId: ffb89e0b86c093ca3bdeae6f85537737a4e3b42d)
      #10 0x55cbbd284026 in main (/root/fuzz_dir/scratch/fuzz_gen/code/src/test/fuzz/fuzz+0x1928026) (BuildId: ffb89e0b86c093ca3bdeae6f85537737a4e3b42d)
      #11 0x7fe4aa8280cf  (/lib/x86_64-linux-gnu/libc.so.6+0x280cf) (BuildId: 96ab1a8f3b2c9a2ed37c7388615e6a726d037e89)
      #12 0x7fe4aa828188 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x28188) (BuildId: 96ab1a8f3b2c9a2ed37c7388615e6a726d037e89)
      #13 0x55cbbd24e494 in _start (/root/fuzz_dir/scratch/fuzz_gen/code/src/test/fuzz/fuzz+0x18f2494) (BuildId: ffb89e0b86c093ca3bdeae6f85537737a4e3b42d)

  SUMMARY: UndefinedBehaviorSanitizer: implicit-integer-sign-change policy/fees.cpp:632:27 in
  ```

  ```
  # base64 /tmp/crash-154b42214e70781a9c1ad72d3f2693913dcf8c06
  AQEAAAAAADkFlVwAAQEAAAAAADkFlZVcACTDSSsP3746IAZrH48khwMAAQEB/QEALQAACwAAAAAA
  FgAAAAAAAQAABgAAAAAAAAAAAAAAAAAAACcQAAAAAAAAAAAAAAAAAAAAAAD6AAAAOQWVXAABAQAA
  AAAAOQWVlVwAIMNJKw/fvjogBmsfjySHAwABAQH9AQAtAAALAAAAAAAAAAABAAAGAAAAAAAAAAAA
  AAAAAAAAJxAAAAAAAAAAAAAAAAAAAAAAAPr/AAAAAAAAAAAAAAQAAAAA/wAAAAAAAAAAAAAEAAAA
  AAEBAeAIAVwBXAAA/jbSBvwBKABSKBwBYgEB2wAEkvXInHYAAAAAAAAAvgAAAAAA/9//6v8e/xIk
  MgAlAiUAOw==

ACKs for top commit:
  fanquake:
    ACK fa9dc92
  dergoegge:
    utACK fa9dc92

Tree-SHA512: 3898c17c928ecc2bcc8c7086359e9ae00da2197b4d8e10c7bf6d12415326c9bca3ef6e1d8d3b83172ccfa604ce7e7371415262ba705225f9ea4da8b1a7eb0306
adamjonas pushed a commit that referenced this pull request Mar 15, 2024
@fanquake
Merge bitcoin#28969: fuzz: Avoid signed-integer-overflow in wallet_no…
7bc8c53 
…tifications fuzz target

fab164f fuzz: Avoid signed-integer-overflow in wallet_notifications fuzz target (MarcoFalke)

Pull request description:

  Should avoid

  ```
  policy/feerate.cpp:29:63: runtime error: signed integer overflow: 77600710321911316 * 149 cannot be represented in type 'int64_t' (aka 'long')
      #0 0x563a1775ed66 in CFeeRate::GetFee(unsigned int) const src/policy/feerate.cpp:29:63
      bitcoin#1 0x563a15913a69 in wallet::COutput::COutput(COutPoint const&, CTxOut const&, int, int, bool, bool, bool, long, bool, std::optional<CFeeRate>) src/./wallet/coinselection.h:91:57
      #2 0x563a16fa6a6d in wallet::FetchSelectedInputs(wallet::CWallet const&, wallet::CCoinControl const&, wallet::CoinSelectionParams const&) src/wallet/spend.cpp:297:17
      #3 0x563a16fc4512 in wallet::CreateTransactionInternal(wallet::CWallet&, std::vector<wallet::CRecipient, std::allocator<wallet::CRecipient>> const&, int, wallet::CCoinControl const&, bool) src/wallet/spend.cpp:1105:33
      #4 0x563a16fbec74 in wallet::CreateTransaction(wallet::CWallet&, std::vector<wallet::CRecipient, std::allocator<wallet::CRecipient>> const&, int, wallet::CCoinControl const&, bool) src/wallet/spend.cpp:1291:16
      #5 0x563a16fcf6df in wallet::FundTransaction(wallet::CWallet&, CMutableTransaction&, long&, int&, bilingual_str&, bool, std::set<int, std::less<int>, std::allocator<int>> const&, wallet::CCoinControl) src/wallet/spend.cpp:1361:16
      #6 0x563a1597b7b9 in wallet::(anonymous namespace)::FuzzedWallet::FundTx(FuzzedDataProvider&, CMutableTransaction) src/wallet/test/fuzz/notifications.cpp:162:15
      #7 0x563a15958240 in wallet::(anonymous namespace)::wallet_notifications_fuzz_target(Span<unsigned char const>)::$_0::operator()() const src/wallet/test/fuzz/notifications.cpp:228:23
      #8 0x563a15958240 in unsigned long CallOneOf<wallet::(anonymous namespace)::wallet_notifications_fuzz_target(Span<unsigned char const>)::$_0, wallet::(anonymous namespace)::wallet_notifications_fuzz_target(Span<unsigned char const>)::$_1>(FuzzedDataProvider&, wallet::(anonymous namespace)::wallet_notifications_fuzz_target(Span<unsigned char const>)::$_0, wallet::(anonymous namespace)::wallet_notifications_fuzz_target(Span<unsigned char const>)::$_1) src/./test/fuzz/util.h:43:27
      #9 0x563a15958240 in wallet::(anonymous namespace)::wallet_notifications_fuzz_target(Span<unsigned char const>) src/wallet/test/fuzz/notifications.cpp:196:9
      #10 0x563a15fdef0c in std::function<void (Span<unsigned char const>)>::operator()(Span<unsigned char const>) const /usr/bin/../lib/gcc/x86_64-linux-gnu/13/../../../../include/c++/13/bits/std_function.h:591:9
      #11 0x563a15fdef0c in LLVMFuzzerTestOneInput src/test/fuzz/fuzz.cpp:178:5
      #12 0x563a158032a4 in fuzzer::Fuzzer::ExecuteCallback(unsigned char const*, unsigned long) (/ci_container_base/ci/scratch/build/bitcoin-x86_64-pc-linux-gnu/src/test/fuzz/fuzz+0x19822a4) (BuildId: 8acb42ad599d7f6d25b6f93e18fd564d80df7c06)
      #13 0x563a15802999 in fuzzer::Fuzzer::RunOne(unsigned char const*, unsigned long, bool, fuzzer::InputInfo*, bool, bool*) (/ci_container_base/ci/scratch/build/bitcoin-x86_64-pc-linux-gnu/src/test/fuzz/fuzz+0x1981999) (BuildId: 8acb42ad599d7f6d25b6f93e18fd564d80df7c06)
      #14 0x563a15804586 in fuzzer::Fuzzer::ReadAndExecuteSeedCorpora(std::vector<fuzzer::SizedFile, std::allocator<fuzzer::SizedFile>>&) (/ci_container_base/ci/scratch/build/bitcoin-x86_64-pc-linux-gnu/src/test/fuzz/fuzz+0x1983586) (BuildId: 8acb42ad599d7f6d25b6f93e18fd564d80df7c06)
      #15 0x563a15804aa7 in fuzzer::Fuzzer::Loop(std::vector<fuzzer::SizedFile, std::allocator<fuzzer::SizedFile>>&) (/ci_container_base/ci/scratch/build/bitcoin-x86_64-pc-linux-gnu/src/test/fuzz/fuzz+0x1983aa7) (BuildId: 8acb42ad599d7f6d25b6f93e18fd564d80df7c06)
      #16 0x563a157f21fb in fuzzer::FuzzerDriver(int*, char***, int (*)(unsigned char const*, unsigned long)) (/ci_container_base/ci/scratch/build/bitcoin-x86_64-pc-linux-gnu/src/test/fuzz/fuzz+0x19711fb) (BuildId: 8acb42ad599d7f6d25b6f93e18fd564d80df7c06)
      #17 0x563a1581c766 in main (/ci_container_base/ci/scratch/build/bitcoin-x86_64-pc-linux-gnu/src/test/fuzz/fuzz+0x199b766) (BuildId: 8acb42ad599d7f6d25b6f93e18fd564d80df7c06)
      bitcoin#18 0x7f499e17b0cf  (/lib/x86_64-linux-gnu/libc.so.6+0x280cf) (BuildId: 96ab1a8f3b2c9a2ed37c7388615e6a726d037e89)
      bitcoin#19 0x7f499e17b188 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x28188) (BuildId: 96ab1a8f3b2c9a2ed37c7388615e6a726d037e89)
      bitcoin#20 0x563a157e70c4 in _start (/ci_container_base/ci/scratch/build/bitcoin-x86_64-pc-linux-gnu/src/test/fuzz/fuzz+0x19660c4) (BuildId: 8acb42ad599d7f6d25b6f93e18fd564d80df7c06)

  SUMMARY: UndefinedBehaviorSanitizer: signed-integer-overflow policy/feerate.cpp:29:63 in
  MS: 0 ; base unit: 0000000000000000000000000000000000000000
  0x3f,0x0,0x2f,0x5f,0x5f,0x5f,0x7d,0x7d,0x7d,0x7d,0x7d,0x7d,0x7d,0x7d,0x7d,0x7d,0x7d,0x7d,0x7d,0x7d,0x7d,0x7d,0x7d,0x7d,0x7d,0x7d,0xff,0xff,0xff,0xff,0xff,0x53,0xff,0xff,0xff,0xff,0xff,0x0,0x0,0x0,0x0,0x0,0x0,0x13,0x5e,0x5f,0x5f,0x8,0x25,0x0,0x5f,0x5f,0x5f,0x5f,0x5f,0x5f,0x8,0x25,0xca,0x7f,0x5f,0x5f,0x5f,0x13,0x13,0x5f,0x5f,0x5f,0x2,0xdb,0xca,0x0,0x0,0xe7,0xe6,0x66,0x65,0x0,0x0,0x0,0x0,0x44,0x3f,0xa,0xa,0xff,0xff,0xff,0xff,0xff,0x61,0x76,0x6f,0x69,0x0,0xb5,0x15,
  ?\000/___}}}}}}}}}}}}}}}}}}}}\377\377\377\377\377S\377\377\377\377\377\000\000\000\000\000\000\023^__\010%\000______\010%\312\177___\023\023___\002\333\312\000\000\347\346fe\000\000\000\000D?\012\012\377\377\377\377\377avoi\000\265\025
  artifact_prefix='./'; Test unit written to ./crash-4d3bac8a64d4e58b2f0943e6d28e6e1f16328d7d
  Base64: PwAvX19ffX19fX19fX19fX19fX19fX19fX3//////1P//////wAAAAAAABNeX18IJQBfX19fX18IJcp/X19fExNfX18C28oAAOfmZmUAAAAARD8KCv//////YXZvaQC1FQ==

ACKs for top commit:
  dergoegge:
    ACK fab164f
  brunoerg:
    ACK fab164f

Tree-SHA512: f416828f4394aa7303ee437f141e9bbd23c0e0f1b830e4ef3932338858249ba68a811b9837c5b7ad8c6ab871b6354996434183597c1a910a8d8e8d829693e4b2
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2 participants
@adamjonas @mikehearn