Don't allow immediate inv driven block downloads if
a peer already has MAX_BLOCKS_IN_TRANSIT_PER_PEER
active downloads. Prevents bogus inv spam from
blowing up block transfer tracking data structures.
This still leaves transactions in mempool that are potentially
invalid if the maturity period has been reorged out of, but at
least they're not missing inputs entirely.
There are 3 pieces of data that are maintained on disk. The actual block
and undo data, the block index (which can refer to positions on disk),
and the chainstate (which refers to the best block hash).
Earlier, there was no guarantee that blocks were written to disk before
block index entries referring to them were written. This commit introduces
dirty flags for block index data, and delays writing entries until the actual
block data is flushed.
With this stricter ordering in writes, it is now safe to not always flush
after every block, so there is no need for the IsInitialBlockDownload()
check there - instead we just write whenever enough time has passed or
the cache size grows too large. Also updating the wallet's best known block
is delayed until this is done, otherwise the wallet may end up referring to an
unknown block.
In addition, only do a write inside the block processing loop if necessary
(because of cache size exceeded). Otherwise, move the writing to a point
after processing is done, after relaying.
Like in a real world situation, a safe mode test should also be visible in the
UI. A test of safe mode is furthermore mostly relevant for developers, so it
should not be overwritten by a warning about a pre-release test build.
Previously, AcceptBlockHeader did not check the header (in particular
PoW). This made the client accept invalid-PoW-headers from peers in
headers-first sync.
Previously transactions were only tested again the
STANDARD_SCRIPT_VERIFY_FLAGS prior to mempool acceptance, so any bugs in
those flags that allowed actually-invalid transactions to pass would
result in allowing invalid transactions into the mempool. Fortunately
there is a second check in CreateNewBlock() that would prevent those
transactions from being mined, resulting in an invalid block, however
this could still be exploited as a DoS attack.
This is a simplified re-do of closed pull #3088.
This patch eliminates the privacy and reliability problematic use
of centralized web services for discovering the node's addresses
for advertisement.
The Bitcoin protocol already allows your peers to tell you what
IP they think you have, but this data isn't trustworthy since
they could lie. So the challenge is using it without creating a
DOS vector.
To accomplish this we adopt an approach similar to the one used
by P2Pool: If we're announcing and don't have a better address
discovered (e.g. via UPNP) or configured we just announce to
each peer the address that peer told us. Since peers could
already replace, forge, or drop our address messages this cannot
create a new vulnerability... but if even one of our peers is
giving us a good address we'll eventually make a useful
advertisement.
We also may randomly use the peer-provided address for the
daily rebroadcast even if we otherwise have a seemingly routable
address, just in case we've been misconfigured (e.g. by UPNP).
To avoid privacy problems, we only do these things if discovery
is enabled.
Cory Fields