SSH已经不能指望了，怎么办？
想法简单，不足道，仅仅是个POC，也希望能有人一起讨论：
注册一个新的四层协议，除了TCP/UDP/ICMP等熟知协议之外的新协议，这是为了避免每一个数据包都要经过过滤，避免影响性能。
事先分配skb，避免当事故发生时回送信息时分配skb失败。
好了，看代码，先给出载入内核的代码，这个代码的大部分都是我从网上抄来的，并不是自己写的，我只是重组了逻辑：
include #include #include #include
define IPPROTO_MYPROTO 123#define QUOTA 30
struct sk_buff *eskb[QUOTA];
static int quota = QUOTA - 1;//module_param(quota, int, 0644);//MODULE_PARM_DESC(quota, "soft_lockup");
unsigned short _csum(unsigned short* data, int len){
int pad = 0;
int i = 0;
unsigned short ret = 0;
unsigned int sum = 0;
if (len % 2 != 0)
pad = 1;
len /= 2;
for ( i = 0; i < len; i++) {
sum += data[i];
}
if (pad == 1)
sum += ((unsigned char*)(data + len))[0] ;
sum = (sum & 0xffff) + (sum >> 16);
sum += (sum >> 16);
ret = ~sum;
return ret;}int myproto_rcv(struct sk_buff *skb){
struct udphdr *uh, *euh;
struct iphdr *iph, *eiph;
struct ethhdr *eh, *ethh;
char esaddr[6];
unsigned char *pos;
if (quota < 0) {
goto end;
}
iph = ip_hdr(skb);
uh = udp_hdr(skb);
eh = (struct ethhdr *)(((unsigned char *)iph) - sizeof(struct ethhdr));
// 出事的时候，直接构造已经分配的skb
eskb[quota]->ip_summed = CHECKSUM_NONE;
eskb[quota]->protocol = htons(ETH_P_IP);
eskb[quota]->priority = 0;
eskb[quota]->dev = skb->dev;
eskb[quota]->pkt_type = PACKET_OTHERHOST;
skb_reserve(eskb[quota], 1300 + sizeof(struct ethhdr) + sizeof(struct iphdr) + sizeof(struct udphdr));
pos = skb_push(eskb[quota], 1300);
strcpy(pos, "abcdefghijk123456789");
pos = skb_push(eskb[quota], sizeof(struct udphdr));
skb_reset_transport_header(eskb[quota]);
euh = (struct udphdr *)pos;
euh->source = uh->dest;
euh->dest = uh->source;
euh->len = htons(1300 + sizeof(struct udphdr));
euh->check = 0;
memcpy(pos - 12, &iph->daddr, 4);
memcpy(pos - 8, &iph->saddr, 4);
((unsigned short *)(pos - 4))[0] = 0x1100;
memcpy(pos - 2, &euh->len, sizeof(euh->len));
euh->check = _csum((unsigned short*)(pos - 12), 12 + 1300 + sizeof(struct udphdr));
pos = skb_push(eskb[quota], sizeof(struct iphdr));
skb_reset_network_header(eskb[quota]);
eiph = (struct iphdr *)pos;
eiph->version = 4;
eiph->ihl = 5;
eiph->tos = 0;
eiph->tot_len = htons(1300 + sizeof(struct udphdr) + sizeof(struct iphdr));
eiph->id = 0x1122;
eiph->frag_off = 0;
eiph->ttl = 64;
eiph->protocol = 0x11;
eiph->check = 0;
eiph->saddr = iph->daddr;
eiph->daddr = iph->saddr;
eiph->check = _csum((unsigned short*)pos, sizeof(struct iphdr));
pos = skb_push(eskb[quota], sizeof(struct ethhdr));
skb_reset_mac_header(eskb[quota]);
ethh = (struct ethhdr *)pos;
memcpy(esaddr, eh->h_dest, 6);
memcpy(ethh->h_dest, eh->h_source, ETH_ALEN);
memcpy(ethh->h_source, eh->h_dest, ETH_ALEN);
ethh->h_proto = htons(ETH_P_IP);
printk("myproto_rcv is called, length:%d %x %x\n", skb->len, esaddr[2], esaddr[3]);
dev_queue_xmit(eskb[quota]);
quota --;end:
kfree_skb(skb);
return 0;}int myproto_rcv_err(struct sk_buff *skb, unsigned int err){
printk("myproto_rcv is called:%d\n", err);
kfree_skb(skb);
return 0;}static const struct net_protocol myproto_protocol = {
.handler = myproto_rcv,
.err_handler = myproto_rcv_err,
.no_policy = 1,
.netns_ok = 1,};int init_module(void){
int ret = 0, i;
// 事先分配skb
for (i = 0; i < QUOTA; i++) {
eskb[i] = alloc_skb(1300 + sizeof(struct ethhdr) + sizeof(struct iphdr) + sizeof(struct udphdr), GFP_ATOMIC);
if (eskb[i] == NULL) {
//int j;
//for () {
//}
printk("alloc failed\n");
return -1;
// 注册123协议，它不是TCP,UDP,ICMP
ret = inet_add_protocol(&myproto_protocol, IPPROTO_MYPROTO);
if (ret) {
printk("failed\n");
return ret;
printk("successful\n");
return 0;}void cleanup_module(void){
int rc = 0;
inet_del_protocol(&myproto_protocol, IPPROTO_MYPROTO);
//for (i = quota; i >=0; i--) {
//kfree_skb(eskb[i]);
//}
return;}int init_module(void);void cleanup_module(void);MODULE_LICENSE("GPL");
来来来，看一下客户端的代码。
客户端需要通过raw跟单网gendan5.com套接字发送一个“请求”，它的传输层协议是123，然而回复的却是一个标准的UDP报文，所以客户端需要在该UDP上接收。
代码如下：
include #include #include #include #include #include #include #include
define PCKT_LEN 8192
unsigned short csum(unsigned short *buf, int nwords){
unsigned long sum;
for(sum=0; nwords>0; nwords--)
sum += *buf++;sum = (sum >> 16) + (sum &0xffff);
sum += (sum >> 16);
return (unsigned short)(~sum);}
int main(int argc, char const *argv[]){
int sd, usd;
struct iphdr *ip;
struct udphdr *udp;
struct sockaddr_in sin, usin, csin;
u_int16_t src_port, dst_port;
u_int32_t src_addr, dst_addr;
int one = 1;
const int *val = &one;
int dlen, rlen, clen = sizeof(csin);
char *data;
char buf[1300];
if (argc != 6) {
printf("Usage: %s \n", argv[0]);
exit(1);
src_addr = inet_addr(argv[1]);
dst_addr = inet_addr(argv[3]);
src_port = atoi(argv[2]);
dst_port = atoi(argv[4]);
dlen = atoi(argv[5]); data = malloc(sizeof(struct iphdr) + sizeof(struct udphdr) + dlen);
ip = (struct iphdr *)data;
udp = (struct udphdr *)(data + sizeof(struct iphdr));
sd = socket(PF_INET, SOCK_RAW, IPPROTO_UDP);
if (sd < 0) {
perror("raw error");
exit(2);if(setsockopt(sd, IPPROTO_IP, IP_HDRINCL, val, sizeof(one)) < 0) {
perror("setsockopt() error");
exit(2);
sin.sin_family = AF_INET;
sin.sin_port = htons(dst_port);
sin.sin_addr.s_addr = inet_addr(argv[3]);ip->ihl = 5;
ip->version = 4;
ip->tos = 16; // low delay
ip->tot_len = sizeof(struct iphdr) + sizeof(struct udphdr) + dlen;
ip->id = htons(54321);
ip->ttl = 64; // hops
ip->protocol = 123; // UDP
ip->saddr = src_addr;
ip->daddr = dst_addr;udp->source = htons(src_port);
udp->dest = htons(dst_port);
udp->len = htons(sizeof(struct udphdr) + dlen);ip->check = csum((unsigned short *)data, sizeof(struct iphdr) + sizeof(struct udphdr) + dlen);
usd = socket(AF_INET, SOCK_DGRAM, 0);
if (usd < 0) {
perror("usd error");
bzero(&usin, sizeof(usin));
usin.sin_family = AF_INET;
usin.sin_port = htons(src_port);
usin.sin_addr.s_addr = inet_addr(argv[1]);if (bind(usd, (struct sockaddr *)&usin, sizeof(usin))) {
perror("bind error");
exit(2);
if (sendto(sd, data, ip->tot_len, 0, (struct sockaddr *)&sin, sizeof(sin)) < 0) {
perror("sendto()");
exit(3);
rlen = recvfrom(usd, buf, sizeof(buf), 0, (struct sockaddr*)&csin, &clen);
printf("recv:%s\n", buf);
close(sd);
return 0;}