diff --git a/src/net_processing.cpp b/src/net_processing.cpp --- a/src/net_processing.cpp +++ b/src/net_processing.cpp @@ -2834,7 +2834,17 @@ std::make_pair(pfrom->GetId(), false)); } bool fNewBlock = false; - ProcessNewBlock(config, pblock, true, &fNewBlock); + // Setting fForceProcessing to true means that we bypass some of + // our anti-DoS protections in AcceptBlock, which filters + // unrequested blocks that might be trying to waste our resources + // (eg disk space). Because we only try to reconstruct blocks when + // we're close to caught up (via the CanDirectFetch() requirement + // above, combined with the behavior of not requesting blocks until + // we have a chain with at least nMinimumChainWork), and we ignore + // compact blocks with less work than our tip, it is safe to treat + // reconstructed compact blocks as having been requested. + ProcessNewBlock(config, pblock, /*fForceProcessing=*/true, + &fNewBlock); if (fNewBlock) { pfrom->nLastBlockTime = GetTime(); } @@ -2929,7 +2939,12 @@ // Since we requested this block (it was in mapBlocksInFlight), // force it to be processed, even if it would not be a candidate for // new tip (missing previous block, chain not long enough, etc) - ProcessNewBlock(config, pblock, true, &fNewBlock); + // This bypasses some anti-DoS logic in AcceptBlock (eg to prevent + // disk-space attacks), but this should be safe due to the + // protections in the compact block handler -- see related comment + // in compact block optimistic reconstruction handling. + ProcessNewBlock(config, pblock, /*fForceProcessing=*/true, + &fNewBlock); if (fNewBlock) { pfrom->nLastBlockTime = GetTime(); } diff --git a/src/validation.cpp b/src/validation.cpp --- a/src/validation.cpp +++ b/src/validation.cpp @@ -3582,6 +3582,14 @@ if (fTooFarAhead) { return true; } + + // Protect against DoS attacks from low-work chains. + // If our tip is behind, a peer could try to send us + // low-work blocks on a fake chain that we would never + // request; don't process these. + if (pindex->nChainWork < nMinimumChainWork) { + return true; + } } if (fNewBlock) { diff --git a/test/functional/p2p-acceptblock.py b/test/functional/p2p-acceptblock.py --- a/test/functional/p2p-acceptblock.py +++ b/test/functional/p2p-acceptblock.py @@ -16,17 +16,22 @@ versus non-whitelisted peers, this tests the behavior of both (effectively two separate tests running in parallel). -Setup: two nodes, node0 and node1, not connected to each other. Node0 does not +Setup: three nodes, node0+node1+node2, not connected to each other. Node0 does not whitelist localhost, but node1 does. They will each be on their own chain for -this test. +this test. Node2 will have nMinimumChainWork set to 0x10, so it won't process +low-work unrequested blocks. -We have one NodeConn connection to each, test_node and white_node respectively. +We have one NodeConn connection to each, test_node, white_node, and min_work_node, +respectively. The test: 1. Generate one block on each node, to leave IBD. 2. Mine a new block on each tip, and deliver to each node from node's peer. - The tip should advance. + The tip should advance for node0 and node1, but node2 should skip processing + due to nMinimumChainWork. + +Node2 is unused in tests 3-7: 3. Mine a block that forks the previous block, and deliver to each node from corresponding peer. @@ -54,6 +59,10 @@ 7. Send Node0 the missing block again. Node0 should process and the tip should advance. + +8. Test Node2 is able to sync when connected to node0 (which should have sufficient +work on its chain). + ''' @@ -66,56 +75,67 @@ def set_test_params(self): self.setup_clean_chain = True - self.num_nodes = 2 - self.extra_args = [[], ["-whitelist=127.0.0.1"]] + self.num_nodes = 3 + self.extra_args = [[], ["-whitelist=127.0.0.1"], + ["-minimumchainwork=0x10"]] def setup_network(self): # Node0 will be used to test behavior of processing unrequested blocks # from peers which are not whitelisted, while Node1 will be used for # the whitelisted case. + # Node2 will be used for non-whitelisted peers to test the interaction + # with nMinimumChainWork. self.setup_nodes() def run_test(self): # Setup the p2p connections and start up the network thread. test_node = NodeConnCB() # connects to node0 (not whitelisted) white_node = NodeConnCB() # connects to node1 (whitelisted) + min_work_node = NodeConnCB() # connects to node2 (not whitelisted) connections = [] connections.append( NodeConn('127.0.0.1', p2p_port(0), self.nodes[0], test_node)) connections.append( NodeConn('127.0.0.1', p2p_port(1), self.nodes[1], white_node)) + connections.append(NodeConn('127.0.0.1', p2p_port(2), + self.nodes[2], min_work_node)) test_node.add_connection(connections[0]) white_node.add_connection(connections[1]) + min_work_node.add_connection(connections[2]) NetworkThread().start() # Start up network handling in another thread # Test logic begins here test_node.wait_for_verack() white_node.wait_for_verack() + min_work_node.wait_for_verack() - # 1. Have both nodes mine a block (leave IBD) + # 1. Have nodes mine a block (nodes1/2 leave IBD) [n.generate(1) for n in self.nodes] tips = [int("0x" + n.getbestblockhash(), 0) for n in self.nodes] # 2. Send one block that builds on each tip. - # This should be accepted. + # This should be accepted by nodes 1/2 blocks_h2 = [] # the height 2 blocks on each node's chain block_time = int(time.time()) + 1 - for i in range(2): - blocks_h2.append( - create_block(tips[i], create_coinbase(2), block_time)) + for i in range(3): + blocks_h2.append(create_block( + tips[i], create_coinbase(2), block_time)) blocks_h2[i].solve() block_time += 1 test_node.send_message(msg_block(blocks_h2[0])) white_node.send_message(msg_block(blocks_h2[1])) + min_work_node.send_message(msg_block(blocks_h2[2])) - for x in [test_node, white_node]: + for x in [test_node, white_node, min_work_node]: x.sync_with_ping() assert_equal(self.nodes[0].getblockcount(), 2) assert_equal(self.nodes[1].getblockcount(), 2) - self.log.info("First height 2 block accepted by both nodes") + assert_equal(self.nodes[2].getblockcount(), 1) + self.log.info( + "First height 2 block accepted by node0/node1; correctly rejected by node2") # 3. Send another block that builds on the original tip. blocks_h2f = [] # Blocks at height 2 that fork off the main chain @@ -242,6 +262,13 @@ [c.disconnect_node() for c in connections] + # 8. Connect node2 to node0 and ensure it is able to sync + connect_nodes(self.nodes[0], 2) + sync_blocks([self.nodes[0], self.nodes[2]]) + self.log.info("Successfully synced nodes 2 and 0") + + [c.disconnect_node() for c in connections] + if __name__ == '__main__': AcceptBlockTest().main()