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feat: using new method to parse dns's response
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Signed-off-by: Dengfeng Liu <[email protected]>
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@liudf0716
liudf0716 committed Jun 12, 2024
1 parent 8acbcab commit d588c25
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Showing 3 changed files with 100 additions and 83 deletions.
3 changes: 2 additions & 1 deletion src/conf.h
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Original file line number Diff line number Diff line change
Expand Up @@ -204,7 +204,8 @@ typedef struct _popular_server_t {
*/

typedef struct _ip_trusted_t {
char ip[HTTP_IP_ADDR_LEN];
char ip[INET_ADDRSTRLEN];
unsigned int uip;
struct _ip_trusted_t *next;
} t_ip_trusted;

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162 changes: 80 additions & 82 deletions src/dns_forward.c
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Original file line number Diff line number Diff line change
Expand Up @@ -42,110 +42,108 @@ strrstr(const char *haystack, const char *needle)
return result;
};

static void
parse_name(unsigned char *response, unsigned char **ptr, char *name) {
int jumped = 0, offset;
unsigned char *pos = *ptr;
char *name_pos = name;

while (*pos) {
if (*pos >= 192) {
offset = ((*pos) << 8 | *(pos + 1)) & 0x3FFF;
pos = response + offset;
jumped = 1;
} else {
int segment_len = *pos;
pos++;
memcpy(name_pos, pos, segment_len);
name_pos += segment_len;
pos += segment_len;
*name_pos++ = '.';
}
if (!jumped) (*ptr)++;
}
*name_pos = '\0';
if (!jumped) (*ptr)++;
}

static int
parse_dns_response_ex(unsigned char *response, int response_len) {
process_dns_response(unsigned char *response, int response_len) {
s_config *config = config_get_config();
unsigned char *ptr = response + 12; // Skip the DNS header
int qdcount = ntohs(*(unsigned short *)(response + 4));
int ancount = ntohs(*(unsigned short *)(response + 6));

if (response_len <= sizeof(struct dns_header)) {
debug(LOG_WARNING, "Invalid DNS response");
return -1;
}
struct dns_header *header = (struct dns_header *)response;
if (header->qr != 1 || header->opcode != 0 || header->rcode != 0) {
debug(LOG_WARNING, "Invalid DNS response");
return -1;
}

char query_name[MAX_DNS_NAME] = {0};
int qdcount = ntohs(header->qdcount);
int ancount = ntohs(header->ancount);
unsigned char *ptr = response + sizeof(struct dns_header); // Skip the DNS header
debug(LOG_DEBUG, "DNS response: qdcount=%d, ancount=%d", qdcount, ancount);

// Skip the question section
assert(qdcount == 1); // Only handle one question (A record)
for (int i = 0; i < qdcount; i++) {
while (*ptr != 0) ptr++;
ptr += 5; // Skip null byte, type, and class
parse_name(response, &ptr, query_name);
ptr += 4; // Skip QTYPE and QCLASS
}
debug(LOG_DEBUG, "DNS query: %s", query_name);
// find the trusted domain in the query_name
t_domain_trusted *p = config->pan_domains_trusted;
while (p) {
if (strrstr(query_name, p->domain)) {
debug(LOG_DEBUG, "Find trusted wildcard domain: %s", p->domain);
break;
}
p = p->next;
}

if (!p) {
debug(LOG_DEBUG, "No trusted wildcard domain found in the query");
return 0;
}

// Parse the answer section
for (int i = 0; i < ancount; i++) {
char domain[256];
int len = 0;

while (*ptr != 0) {
if (*ptr >= 192) { // Handle pointers
ptr += 2;
break;
}
memcpy(domain + len, ptr + 1, *ptr);
len += *ptr;
domain[len++] = '.';
ptr += *ptr + 1;
}
domain[--len] = '\0'; // Null-terminate the domain string
ptr++;
char answer_name[MAX_DNS_NAME] = {0};
parse_name(response, &ptr, answer_name);

unsigned short type = ntohs(*(unsigned short *)ptr);
ptr += 2;
ptr += 8; // Skip class, TTL, and data length
unsigned short data_len = ntohs(*(unsigned short *)ptr);
ptr += 2;

if (type == 1 && data_len == 4) { // Type A
char ip[INET_ADDRSTRLEN];
inet_ntop(AF_INET, ptr, ip, sizeof(ip));
t_domain_trusted *p = config->pan_domains_trusted;
while (p) {
if (strstr(domain, p->domain)) {
t_ip_trusted *ip_entry = malloc(sizeof(t_ip_trusted));
strcpy(ip_entry->ip, ip);
ip_entry->next = p->ips_trusted;
p->ips_trusted = ip_entry;
printf("Trusted domain: %s -> %s\n", domain, ip);
if (type == 1 && data_len == 4) { // Type A record
t_ip_trusted *ip_trusted = p->ips_trusted;
while(ip_trusted) {
if (ip_trusted->uip == *(unsigned int *)ptr) {
break;
}
p = p->next;
ip_trusted = ip_trusted->next;
}
if (!ip_trusted) {
char ip[INET_ADDRSTRLEN] = {0};
inet_ntop(AF_INET, ptr, ip, sizeof(ip));
debug(LOG_DEBUG, "Trusted domain: %s -> %s", query_name, ip);
t_ip_trusted *new_ip_trusted = (t_ip_trusted *)malloc(sizeof(t_ip_trusted));
new_ip_trusted->uip = *(unsigned int *)ptr;
new_ip_trusted->next = p->ips_trusted;
p->ips_trusted = new_ip_trusted;
char cmd[128] = {0};
snprintf(cmd, sizeof(cmd), "nft add element set wifidogx_inner_trust_domains %s", ip);
system(cmd);
}
}
ptr += data_len;
}
return 0;
}

static void
process_dns_response(char *response, int response_len)
{
ns_msg handle;
s_config *config = config_get_config();


if (ns_initparse((const uint8_t *)response, response_len, &handle) < 0) {
debug(LOG_WARNING, "ns_initparse: %s", strerror(errno));
return;
}

int msg_count = ns_msg_count(handle, ns_s_an);
debug(LOG_DEBUG, "DNS response contains %d answers, response_len %d", msg_count, response_len);
for (int i = 0; i < msg_count; i++) {
ns_rr rr;
int nret;
if (ns_parserr(&handle, ns_s_an, i, &rr) < 0) {
debug(LOG_WARNING, "ns_parserr: %s", strerror(errno));
continue;
}
debug(LOG_DEBUG, "DNS response type: %d", ns_rr_type(rr));

if (ns_rr_type(rr) == ns_t_a) {
t_domain_trusted *p = NULL;
char domain[4096] = {0};
nret = ns_name_uncompress(ns_msg_base(handle), ns_msg_end(handle), ns_rr_name(rr), domain, sizeof(domain));
if (nret < 0) {
debug(LOG_WARNING, "ns_name_uncompress: %s", strerror(errno));
continue;
}
debug(LOG_DEBUG, "Get dns response domain: %s", domain);
for (p = config->pan_domains_trusted; p; p = p->next) {
// reverse match the domain, check if the domain include p->domain
if (strrstr(domain, p->domain) != NULL) {
struct in_addr addr;
char cmd[128] = {0};
memcpy(&addr, ns_rr_rdata(rr), sizeof(addr));
debug(LOG_DEBUG, "Trusted domain: %s -> %s", domain, inet_ntoa(addr));
snprintf(cmd, sizeof(cmd), "nft add element set wifidogx_inner_trust_domains %s", inet_ntoa(addr));
system(cmd);
break;
}
}
}
}
return 0;
}

static void
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18 changes: 18 additions & 0 deletions src/dns_forward.h
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,24 @@

#define DNS_FORWARD_PORT 15353
#define LOCAL_DNS_PORT 53
#define MAX_DNS_NAME 256

// define a structure to hold the DNS header
struct dns_header {
unsigned short id;
unsigned char rd :1;
unsigned char tc :1;
unsigned char aa :1;
unsigned char opcode :4;
unsigned char qr :1;
unsigned char rcode :4;
unsigned char z :3;
unsigned char ra :1;
unsigned short qdcount;
unsigned short ancount;
unsigned short nscount;
unsigned short arcount;
};

void *dns_forward_thread(void *);

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