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network: smarter switch_unwanted_fork_interface

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Previously this function would not switch to a different chain if the
current chain contained the preferred block. This was not the intended
behaviour: if there is a *stronger* chain that *also* contains the
preferred block, we should jump to that.

Note that with this commit there will now always be a preferred block
(defaults to genesis). Previously, it might seem that often there was none,
but actually in practice if the user used the GUI context menu to switch
servers even once, there was one (usually genesis).

Hence, with the old code, if an attacker mined a single header which
then got reorged, auto_connect clients which were connected to the
attacker's server would never switch servers (jump chains) even
without the user explicitly configuring preference for the stale branch.
This commit is contained in:
SomberNight
2020-06-21 11:31:54 +02:00
parent 9385d2dae3
commit 2eec7e1600
3 changed files with 92 additions and 33 deletions
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48
electrum/tests/test_blockchain.py
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@@ -336,6 +336,54 @@ class TestBlockchain(ElectrumTestCase):
for b in (chain_u, chain_l, chain_z):
self.assertTrue(all([b.can_connect(b.read_header(i), False) for i in range(b.height())]))
def get_chains_that_contain_header_helper(self, header: dict):
height = header['block_height']
header_hash = hash_header(header)
return blockchain.get_chains_that_contain_header(height, header_hash)
def test_get_chains_that_contain_header(self):
blockchain.blockchains[constants.net.GENESIS] = chain_u = Blockchain(
config=self.config, forkpoint=0, parent=None,
forkpoint_hash=constants.net.GENESIS, prev_hash=None)
open(chain_u.path(), 'w+').close()
self._append_header(chain_u, self.HEADERS['A'])
self._append_header(chain_u, self.HEADERS['B'])
self._append_header(chain_u, self.HEADERS['C'])
self._append_header(chain_u, self.HEADERS['D'])
self._append_header(chain_u, self.HEADERS['E'])
self._append_header(chain_u, self.HEADERS['F'])
self._append_header(chain_u, self.HEADERS['O'])
self._append_header(chain_u, self.HEADERS['P'])
self._append_header(chain_u, self.HEADERS['Q'])
chain_l = chain_u.fork(self.HEADERS['G'])
self._append_header(chain_l, self.HEADERS['H'])
self._append_header(chain_l, self.HEADERS['I'])
self._append_header(chain_l, self.HEADERS['J'])
self._append_header(chain_l, self.HEADERS['K'])
self._append_header(chain_l, self.HEADERS['L'])
chain_z = chain_l.fork(self.HEADERS['M'])
self.assertEqual([chain_l, chain_z, chain_u], self.get_chains_that_contain_header_helper(self.HEADERS['A']))
self.assertEqual([chain_l, chain_z, chain_u], self.get_chains_that_contain_header_helper(self.HEADERS['C']))
self.assertEqual([chain_l, chain_z, chain_u], self.get_chains_that_contain_header_helper(self.HEADERS['F']))
self.assertEqual([chain_l, chain_z], self.get_chains_that_contain_header_helper(self.HEADERS['G']))
self.assertEqual([chain_l, chain_z], self.get_chains_that_contain_header_helper(self.HEADERS['I']))
self.assertEqual([chain_z], self.get_chains_that_contain_header_helper(self.HEADERS['M']))
self.assertEqual([chain_l], self.get_chains_that_contain_header_helper(self.HEADERS['K']))
self._append_header(chain_z, self.HEADERS['N'])
self._append_header(chain_z, self.HEADERS['X'])
self._append_header(chain_z, self.HEADERS['Y'])
self._append_header(chain_z, self.HEADERS['Z'])
self.assertEqual([chain_z, chain_l, chain_u], self.get_chains_that_contain_header_helper(self.HEADERS['A']))
self.assertEqual([chain_z, chain_l, chain_u], self.get_chains_that_contain_header_helper(self.HEADERS['C']))
self.assertEqual([chain_z, chain_l, chain_u], self.get_chains_that_contain_header_helper(self.HEADERS['F']))
self.assertEqual([chain_u], self.get_chains_that_contain_header_helper(self.HEADERS['O']))
self.assertEqual([chain_z, chain_l], self.get_chains_that_contain_header_helper(self.HEADERS['I']))
class TestVerifyHeader(ElectrumTestCase):