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The _ssl module uses an helper function check_socket_and_wait_for_timeout() to poll until the socket is ready (got data or became writable). check_socket_and_wait_for_timeout() always uses the socket timeout. If select() or poll() is interrupted by a signal (fails with EINTR), check_socket_and_wait_for_timeout() is restarted with the same timeout, which doesn't respect the contract of the timeout: the operation must timeout if it takes more than timeout seconds.
The code must be modified to recompute the timeout, as done in the new sock_call() function of Modules/socketmodule.c (issue #23618). At least, the timeout must decreases when select()/poll() fails with EINTR.
Currently, the timeout is reset after each read/write/handshake operation. IMO the timeout must apply on the total duration of the ssl method, not be reset. But changing this may break backward compatibility :-/
Note: if the signal handler raises an exception, the ssl method fails with the exception. This issue is specific to signal handlers not raising an exception.

test_ssl_bug.patch: Modify test_handshake_timeout() of test_ssl to show the bug: test_handshake_timeout() hangs with the patch (which sends a signal every millisecond).

New changeset 753233baf27e by Victor Stinner in branch 'default':
Issue #23853: Cleanup _ssl.c
https://hg.python.org/cpython/rev/753233baf27e 

Here is a patch to fix the issue: recompute the timeout.
It's unclear to me if we should reset the timeout after each successful read/write, or if the timeout is "global" (total duration of the ssl method). I asked the question on the python-dev mailing list.
https://mail.python.org/pipermail/python-dev/2015-April/139001.html
My patch uses a global timeout (never reset the timeout), whereas socket.sendall() resets the timeout at each send() success.

New changeset cdc83da0b0f8 by Victor Stinner in branch 'default':
Issue #23853: socket.socket.sendall() does no more reset the socket timeout
https://hg.python.org/cpython/rev/cdc83da0b0f8
New changeset 5983f3fdacdb by Victor Stinner in branch 'default':
Issue #23853: Methods of SSL socket don't reset the socket timeout anymore each
https://hg.python.org/cpython/rev/5983f3fdacdb