New subject: [PATCH 2/2] unit: Add TLS tests for cert's DNSName matching

Friday, 23 August 2019

Also return success in the domain_mask check if any of the DNSNames in
the peer certificate's subjectAltName extension matches any of the mask
strings supplied.
---
 ell/tls.c | 70 ++++++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 62 insertions(+), 8 deletions(-)

diff --git a/ell/tls.c b/ell/tls.c
index cbcdfa4..d0e2a66 100644
--- a/ell/tls.c
+++ b/ell/tls.c
@@ -673,26 +673,80 @@ ok_next:
 	}
 }
 
+static const struct asn1_oid subject_alt_name_oid =
+	{ 3, { 0x55, 0x1d, 0x11 } };
 static const struct asn1_oid dn_common_name_oid =
 	{ 3, { 0x55, 0x04, 0x03 } };
 
+#define SAN_DNS_NAME_ID ASN1_CONTEXT_IMPLICIT(2)
+
 static bool tls_cert_domains_match_mask(struct l_cert *cert, char **mask)
 {
-	const uint8_t *dn, *end;
-	size_t dn_size;
+	const uint8_t *san, *dn, *end;
+	size_t san_len, dn_len;
+	uint8_t san_tag;
 	const char *cn = NULL;
 	size_t cn_len;
+	char **i;
+	bool dns_name_present = false;
+
+	/*
+	 * Locate SubjectAltName (RFC5280 Section 4.2.1.6) and descend into
+	 * the sole SEQUENCE element, check if any DNSName matches.
+	 */
+	san = cert_get_extension(cert, &subject_alt_name_oid, NULL, &san_len);
+	if (san) {
+		san = asn1_der_find_elem(san, san_len, 0, &san_tag, &san_len);
+		if (unlikely(!san || san_tag != ASN1_ID_SEQUENCE))
+			return false;
+
+		end = san + san_len;
+		while (san < end) {
+			const uint8_t *value;
+			uint8_t tag;
+			size_t len;
+
+			value = asn1_der_find_elem(san, end - san,
+							SAN_DNS_NAME_ID,
+							&tag, &len);
+			if (!value)
+				break;
+
+			/* Type is implicitly IA5STRING */
+
+			for (i = mask; *i; i++)
+				if (tls_domain_match_mask((const char *) value,
+							len, *i, strlen(*i)))
+					return true;
+
+			san = value + len;
+			dns_name_present = true;
+		}
+	}
 
 	/*
 	 * Retrieve the Common Name from the Subject DN and check if it
-	 * matches.  TODO: possibly also look at SubjectAltName.
+	 * matches.
+	 *
+	 * We look at the Common Name only if no DNSNames were present in
+	 * the certificate, following Wi-Fi Alliance's Hotspot 2.0
+	 * Specification v3.1 section 7.3.3.2 step 2:
+	 * "Verify in the AAA server certificate that the domain name from
+	 * the FQDN [...] is a suffix match of the domain name in at least
+	 * one of the DNSName SubjectAltName extensions. If a SubjectAltName
+	 * of type DNSName is not present, then the domain name from the
+	 * FQDN shall be a suffix match to the CommonName portion of the
+	 * SubjectName. If neither of these conditions holds, then
+	 * verification fails."
 	 */
+	if (unlikely(dns_name_present))
+		return false;
 
-	dn = l_cert_get_dn(cert, &dn_size);
+	dn = l_cert_get_dn(cert, &dn_len);
 	if (unlikely(!dn))
 		return false;
 
-	end = dn + dn_size;
+	end = dn + dn_len;
 	while (dn < end) {
 		const uint8_t *set, *seq, *oid, *name;
 		uint8_t tag;
@@ -725,11 +779,11 @@ static bool tls_cert_domains_match_mask(struct l_cert *cert, char
**mask)
 		}
 	}
 
-	if (!cn)
+	if (unlikely(!cn))
 		return false;
 
-	for (; *mask; mask++)
-		if (tls_domain_match_mask(cn, cn_len, *mask, strlen(*mask)))
+	for (i = mask; *i; i++)
+		if (tls_domain_match_mask(cn, cn_len, *i, strlen(*i)))
 			return true;
 
 	return false;
-- 
2.20.1


    

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[PATCH 1/2] tls: Validate peer certificate's DNSNames against mask