pyca / pyca/pyopenssl

Setting socket timeouts breaks handshake

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#168 18 comments 2 reactions 0 assignees View on GitHub

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Dominant language
Python
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Description

I'm seeing a weird issue when starting a TLS connection to any host. If I don't set any timeout on the socket, it works fine. If I do, it breaks before the handshake with a OpenSSL.SSL.WantReadError. For example if I set timeout to 100, it will break after a second anyway.

For now I use a workaround of setting a timeout on connection, but then removing it before the handshake.

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.settimeout(2)

ctx = OpenSSL.SSL.Context(OpenSSL.SSL.TLSv1_METHOD)
ctx.set_options(OpenSSL.SSL.OP_NO_SSLv2 | OpenSSL.SSL.OP_NO_SSLv3)
ctx.set_verify(OpenSSL.SSL.VERIFY_NONE, lambda _a, _b, _c, _d, _e: None)
conn = OpenSSL.SSL.Connection(ctx, s)
conn.set_tlsext_host_name(hostname.encode('utf-8'))
conn.connect((ip, port))

# s.settimeout(None)  # the workaround

try:
    conn.do_handshake()
except OpenSSL.SSL.WantReadError:
    # this happens on every connection

I'm running on Python 3.4.1, OpenSSL 0.14.

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First steps

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  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the socket-timeout reproducer in the issue and inspect OpenSSL.SSL.Connection.connect() and do_handshake() behavior when the underlying socket has a timeout. Compare it with the documented workaround that removes the timeout before the handshake. Done means a TLS handshake succeeds without requiring that workaround while preserving timeout behavior.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
networking, security
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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