bpo-33136: Harden ssl module against CVE-2018-8970 (GH-6229)

Harden ssl module against LibreSSL CVE-2018-8970.
X509_VERIFY_PARAM_set1_host() is called with an explicit namelen. A new test
ensures that NULL bytes are not allowed.

Signed-off-by: Christian Heimes <christian@python.org>
3 files changed