Client-side namecheck wildcards.

A client reference identity of ".example.com" matches a server
certificate presented identity that is any sub-domain of "example.com"
(e.g. "www.sub.example.com).

With the X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS flag, it matches
only direct child sub-domains (e.g. "www.sub.example.com").

crypto/x509v3/v3_utl.c

@@ -572,11 +572,50 @@ typedef int (*equal_fn)(const unsigned char *pattern, size_t pattern_len,
 			const unsigned char *subject, size_t subject_len,
 			unsigned int flags);
 
+/* Skip pattern prefix to match "wildcard" subject */
+static void skip_prefix(const unsigned char **p, size_t *plen,
+			const unsigned char *subject, size_t subject_len,
+			unsigned int flags)
+	{
+	const unsigned char *pattern = *p;
+	size_t pattern_len = *plen;
+
+	/*
+	 * If subject starts with a leading '.' followed by more octets, and
+	 * pattern is longer, compare just an equal-length suffix with the
+	 * full subject (starting at the '.'), provided the prefix contains
+	 * no NULs.  (We check again that subject starts with '.' and
+	 * contains at least one subsequent character, just in case the
+	 * internal _X509_CHECK_FLAG_DOT_SUBDOMAINS flag was erroneously
+	 * set by the user).
+	 */
+	if ((flags & _X509_CHECK_FLAG_DOT_SUBDOMAINS) == 0 ||
+	    subject_len <= 1 || subject[0] != '.')
+		return;
+
+	while (pattern_len > subject_len && *pattern)
+		{
+		if ((flags & X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS) &&
+		    *pattern == '.')
+			break;
+		++pattern;
+		--pattern_len;
+		}
+
+	/* Skip if entire prefix acceptable */
+	if (pattern_len == subject_len)
+		{
+		*p = pattern;
+		*plen = pattern_len;
+		}
+	}
+
 /* Compare while ASCII ignoring case. */
 static int equal_nocase(const unsigned char *pattern, size_t pattern_len,
 			const unsigned char *subject, size_t subject_len,
-			unsigned int unused_flags)
+			unsigned int flags)
 	{
+	skip_prefix(&pattern, &pattern_len, subject, subject_len, flags);
 	if (pattern_len != subject_len)
 		return 0;
 	while (pattern_len)
@@ -605,11 +644,9 @@ static int equal_nocase(const unsigned char *pattern, size_t pattern_len,
 /* Compare using memcmp. */
 static int equal_case(const unsigned char *pattern, size_t pattern_len,
 		      const unsigned char *subject, size_t subject_len,
-		      unsigned int unused_flags)
+		      unsigned int flags)
 {
-	/* The pattern must not contain NUL characters. */
-	if (memchr(pattern, '\0', pattern_len) != NULL)
-		return 0;
+	skip_prefix(&pattern, &pattern_len, subject, subject_len, flags);
 	if (pattern_len != subject_len)
 		return 0;
 	return !memcmp(pattern, subject, pattern_len);
@@ -797,7 +834,14 @@ static int equal_wildcard(const unsigned char *pattern, size_t pattern_len,
 			  const unsigned char *subject, size_t subject_len,
 			  unsigned int flags)
 	{
-	const unsigned char *star = valid_star(pattern, pattern_len, flags);
+	const unsigned char *star = NULL;
+
+	/*
+	 * Subject names starting with '.' can only match a wildcard pattern
+	 * via a subject sub-domain pattern suffix match.
+	 */
+	if (!(subject_len > 1 && subject[0] == '.'))
+		star = valid_star(pattern, pattern_len, flags);
 	if (star == NULL)
 		return equal_nocase(pattern, pattern_len,
 				    subject, subject_len, flags);
@@ -860,6 +904,9 @@ static int do_x509_check(X509 *x, const unsigned char *chk, size_t chklen,
 	else if (check_type == GEN_DNS)
 		{
 		cnid = NID_commonName;
+		/* Implicit client-side DNS sub-domain pattern */
+		if (chklen > 1 && chk[0] == '.')
+			flags |= _X509_CHECK_FLAG_DOT_SUBDOMAINS;
 		alt_type = V_ASN1_IA5STRING;
 		if (flags & X509_CHECK_FLAG_NO_WILDCARDS)
 			equal = equal_nocase;

crypto/x509v3/v3nametest.c

@@ -11,6 +11,7 @@ static const char *const names[] =
 	"*@example.com", "test@*.example.com", "example.com", "www.example.com",
 	"test.www.example.com", "*.example.com", "*.www.example.com",
 	"test.*.example.com", "www.*.com",
+	".www.example.com", "*www.example.com",
 	"example.net", "xn--rger-koa.example.com",
 	"a.example.com", "b.example.com",
 	"postmaster@example.com", "Postmaster@example.com",
@@ -25,6 +26,11 @@ static const char *const exceptions[] =
 	"set CN: host: [*.example.com] matches [www.example.com]",
 	"set CN: host: [*.example.com] matches [xn--rger-koa.example.com]",
 	"set CN: host: [*.www.example.com] matches [test.www.example.com]",
+	"set CN: host: [*.www.example.com] matches [.www.example.com]",
+	"set CN: host: [*www.example.com] matches [www.example.com]",
+	"set CN: host: [test.www.example.com] matches [.www.example.com]",
+	"set CN: host-no-wildcards: [*.www.example.com] matches [.www.example.com]",
+	"set CN: host-no-wildcards: [test.www.example.com] matches [.www.example.com]",
 	"set emailAddress: email: [postmaster@example.com] does not match [Postmaster@example.com]",
 	"set emailAddress: email: [postmaster@EXAMPLE.COM] does not match [Postmaster@example.com]",
 	"set emailAddress: email: [Postmaster@example.com] does not match [postmaster@example.com]",
@@ -34,6 +40,11 @@ static const char *const exceptions[] =
 	"set dnsName: host: [*.example.com] matches [b.example.com]",
 	"set dnsName: host: [*.example.com] matches [xn--rger-koa.example.com]",
 	"set dnsName: host: [*.www.example.com] matches [test.www.example.com]",
+	"set dnsName: host-no-wildcards: [*.www.example.com] matches [.www.example.com]",
+	"set dnsName: host-no-wildcards: [test.www.example.com] matches [.www.example.com]",
+	"set dnsName: host: [*.www.example.com] matches [.www.example.com]",
+	"set dnsName: host: [*www.example.com] matches [www.example.com]",
+	"set dnsName: host: [test.www.example.com] matches [.www.example.com]",
 	"set rfc822Name: email: [postmaster@example.com] does not match [Postmaster@example.com]",
 	"set rfc822Name: email: [Postmaster@example.com] does not match [postmaster@example.com]",
 	"set rfc822Name: email: [Postmaster@example.com] does not match [postmaster@EXAMPLE.COM]",

crypto/x509v3/x509v3.h

@@ -710,6 +710,14 @@ STACK_OF(OPENSSL_STRING) *X509_get1_ocsp(X509 *x);
 #define X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS 0x4
 /* Allow (non-partial) wildcards to match multiple labels. */
 #define X509_CHECK_FLAG_MULTI_LABEL_WILDCARDS 0x8
+/* Constraint verifier subdomain patterns to match a single labels. */
+#define X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS 0x10
+/*
+ * Match reference identifiers starting with "." to any sub-domain.
+ * This is a non-public flag, turned on implicitly when the subject
+ * reference identity is a DNS name.
+ */
+#define _X509_CHECK_FLAG_DOT_SUBDOMAINS 0x8000
 
 int X509_check_host(X509 *x, const unsigned char *chk, size_t chklen,
 					unsigned int flags);

doc/crypto/X509_check_host.pod

@@ -27,7 +27,10 @@ X509_check_host() checks if the certificate matches the specified
 host name, which must be encoded in the preferred name syntax
 described in section 3.5 of RFC 1034. The B<namelen> argument must be
 the number of characters in the name string or zero in which case the
-length is calculated with strlen(name).
+length is calculated with strlen(name).  When B<name> starts with
+a dot (e.g ".example.com"), it will be matched by a certificate
+valid for any sub-domain of B<name>, (see also
+B<X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS> below).
 
 X509_check_email() checks if the certificate matches the specified
 email address.  Only the mailbox syntax of RFC 822 is supported,
@@ -59,6 +62,8 @@ flags:
 
 =item B<X509_CHECK_FLAG_MULTI_LABEL_WILDCARDS>.
 
+=item B<X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS>.
+
 =back
 
 The B<X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT> flag causes the function
@@ -74,10 +79,18 @@ If set, B<X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS> suppresses support
 for "*" as wildcard pattern in labels that have a prefix or suffix,
 such as: "www*" or "*www"; this only aplies to B<X509_check_host>.
 
-If set, B<X509_CHECK_FLAG_MULTI_LABEL_WILDCARDS>, allows a "*"
-that constitutes the complete label of a DNS name (e.g.
-"*.example.com") to match more than one label in B<name>;
-this only applies to B<X509_check_host>.
+If set, B<X509_CHECK_FLAG_MULTI_LABEL_WILDCARDS> allows a "*" that
+constitutes the complete label of a DNS name (e.g. "*.example.com")
+to match more than one label in B<name>; this flag only applies
+to B<X509_check_host>.
+
+If set, B<X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS> restricts B<name>
+values which start with ".", that would otherwise match any sub-domain
+in the peer certificate, to only match direct child sub-domains.
+Thus, for instance, with this flag set a B<name> of ".example.com"
+would match a peer certificate with a DNS name of "www.example.com",
+but would not match a peer certificate with a DNS name of
+"www.sub.example.com"; this flag only applies to B<X509_check_host>.
 
 =head1 RETURN VALUES