From 0264247fffed19a9bcb21543be68d2d304a9a8b4 Mon Sep 17 00:00:00 2001
From: eric <eric@openbsd.org>
Date: Fri, 23 Aug 2019 07:09:52 +0000
Subject: [PATCH] res_hnok() is too lenient wrt to acceptable domain name in
 mail addresses. replace it with a valid_domainname() check that implements
 something closer to RFC 5321, but still usable in real-life.

ok gilles@ millert@
---
 usr.sbin/smtpd/smtpd.h |  3 ++-
 usr.sbin/smtpd/util.c  | 45 ++++++++++++++++++++++++++++++++----------
 2 files changed, 37 insertions(+), 11 deletions(-)

diff --git a/usr.sbin/smtpd/smtpd.h b/usr.sbin/smtpd/smtpd.h
index 9aab6dcd5cf..00551d8b315 100644
--- a/usr.sbin/smtpd/smtpd.h
+++ b/usr.sbin/smtpd/smtpd.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: smtpd.h,v 1.631 2019/08/10 16:07:02 gilles Exp $	*/
+/*	$OpenBSD: smtpd.h,v 1.632 2019/08/23 07:09:52 eric Exp $	*/
 
 /*
  * Copyright (c) 2008 Gilles Chehade <gilles@poolp.org>
@@ -1656,6 +1656,7 @@ int hostname_match(const char *, const char *);
 int mailaddr_match(const struct mailaddr *, const struct mailaddr *);
 int valid_localpart(const char *);
 int valid_domainpart(const char *);
+int valid_domainname(const char *);
 int valid_smtp_response(const char *);
 int secure_file(int, char *, char *, uid_t, int);
 int  lowercase(char *, const char *, size_t);
diff --git a/usr.sbin/smtpd/util.c b/usr.sbin/smtpd/util.c
index 4b3ad22def8..61a3e98985a 100644
--- a/usr.sbin/smtpd/util.c
+++ b/usr.sbin/smtpd/util.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: util.c,v 1.144 2019/08/10 15:46:22 gilles Exp $	*/
+/*	$OpenBSD: util.c,v 1.145 2019/08/23 07:09:52 eric Exp $	*/
 
 /*
  * Copyright (c) 2000,2001 Markus Friedl.  All rights reserved.
@@ -510,7 +510,6 @@ valid_domainpart(const char *s)
 	struct in6_addr	 ina6;
 	char		*c, domain[SMTPD_MAXDOMAINPARTSIZE];
 	const char	*p;
-	size_t		 dlen;
 
 	if (*s == '[') {
 		if (strncasecmp("[IPv6:", s, 6) == 0)
@@ -535,17 +534,43 @@ valid_domainpart(const char *s)
 		return 0;
 	}
 
-	if (*s == '\0')
-		return 0;
+	return valid_domainname(s);
+}
 
-	dlen = strlen(s);
-	if (dlen >= sizeof domain)
-		return 0;
+#define charok(c) ((c) == '-' || (c) == '_' || isalpha((int)(c)) || isdigit((int)(c)))
 
-	if (s[dlen - 1] == '.')
-		return 0;
+#define MAXLABELSIZE 64
+#define MAXDNAMESIZE 254
+
+int
+valid_domainname(const char *dname)
+{
+	const char *label, *s = dname;
 
-	return res_hnok(s);
+	/* read a sequence of dot-separated label */
+	for (;;) {
+
+		/* label must have at least one char */
+		if (!charok(*s))
+			return 0;
+		label = s;
+		s++;
+
+		/* read all chars */
+		while (charok(*s))
+			s++;
+		if (s - label >= MAXLABELSIZE)
+			return 0;
+
+		if (*s == '\0') {
+			if (s - dname >= MAXDNAMESIZE)
+				return 0;
+			return 1;
+		}
+		if (*s != '.')
+			return 0;
+		s++;
+	}
 }
 
 int
-- 
2.20.1