Fwd: [Eventletdev] important security fix test required

[Victor Stinner]

Hi,

I got this email from the eventlet mailing list. Does asyncio have a
similar issue?

Victor


---------- Forwarded message ----------
From: Sergey Shepelev <tem...@gmail.com>
Date: 2016-02-28 21:25 GMT+01:00
Subject: [Eventletdev] important security fix test required
To: eventletdev <event...@lists.secondlife.com>


Hello.

TL;DR: if you use SSL and Eventlet in one program, please run this
version, DoS attack fixed. If there are no regressions, it will be
released shortly.

Details: most likely you had a server with similar loop:

while True:
conn, _ = server_sock.accept()
spawn(process, conn)

Which is fine, but if server socket already was SSL wrapped, then by
default accept() tries to perform SSL handshake before returning the
connection. But handshake is a blocking operation so malicious client
could just connect and not start handshake and thus block server
before next accept().

--
Sergey Shepelev
Skype: sergey.shepelev
+79996126031
http://temoto.ru/

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[Guido van Rossum]

It looks like asyncio is much more sophisticated, but you should
probably ask Antoine.

--
--Guido van Rossum (python.org/~guido)

[Andrew Svetlov]

IIRC latest asyncio uses BIO (not socket wrapper) for SSL processing,
so it does never block.

--
Thanks,
Andrew Svetlov

[Victor Stinner]

2016-02-29 14:10 GMT+01:00 Andrew Svetlov <andrew....@gmail.com>:
> IIRC latest asyncio uses BIO (not socket wrapper) for SSL processing,
> so it does never block.

What about Python 3.4 which doesn't support BIO? Do you think that the
SSL/TLS handshake can block? We use it in asynchronous mode, no?

_SelectorSslTransport:
...
sslsock = sslcontext.wrap_socket(rawsock, do_handshake_on_connect=False, ...)
...

The socket is in non-blocking mode, no?

In the C code, _ssl__SSLSocket_do_handshake_impl():

nonblocking = (sock->sock_timeout >= 0);
BIO_set_nbio(SSL_get_rbio(self->ssl), nonblocking);
BIO_set_nbio(SSL_get_wbio(self->ssl), nonblocking);
...
ret = SSL_do_handshake(self->ssl);
...
} else if (sockstate == SOCKET_IS_NONBLOCKING) {
break;

Victor