Update project

src/common.h

@@ -28,6 +28,12 @@ struct event {
     char ans[32];
 };
 
+struct query_section{
+    char qname[QNAME_SIZE];
+    int class;
+    int type;
+};
+
 struct dns_answer {
     uint16_t tid;
     char qname[QNAME_SIZE];

src/dns-trace.ebpf.c

@@ -35,22 +35,59 @@ struct {
     __type(value, struct dns_answer);
 } m_tid SEC(".maps");
 
+static size_t get_labels(struct __sk_buff *skb, size_t offset, size_t end, struct event *s_event, struct query_section *s_query){
+    size_t len;
+    unsigned char buf[256];
+    unsigned char *c;
+    int index = 0;
+    int qname_len = 0; // Full length of the qname field
+
+    bpf_skb_load_bytes(skb, offset, &buf, 41);
+    c = buf;
+
+    while (*(c++) != '\0') {
+        if(*c >= 'a' && *c <= 'z')
+            s_event->qname[index] = *c;
+        else if(*c >= 'A' && *c <= 'Z')
+            s_event->qname[index] = *c;
+        else
+            s_event->qname[index] = '.';
+        index++;
+        qname_len++;
+    }
+    s_event->qname[--index] = '\0';
+    qname_len++; // For the null character
+
+    return len;
+}
 
 /*
  * This function get the query field and the return the length of it
  */
-static size_t get_query(struct __sk_buff *skb, struct event *s_event, uint16_t *class, uint16_t *type, size_t tlen){
+//static size_t get_query_section(struct __sk_buff *skb, struct event *s_event, uint16_t *class, uint16_t *type, uint8_t tlen){
+static size_t get_query_section(struct __sk_buff *skb, struct event *s_event, struct query_section *s_query, uint8_t offset){
     size_t len;
-    char buf[QNAME_SIZE] = {0};
+    char buf[256] = {0};
     int index = 0;
     int qname_len = 0; // Full length of the qname field
     char qname[QNAME_SIZE] = {0};
     char *c;
+    uint8_t flen = skb->len;
+    /*
+        We get the size for the buffer
+        We substract the full size of the buffer (skb->len) with the sizes of each headers (eth + ip + udp + dns header)
+     */
+    uint8_t l = flen - offset; 
+   
+    if (l < 0)
+        return 0;
 
-    
-    bpf_skb_load_bytes(skb, tlen, &buf, 41);
+    //bpf_skb_load_bytes(skb, tlen, &buf, l);
+    bpf_skb_load_bytes(skb, offset, &buf, 41);
     c = buf;
 
+    // get_labels(struct __sk_buff *skb, size_t offset, size_t end, struct event *s_event, struct query_section *s_query)
+    // get_labels(skb, offset, 41, s_event, s_query);
     /*
      * The qname is composed by a the number of bytes then follow by the label
      * For instance, for the qname www.bucchino.org,
@@ -72,18 +109,35 @@ static size_t get_query(struct __sk_buff *skb, struct event *s_event, uint16_t *
     }
     s_event->qname[--index] = '\0';
     qname_len++; // For the null character
-    bpf_printk("%s (%d) %d", s_event->qname, index, qname_len);
+    // bpf_printk("l: %d", l);
 
     // Get class and type
     len = qname_len;
-    bpf_skb_load_bytes(skb, tlen + qname_len, type, sizeof(uint16_t));
+    bpf_skb_load_bytes(skb, offset + qname_len, &s_query->type, sizeof(uint16_t));
     len += 2;
-    bpf_skb_load_bytes(skb, tlen + qname_len + 2, class, sizeof(uint16_t));
+    bpf_skb_load_bytes(skb, offset + qname_len + 2, &s_query->class, sizeof(uint16_t));
     len += 2;
 
     return len;
 }
+static size_t get_answer(struct __sk_buff *skb, struct event *s_event, size_t tlen){
+    size_t len = 0;
+    unsigned char buf[256] = {0}; // Need to be unsigned, otherwise, the result is fffff
 
+    if(bpf_skb_load_bytes(skb, tlen, &buf, 2) < 0)
+        return 0;
+    /*
+     * According to the RFC 1035 (https://datatracker.ietf.org/doc/html/rfc1035#section-4.1.4)
+     * In the section 4.1.4, message compression, the first two bits are set at 11 (0xc),
+     * that's means, it's a pointer.
+     * For instance, the two bytes 0xc00c, 0xc it's the pointer and 0x00c is the position in the DNS header
+     */
+    if (buf[0] == 0xc0){
+        bpf_printk("Pointer to %x", buf[1]);
+    }
+
+    return len;
+}
 /*
  * https://datatracker.ietf.org/doc/html/rfc1035
  */
@@ -91,8 +145,7 @@ static int dnsquery(struct __sk_buff *skb, struct ethhdr eth, struct iphdr ip, s
     struct event *s_event;
     struct dnshdr dns = {0};
     char saddr[32];
-    uint16_t class, type;
-    //struct dns_answer s_dnsanswer;
+    struct query_section s_query = {0};
     // bpf_printk("udp len: %d", ntohs(udp.len));
 
     s_event = bpf_ringbuf_reserve(&m_data, sizeof(*s_event), 0);
@@ -105,6 +158,15 @@ static int dnsquery(struct __sk_buff *skb, struct ethhdr eth, struct iphdr ip, s
     /* Get DNS header */
     bpf_skb_load_bytes(skb, sizeof(struct ethhdr) + sizeof(struct iphdr) + sizeof(struct udphdr), &dns, sizeof(struct dnshdr));
 
+    // Check OpCode
+    uint16_t flags = ntohs(dns.flags);
+    uint16_t qr = flags & 0xF000; // Get the QR code: 0 -> query, 1 -> response
+    if (qr == 0x0)
+        bpf_printk("Query");
+    else if(qr == 0x8000)
+        bpf_printk("Response");
+    bpf_printk("Flags: %x %x", flags, qr);
+
     if (ntohs(dns.nbQuestions) == 0){
         bpf_ringbuf_discard(s_event, 0);
         return 0;
@@ -123,14 +185,15 @@ static int dnsquery(struct __sk_buff *skb, struct ethhdr eth, struct iphdr ip, s
 
 
     /* Get the query structure */
-    size_t tlen = sizeof(struct ethhdr) + sizeof(struct iphdr) + sizeof(struct udphdr) + sizeof(struct dnshdr);
-    size_t query_len = get_query(skb, s_event, &class, &type, tlen);
+    uint8_t tlen = sizeof(struct ethhdr) + sizeof(struct iphdr) + sizeof(struct udphdr) + sizeof(struct dnshdr);
+    // size_t query_len = get_query_section(skb, s_event, &class, &type, tlen);
+    size_t query_len = get_query_section(skb, s_event, &s_query, tlen);
 
     // https://docs.cilium.io/en/stable/reference-guides/bpf/progtypes/
     s_event->dport = dport;
     s_event->sport = sport;
-    s_event->class = ntohs(class);
-    s_event->type = ntohs(type);
+    s_event->class = ntohs(s_query.class);
+    s_event->type = ntohs(s_query.type);
     //if(bpf_probe_read_user_str(&s_event->qname, sizeof(s_event->qname), qname) < 0)
     //    bpf_printk("Failed to copy qname");
 
@@ -146,14 +209,26 @@ static int dnsanswer(struct __sk_buff *skb, struct ethhdr eth, struct iphdr ip,
     struct dnshdr dns = {0};
     uint16_t tid = 0;
     struct dns_answer s_dnsanswer;
-
-    /* Get DNS header */
-    bpf_skb_load_bytes(skb, sizeof(struct ethhdr) + sizeof(struct iphdr) + sizeof(struct udphdr), &dns, sizeof(struct dnshdr));
+    struct query_section s_query = {0};
 
     s_event = bpf_ringbuf_reserve(&m_data, sizeof(*s_event), 0);
     if (!s_event)
        return 0;
 
+    /* Get DNS header */
+    bpf_skb_load_bytes(skb, sizeof(struct ethhdr) + sizeof(struct iphdr) + sizeof(struct udphdr), &dns, sizeof(struct dnshdr));
+
+    // Check OpCode
+    uint16_t flags = ntohs(dns.flags);
+    uint16_t qr = flags & 0xF000; // Get the QR code: 0 -> query, 1 -> response
+    if (qr == 0x0){} // Query
+    else if(qr == 0x8000){} // Response
+
+    if (ntohs(dns.nbQuestions) == 0 && ntohs(dns.nbAnswerRRs)){
+        bpf_ringbuf_discard(s_event, 0);
+        return 0;
+    }
+
     /* Get the Transaction ID */
     tid = ntohs(dns.transactionID);
     bpf_printk("tid: %x", tid);
@@ -176,13 +251,19 @@ static int dnsanswer(struct __sk_buff *skb, struct ethhdr eth, struct iphdr ip,
      */
 
     /* Get the query response */
-    size_t tlen = sizeof(struct ethhdr) + sizeof(struct iphdr) + sizeof(struct udphdr) + sizeof(struct dnshdr);
+    uint8_t tlen = sizeof(struct ethhdr) + sizeof(struct iphdr) + sizeof(struct udphdr) + sizeof(struct dnshdr);
     uint16_t class, type;
-    size_t query_len = get_query(skb, s_event, &class, &type, tlen);
+    // size_t query_len = get_query_section(skb, s_event, &class, &type, tlen);
+    size_t query_len = get_query_section(skb, s_event, &s_query, tlen);
     bpf_printk("answer qname: %s", s_event->qname);
+    s_event->dport = dport;
+    s_event->sport = sport;
+    s_event->class = ntohs(class);
+    s_event->type = ntohs(type);
 
     /* Get the answer */
-
+    tlen += query_len;
+    size_t answer_len = get_answer(skb, s_event, tlen);
     bpf_ringbuf_submit(s_event, 0);
     
     return 0;