youtubeUnblock/mangle.c

#include "mangle.h"

#ifdef KERNEL_SPACE
static __u16 nfq_checksum(__u32 sum, __u16 *buf, int size)
{
        while (size > 1) {
                sum += *buf++;
                size -= sizeof(__u16);
        }
        if (size) {
#ifdef __LITTLE_ENDIAN
                sum += (uint16_t)*(uint8_t *)buf << 8;
#else
                sum += (__u16)*(__u8 *)buf;
#endif
        }

        sum = (sum >> 16) + (sum & 0xffff);
        sum += (sum >> 16);

        return (__u16)(~sum);
}

static __u16 nfq_checksum_tcpudp_ipv4(struct iphdr *iph, __u16 protonum)
{
        __u32 sum = 0;
        __u32 iph_len = iph->ihl*4;
        __u32 len = ntohs(iph->tot_len) - iph_len;
        __u8 *payload = (__u8 *)iph + iph_len;

        sum += (iph->saddr >> 16) & 0xFFFF;
        sum += (iph->saddr) & 0xFFFF;
        sum += (iph->daddr >> 16) & 0xFFFF;
        sum += (iph->daddr) & 0xFFFF;
        sum += htons(protonum);
        sum += htons(len);

        return nfq_checksum(sum, (__u16 *)payload, len);
}

static void nfq_ip_set_checksum(struct iphdr *iph)
{
        __u32 iph_len = iph->ihl * 4;

        iph->check = 0;
        iph->check = nfq_checksum(0, (__u16 *)iph, iph_len);
}

static void 
nfq_tcp_compute_checksum_ipv4(struct tcphdr *tcph, struct iphdr *iph)
{
        /* checksum field in header needs to be zero for calculation. */
        tcph->check = 0;
        tcph->check = nfq_checksum_tcpudp_ipv4(iph, IPPROTO_TCP);
}
#else 
#include <stdio.h>
#include <libnetfilter_queue/libnetfilter_queue_ipv4.h>
#include <libnetfilter_queue/libnetfilter_queue_tcp.h>

typedef uint8_t __u8;
typedef uint32_t __u32;
typedef uint16_t __u16;
#endif


int ip4_payload_split(__u8 *pkt, __u32 buflen,
		       struct iphdr **iph, __u32 *iph_len, 
		       __u8 **payload, __u32 *plen) {
	if (pkt == NULL || buflen < sizeof(struct iphdr)) {
		return -EINVAL;
	}

	struct iphdr *hdr = (struct iphdr *)pkt;
	if (hdr->version != IPVERSION) return -EINVAL;

	__u32 hdr_len = hdr->ihl * 4;
	__u32 pktlen = ntohs(hdr->tot_len);
	if (pktlen < buflen || hdr_len > pktlen) return -EINVAL;

	if (iph) 
		*iph = hdr;
	if (iph_len)
		*iph_len = hdr_len;
	if (payload)
		*payload = pkt + hdr_len;
	if (plen)
		*plen = pktlen - hdr_len;

	return 0;
}

int tcp4_payload_split(__u8 *pkt, __u32 buflen,
		       struct iphdr **iph, __u32 *iph_len,
		       struct tcphdr **tcph, __u32 *tcph_len,
		       __u8 **payload, __u32 *plen) {
	struct iphdr *hdr;
	__u32 hdr_len;
	struct tcphdr *thdr;
	__u32 thdr_len;
	
	__u8 *tcph_pl;
	__u32 tcph_plen;

	if (ip4_payload_split(pkt, buflen, &hdr, &hdr_len, 
			&tcph_pl, &tcph_plen)){
		return -EINVAL;
	}

	if (
		hdr->protocol != IPPROTO_TCP || 
		!(ntohs(hdr->frag_off) & IP_DF) ||
		tcph_plen < sizeof(struct tcphdr)) {
		return -EINVAL;
	}


	thdr = (struct tcphdr *)(tcph_pl);
	thdr_len = (*tcph)->doff * 4;

	if (thdr_len > tcph_plen) {
		return -EINVAL;
	}

	if (iph) *iph = hdr;
	if (iph_len) *iph_len = hdr_len;
	if (tcph) *tcph = thdr;
	if (tcph_len) *tcph_len = thdr_len;
	if (payload) *payload = tcph_pl + thdr_len;
	if (plen) *plen = tcph_plen - thdr_len;

	return 0;
}

// split packet to two ipv4 fragments.
int ip4_frag(const __u8 *pkt, __u32 buflen, __u32 payload_offset, 
			__u8 *frag1, __u32 *f1len, 
			__u8 *frag2, __u32 *f2len) {
	
	struct iphdr *hdr;
	const __u8 *payload;
	__u32 plen;
	__u32 hdr_len;

	if (ip4_payload_split(
		(__u8 *)pkt, buflen, 
		&hdr, &hdr_len, (__u8 **)&payload, &plen)) {
		return -EINVAL;
	}

	if (plen <= payload_offset) {
		return -EINVAL;
	}

	if (payload_offset & ((1 << 3) - 1)) {
#ifdef KERNEL_SPACE 
#else
		errno = EINVAL;
		perror("Payload offset MUST be a multiply of 8!");
#endif

		return -EINVAL;
	}

	__u32 f1_plen = payload_offset;
	__u32 f1_dlen = f1_plen + hdr_len;

	__u32 f2_plen = plen - payload_offset;
	__u32 f2_dlen = f2_plen + hdr_len;

	if (*f1len < f1_dlen || *f2len < f2_dlen) {
		return -ENOMEM;
	}
	*f1len = f1_dlen;
	*f2len = f2_dlen;

	memcpy(frag1, hdr, hdr_len);
	memcpy(frag2, hdr, hdr_len);

	memcpy(frag1 + hdr_len, payload, f1_plen);
	memcpy(frag2 + hdr_len, payload + payload_offset, f2_plen);

	struct iphdr *f1_hdr = (void *)frag1;
	struct iphdr *f2_hdr = (void *)frag2;

	__u16 f1_frag_off = ntohs(f1_hdr->frag_off);
	__u16 f2_frag_off = ntohs(f2_hdr->frag_off);

	f1_frag_off &= IP_OFFMASK;
	f1_frag_off |= IP_MF;
	
	if ((f2_frag_off & ~IP_OFFMASK) == IP_MF) {
		f2_frag_off &= IP_OFFMASK;
		f2_frag_off |= IP_MF;
	} else {
		f2_frag_off &= IP_OFFMASK;
	}
	
	f2_frag_off += (__u16)payload_offset / 8;

	f1_hdr->frag_off = htons(f1_frag_off);
	f1_hdr->tot_len = htons(f1_dlen);

	f2_hdr->frag_off = htons(f2_frag_off);
	f2_hdr->tot_len = htons(f2_dlen);


#if defined(DEBUG) && !defined(KERNEL_SPACE)
	printf("Packet split in portion %u %u\n", f1_plen, f2_plen);
#endif

	nfq_ip_set_checksum(f1_hdr);
	nfq_ip_set_checksum(f2_hdr);

	return 0;
}

// split packet to two tcp-on-ipv4 segments.
int tcp4_frag(const __u8 *pkt, __u32 buflen, __u32 payload_offset, 
			__u8 *seg1, __u32 *s1len, 
			__u8 *seg2, __u32 *s2len) {

	struct iphdr *hdr;
	__u32 hdr_len;
	struct tcphdr *tcph;
	__u32 tcph_len;
	__u32 plen;
	const __u8 *payload;

	if (tcp4_payload_split((__u8 *)pkt, buflen,
				&hdr, &hdr_len,
				&tcph, &tcph_len,
				(__u8 **)&payload, &plen)) {
		return -EINVAL;
	}

	if (plen <= payload_offset) {
		return -EINVAL;
	}

	__u32 s1_plen = payload_offset;
	__u32 s1_dlen = s1_plen + hdr_len + tcph_len;

	__u32 s2_plen = plen - payload_offset;
	__u32 s2_dlen = s2_plen + hdr_len + tcph_len;

	if (*s1len < s1_dlen || *s2len < s2_dlen) return -ENOMEM;

	*s1len = s1_dlen;
	*s2len = s2_dlen;

	memcpy(seg1, hdr, hdr_len);
	memcpy(seg2, hdr, hdr_len);

	memcpy(seg1 + hdr_len, tcph, tcph_len);
	memcpy(seg2 + hdr_len, tcph, tcph_len);

	memcpy(seg1 + hdr_len + tcph_len, payload, s1_plen);
	memcpy(seg2 + hdr_len + tcph_len, payload + payload_offset, s2_plen);

	struct iphdr *s1_hdr = (void *)seg1;
	struct iphdr *s2_hdr = (void *)seg2;

	struct tcphdr *s1_tcph = (void *)(seg1 + hdr_len);
	struct tcphdr *s2_tcph = (void *)(seg2 + hdr_len);

	s1_hdr->tot_len = htons(s1_dlen);
	s2_hdr->tot_len = htons(s2_dlen);

	s2_tcph->seq = htonl(ntohl(s2_tcph->seq) + payload_offset);
	
#if defined(DEBUG) && !defined(KERNEL_SPACE)
	printf("Packet split in portion %u %u\n", s1_plen, s2_plen);
#endif

	nfq_tcp_compute_checksum_ipv4(s1_tcph, s1_hdr);
	nfq_tcp_compute_checksum_ipv4(s2_tcph, s2_hdr);

	return 0;
}

#define TLS_CONTENT_TYPE_HANDSHAKE 0x16
#define TLS_HANDSHAKE_TYPE_CLIENT_HELLO 0x01
#define TLS_EXTENSION_SNI 0x0000
#define TLS_EXTENSION_CLIENT_HELLO_ENCRYPTED 0xfe0d

const char googlevideo_ending[] = "googlevideo.com";
const int googlevideo_len = 15;

#define GOOGLEVIDEO_MARK 0xfc74


typedef __u8 uint8_t;
typedef __u32 uint32_t;
typedef __u16 uint16_t;

/**
 * Processes tls payload of the tcp request.
 * 
 * data Payload data of TCP.
 * dlen Length of `data`.
 */
struct verdict analyze_tls_data(
	const uint8_t *data, 
	uint32_t dlen) 
{
	struct verdict vrd = {0};

	size_t i = 0;
	const uint8_t *data_end = data + dlen;

	while (i + 4 < dlen) {
		const uint8_t *msgData = data + i;

		uint8_t tls_content_type = *msgData;
		uint8_t tls_vmajor = *(msgData + 1);
		uint8_t tls_vminor = *(msgData + 2);
		uint16_t message_length = ntohs(*(uint16_t *)(msgData + 3));
		const uint8_t *message_length_ptr = msgData + 3;


		if (i + 5 + message_length > dlen) break;

		if (tls_content_type != TLS_CONTENT_TYPE_HANDSHAKE) 
			goto nextMessage;


		const uint8_t *handshakeProto = msgData + 5;

		if (handshakeProto + 1 >= data_end) break;

		uint8_t handshakeType = *handshakeProto;

		if (handshakeType != TLS_HANDSHAKE_TYPE_CLIENT_HELLO)
			goto nextMessage;

		const uint8_t *msgPtr = handshakeProto;
		msgPtr += 1; 
		const uint8_t *handshakeProto_length_ptr = msgPtr + 1;
		msgPtr += 3 + 2 + 32;

		if (msgPtr + 1 >= data_end) break;
		uint8_t sessionIdLength = *msgPtr;
		msgPtr++;
		msgPtr += sessionIdLength;

		if (msgPtr + 2 >= data_end) break;
		uint16_t ciphersLength = ntohs(*(uint16_t *)msgPtr);
		msgPtr += 2;
		msgPtr += ciphersLength;

		if (msgPtr + 1 >= data_end) break;
		uint8_t compMethodsLen = *msgPtr;
		msgPtr++;
		msgPtr += compMethodsLen;

		if (msgPtr + 2 >= data_end) break;
		uint16_t extensionsLen = ntohs(*(uint16_t *)msgPtr);
		const uint8_t *extensionsLen_ptr = msgPtr;
		msgPtr += 2;

		const uint8_t *extensionsPtr = msgPtr;
		const uint8_t *extensions_end = extensionsPtr + extensionsLen;
		if (extensions_end > data_end) break;

		while (extensionsPtr < extensions_end) {
			const uint8_t *extensionPtr = extensionsPtr;
			if (extensionPtr + 4 >= extensions_end) break;

			uint16_t extensionType = 
				ntohs(*(uint16_t *)extensionPtr);
			extensionPtr += 2;

			uint16_t extensionLen = 
				ntohs(*(uint16_t *)extensionPtr);
			const uint8_t *extensionLen_ptr = extensionPtr;
			extensionPtr += 2;


			if (extensionPtr + extensionLen > extensions_end) 
				break;

			if (extensionType != TLS_EXTENSION_SNI) 
				goto nextExtension;

			const uint8_t *sni_ext_ptr = extensionPtr;

			if (sni_ext_ptr + 2 >= extensions_end) break;
			uint16_t sni_ext_dlen = ntohs(*(uint16_t *)sni_ext_ptr);

			const uint8_t *sni_ext_dlen_ptr = sni_ext_ptr;
			sni_ext_ptr += 2;

			const uint8_t *sni_ext_end = sni_ext_ptr + sni_ext_dlen;
			if (sni_ext_end >= extensions_end) break;
			
			if (sni_ext_ptr + 3 >= sni_ext_end) break;
			uint8_t sni_type = *sni_ext_ptr++;
			uint16_t sni_len = ntohs(*(uint16_t *)sni_ext_ptr);
			sni_ext_ptr += 2;

			if (sni_ext_ptr + sni_len > sni_ext_end) break;

			char *sni_name = (char *)sni_ext_ptr;
			// sni_len

			vrd.sni_offset = (uint8_t *)sni_name - data;
			vrd.sni_len = sni_len;

			char *gv_startp = sni_name + sni_len - googlevideo_len;
			if (sni_len >= googlevideo_len &&
				sni_len < 128 && 
				!strncmp(gv_startp, 
				googlevideo_ending, 
				googlevideo_len)) {

				vrd.gvideo_hello = 1;
			}

nextExtension:
			extensionsPtr += 2 + 2 + extensionLen;
		}
nextMessage:
		i += 5 + message_length;
	}

	return vrd;
}