From 839a9de688f0a3c09ab8ef00337ca03c32c44796 Mon Sep 17 00:00:00 2001
From: Jonas Gunz <himself@jonasgunz.de>
Date: Sun, 19 Sep 2021 23:15:27 +0200
Subject: add fqdn_check()

---
 src/dns.c   | 29 +++++++++++++++++++++++++++++
 src/dns.h   |  6 ++++++
 tests/dns.c |  5 ++++-
 3 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/src/dns.c b/src/dns.c
index 50db12c..647c1b2 100644
--- a/src/dns.c
+++ b/src/dns.c
@@ -228,6 +228,35 @@ int fqdn_to_qname( char* _source, int _sourcelen, char* _sink ,int _sinklen )
 	return i+2;
 }
 
+int fqdn_check ( char* _source, int _sourcelen ) {
+	int i;
+	char c;
+
+	if ( !_source || _sourcelen <= 0 )
+		return -1;
+
+	for( i=0; i<_sourcelen; i++ ) {
+		c = _source[i];
+		if (!c)
+			break;
+		if (
+			!(c>='0' && c<='9') &&
+			!(c>='A' && c<='Z') &&
+			!(c>='a' && c<='z') &&
+			!(c== '-') && !(c=='_') && !(c=='.')
+			) {
+			return i+1;
+		}
+	}
+
+	if ( _source[ i-1 ] != '.' )
+		return i;
+	if ( _source[ 0 ] == '-' )
+		return 1;
+
+	return 0;
+}
+
 int qname_to_fqdn( char* _source, int _sourcelen, char* _sink, int _sinklen )
 {
 	unsigned int next_dot;
diff --git a/src/dns.h b/src/dns.h
index 7357bf0..7d51b0e 100644
--- a/src/dns.h
+++ b/src/dns.h
@@ -197,6 +197,12 @@ int dns_parse_packet ( char* _buffer, int _bufflen, dns_message_t* _msg );
  * */
 int fqdn_to_qname( char* _source, int _sourcelen, char* _sink, int _sinklen );
 
+/**
+ * Check FQDN validity
+ * Returns: 0 when valid, <0 for string errors, position > 0 of invalid character
+ */
+int fqdn_check ( char* _source, int _sourcelen );
+
 /**
  * Convert a QNAME back to a FQDN, reversing fqdn_to_qname( )
  * returns: length of string in _sink, < 0 on failure
diff --git a/tests/dns.c b/tests/dns.c
index a282b8b..49310ba 100644
--- a/tests/dns.c
+++ b/tests/dns.c
@@ -23,7 +23,8 @@ START_TEST (dns_qname) {
 
 	/* Check for working invalid protection */
 	ck_assert_int_gt( fqdn_to_qname (inval_fqdn,strlen(inval_fqdn),out,128), 0 );
-	ck_assert_int_lt( qname_check(out,128), 0 );
+	ck_assert_int_ne( qname_check(out,128), 0 );
+	ck_assert_int_ne( fqdn_check(inval_fqdn,strlen(inval_fqdn)), 0 );
 } END_TEST
 
 START_TEST (dns_qname_fuzz) {
@@ -44,6 +45,7 @@ START_TEST (dns_qname_fuzz) {
 		}
 	}
 
+	/* Do not allow more than 10% false-positives */
 	ck_assert_float_le( (float)valid_cnt / (float)limit * 100, 10);
 } END_TEST
 
@@ -69,6 +71,7 @@ START_TEST (dns_message_fuzz) {
 		}
 	}
 
+	/* Do not allow more than 10% false-positives */
 	ck_assert_float_le( (float)valid_cnt / (float)limit * 100, 10);
 } END_TEST
 
-- 
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