update

.gitignore

@@ -0,0 +1,2 @@
+src/**.swp
+**.log

Makefile

@@ -7,7 +7,7 @@ LIBS=-L../libbpf/src -l:libbpf.a -lelf -lz
 all: dns-trace.ebpf.o dns-trace
 
 dns-trace.ebpf.o: src/dns-trace.ebpf.c
-	$(CL) -g -O2 -target bpf -D __TARGET_ARCH_x86_64 -D __BPF_TRACING__ -L../libbpf/src -l:libbpf.a -c src/dns-trace.ebpf.c -o src/dns-trace.ebpf.o
+	$(CL) -Wall -g -O2 -target bpf -D __TARGET_ARCH_x86_64 -D __BPF_TRACING__ -c src/dns-trace.ebpf.c -o src/dns-trace.ebpf.o
 
 dns-trace: src/dns-trace.c
 	$(GCC) $(CFLAGS) src/dns-trace.c -o dns-trace $(LIBS)

exec.sh

@@ -1,6 +1,6 @@
 #!/usr/bin/sh
 
 
-sudo bpftool btf dump file /sys/kernel/btf/vmlinux format c > src/vmlinux.h
+#sudo bpftool btf dump file /sys/kernel/btf/vmlinux format c > src/vmlinux.h
 make clean
-make all && sudo ./dns-trace
+make all && sudo ./dns-trace -i wlp0s20f3 -f dns-trace_`$(echo date '+%F')`.log

src/common.h

@@ -32,18 +32,4 @@ struct event {
     unsigned char buf[MAX_UDP_PAYLOAD]; // On stocke la data au format size + data
 };
 
-struct query_section{
-    char qname[QNAME_SIZE];
-    size_t qname_len;
-    uint16_t class;
-    uint16_t type;
-};
-
-struct dns_answer {
-    char data[512];
-    uint16_t class;
-    uint16_t type;
-    uint32_t ttl;
-};
-
 #endif

src/dns-trace.c

@@ -9,6 +9,7 @@
 #include <string.h>
 #include <signal.h>
 #include <unistd.h>
+#include <time.h>
 #include <fcntl.h>
 #include <net/if.h> /* if_nametoindex */
 #include <linux/if_ether.h>
@@ -17,10 +18,15 @@
 
 #include "common.h"
 
+/* Global variables */
 static struct arguments arguments;
 static int running = 1;
+static FILE *f;
+static char hostname[127];
+
 
 struct arguments {
+    char *interface;
     char *filename;
     int to_output;
 };
@@ -31,7 +37,7 @@ struct arguments {
  */
 
 static char doc[] = "DNS Trace usage:";
-static char args_doc[] = "ARG1 ARG2";
+static char args_doc[] = "[ARGS]";
 
 static error_t parse_opts(int key, char *arg, struct argp_state *state){
     struct arguments *arguments = state->input;
@@ -40,6 +46,9 @@ static error_t parse_opts(int key, char *arg, struct argp_state *state){
             arguments->filename = arg;
             arguments->to_output = 0;
             break;
+        case 'i':
+            arguments->interface = arg;
+            break;
         case 'o':
             arguments->to_output = 1;
             break;
@@ -56,12 +65,14 @@ static error_t parse_opts(int key, char *arg, struct argp_state *state){
 
 struct arguments parse_args(int argc, char *argv[]){
     static const struct argp_option opts[] = {
+        {"interface", 'i', "INTERFACE", 0, "Ifname for listening"},
         {"filename", 'f', "FILENAME", 0, "Save result to logs"},
         {"to-output", 'o', NULL, 0, "Print to output"},
         {NULL, 'h', NULL, OPTION_HIDDEN, "help"},
         {},
     };
     struct arguments arguments;
+    arguments.interface = NULL;
     arguments.filename = NULL;
     arguments.to_output = 1;
     static struct argp argp = {opts, parse_opts, args_doc, doc};
@@ -75,9 +86,10 @@ struct arguments parse_args(int argc, char *argv[]){
 static void signalHandler(int signum){
     running = 0;
 }
-
-static int open_raw_sock(const char *name)
-{
+/*
+ * This function create a raw socket and bind it to the ifname
+ */
+static int create_rsock(const char *name) {
 	struct sockaddr_ll sll;
 	int sock;
 
@@ -92,7 +104,6 @@ static int open_raw_sock(const char *name)
 	sll.sll_ifindex = if_nametoindex(name);
 	sll.sll_protocol = htons(ETH_P_ALL);
 	if (bind(sock, (struct sockaddr *)&sll, sizeof(sll)) < 0) {
-		//printf("bind to %s: %s\n", name, strerror(errno));
         printf("Failed to bind the interface %s\n", name);
 		close(sock);
 		return -1;
@@ -101,6 +112,9 @@ static int open_raw_sock(const char *name)
 	return sock;
 }
 
+/*
+ * This function map the type of DNS request 
+ */
 static char *mapReqType(const int req){
     char *tmp = malloc(8);
     if (tmp == NULL)
@@ -118,6 +132,9 @@ static char *mapReqType(const int req){
     };
     return tmp;
 }
+/*
+ * This function map the DNS class RR
+ */
 static char *mapClass(const int class){
     char *tmp = malloc(8);
     if (tmp == NULL)
@@ -143,6 +160,9 @@ static char *mapClass(const int class){
     }
     return tmp;
 }
+/*
+ * This function map the DNS type RR
+ */
 static char *mapType(const int type){
     char *tmp = malloc(8);
     if (tmp == NULL)
@@ -212,16 +232,43 @@ static char *mapType(const int type){
     return tmp;
 }
 
+/*
+ * This function get the localtime into the rsyslog format
+ */
+static int syslog_time(time_t ts, char t[32], size_t l){
+    const char format[] = "%b %d %T";
+    struct tm *lt = localtime(&ts);
+    if(strftime(t, l, format, lt) == 0)
+        return -1;
+    return 0;
+}
+/*
+ * This function get the hostname of the system
+ * If not find, the hostname is ubuntu
+ */
+static void get_hostname(){
+    /* Get the hostname */
+    if (gethostname(hostname, 127) == -1){
+        printf("Failed to get the hostname\n");
+        strncpy(hostname, "ubuntu", 7);
+    }
+}
+/*
+ * This function print to the stdout the query section
+ */
 static void print_query(struct event *s_event){
     char *req_type, *class, *type;
-    printf("%s:%-10d", inet_ntoa(*(struct in_addr*)&s_event->client), s_event->dport);
-    printf("%-5x", s_event->tid);
+    char t[32];
+    time_t ts = time(NULL);
+    syslog_time(ts, t, sizeof(t));
+    printf("%-20s", t);
 
     req_type = mapReqType(s_event->req_type);
-    printf("%-10s", req_type);
+    printf("%s ", req_type);
     free(req_type);
 
-    printf("%-30s", s_event->qname);
+    printf("%5s:%d\t", inet_ntoa(*(struct in_addr*)&s_event->client), s_event->dport);
+    printf("%x\t", s_event->tid);
 
     class = mapClass(s_event->class);
     printf("%-5s", class);
@@ -231,7 +278,68 @@ static void print_query(struct event *s_event){
     printf("%-5s", type);
     free(type);
 
+    printf("%s", s_event->qname);
+    printf("\n");
 }
+/*
+ * This function save to rsyslog file the common information
+ */
+static void header_to_log(struct event *s_event){
+    char t[32];
+    char tid[12];
+    char src[40];
+    char *req_type;
+    time_t ts = time(NULL);
+
+    if (syslog_time(ts, t, sizeof(t)) == 0)
+        fwrite(t, strlen(t), 1, f);
+
+    fwrite(" ", 1, 1, f);
+    fwrite(hostname, strlen(hostname), 1, f);
+
+    fwrite(" dns-trace: ", 12, 1, f);
+    fwrite("<info> ", 7, 1, f);
+
+    req_type = mapReqType(s_event->req_type);
+    fwrite(req_type, strlen(req_type), 1, f);
+    free(req_type);
+    fwrite(";", 1, 1, f);
+
+    snprintf(tid, 12, "tid=%x;", s_event->tid);
+    fwrite(tid, strlen(tid), 1, f);
+
+    snprintf(src, 40, "%s:%d;", inet_ntoa(*(struct in_addr*)&s_event->client), s_event->dport);
+    fwrite(src, strlen(src), 1, f);
+}
+/*
+ * This function save to log file the query section in rsylog format
+ * <time> <hostname> <procname>: <info> <data>
+ */
+static void query_to_log(struct event *s_event){
+    char *class, *type;
+    char s_class[16], s_type[16];
+
+    header_to_log(s_event);
+
+
+    class = mapClass(s_event->class);
+    snprintf(s_class, 16, "class=%s;", class);
+    fwrite(s_class, strlen(s_class), 1, f);
+    free(class);
+
+    type = mapType(s_event->type);
+    snprintf(s_type, 16, "type=%s;", type);
+    fwrite(s_type, strlen(s_type), 1, f);
+    free(type);
+
+    fwrite("domain=", 7, 1, f);
+    fwrite(s_event->qname, strlen(s_event->qname), 1, f);
+
+    fwrite(";\n", 2, 1, f);
+}
+/*
+ * This function get labels from DNS answer
+ */
 static void get_labels(unsigned char *buf, char *qname){
     int pos = 0;
     while (*buf++ != '\0') {
@@ -245,67 +353,190 @@ static void get_labels(unsigned char *buf, char *qname){
     }
     qname[pos - 1] = '\0';
 }
+/*
+ * This function read the event buf which contains the DNS answer section
+ */
+static void get_answer(struct event *s_event, uint16_t *class, uint16_t *type, uint16_t *size, uint32_t *ttl, int *pos){
+    int p = *pos;
+
+    *type = s_event->buf[p++];
+    *type |= s_event->buf[p++] << 8;
+
+    *class = s_event->buf[p++];
+    *class |= s_event->buf[p++] << 8;
+
+    *ttl = s_event->buf[p++];
+    *ttl |= s_event->buf[p++] << 8;
+    *ttl |= s_event->buf[p++] << 16;
+    *ttl |= s_event->buf[p++] << 24;
+
+    *size = s_event->buf[p++];
+    *size |= s_event->buf[p++] << 8;
+
+    *pos = p;
+}
+/*
+ * This function save to rsyslog format the answer section
+ */
+static void answer_to_log(struct event *s_event){
+    int pos = 0;
+    for (int i = 0; i < s_event->numAns; i++){
+        char *s_class, *s_type;
+        uint16_t i_type, i_class, i_size;
+        uint32_t i_ttl;
+        char b_class[16], b_type[16], b_ttl[16];
+        /*
+         * 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 (11) it's the pointer and 0x00c is the position in the DNS header
+         */
+        uint16_t msg = s_event->buf[pos++];
+        msg |= s_event->buf[pos++] << 8;
+
+        header_to_log(s_event);
+
+        get_answer(s_event, &i_class, &i_type, &i_size, &i_ttl, &pos);
+
+        i_type = ntohs(i_type);
+        i_class = ntohs(i_class);
+        i_ttl = ntohl(i_ttl);
+        i_size = ntohs(i_size);
+
+        s_class = mapClass(i_class);
+        snprintf(b_class, 16, "class=%s;", s_class);
+        fwrite(b_class, strlen(b_class), 1, f);
+        free(s_class);
+
+        s_type = mapType(i_type);
+        snprintf(b_type, 16, "type=%s;", s_type);
+        fwrite(b_type, strlen(b_type), 1, f);
+        free(s_type);
+
+        snprintf(b_ttl, 16, "ttl=%d;", i_ttl);
+        fwrite(b_ttl, strlen(b_ttl), 1, f);
+
+        // Decode data
+        if (i_type == 1) { // -> A
+            uint32_t ip = s_event->buf[pos] + (s_event->buf[pos+1] << 8) + (s_event->buf[pos+2] << 16) + (s_event->buf[pos+3] << 24);
+            char s_ip[36];
+            snprintf(s_ip, 36, "ip=%s;", inet_ntoa(*(struct in_addr*)&ip));
+            fwrite(s_ip, strlen(s_ip), 1, f);
+        }
+        if (i_type == 5) { // -> CNAME
+            char cname[i_size];
+            char buf[i_size + 7]; // 7 -> cname=;
+            get_labels(s_event->buf + pos, cname);
+            snprintf(buf, i_size + 7, "cname=%s;", cname);
+            fwrite(buf, strlen(buf), 1, f);
+        }
+        if (i_type == 28){ // -> AAAA
+            char buf[128];
+            snprintf(buf, 128, "ipv6=%x%x:%x%x:%x%x:%x%x:%x%x:%x%x:%x%x:%x%x;", 
+                s_event->buf[pos], s_event->buf[pos + 1],
+                s_event->buf[pos + 2], s_event->buf[pos + 3],
+                s_event->buf[pos + 4], s_event->buf[pos + 5],
+                s_event->buf[pos + 6], s_event->buf[pos + 7],
+                s_event->buf[pos + 8], s_event->buf[pos + 9],
+                s_event->buf[pos + 10], s_event->buf[pos + 11],
+                s_event->buf[pos + 12], s_event->buf[pos + 13],
+                s_event->buf[pos + 14], s_event->buf[pos + 15]);
+            fwrite(buf, strlen(buf), 1, f);
+        }
+
+        pos += i_size;
+
+        fwrite("\n", 1, 1, f);
+    }
+}
+/*
+ * This function print to the stdout the answer section
+ */
+static void print_answer(struct event *s_event){
+    char *req_type;
+    int pos = 0;
+    char t[32];
+    time_t ts = time(NULL);
+
+    for (int i = 0; i < s_event->numAns; i++){
+        uint16_t type, class, size;
+        char *s_type, *s_class;
+        uint32_t ttl;
+        uint16_t msg = s_event->buf[pos++];
+        msg |= s_event->buf[pos++] << 8;
+
+        /* Print answer hdr */
+        syslog_time(ts, t, sizeof(t));
+        printf("%-20s", t);
+
+        req_type = mapReqType(s_event->req_type);
+        printf("%s ", req_type);
+        free(req_type);
+
+        printf("%5s:%5d\t", inet_ntoa(*(struct in_addr*)&s_event->client), s_event->dport);
+        printf("%x\t", s_event->tid);
+
+        get_answer(s_event, &class, &type, &size, &ttl, &pos);
+
+        type = ntohs(type);
+        class = ntohs(class);
+        ttl = ntohl(ttl);
+        size = ntohs(size);
+
+        /* Print answer data */
+        s_class = mapClass(class);
+        printf("%-5s", s_class);
+        free(s_class);
+
+        s_type = mapType(type);
+        printf("%s\t", s_type);
+        free(s_type);
+
+        if (type == 1) { // -> A
+            uint32_t ip = s_event->buf[pos] + (s_event->buf[pos+1] << 8) + (s_event->buf[pos+2] << 16) + (s_event->buf[pos+3] << 24);
+            printf("%s %5d", inet_ntoa(*(struct in_addr*)&ip), ttl);
+        }
+        if (type == 5) { // -> CNAME
+            char cname[size];
+            get_labels(s_event->buf + pos, cname);
+            printf("%s %d ", cname, ttl);
+        }
+        if (type == 28){ // -> AAAA
+            for (int i = 0; i < size; i++){
+                if (i % 2 == 0)
+                    printf("%x", s_event->buf[pos]);
+                else{
+                    if (i < (size - 1))
+                        printf("%x:", s_event->buf[pos]);
+                    else
+                        printf("%x", s_event->buf[pos]);
+                }
+                pos++;
+            }
+            printf(" %d ", ttl);
+        }
+        pos += size;
+        printf("\n");
+    }
+}
+/*
+ * This function is called when a new event is pushed in the ring buffer from the eBPf program
+ */
 int handle_event(void *ctx, void *data, size_t data_sz){
     struct event *s_event = (struct event*)data;
     if (s_event->req_type == REQ_QUERY){
-        print_query(s_event);
+        if (arguments.to_output == 1)
+            print_query(s_event);
+        if (arguments.filename != NULL && f != NULL)
+            query_to_log(s_event);
     }
     if (s_event->req_type == REQ_ANSWER){
-        int pos = 0;
-        /*for (int i = 0; i < 50; i++)
-            printf("%d ", s_event->buf[i]);
-        printf("\n");*/
-        for (int i = 0; i < s_event->numAns; i++){
-            print_query(s_event);
-
-            uint16_t msg = s_event->buf[pos++];
-            msg |= s_event->buf[pos++] << 8;
-
-            uint16_t type = s_event->buf[pos++];
-            type |= s_event->buf[pos++] << 8;
-            uint16_t class = s_event->buf[pos++];
-            class |= s_event->buf[pos++] << 8;
-
-            uint32_t ttl = s_event->buf[pos++];
-            ttl |= s_event->buf[pos++] << 8;
-            ttl |= s_event->buf[pos++] << 16;
-            ttl |= s_event->buf[pos++] << 24;
-            uint16_t size = s_event->buf[pos++];
-            size |= s_event->buf[pos++] << 8;
-
-            type = ntohs(type);
-            class = ntohs(class);
-            ttl = ntohl(ttl);
-            size = ntohs(size);
-            if (type == 1) { // -> A
-                uint32_t ip = s_event->buf[pos] + (s_event->buf[pos+1] << 8) + (s_event->buf[pos+2] << 16) + (s_event->buf[pos+3] << 24);
-                printf("%s (%d)%5d", inet_ntoa(*(struct in_addr*)&ip), type, ttl);
-            }
-            if (type == 5) { // -> CNAME
-                char cname[size];
-                get_labels(s_event->buf + pos, cname);
-                printf("%s ", cname);
-            }
-            if (type == 28){ // -> AAAA
-                int p = 0;
-                for (int i = 0; i < size; i++){
-                    if (i % 2 == 0)
-                        printf("%x", s_event->buf[pos + p++]);
-                    else{
-                        if (i<size - 1)
-                            printf("%x:", s_event->buf[pos + p++]);
-                        else
-                            printf("%x", s_event->buf[pos + p++]);
-                    }
-                }
-            }
-            pos += size;
-            printf("\n");
-        }
+        if (arguments.to_output == 1)
+            print_answer(s_event);
+        if (arguments.filename != NULL && f != NULL)
+            answer_to_log(s_event);
     }
 
-    printf("\n");
-    
     return 0;
 }
 int main(int argc, char *argv[]){
@@ -315,9 +546,31 @@ int main(int argc, char *argv[]){
     struct ring_buffer *rb;
     int err;
     int fd_map_data;
+    int sock;
 
     arguments = parse_args(argc, argv); // Parsing arguments
 
+    if (arguments.interface == NULL){
+        printf("You must specified the interface name\n");
+        exit(-1);
+    }
+    printf("Listen to %s\n", arguments.interface);
+
+    sock = create_rsock(arguments.interface);
+    if (sock == -1){
+        printf("Failed to listen to the interface %s\n", arguments.interface);
+        exit(-1);
+    }
+
+    if (arguments.filename != NULL){
+        f = fopen(arguments.filename, "a");
+        if (f == NULL){
+            printf("Failed to create the file %s\n", arguments.filename);
+            return -1;
+        }
+        printf("Save to %s\n", arguments.filename);
+    }
+
     signal(SIGINT, signalHandler);
 
     /* Open and load our eBPF object */
@@ -351,14 +604,13 @@ int main(int argc, char *argv[]){
     }
 
     bpf_program__attach(programSkb);
-    // int sock = open_raw_sock("wlp0s20f3");
-    //int sock = open_raw_sock("enx98e743c667fc");
-    int sock = open_raw_sock("lo");
-    printf("Socket: %d\n", sock);
     int prog_fd = bpf_program__fd(programSkb);
-    printf("Program fd: %d\n", prog_fd);
+
     setsockopt(sock, SOL_SOCKET, SO_ATTACH_BPF, &prog_fd, sizeof(int));
 
+    /* Get the hostname of the system */
+    get_hostname();
+
     /* Start the ringbuffer */
     rb = ring_buffer__new(fd_map_data, handle_event, NULL, NULL);
     if (!rb){
@@ -376,6 +628,9 @@ int main(int argc, char *argv[]){
          }
     }
 
+    if (f != NULL)
+        fclose(f);
+
     ring_buffer__free(rb);
     bpf_object__close(obj);
 

src/dns-trace.ebpf.c

@@ -16,14 +16,6 @@
 #include "common.h"
 
 
-/*
- * Helper:
- * Issue: invalid indirect read from stack R2 off
- *   Fix: check if all variables is initialised
- * Issue: R1 invalid mem access 'inv'
- *   Fix: the value can be NULL
- */
-
 struct {
     __uint(type, BPF_MAP_TYPE_RINGBUF);
     __uint(max_entries, 256 * 1024 /* 256kb */);
@@ -47,7 +39,7 @@ static size_t get_labels(struct __sk_buff *skb, size_t offset, struct event *s_e
     while (c != '\0') {
         bpf_skb_load_bytes(skb, offset + pos++, &c, 1);
 
-        if(c >= 'a' && c <= 'z' || c >= 'A' && c <= 'Z')
+        if((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z'))
             s_event->qname[qname_len] = c;
         else if(c >= '0' && c <= '9')
             s_event->qname[qname_len] = c;
@@ -59,8 +51,6 @@ static size_t get_labels(struct __sk_buff *skb, size_t offset, struct event *s_e
     }
     s_event->qname[qname_len - 1] = '\0';
     qname_len++;
-    // dquery->qname_len = qname_len;
-    // bpf_printk("qname: %s", s_event->qname);
     // bpf_printk("qname len: %d", qname_len);
     return qname_len;
 }
@@ -87,91 +77,19 @@ static size_t get_query_section(struct __sk_buff *skb, struct event *s_event, ui
 
     return len;
 }
-static unsigned int get_answer(struct __sk_buff *skb, struct event *s_event, size_t tlen, unsigned int index){
-    unsigned char buf[2] = {0}; // Need to be unsigned, otherwise, the result is fffff
-    unsigned int offset = index;
-
-    // Get the 2 first bytes to identify if it's a message compression or not
-    if(bpf_skb_load_bytes(skb, tlen, &buf, 2) < 0)
-        return 0;
-    tlen += 2; // For the message compression
-
-    /*
-     * 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 (11) it's the pointer and 0x00c is the position in the DNS header
-     */
-    if (buf[0] == 0xc0){
-        /*
-         * I cannot read the labels, because the eBPF verifier considerate as a infinity loop
-         */
-
-        /* 
-         * According to the RFC 1035, the structure of answer is like that:
-         * https://datatracker.ietf.org/doc/html/rfc1035#section-4.1.3
-         */
-
-        // Get the class and type
-        if ((void*)(offset) >= MAX_UDP_PAYLOAD - sizeof(uint16_t))
-            return 0;
-
-        bpf_skb_load_bytes(skb, tlen, s_event->buf + offset, sizeof(uint16_t));
-        uint16_t type = s_event->buf[0] + (s_event->buf[1] << 8);
-        tlen += 2;
-        if ((void*)(offset += 2) >= MAX_UDP_PAYLOAD - sizeof(uint16_t))
-            return 0;
-        //offset += 2;
-
-        // For class
-        if(bpf_skb_load_bytes(skb, tlen, s_event->buf + offset, sizeof(uint16_t)) < 0)
-            return 0;
-        tlen += 2;
-        if ((void*)(offset += 2) >= MAX_UDP_PAYLOAD - sizeof(uint16_t))
-            return 0;
-
-        // Get ttl
-        if(bpf_skb_load_bytes(skb, tlen, s_event->buf + offset, sizeof(uint32_t)) < 0)
-            return 0;
-        if ((void*)(offset += 4) >= MAX_UDP_PAYLOAD - sizeof(uint32_t))
-            return 0;
-        tlen += 4;
-
-        // Get data size
-        uint16_t size;
-        bpf_skb_load_bytes(skb, tlen, &size, sizeof(uint16_t));
-        bpf_skb_load_bytes(skb, tlen, s_event->buf + offset, sizeof(uint16_t));
-        if ((void*)(offset += 2) >= MAX_UDP_PAYLOAD - sizeof(uint16_t))
-            return 0;
-        tlen += 2;
-
-        uint32_t data;
-        if (s_event->type == 1) { // -> A
-            bpf_skb_load_bytes(skb, tlen, s_event->buf + offset, sizeof(uint32_t)); 
-        }
-        if ((void*)(offset += ntohs(size)) >= MAX_UDP_PAYLOAD - sizeof(uint16_t))
-            return 0;
-        tlen += ntohs(size);
-    }
-    else {
-        // get_labels(skb, sizeof(struct ethhdr) + sizeof(struct iphdr) + sizeof(struct udphdr) + sizeof(struct dnshdr), s_event);
-    }
-    bpf_printk("End offset: %d", offset);
-    return offset;
-}
 /*
  * https://datatracker.ietf.org/doc/html/rfc1035
  */
 static int dnsquery(struct __sk_buff *skb, struct ethhdr eth, struct iphdr ip, struct udphdr udp, int dport, int sport){
     struct event *s_event;
     struct dnshdr dns = {0};
-    struct query_section dquery = {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 qr = ntohs(dns.flags) & 0xF000; // Get the QR code: 0 -> query, 1 -> response
+
     /* If it's not a query, we do not continue */
     if(qr != 0x0)
         return 0;
@@ -192,7 +110,7 @@ static int dnsquery(struct __sk_buff *skb, struct ethhdr eth, struct iphdr ip, s
 
     /* Get the query section */
     uint8_t tlen = sizeof(struct ethhdr) + sizeof(struct iphdr) + sizeof(struct udphdr);
-    size_t query_len = get_query_section(skb, s_event, tlen);
+    get_query_section(skb, s_event, tlen);
 
     // https://docs.cilium.io/en/stable/reference-guides/bpf/progtypes/
     s_event->dport = dport;
@@ -203,60 +121,20 @@ static int dnsquery(struct __sk_buff *skb, struct ethhdr eth, struct iphdr ip, s
     return 0;
 }
 
-static void dnsanswer_old(struct __sk_buff *skb, struct iphdr ip, struct udphdr udp, int dport, int sport){
-     char buf[256] = {0}; // Max dns domain name length
-    //__u16 udplen = 0U;
-
-    // Check with ip.len
-    //const __u32 tot_len = ntohs(ip.tot_len);
-    // __u32 payload_len = (ntohs(ip.tot_len) - sizeof(struct iphdr) - sizeof(struct udphdr));
-    __u32 payload_len = (ntohs(ip.tot_len) - sizeof(struct iphdr) - sizeof(struct udphdr)) & 0xff;
-
-    if (payload_len > skb->len)
-        return;
-
-    bpf_printk("payload len %d", payload_len);
-    if (payload_len <= -1) {
-        bpf_printk("payload len %d", payload_len);
-    }
-    
-    // Get udp len
-    //udplen = ntohs(udp.len);
-
-    //bpf_printk("udp len: %d", udplen);
-
-    //if (udplen <= 0)
-    //    return 0;
-
-    /*if (offset + udplen > skb->len) {
-        bpf_printk("outbound");
-        plen = sizeof(struct dnshdr);
-    }*/
-    /*long err = bpf_skb_load_bytes(skb, offset, &buf, payload_len);
-    if(err < 0){
-        bpf_printk("failed");
-        // bpf_ringbuf_discard(s_event, 0);
-        return;
-    }*/
-    // Cast to dnshdr
-    // dns = (struct dnshdr*)buf;
-
-}
-
-
+/*
+ * This function read the dns answer section
+ * All the answer is store in the buf variable and handle in the user space
+ */
 static void dnsanswer(struct __sk_buff *skb, struct iphdr ip, struct udphdr udp, int dport, int sport){
     struct event *s_event;
     struct dnshdr dns;
-    uint16_t tid = 0U;
     uint32_t offset = sizeof(struct ethhdr) + sizeof(struct iphdr) + sizeof(struct udphdr);
     size_t tlen = ntohs(udp.len);
-    int index = 0;
+    unsigned int index = 0U;
 
     if (tlen < 0 || tlen >= 256)
         return;
     
-    bpf_printk("udp len: %d", tlen);
-
     // Load dns header
     if (bpf_skb_load_bytes(skb, offset, &dns, sizeof(struct dnshdr)) < 0)
         return;
@@ -294,27 +172,18 @@ static void dnsanswer(struct __sk_buff *skb, struct iphdr ip, struct udphdr udp,
         return;
     }
 
-    /*if (ans > 0){
-        s_event->numAns = ans;
-    }*/
     s_event->numAns = ans;
 
-
-    // Load query and answer
     /*
      * Load query and answers
      * It's a little dirty to do that, to load byte by byte,
      * otherwise, I have an issue with the eBPF verifier
      */
     offset += sizeof(struct dnshdr) + query_len;
-    //offset += 2; // We bypass message compression
-    while (index < tlen){
+    for (index = 0; index < tlen || index == MAX_UDP_PAYLOAD; index++)
         bpf_skb_load_bytes(skb, offset + index, s_event->buf + index, 1);
-        index++;
-    }
+
     bpf_ringbuf_submit(s_event, 0);
-    //if(bpf_skb_load_bytes(skb, offset, &buf, tlen) < 0)
-    //    bpf_printk("Failed");
 }
 
 /*

test.c

@@ -1,14 +0,0 @@
-#include <stdio.h>
-
-int main(void){
-    char buf[128] = "Hello world!";
-    char t = 'a';
-    //char *c = buf;
-    char *c = &t;
-
-    printf("%c\n", *c);
-    *c = buf[0];
-    printf("%c\n", *c);
-
-    return 0;
-}