In principle, the checksums of P2P packets are simply 4-byte blobs which
are the first four bytes of SHA256(SHA256(payload)).
Currently they are handled as little-endian 32-bit integers half of the
time, as blobs the other half, sometimes copying the one to the other,
resulting in somewhat confused code.
This PR changes the handling to be consistent both at packet creation
and receiving, making it (I think) easier to understand.
After #8594 the addrFrom sent by a node is not used anymore at all,
so don't bother sending it.
Also mitigates the privacy issue in (#8616). It doesn't completely solve
the issue as GetLocalAddress is also called in AdvertiseLocal, but at
least when advertising addresses it stands out less as *our* address.
This was broken by 63cafa6329.
Note that while this fixes the settings, it doesn't fix the actual usage of
-maxuploadtarget completely, as there is currently a bug in the
nOptimisticBytesWritten accounting that causes a delayed response if the target
is reached. That bug will be addressed separately.
In the case of (for example) an already-running bitcoind, the shutdown sequence
begins before CConnman has been created, leading to a null-pointer dereference
when g_connman->Stop() is called.
Instead, Just let the CConnman dtor take care of stopping.
CConnman then passes the current best height into CNode at creation time.
This way CConnman/CNode have no dependency on main for height, and the signals
only move in one direction.
This also helps to prevent identity leakage a tiny bit. Before this change, an
attacker could theoretically make 2 connections on different interfaces. They
would connect fully on one, and only establish the initial connection on the
other. Once they receive a new block, they would relay it to your first
connection, and immediately commence the version handshake on the second. Since
the new block height is reflected immediately, they could attempt to learn
whether the two connections were correlated.
This is, of course, incredibly unlikely to work due to the small timings
involved and receipt from other senders. But it doesn't hurt to lock-in
nBestHeight at the time of connection, rather than letting the remote choose
the time.
This behavior seems to have been quite racy and broken.
Move nLocalHostNonce into CNode, and check received nonces against all
non-fully-connected nodes. If there's a match, assume we've connected
to ourself.
Tests if addresses are online or offline by briefly connecting to them. These short lived connections are referred to as feeler connections. Feeler connections are designed to increase the number of fresh online addresses in tried by selecting and connecting to addresses in new. One feeler connection is attempted on average once every two minutes.
This change was suggested as Countermeasure 4 in
Eclipse Attacks on Bitcoin’s Peer-to-Peer Network, Ethan Heilman,
Alison Kendler, Aviv Zohar, Sharon Goldberg. ePrint Archive Report
2015/263. March 2015.
Wladimir J. van der Laan