open.source/magic-wormhole
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

subchannel: check MAX_FRAME_LENGTH, 2**32 minus headers

Browse Source 
Anyone sending 4GB in a single `transport.write()` is in for a surprise, but
at least we'll surprise them with an assertion *before* spending the time and
memory encrypting that monster.
This commit is contained in:
Brian Warner 2019-07-07 23:59:54 -07:00
parent d1aefa815d
commit 575cf5d789
1 changed files with 8 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
src/wormhole/_dilation/subchannel.py
View File

@ -12,6 +12,13 @@ from twisted.internet.error import ConnectionDone
from automat import MethodicalMachine from automat import MethodicalMachine
from .._interfaces import ISubChannel, IDilationManager from .._interfaces import ISubChannel, IDilationManager
# each subchannel frame (the data passed into transport.write(data)) gets a
# 9-byte header prefix (type, subchannel id, and sequence number), then gets
# encrypted (adding a 16-byte authentication tag). The result is transmitted
# with a 4-byte length prefix (which only covers the padded message, not the
# length prefix itself), so the padded message must be less than 2**32 bytes
# long.
MAX_FRAME_LENGTH = 2**32 - 1 - 9 - 16;
@attrs @attrs
class Once(object): class Once(object):
@ -173,6 +180,7 @@ class SubChannel(object):
# ITransport # ITransport
def write(self, data): def write(self, data):
assert isinstance(data, type(b"")) assert isinstance(data, type(b""))
assert len(data) <= MAX_FRAME_LENGTH
self.local_data(data) self.local_data(data)
def writeSequence(self, iovec): def writeSequence(self, iovec):