p2p: Try to preserve outbound block-relay-only connections during restart #17428

hebasto · 2019-11-09T22:46:25Z

This is an implementation of #17326:

all (currently 2) outbound block-relay-only connections (p2p: Add 2 outbound block-relay-only connections #15759) are dumped to anchors.dat file
on restart a node tries to connect to the addresses from anchors.dat

This PR prevents a type of eclipse attack when an attacker exploits a victim node restart to force it to connect to new, probably adversarial, peers.

DrahtBot · 2019-11-09T23:42:26Z

The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

Conflicts

Reviewers, this pull request conflicts with the following ones:

Better intervals between feelers #19869 (Better intervals between feelers by naumenkogs)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

laanwj · 2019-11-10T11:03:57Z

Don't think this should get in the way of implementing something like this, but have to note here, as it's a significant change of behavior from before: reconnecting to peers "aggressively", was, up to now, the reserve of spy nodes and mass-connectors and such. For normal nodes the chance of making the same outgoing connection twice was pretty low. Historically this has been one of the ways used to detect these.

gmaxwell · 2019-11-13T18:11:05Z

It would be really good to limit it so that an honest node won't attempt to connect twice to the same peer through this mechanism for some prudent amount of time... like two minutes.

I don't think it would cause any harm to the intent of this mechanism to not bring them up as fast as possible, and it would avoid tripping up detection of aggressive mass connectors.

sdaftuar · 2019-11-14T20:49:50Z

Not sure if I’m misreading this code (I haven’t tested it), but it looks like on restart we would only attempt to connect once to each anchor, and then it gets removed from consideration. Does that satisfy the concern about rapid reconnects? I guess if a user rapidly restarted their node, we could see rapid connections to the same peers, but that seems pretty weird.

Anyway I just skimmed the discussion in #17326. I think Greg or Matt commented that we shouldn’t do this with all our block-relay-only connections, but since we only have 2 at the moment, perhaps it’s fine for now. And then in the future if we expand to say 8 block-relay peers we might still cap the anchors at 2. Does that reflect the thinking of others as well?

src/net.cpp

hebasto · 2019-11-21T09:56:23Z

@sdaftuar

Thank you for your review. Your comment has been addressed.

Also, an additional safety check added to "p2p: Integrate ReadAnchors() into CConnman()" commit in the latest push.

ariard

Concept ACK on the idea but see my concerns in #17326 (comment).

IMO before to go forward we need to agree on a) the scope of anchors: full-relay, block-relay, both, b) anchors selection & lifecyle, i.e after how much time do we select them or based on any metrics, do we prune them from anchors.dat, do we keep a bigger file and select randomly from it

ariard · 2020-01-15T19:14:13Z

src/net.cpp

+    m_anchors = ReadAnchors(m_anchors_db_path);
+    if (m_anchors.size() > m_max_outbound_block_relay) {
+        // Keep our policy safe.
+        m_anchors.clear();


Why clear the whole instead of picking randomly m_max_outbound_block_relay among the anchors set? If one of our most recent anchors isn't reliable we should be allowed to pick up among older anchors to still of the counter-measure.

The worst case is assumed. If condition m_anchors.size() > m_max_outbound_block_relay is satisfied, we could suppose that the anchors.dat file is wrong or corrupted.

No you're melting 2 different problems, tracking the anchors set and connecting to peers among this one. I don't understand why reaching the m_max_outbound_block_relay means we have to delete our whole repository of maybe-good anchors peers.

In the scenario you're aiming, if victim restarts and the 2 anchors peers are honest but unreliable, you're going to drop them and pick maybe new outbound peers from attacker-provided ones. You can avoid this if you have a bigger set of potential anchor peers.

the logic implemented in this PR is minimal, and I think that makes sense for keeping it simple to reason about.

with this implementation, its possible for an attacker to poison the anchors and execute an eclipse attack, its just increases the cost of doing so.

until we develop more robust logic around ensuring our anchors are not malicious, I don't think it makes sense to give priority to all historic anchors. I think it could sometimes be beneficial but other times degrade security, eg. if you historically were connected to a malicious peer but now your addrman is clear.

src/net.cpp

ariard · 2020-01-15T19:48:43Z

src/net.cpp

@@ -1805,11 +1807,24 @@ void CConnman::ThreadOpenConnections(const std::vector<std::string> connect)
            if (nTries > 100)
                break;

-            CAddrInfo addr = addrman.SelectTriedCollision();
+            CAddress addr;
+            if (!m_anchors.empty() && (nOutboundBlockRelay < m_max_outbound_block_relay) && !fFeeler) {


May we check here also nOutboundFullRelay, and so keep same connection order, i.e full-relay then block-only or is there any advantage to invert order ?

The order is not inverted. The first target "anchors" is added, and was not present before, i.e., the new order is "anchors" then "full-relay" then "block-relay-only".
If anchors would not the first, they could be connected as other type nodes, and anchoring could not happen.

But anchors nodes are block-only, so now you have block-only-as-anchors, full-relay, block-only-classics. You can still test addresses returned from addrman against m_anchors andon continue in case of equality to avoid the problem you're describing, but don't think that changes something, do we favor first-connected nodes in anyway ?

ariard · 2020-01-15T20:05:50Z

src/net_processing.cpp

@@ -2088,6 +2088,9 @@ bool static ProcessMessage(CNode* pfrom, const std::string& strCommand, CDataStr
                      pfrom->nVersion.load(), pfrom->nStartingHeight,
                      pfrom->GetId(), (fLogIPs ? strprintf(", peeraddr=%s", pfrom->addr.ToString()) : ""),
                      pfrom->m_tx_relay == nullptr ? "block-relay" : "full-relay");
+            if (!pfrom->m_tx_relay) {
+                DumpAnchors(connman->m_anchors_db_path, connman->GetBlockRelayNodeAddresses());


What do you think about waiting some time like 24hours or one block announcement before to qualify node as anchor? That would require at least some good behavior from it, that said and may favor too much well-reliable nodes and decay network-wide connectivity..

nit: you may use scheduler for DumpAnchors like we do for DumpAddresses, that would avoid file syscalls while holding cs_main

I like the idea of moving this onto the scheduler thread, but not a huge deal given this only happens once per blocks-only connection.

nit: you may use scheduler for DumpAnchors like we do for DumpAddresses, that would avoid file syscalls while holding cs_main

I like the idea of moving this onto the scheduler thread, but not a huge deal given this only happens once per blocks-only connection.

Agree that using CScheduler.scheduleFromNow() for DumpAnchors is an improvement. Let's leave it for follow ups.

laanwj · 2020-01-20T20:09:17Z

Added 0.20 milestone as this mitigates a security issue so it would be good to have.

jamesob

d405145 (jamesob/ackr/17428.1.hebasto.p2p_try_to_preserve_outb)

Code looks fine, but seeing some strange behavior locally.

Built, started bitcoind, and noted the current blocks-only peers:

$ ./src/bitcoin-cli -datadir=/data2/bitcoin getpeerinfo | jq '.[] | select(.relaytxes==false) | .addr'

"185.217.241.142:8333"
"2.203.128.83:8333"

Verified the creation of anchors.dat:

$ du -hs /data2/bitcoin/anchors.dat

4.0K    /data2/bitcoin/anchors.dat

Shutdown bitcoind, restarted, checked blocks-only peers:

$ ./src/bitcoin-cli -datadir=/data2/bitcoin getpeerinfo | jq '.[] | select(.relaytxes==false) | .addr'

"2.203.128.83:8333"
"95.216.198.89:8333"

One of the peers has persisted from the first run, but the second is different.
Unexpectedly, my logs don't indicate the anchor connections were ever reused - the
only occurrence of anchor in debug.log is when flushing to anchors.dat.

Show platform data

Tested on Linux-4.15.0-47-generic-x86_64-with-Ubuntu-18.04-bionic

Configured with ./configure LDFLAGS=-L/home/james/src/bitcoin/db4/lib/ CPPFLAGS=-I/home/james/src/bitcoin/db4/include/ CXXFLAGS=-std=c++11 -Wthread-safety-analysis -Werror -Wthread-safety-analysis -Werror --enable-wallet --enable-debug --with-daemon CXX=/usr/bin/clang++-4.0 CC=/usr/bin/clang-4.0 PYTHONPATH= --disable-shared --with-pic --enable-benchmark=no --with-bignum=no --enable-module-recovery --disable-jni --disable-shared --with-pic --enable-benchmark=no --with-bignum=no --enable-module-recovery --disable-jni --no-create --no-recursion

Compiled with /usr/bin/ccache /usr/bin/clang++-4.0 -std=c++11 -mavx -mavx2 -std=c++11 -Wthread-safety-analysis -Werror -Wthread-safety-analysis -Werror -O0 -g3 -ftrapv  -Wstack-protector -fstack-protector-all -msse4 -msha -msse4.1 -msse4.2  i

Compiler version: clang version 4.0.1-10 (tags/RELEASE_401/final)

jamesob · 2020-01-22T20:21:48Z

src/addrdb.cpp

+{
+    int64_t start = GetTimeMillis();
+    SerializeFileDB("anchors", anchors_db_path, anchors);
+    LogPrintf("Flushed %d anchor outbound peer addresses to anchors.dat in %d ms\n", anchors.size(), GetTimeMillis() - start);


Can use logging/timer.h if you care to. (example)

Thanks. Done in the latest push.

jamesob · 2020-01-22T20:36:26Z

src/net_processing.cpp

@@ -2088,6 +2088,9 @@ bool static ProcessMessage(CNode* pfrom, const std::string& strCommand, CDataStr
                      pfrom->nVersion.load(), pfrom->nStartingHeight,
                      pfrom->GetId(), (fLogIPs ? strprintf(", peeraddr=%s", pfrom->addr.ToString()) : ""),
                      pfrom->m_tx_relay == nullptr ? "block-relay" : "full-relay");
+            if (!pfrom->m_tx_relay) {
+                DumpAnchors(connman->m_anchors_db_path, connman->GetBlockRelayNodeAddresses());


I like the idea of moving this onto the scheduler thread, but not a huge deal given this only happens once per blocks-only connection.

hebasto · 2020-01-26T13:09:55Z

@ariard

The only idea of this PR is to make a node to try restore outbound block-relay-only connections as they were just before node restart. It is expected that this change in node behavior mitigates restart-based eclipse attacks without significant other tradeoffs.

IMO before to go forward we need to agree on a) the scope of anchors: full-relay, block-relay, both...

Anchoring as a new procedure, or anchors as "seemingly safe" nodes are out of the scope of this PR.

b) anchors selection & lifecyle, i.e after how much time do we select them or based on any metrics, do we prune them from anchors.dat, do we keep a bigger file and select randomly from it

With an idea to make a node to try restore outbound block-relay-only connections as they were just before node restart, anchors are the last known outbound block-relay-only connections only.

#17428 (comment)

What do you think about waiting some time like 24hours or one block announcement before to qualify node as anchor? That would require at least some good behavior from it, that said and may favor too much well-reliable nodes and decay network-wide connectivity..

In this PR anchors are considered as the last known outbound block-relay-only connections, not as "presumable safe" ones.

hebasto · 2020-01-26T19:37:10Z

Updated d405145 -> f2b4cfd (pr17428.02 -> pr17428.03, compare).

@ariard @jamesob

Thank you for your reviews. Your comments have been addressed.

@jamesob

... seeing some strange behavior locally.

Added additional logging when connecting to an anchor fails.

hebasto · 2020-01-26T20:38:50Z

Pushed a fixup. Ready for testing and (re)reviewing now.

jamesob

ACK 37671dd (jamesob/ackr/17428.2.hebasto.p2p_try_to_preserve_outb)

Built locally, verified that anchors were connected to on restart using the same test as above.

Show platform data

Tested on Linux-4.15.0-47-generic-x86_64-with-Ubuntu-18.04-bionic

Configured with ./configure LDFLAGS=-L/home/james/src/bitcoin/db4/lib/ CPPFLAGS=-I/home/james/src/bitcoin/db4/include/ CXXFLAGS=-std=c++11 -Wthread-safety-analysis -Werror -Wthread-safety-analysis -Werror --enable-wallet --enable-debug --with-daemon CXX=/usr/bin/clang++-4.0 CC=/usr/bin/clang-4.0 PYTHONPATH= --disable-shared --with-pic --enable-benchmark=no --with-bignum=no --enable-module-recovery --disable-jni --disable-shared --with-pic --enable-benchmark=no --with-bignum=no --enable-module-recovery --disable-jni --no-create --no-recursion

Compiled with /usr/bin/ccache /usr/bin/clang++-4.0 -std=c++11 -mavx -mavx2 -std=c++11 -Wthread-safety-analysis -Werror -Wthread-safety-analysis -Werror -O0 -g3 -ftrapv  -Wstack-protector -fstack-protector-all -msse4 -msha -msse4.1 -msse4.2  i

Compiler version: clang version 4.0.1-10 (tags/RELEASE_401/final)

luke-jr · 2020-01-29T03:53:55Z

Couldn't there be a risk here, that if one of the anchor peers is malicious and knows a DoS vulnerability, this ensures they can keep repeatedly crashing your node, even if you setup a watchdog to restart it?

hebasto · 2020-01-29T20:13:06Z

Rebased after #16702 has been merged.

hebasto · 2020-01-29T20:14:43Z

@luke-jr

Couldn't there be a risk here, that if one of the anchor peers is malicious and knows a DoS vulnerability, this ensures they can keep repeatedly crashing your node, even if you setup a watchdog to restart it?

~~Could manual deletion of the anchors.dat file be a remedy?~~ See: #17428 (comment)

ariard · 2020-01-30T01:50:18Z

@hebasto

Concept ACK, reading your comment I do understand that this PR is really-scoped, so don't mind #17326 (comment) and #17428 (comment) but would happily review future work to make anchors better (sorry for the noise)

A note explaining the exact attack scenario mitigated near to m_anchors or somewhere else would be cool to avoid future reviewers relying on wrong-scoped security assumptions.

Goign to test PR soon.

gmaxwell · 2020-01-30T08:15:41Z

@luke-jr oy. uh. forget them if you uncleanly exit?

hebasto · 2020-02-05T21:36:11Z

Rebased after #18023 has been merged.

This is a move-only commit.

hebasto · 2020-10-09T11:32:07Z

Rebased d77ae88 -> a490d07 (pr17428.31 -> pr17428.32) due to the conflict with #20076.

jnewbery · 2020-10-09T12:21:22Z

code review ACK a490d07

laanwj · 2020-10-15T18:19:41Z

Code review ACK a490d07

…onnections during restart a490d07 doc: Add anchors.dat to files.md (Hennadii Stepanov) 0a85e5a p2p: Try to connect to anchors once (Hennadii Stepanov) 5543c7a p2p: Fix off-by-one error in fetching address loop (Hennadii Stepanov) 4170b46 p2p: Integrate DumpAnchors() and ReadAnchors() into CConnman (Hennadii Stepanov) bad16af p2p: Add CConnman::GetCurrentBlockRelayOnlyConns() (Hennadii Stepanov) c29272a p2p: Add ReadAnchors() (Hennadii Stepanov) 567008d p2p: Add DumpAnchors() (Hennadii Stepanov) Pull request description: This is an implementation of bitcoin#17326: - all (currently 2) outbound block-relay-only connections (bitcoin#15759) are dumped to `anchors.dat` file - on restart a node tries to connect to the addresses from `anchors.dat` This PR prevents a type of eclipse attack when an attacker exploits a victim node restart to force it to connect to new, probably adversarial, peers. ACKs for top commit: jnewbery: code review ACK a490d07 laanwj: Code review ACK a490d07 Tree-SHA512: 0f5098a3882f2814be1aa21de308cd09e6654f4e7054b79f3cfeaf26bc02b814ca271497ed00018d199ee596a8cb9b126acee8b666a29e225b08eb2a49b02ddd

maflcko · 2021-01-08T09:10:41Z

There is a TODO to write release notes for this: https://github.com/bitcoin-core/bitcoin-devwiki/wiki/0.21.0-Release-Notes-Draft#p2p-and-network-changes

hebasto · 2021-01-08T09:21:45Z

@MarcoFalke

There is a TODO to write release notes for this: https://github.com/bitcoin-core/bitcoin-devwiki/wiki/0.21.0-Release-Notes-Draft#p2p-and-network-changes

Done.

fe3d17d net: ignore block-relay-only peers when skipping DNS seed (Anthony Towns) Pull request description: Since #17428 bitcoind will attempt to reconnect to two block-relay-only anchors before doing any other outbound connections. When determining whether to use DNS seeds, it will currently see these two peers and decide "we're connected to the p2p network, so no need to lookup DNS" -- but block-relay-only peers don't do address relay, so if your address book is full of invalid addresses (apart from your anchors) this behaviour will prevent you from recovering from that situation. This patch changes it so that it only skips use of DNS seeds when there are two full-outbound peers, not just block-relay-only peers. ACKs for top commit: Sjors: utACK fe3d17d amitiuttarwar: ACK fe3d17d, this impacts the very common case where we stop/start a node, persisting anchors & have a non-empty addrman (although, to be clear, wouldn't be particularly problematic in the common cases where the addrman has valid addresses) mzumsande: ACK fe3d17d jonatack: ACK fe3d17d prayank23: tACK fe3d17d Tree-SHA512: 9814b0d84321d7f45b5013eb40c420a0dd93bf9430f5ef12dce50d1912a18d5de2070d890a8c6fe737a3329b31059b823bc660b432d5ba21f02881dc1d951e94

Summary: > This is an implementation of #17326: > > - all (currently 2) outbound block-relay-only connections are dumped to anchors.dat file > - on restart a node tries to connect to the addresses from anchors.dat This PR prevents a type of eclipse attack when an attacker exploits a victim node restart to force it to connect to new, probably adversarial, peers. This is a backport of [[bitcoin/bitcoin#17428 | core#17428]] [1/7] bitcoin/bitcoin@567008d Test Plan: `ninja` Reviewers: #bitcoin_abc, majcosta Reviewed By: #bitcoin_abc, majcosta Differential Revision: https://reviews.bitcoinabc.org/D10507

Summary: This is a backport of [[bitcoin/bitcoin#17428 | core#17428]] [2/7] bitcoin/bitcoin@c29272a Depends on D10507 Test Plan: `ninja` Reviewers: #bitcoin_abc, majcosta Reviewed By: #bitcoin_abc, majcosta Differential Revision: https://reviews.bitcoinabc.org/D10508

Summary: This is a backport of [[bitcoin/bitcoin#17428 | core#17428]] [3/7] bitcoin/bitcoin@bad16af Depends on D10508 Test Plan: `ninja` Reviewers: #bitcoin_abc, majcosta Reviewed By: #bitcoin_abc, majcosta Differential Revision: https://reviews.bitcoinabc.org/D10509

Summary: This is a backport of [[bitcoin/bitcoin#17428 | core#17428]] [4/7] bitcoin/bitcoin@4170b46 Depends on D10509 Test Plan: `ninja all check-all` Reviewers: #bitcoin_abc, majcosta Reviewed By: #bitcoin_abc, majcosta Subscribers: majcosta Differential Revision: https://reviews.bitcoinabc.org/D10510

Summary: This is a move-only commit. This is a backport of [[bitcoin/bitcoin#17428 | core#17428]] [5/7] bitcoin/bitcoin@5543c7a Depends on D10510 Test Plan: `ninja all check-all` Reviewers: #bitcoin_abc, majcosta Reviewed By: #bitcoin_abc, majcosta Differential Revision: https://reviews.bitcoinabc.org/D10511

Summary: This is a backport of [[bitcoin/bitcoin#17428 | core#17428]] [6/7] bitcoin/bitcoin@0a85e5a Depends on D10511 Test Plan: `ninja all check-all` Reviewers: #bitcoin_abc, majcosta Reviewed By: #bitcoin_abc, majcosta Differential Revision: https://reviews.bitcoinabc.org/D10512

Summary: This is a backport of [[bitcoin/bitcoin#17428 | core#17428]] [7/7] bitcoin/bitcoin@a490d07 Depends on D10512 Test Plan: proofreading Reviewers: #bitcoin_abc, majcosta Reviewed By: #bitcoin_abc, majcosta Differential Revision: https://reviews.bitcoinabc.org/D10513

fanquake added the P2P label Nov 9, 2019

hebasto mentioned this pull request Nov 9, 2019

rfc, p2p: Restart-based eclipse attack mitigation #17326

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sdaftuar reviewed Nov 14, 2019

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hebasto force-pushed the 20191109-anchors branch from 99d6f6f to d405145 Compare November 21, 2019 09:51

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hebasto force-pushed the 20191109-anchors branch from d405145 to f2b4cfd Compare January 26, 2020 19:23

hebasto force-pushed the 20191109-anchors branch from f2b4cfd to 37671dd Compare January 26, 2020 20:05

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hebasto force-pushed the 20191109-anchors branch from 37671dd to a2822de Compare January 29, 2020 20:10

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hebasto force-pushed the 20191109-anchors branch from a2822de to 78b2f95 Compare February 5, 2020 21:35

hebasto added 7 commits October 9, 2020 14:28

p2p: Add DumpAnchors()

567008d

p2p: Add ReadAnchors()

c29272a

p2p: Add CConnman::GetCurrentBlockRelayOnlyConns()

bad16af

p2p: Integrate DumpAnchors() and ReadAnchors() into CConnman

4170b46

p2p: Fix off-by-one error in fetching address loop

5543c7a

This is a move-only commit.

p2p: Try to connect to anchors once

0a85e5a

doc: Add anchors.dat to files.md

a490d07

hebasto force-pushed the 20191109-anchors branch from d77ae88 to a490d07 Compare October 9, 2020 11:30

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laanwj merged commit 9855422 into bitcoin:master Oct 15, 2020

hebasto deleted the 20191109-anchors branch October 15, 2020 18:47

jnewbery mentioned this pull request Oct 26, 2020

Addrman: test-before-evict bugfix and improvements for block-relay-only peers #20187

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ajtowns mentioned this pull request Dec 4, 2020

RPC/Net: Allow changing the connection_type for addnode onetry #20551

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ajtowns mentioned this pull request May 21, 2021

net: ignore block-relay-only peers when skipping DNS seed #22013

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deutschbitte mentioned this pull request Feb 21, 2022

Eclipse Attacks Reread Sjors/nado-book#19

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bitcoin locked as resolved and limited conversation to collaborators Aug 16, 2022

p2p: Try to preserve outbound block-relay-only connections during restart #17428

p2p: Try to preserve outbound block-relay-only connections during restart #17428

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