WIP: dbg DNS over TCP NA fields

Signed-off-by: Mohamed Mahmoud <[email protected]>

bpf/dns_tracker.h

@@ -9,6 +9,7 @@
 #define DNS_PORT        53
 #define DNS_QR_FLAG     0x8000
 #define UDP_MAXMSG      512
+#define EINVAL          22
 
 struct dns_header {
     u16 id;
@@ -71,13 +72,19 @@ static __always_inline void track_dns_packet(struct __sk_buff *skb, pkt_info *pk
 
         u8 len = calc_dns_header_offset(pkt, data_end);
         if (!len) {
+            pkt->dns_errno = EINVAL;
             return;
         }
 
         struct dns_header dns;
+        int ret;
         u32 dns_offset = (long)pkt->l4_hdr - (long)skb->data + len;
+        pkt->dns_offset = dns_offset;
+        pkt->dns_tcp_len = len;
+        pkt->dns_skb_len = skb->len;
 
-        if (bpf_skb_load_bytes(skb, dns_offset, &dns, sizeof(dns)) < 0) {
+        if ((ret = bpf_skb_load_bytes(skb, dns_offset, &dns, sizeof(dns))) < 0) {
+            pkt->dns_errno = -ret;
             return;
         }
 
@@ -97,6 +104,7 @@ static __always_inline void track_dns_packet(struct __sk_buff *skb, pkt_info *pk
                 pkt->dns_latency = ts - *value;
                 pkt->dns_id = dns_id;
                 pkt->dns_flags = flags;
+                pkt->dns_errno = ret;
                 bpf_map_delete_elem(&dns_flows, &dns_req);
              }
         } // end of dns response

bpf/flows.c

@@ -97,6 +97,10 @@ static inline int flow_monitor(struct __sk_buff *skb, u8 direction) {
         aggregate_flow->dns_record.id = pkt.dns_id;
         aggregate_flow->dns_record.flags = pkt.dns_flags;
         aggregate_flow->dns_record.latency = pkt.dns_latency;
+        aggregate_flow->dns_record.errno = pkt.dns_errno;
+        aggregate_flow->dns_record.offset = pkt.dns_offset;
+        aggregate_flow->dns_record.tcp_len = pkt.dns_tcp_len;
+        aggregate_flow->dns_record.skb_len = pkt.dns_skb_len;
         long ret = bpf_map_update_elem(&aggregated_flows, &id, aggregate_flow, BPF_ANY);
         if (trace_messages && ret != 0) {
             // usually error -16 (-EBUSY) is printed here.
@@ -119,6 +123,10 @@ static inline int flow_monitor(struct __sk_buff *skb, u8 direction) {
             .dns_record.id = pkt.dns_id,
             .dns_record.flags = pkt.dns_flags,
             .dns_record.latency = pkt.dns_latency,
+            .dns_record.errno = pkt.dns_errno,
+            .dns_record.offset = pkt.dns_offset,
+            .dns_record.tcp_len = pkt.dns_tcp_len,
+            .dns_record.skb_len = pkt.dns_skb_len,
         };
 
         // even if we know that the entry is new, another CPU might be concurrently inserting a flow

bpf/types.h

@@ -89,6 +89,10 @@ typedef struct flow_metrics_t {
         u16 id;
         u16 flags;
         u64 latency;
+        u8 errno;
+        u32 offset;
+        u32 tcp_len;
+        u32 skb_len;
     } __attribute__((packed)) dns_record;
     u64 flow_rtt;
 } __attribute__((packed)) flow_metrics;
@@ -162,6 +166,10 @@ typedef struct pkt_info_t {
     u16 dns_id;
     u16 dns_flags;
     u64 dns_latency;
+    u8 dns_errno;
+    u32 dns_offset;
+    u32 dns_tcp_len;
+    u32 dns_skb_len;
 } pkt_info;
 
 // Structure for payload metadata

pkg/flow/record_test.go

@@ -43,6 +43,10 @@ func TestRecordBinaryEncoding(t *testing.T) {
 		01, 00, // id
 		0x80, 00, // flags
 		0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, // latency
+		0x00,       // errno
+		0, 0, 0, 0, // dns offset
+		0, 0, 0, 0, // tcp len
+		0, 0, 0, 0, // skb len
 		// u64 flow_rtt
 		0xad, 0xde, 0xef, 0xbe, 0xef, 0xbe, 0xad, 0xde,
 	}))
@@ -82,6 +86,10 @@ func TestRecordBinaryEncoding(t *testing.T) {
 				Id:      0x0001,
 				Flags:   0x0080,
 				Latency: 0x1817161514131211,
+				Errno:   0,
+				Offset:  0,
+				TcpLen:  0,
+				SkbLen:  0,
 			},
 			FlowRtt: 0xdeadbeefbeefdead,
 		},