validate certificates using the cryptography python package as much as...

validate certificates using the cryptography python package as much as possible, shelling out to openssl just once instead of four times per certificate

* Use `cryptography` instead of parsing openssl's output.
* When checking if we can reuse the primary domain certificate or a www-parent-domain certificate for a domain, avoid shelling out to openssl entirely.

CHANGELOG.md

@@ -20,6 +20,7 @@ DNS:
 Control panel:
 * Resetting a user's password now forces them to log in again everywhere.
 * Status checks were not working if an ssh server was not installed.
+* SSL certificate validation now uses the Python cryptography module in some places where openssl was used.
 
 System:
 * The munin system monitoring tool is now installed and accessible at /admin/munin.

management/status_checks.py

@@ -605,103 +605,101 @@ def check_ssl_cert(domain, rounded_time, env, output):
 			output.print_line(cert_status_details)
 			output.print_line("")
 
-def check_certificate(domain, ssl_certificate, ssl_private_key, warn_if_expiring_soon=True, rounded_time=False):
-	# Use openssl verify to check the status of a certificate.
-
-	# First check that the certificate is for the right domain. The domain
-	# must be found in the Subject Common Name (CN) or be one of the
-	# Subject Alternative Names. A wildcard might also appear as the CN
-	# or in the SAN list, so check for that tool.
-	retcode, cert_dump = shell('check_output', [
-		"openssl", "x509",
-		"-in", ssl_certificate,
-		"-noout", "-text", "-nameopt", "rfc2253",
-		], trap=True)
-
-	# If the certificate is catastrophically bad, catch that now and report it.
-	# More information was probably written to stderr (which we aren't capturing),
-	# but it is probably not helpful to the user anyway.
-	if retcode != 0:
-		return ("The SSL certificate appears to be corrupted or not a PEM-formatted SSL certificate file. (%s)" % ssl_certificate, None)
-
-	cert_dump = cert_dump.split("\n")
-	certificate_names = set()
-	cert_expiration_date = None
-	while len(cert_dump) > 0:
-		line = cert_dump.pop(0)
-
-		# Grab from the Subject Common Name. We include the indentation
-		# at the start of the line in case maybe the cert includes the
-		# common name of some other referenced entity (which would be
-		# indented, I hope).
-		m = re.match("        Subject: CN=([^,]+)", line)
-		if m:
-			certificate_names.add(m.group(1))
-	
-		# Grab from the Subject Alternative Name, which is a comma-delim
-		# list of names, like DNS:mydomain.com, DNS:otherdomain.com.
-		m = re.match("            X509v3 Subject Alternative Name:", line)
-		if m:
-			names = re.split(",\s*", cert_dump.pop(0).strip())
-			for n in names:
-				m = re.match("DNS:(.*)", n)
-				if m:
-					certificate_names.add(m.group(1))
-
-		# Grab the expiration date for testing later.
-		m = re.match("            Not After : (.*)", line)
-		if m:
-			cert_expiration_date = dateutil.parser.parse(m.group(1))
+def check_certificate(domain, ssl_certificate, ssl_private_key, warn_if_expiring_soon=True, rounded_time=False, just_check_domain=False):
+	# Check that the ssl_certificate & ssl_private_key files are good
+	# for the provided domain.
 
-	wildcard_domain = re.sub("^[^\.]+", "*", domain)
-	if domain is not None and domain not in certificate_names and wildcard_domain not in certificate_names:
-		return ("The certificate is for the wrong domain name. It is for %s."
-			% ", ".join(sorted(certificate_names)), None)
+	from cryptography.hazmat.primitives.asymmetric.rsa import RSAPrivateKey
+	from cryptography.x509 import Certificate, DNSName, ExtensionNotFound, OID_COMMON_NAME, OID_SUBJECT_ALTERNATIVE_NAME
 
-	# Second, check that the certificate matches the private key. Get the modulus of the
-	# private key and of the public key in the certificate. They should match. The output
-	# of each command looks like "Modulus=XXXXX".
+	# The ssl_certificate file may contain a chain of certificates. We'll
+	# need to split that up before we can pass anything to openssl or
+	# parse them in Python. Parse it with the cryptography library.
+	try:
+		ssl_cert_chain = load_cert_chain(ssl_certificate)
+		cert = load_pem(ssl_cert_chain[0])
+		if not isinstance(cert, Certificate): raise ValueError("This is not a certificate file.")
+	except ValueError as e:
+		return ("There is a problem with the certificate file: %s" % str(e), None)
+
+	# First check that the domain name is one of the names allowed by
+	# the certificate.
+	if domain is not None:
+		# The domain must be found in the Subject Common Name (CN)...
+		certificate_names = set()
+		try:
+			certificate_names.add(
+				cert.subject.get_attributes_for_oid(OID_COMMON_NAME)[0].value
+				)
+		except IndexError:
+			# No common name? Certificate is probably generated incorrectly.
+			# But we'll let it error-out when it doesn't find the domain.
+			pass
+
+		# ... or be one of the Subject Alternative Names.
+		try:
+			sans = cert.extensions.get_extension_for_oid(OID_SUBJECT_ALTERNATIVE_NAME).value.get_values_for_type(DNSName)
+			for san in sans:
+				certificate_names.add(san)
+		except ExtensionNotFound:
+			pass
+
+		# Check that the domain appears among the acceptable names, or a wildcard
+		# form of the domain name (which is a stricter check than the specs but
+		# should work in normal cases).
+		wildcard_domain = re.sub("^[^\.]+", "*", domain)
+		if domain not in certificate_names and wildcard_domain not in certificate_names:
+			return ("The certificate is for the wrong domain name. It is for %s."
+				% ", ".join(sorted(certificate_names)), None)
+
+	# Second, check that the certificate matches the private key.
 	if ssl_private_key is not None:
-		private_key_modulus = shell('check_output', [
-			"openssl", "rsa",
-			"-inform", "PEM",
-			"-noout", "-modulus",
-			"-in", ssl_private_key])
-		cert_key_modulus = shell('check_output', [
-			"openssl", "x509",
-			"-in", ssl_certificate,
-			"-noout", "-modulus"])
-		if private_key_modulus != cert_key_modulus:
-			return ("The certificate installed at %s does not correspond to the private key at %s." % (ssl_certificate, ssl_private_key), None)
+		priv_key = load_pem(open(ssl_private_key, 'rb').read())
+		if not isinstance(priv_key, RSAPrivateKey):
+			return ("The private key file %s is not a private key file." % ssl_private_key, None)
+
+		if priv_key.public_key().public_numbers() != cert.public_key().public_numbers():
+			return ("The certificate does not correspond to the private key at %s." % ssl_private_key, None)
+
+		# We could also use the openssl command line tool to get the modulus
+		# listed in each file. The output of each command below looks like "Modulus=XXXXX".
+		# $ openssl rsa -inform PEM -noout -modulus -in ssl_private_key
+		# $ openssl x509 -in ssl_certificate -noout -modulus
+
+	# Third, check if the certificate is self-signed. Return a special flag string.
+	if cert.issuer == cert.subject:
+		return ("SELF-SIGNED", None)
+
+	# When selecting which certificate to use for non-primary domains, we check if the primary
+	# certificate or a www-parent-domain certificate is good for the domain. There's no need
+	# to run extra checks beyond this point.
+	if just_check_domain:
+		return ("OK", None)
+
+	# Check that the certificate hasn't expired. The datetimes returned by the
+	# certificate are 'naive' and in UTC. We need to get the current time in UTC.
+	now = datetime.datetime.utcnow()
+	if not(cert.not_valid_before <= now <= cert.not_valid_after):
+		return ("The certificate has expired or is not yet valid. It is valid from %s to %s." % (cert.not_valid_before, cert.not_valid_after), None)
 
 	# Next validate that the certificate is valid. This checks whether the certificate
 	# is self-signed, that the chain of trust makes sense, that it is signed by a CA
 	# that Ubuntu has installed on this machine's list of CAs, and I think that it hasn't
 	# expired.
 
-	# In order to verify with openssl, we need to split out any
-	# intermediary certificates in the chain (if any) from our
-	# certificate (at the top). They need to be passed separately.
-
-	cert = open(ssl_certificate).read()
-	m = re.match(r'(-*BEGIN CERTIFICATE-*.*?-*END CERTIFICATE-*)(.*)', cert, re.S)
-	if m == None:
-		return ("The certificate file is an invalid PEM certificate.", None)
-	mycert, chaincerts = m.groups()
-
+	# The certificate chain has to be passed separately and is given via STDIN.
 	# This command returns a non-zero exit status in most cases, so trap errors.
-
 	retcode, verifyoutput = shell('check_output', [
 		"openssl",
 		"verify", "-verbose",
 		"-purpose", "sslserver", "-policy_check",]
-		+ ([] if chaincerts.strip() == "" else ["-untrusted", "/dev/stdin"])
+		+ ([] if len(ssl_cert_chain) == 1 else ["-untrusted", "/dev/stdin"])
 		+ [ssl_certificate],
-		input=chaincerts.encode('ascii'),
+		input=b"\n\n".join(ssl_cert_chain[1:]),
 		trap=True)
 
 	if "self signed" in verifyoutput:
-		# Certificate is self-signed.
+		# Certificate is self-signed. Probably we detected this above.
 		return ("SELF-SIGNED", None)
 
 	elif retcode != 0:
@@ -716,7 +714,7 @@ def check_certificate(domain, ssl_certificate, ssl_private_key, warn_if_expiring
 		# good.
 
 		# But is it expiring soon?
-		now = datetime.datetime.now(dateutil.tz.tzlocal())
+		cert_expiration_date = cert.not_valid_after
 		ndays = (cert_expiration_date-now).days
 		if not rounded_time or ndays < 7:
 			expiry_info = "The certificate expires in %d days on %s." % (ndays, cert_expiration_date.strftime("%x"))
@@ -733,6 +731,30 @@ def check_certificate(domain, ssl_certificate, ssl_private_key, warn_if_expiring
 		# Return the special OK code.
 		return ("OK", expiry_info)
 
+def load_cert_chain(pemfile):
+	# A certificate .pem file may contain a chain of certificates.
+	# Load the file and split them apart.
+	re_pem = rb"(-+BEGIN (?:.+)-+[\r\n](?:[A-Za-z0-9+/=]{1,64}[\r\n])+-+END (?:.+)-+[\r\n])"
+	with open(pemfile, "rb") as f:
+		pem = f.read() + b"\n" # ensure trailing newline
+		pemblocks = re.findall(re_pem, pem)
+		if len(pemblocks) == 0:
+			raise ValueError("File does not contain valid PEM data.")
+		return pemblocks
+
+def load_pem(pem):
+	# Parse a "---BEGIN .... END---" PEM string and return a Python object for it
+	# using classes from the cryptography package.
+	from cryptography.x509 import load_pem_x509_certificate
+	from cryptography.hazmat.primitives import serialization
+	from cryptography.hazmat.backends import default_backend
+	pem_type = re.match(b"-+BEGIN (.*?)-+\n", pem).group(1)
+	if pem_type == b"RSA PRIVATE KEY":
+		return serialization.load_pem_private_key(pem, password=None, backend=default_backend())
+	if pem_type == b"CERTIFICATE":
+		return load_pem_x509_certificate(pem, default_backend())
+	raise ValueError("Unsupported PEM object type: " + pem_type.decode("ascii", "replace"))
+
 _apt_updates = None
 def list_apt_updates(apt_update=True):
 	# See if we have this information cached recently.

management/web_update.py

@@ -201,14 +201,14 @@ def get_domain_ssl_files(domain, env, allow_shared_cert=True):
 		# the user has uploaded a different private key for this domain.
 		if not ssl_key_is_alt and allow_shared_cert:
 			from status_checks import check_certificate
-			if check_certificate(domain, ssl_certificate_primary, None)[0] == "OK":
+			if check_certificate(domain, ssl_certificate_primary, None, just_check_domain=True)[0] == "OK":
 				ssl_certificate = ssl_certificate_primary
 				ssl_via = "Using multi/wildcard certificate of %s." % env['PRIMARY_HOSTNAME']
 
 			# For a 'www.' domain, see if we can reuse the cert of the parent.
 			elif domain.startswith('www.'):
 				ssl_certificate_parent = os.path.join(env["STORAGE_ROOT"], 'ssl/%s/ssl_certificate.pem' % safe_domain_name(domain[4:]))
-				if os.path.exists(ssl_certificate_parent) and check_certificate(domain, ssl_certificate_parent, None)[0] == "OK":
+				if os.path.exists(ssl_certificate_parent) and check_certificate(domain, ssl_certificate_parent, None, just_check_domain=True)[0] == "OK":
 					ssl_certificate = ssl_certificate_parent
 					ssl_via = "Using multi/wildcard certificate of %s." % domain[4:]
 

setup/management.sh

@@ -2,8 +2,10 @@
 
 source setup/functions.sh
 
-apt_install python3-flask links duplicity libyaml-dev python3-dnspython python3-dateutil
-hide_output pip3 install rtyaml "email_validator==0.1.0-rc5"
+# build-essential libssl-dev libffi-dev python3-dev: Required to pip install cryptography.
+apt_install python3-flask links duplicity libyaml-dev python3-dnspython python3-dateutil \
+	build-essential libssl-dev libffi-dev python3-dev
+hide_output pip3 install rtyaml "email_validator==0.1.0-rc5" cryptography
 	# email_validator is repeated in setup/questions.sh
 
 # Create a backup directory and a random key for encrypting backups.