dns: add a check before setting `NDPI_MALFORMED_PACKET` risk (#2558)

"Invalid DNS Header"-risk should be set only if the flow has been
already classified as DNS. Otherwise, almost any non-DNS flows on port 53
will end up having the `NDPI_MALFORMED_PACKET` risk set, which is a little
bit confusing for non DNS traffic

3 files changed, 6 insertions, 5 deletions

diff --git a/src/lib/protocols/dns.c b/src/lib/protocols/dns.c
index 94367d318..4e3b09d5b 100644
--- a/src/lib/protocols/dns.c
+++ b/src/lib/protocols/dns.c
@@ -320,7 +320,8 @@ static int search_valid_dns(struct ndpi_detection_module_struct *ndpi_struct,
 	  x++;
       }
     } else {
-      ndpi_set_risk(flow, NDPI_MALFORMED_PACKET, "Invalid DNS Header");
+      if(flow->detected_protocol_stack[0] != NDPI_PROTOCOL_UNKNOWN)
+        ndpi_set_risk(flow, NDPI_MALFORMED_PACKET, "Invalid DNS Header");
       return(1 /* invalid */);
     }
   } else {
diff --git a/tests/cfgs/default/result/fuzz-2006-06-26-2594.pcap.out b/tests/cfgs/default/result/fuzz-2006-06-26-2594.pcap.out
index 978d0a6e2..e27a1033d 100644
--- a/tests/cfgs/default/result/fuzz-2006-06-26-2594.pcap.out
+++ b/tests/cfgs/default/result/fuzz-2006-06-26-2594.pcap.out
@@ -182,9 +182,9 @@ Unrated                         34 4212          34
 	139	UDP 0.168.1.2:2783 -> 192.168.1.1:53 [proto: 5/DNS][IP: 0/Unknown][ClearText][Confidence: DPI][FPC: 5/DNS, Confidence: DPI][DPI packets: 1][cat: Network/14][1 pkts/86 bytes -> 0 pkts/0 bytes][Goodput ratio: 51/0][< 1 sec][Hostname/SNI: _sip._udp.sip.cybercity.dk][::][Risk: ** Unidirectional Traffic **][Risk Score: 10][Risk Info: No server to client traffic][PLAIN TEXT (cybercity)][Plen Bins: 0,100,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
 	140	UDP 14.168.1.2:2754 -> 192.168.1.1:53 [proto: 5/DNS][IP: 0/Unknown][ClearText][Confidence: DPI][FPC: 5/DNS, Confidence: DPI][DPI packets: 1][cat: Network/14][1 pkts/86 bytes -> 0 pkts/0 bytes][Goodput ratio: 51/0][< 1 sec][Hostname/SNI: _sip._udp.sip.cybercity.dk][::][Risk: ** Unidirectional Traffic **][Risk Score: 10][Risk Info: No server to client traffic][PLAIN TEXT (cybercity)][Plen Bins: 0,100,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
 	141	UDP 116.168.1.2:2829 -> 192.168.1.1:53 [proto: 5/DNS][IP: 0/Unknown][ClearText][Confidence: DPI][FPC: 5/DNS, Confidence: DPI][DPI packets: 1][cat: Network/14][1 pkts/86 bytes -> 0 pkts/0 bytes][Goodput ratio: 51/0][< 1 sec][Hostname/SNI: _sip._udp.sip.cybercity.dk][::][Risk: ** Unidirectional Traffic **][Risk Score: 10][Risk Info: No server to client traffic][PLAIN TEXT (cybercity)][Plen Bins: 0,100,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
-	142	UDP 128.168.1.2:2810 -> 192.168.1.1:53 [proto: 5/DNS][IP: 0/Unknown][ClearText][Confidence: Match by port][FPC: 0/Unknown, Confidence: Unknown][DPI packets: 1][cat: Network/14][1 pkts/86 bytes -> 0 pkts/0 bytes][Goodput ratio: 51/0][< 1 sec][::][Risk: ** Malformed Packet **** Unidirectional Traffic **][Risk Score: 20][Risk Info: No server to client traffic / Invalid DNS Header][PLAIN TEXT (cybescity)][Plen Bins: 0,100,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
+	142	UDP 128.168.1.2:2810 -> 192.168.1.1:53 [proto: 5/DNS][IP: 0/Unknown][ClearText][Confidence: Match by port][FPC: 0/Unknown, Confidence: Unknown][DPI packets: 1][cat: Network/14][1 pkts/86 bytes -> 0 pkts/0 bytes][Goodput ratio: 51/0][< 1 sec][::][Risk: ** Unidirectional Traffic **][Risk Score: 10][Risk Info: No server to client traffic][PLAIN TEXT (cybescity)][Plen Bins: 0,100,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
 	143	UDP 172.168.1.2:2734 -> 192.168.1.1:53 [proto: 5/DNS][IP: 276/Azure][ClearText][Confidence: DPI][FPC: 5/DNS, Confidence: DPI][DPI packets: 1][cat: Network/14][1 pkts/86 bytes -> 0 pkts/0 bytes][Goodput ratio: 51/0][< 1 sec][Hostname/SNI: _sip._udp.sip.cybercity.dk][::][Risk: ** Unidirectional Traffic **][Risk Score: 10][Risk Info: No server to client traffic][PLAIN TEXT (cybercity)][Plen Bins: 0,100,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
-	144	UDP 192.22.1.2:2760 -> 192.168.1.1:53 [proto: 5/DNS][IP: 0/Unknown][ClearText][Confidence: Match by port][FPC: 0/Unknown, Confidence: Unknown][DPI packets: 1][cat: Network/14][1 pkts/86 bytes -> 0 pkts/0 bytes][Goodput ratio: 51/0][< 1 sec][::][Risk: ** Malformed Packet **** Unidirectional Traffic **][Risk Score: 20][Risk Info: No server to client traffic / Invalid DNS Header][PLAIN TEXT (cybercity)][Plen Bins: 0,100,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
+	144	UDP 192.22.1.2:2760 -> 192.168.1.1:53 [proto: 5/DNS][IP: 0/Unknown][ClearText][Confidence: Match by port][FPC: 0/Unknown, Confidence: Unknown][DPI packets: 1][cat: Network/14][1 pkts/86 bytes -> 0 pkts/0 bytes][Goodput ratio: 51/0][< 1 sec][::][Risk: ** Unidirectional Traffic **][Risk Score: 10][Risk Info: No server to client traffic][PLAIN TEXT (cybercity)][Plen Bins: 0,100,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
 	145	UDP 192.98.1.2:2752 -> 25.168.1.1:53 [proto: 5/DNS][IP: 0/Unknown][ClearText][Confidence: DPI][FPC: 5/DNS, Confidence: DPI][DPI packets: 1][cat: Network/14][1 pkts/86 bytes -> 0 pkts/0 bytes][Goodput ratio: 51/0][< 1 sec][Hostname/SNI: _sip._udp.sip.cybercity.dk][::][Risk: ** Unidirectional Traffic **][Risk Score: 10][Risk Info: No server to client traffic][PLAIN TEXT (cybercity)][Plen Bins: 0,100,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
 	146	UDP 192.168.1.2:202 -> 192.168.37.115:53 [proto: 5/DNS][IP: 0/Unknown][ClearText][Confidence: DPI][FPC: 5/DNS, Confidence: DPI][DPI packets: 1][cat: Network/14][1 pkts/86 bytes -> 0 pkts/0 bytes][Goodput ratio: 51/0][< 1 sec][Hostname/SNI: _sip._udp.sip.cybercity.dk][::][Risk: ** Unidirectional Traffic **][Risk Score: 10][Risk Info: No server to client traffic][PLAIN TEXT (cybercity)][Plen Bins: 0,100,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
 	147	UDP 192.168.1.2:2568 -> 192.168.1.1:53 [proto: 5/DNS][IP: 0/Unknown][ClearText][Confidence: DPI][FPC: 5/DNS, Confidence: DPI][DPI packets: 1][cat: Network/14][1 pkts/86 bytes -> 0 pkts/0 bytes][Goodput ratio: 51/0][< 1 sec][Hostname/SNI: _sip._udp.sip.cybercity.dk][::][Risk: ** Unidirectional Traffic **][Risk Score: 10][Risk Info: No server to client traffic][PLAIN TEXT (cybercity)][Plen Bins: 0,100,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
@@ -214,7 +214,7 @@ Unrated                         34 4212          34
 	171	UDP 192.168.1.110:2713 -> 192.168.1.1:53 [proto: 5/DNS][IP: 0/Unknown][ClearText][Confidence: DPI][FPC: 5/DNS, Confidence: DPI][DPI packets: 1][cat: Network/14][1 pkts/86 bytes -> 0 pkts/0 bytes][Goodput ratio: 51/0][< 1 sec][::][Risk: ** Malformed Packet **** Unidirectional Traffic **][Risk Score: 20][Risk Info: No server to client traffic / Invalid DNS Query Lenght][PLAIN TEXT (cybercity)][Plen Bins: 0,100,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
 	172	UDP 192.168.1.172:2766 -> 192.168.1.1:53 [proto: 5/DNS][IP: 0/Unknown][ClearText][Confidence: DPI][FPC: 5/DNS, Confidence: DPI][DPI packets: 1][cat: Network/14][1 pkts/86 bytes -> 0 pkts/0 bytes][Goodput ratio: 51/0][< 1 sec][Hostname/SNI: _sip._udp.sip.cybercity.dk][::][Risk: ** Unidirectional Traffic **][Risk Score: 10][Risk Info: No server to client traffic][PLAIN TEXT (cybercity)][Plen Bins: 0,100,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
 	173	UDP 192.168.9.2:2774 -> 192.168.1.1:53 [proto: 5/DNS][IP: 0/Unknown][ClearText][Confidence: DPI][FPC: 5/DNS, Confidence: DPI][DPI packets: 1][cat: Network/14][1 pkts/86 bytes -> 0 pkts/0 bytes][Goodput ratio: 51/0][< 1 sec][Hostname/SNI: _sip._udp.sip.cybercity.dk][::][Risk: ** Unidirectional Traffic **][Risk Score: 10][Risk Info: No server to client traffic][PLAIN TEXT (cybercity)][Plen Bins: 0,100,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
-	174	UDP 192.168.37.115:2758 -> 128.168.1.1:53 [proto: 5/DNS][IP: 0/Unknown][ClearText][Confidence: Match by port][FPC: 0/Unknown, Confidence: Unknown][DPI packets: 1][cat: Network/14][1 pkts/86 bytes -> 0 pkts/0 bytes][Goodput ratio: 51/0][< 1 sec][::][Risk: ** Malformed Packet **** Unidirectional Traffic **][Risk Score: 20][Risk Info: No server to client traffic / Invalid DNS Header][PLAIN TEXT (cybercity)][Plen Bins: 0,100,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
+	174	UDP 192.168.37.115:2758 -> 128.168.1.1:53 [proto: 5/DNS][IP: 0/Unknown][ClearText][Confidence: Match by port][FPC: 0/Unknown, Confidence: Unknown][DPI packets: 1][cat: Network/14][1 pkts/86 bytes -> 0 pkts/0 bytes][Goodput ratio: 51/0][< 1 sec][::][Risk: ** Unidirectional Traffic **][Risk Score: 10][Risk Info: No server to client traffic][PLAIN TEXT (cybercity)][Plen Bins: 0,100,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
 	175	UDP 192.168.54.2:2829 -> 192.168.1.1:53 [proto: 5/DNS][IP: 0/Unknown][ClearText][Confidence: DPI][FPC: 5/DNS, Confidence: DPI][DPI packets: 1][cat: Network/14][1 pkts/86 bytes -> 0 pkts/0 bytes][Goodput ratio: 51/0][< 1 sec][::][Risk: ** Malformed Packet **** Unidirectional Traffic **][Risk Score: 20][Risk Info: No server to client traffic / Invalid DNS Query Lenght][PLAIN TEXT (cibercity)][Plen Bins: 0,100,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
 	176	UDP 192.168.79.2:2791 -> 192.168.1.1:53 [proto: 5/DNS][IP: 0/Unknown][ClearText][Confidence: DPI][FPC: 5/DNS, Confidence: DPI][DPI packets: 1][cat: Network/14][1 pkts/86 bytes -> 0 pkts/0 bytes][Goodput ratio: 51/0][< 1 sec][Hostname/SNI: _sip._udp.sip.cybercity.dk][::][Risk: ** Unidirectional Traffic **][Risk Score: 10][Risk Info: No server to client traffic][PLAIN TEXT (cybercity)][Plen Bins: 0,100,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
 	177	UDP 192.170.1.2:2810 -> 192.168.1.1:53 [proto: 5/DNS][IP: 0/Unknown][ClearText][Confidence: DPI][FPC: 5/DNS, Confidence: DPI][DPI packets: 1][cat: Network/14][1 pkts/86 bytes -> 0 pkts/0 bytes][Goodput ratio: 51/0][< 1 sec][::][Risk: ** Malformed Packet **** Unidirectional Traffic **][Risk Score: 20][Risk Info: No server to client traffic / Invalid DNS Query Lenght][PLAIN TEXT (cybercity)][Plen Bins: 0,100,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
diff --git a/tests/cfgs/default/result/portable_executable.pcap.out b/tests/cfgs/default/result/portable_executable.pcap.out
index 91130848d..bdcfe5d56 100644
--- a/tests/cfgs/default/result/portable_executable.pcap.out
+++ b/tests/cfgs/default/result/portable_executable.pcap.out
@@ -29,7 +29,7 @@ DNS	15	12154	1
 Acceptable                      15 12154         1            
 Unrated                         15 12160         1            
 
-	1	TCP 64.227.107.71:53 <-> 172.16.99.10:49652 [proto: 5/DNS][IP: 0/Unknown][ClearText][Confidence: Match by port][FPC: 0/Unknown, Confidence: Unknown][DPI packets: 15][cat: Network/14][11 pkts/11914 bytes <-> 4 pkts/240 bytes][Goodput ratio: 95/0][0.37 sec][::][bytes ratio: 0.961 (Upload)][IAT c2s/s2c min/avg/max/stddev: 0/0 40/182 362/364 114/182][Pkt Len c2s/s2c min/avg/max/stddev: 58/60 1083/60 1310/60 481/0][Risk: ** Binary App Transfer **** Malformed Packet **** Susp Entropy **][Risk Score: 170][Risk Info: Invalid DNS Header / Portable Executable (PE32/PE32+) found / Entropy: 5.990 (Executable?)][PLAIN TEXT (This program cannot be run in D)][Plen Bins: 10,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,90,0,0,0,0,0,0,0,0]
+	1	TCP 64.227.107.71:53 <-> 172.16.99.10:49652 [proto: 5/DNS][IP: 0/Unknown][ClearText][Confidence: Match by port][FPC: 0/Unknown, Confidence: Unknown][DPI packets: 15][cat: Network/14][11 pkts/11914 bytes <-> 4 pkts/240 bytes][Goodput ratio: 95/0][0.37 sec][::][bytes ratio: 0.961 (Upload)][IAT c2s/s2c min/avg/max/stddev: 0/0 40/182 362/364 114/182][Pkt Len c2s/s2c min/avg/max/stddev: 58/60 1083/60 1310/60 481/0][Risk: ** Binary App Transfer **** Susp Entropy **][Risk Score: 160][Risk Info: Portable Executable (PE32/PE32+) found / Entropy: 5.990 (Executable?)][PLAIN TEXT (This program cannot be run in D)][Plen Bins: 10,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,90,0,0,0,0,0,0,0,0]
 
 
 Undetected flows: