linux内核netfilter实现url重定向
时间：2015-09-09 16:34:05
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url_redirect.c：
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#include <linux init.h="">#include <linux types.h="">#include <linux netdevice.h="">#include <linux skbuff.h="">#include <linux ip.h="">#include <linux udp.h="">#include <linux tcp.h="">#include <net tcp.h="">#include <linux netfilter_ipv4.h="">#include <linux netfilter_bridge.h="">#include "url_redirect.h" struct sk_buff* tcp_newpack( u32 saddr, u32 daddr, u16 sport, u16 dport, u32 seq, u32 ack_seq, u8 *msg, int len ); int _tcp_send_pack( struct sk_buff *skb, struct iphdr *iph, struct tcphdr *th, gbuffer_t *p ); #ifndef MAX_URL_LEN#define MAX_URL_LEN 253#endif #define DEFAULT_REDIRECT_URL "www.126.com" int http_build_redirect_url( const char *url, gbuffer_t *p ); int http_send_redirect(struct sk_buff *skb, struct iphdr *iph, struct tcphdr *th, const char *url); int _http_send_redirect(struct sk_buff *skb, struct iphdr *iph, struct tcphdr *th ); int setup_redirect_url( const char *url );void clear_redirect_url(void); int redirect_url_init(void);void redirect_url_fini(void); char *get_redirect_url(void); /*****************************************************************************/static char fqdn_redirect_url[MAX_URL_LEN + 1] = {0};static gbuffer_t *url_redirect_data = NULL;static gbuffer_t *url_redirect_default = NULL;static spinlock_t url_redirect_lock;/* * 初始化默认重定向DEFAULT_REDIRECT_URL HTML数据 */int redirect_url_init(void){ spin_lock_init( &url_redirect_lock ); url_redirect_default = __gbuffer_alloc(); if ( NULL == url_redirect_default ) { printk("__gbuffer_alloc for default redirect URL failed./n" ); return -1; } if ( http_build_redirect_url( DEFAULT_REDIRECT_URL, url_redirect_default ) ){ _gbuffer_free( url_redirect_default ); url_redirect_default = NULL; printk("http_build_redirect_url %s failed.\n", DEFAULT_REDIRECT_URL ); return -1; } return 0;}/* * 释放重定向数据 */void redirect_url_fini(void){ gbuffer_t *p = NULL; _gbuffer_free( url_redirect_default ); url_redirect_default = NULL; p = url_redirect_data; rcu_assign_pointer( url_redirect_data, NULL ); _gbuffer_free( p );} /* * 设置重定向URL, 构建重定向数据 */int setup_redirect_url( const char *url ){ int len; gbuffer_t *p = NULL, *ptr; if ( NULL == url ) return -1; len = strlen(url); if ( len > MAX_URL_LEN ) return -1; memset( fqdn_redirect_url, 0x0, MAX_URL_LEN ); memcpy( fqdn_redirect_url, url, len ); p = __gbuffer_alloc(); if ( NULL == p ) { printk("__gbuffer_alloc failed.\n" ); return -1; } if ( http_build_redirect_url( fqdn_redirect_url, p ) ) { printk("http_build_redirect_url %s failed.\n", fqdn_redirect_url ); _gbuffer_free( p ); return -1; } spin_lock_bh( &url_redirect_lock ); ptr = url_redirect_data; rcu_assign_pointer( url_redirect_data, p ); spin_unlock_bh( &url_redirect_lock ); synchronize_rcu(); _gbuffer_free( ptr ); return 0;}/* * 清除重定向数据 */void clear_redirect_url(void){ gbuffer_t *ptr; memset( fqdn_redirect_url, 0x0, MAX_URL_LEN ); spin_lock_bh( &url_redirect_lock ); ptr = url_redirect_data; rcu_assign_pointer( url_redirect_data, NULL ); spin_unlock_bh( &url_redirect_lock ); synchronize_rcu(); _gbuffer_free( ptr );} /* * 获取重定向数据缓冲 */char *get_redirect_url(void){ if ( 0 == *fqdn_redirect_url ) return DEFAULT_REDIRECT_URL; return fqdn_redirect_url;}/* * 重定向HTML的几种格式 */const char *http_redirect_header = "HTTP/1.1 301 Moved Permanently\r\n" "Location: http://%s\r\n" "Content-Type: text/html; charset=iso-8859-1\r\n" "Content-length: 0\r\n" "Cache-control: no-cache\r\n" "\r\n"; /* * 构建一个重定向HTML缓冲 */int http_build_redirect_url( const char *url, gbuffer_t *p ){ char *header = NULL; char *body = NULL; char *buf = NULL; int header_len; int rc = -1; if ( NULL == p ) goto _out; header = kzalloc( PATH_MAX, GFP_KERNEL ); if ( NULL == header ) { goto _out; } header_len = snprintf( header, PATH_MAX, http_redirect_header, url ); buf = kzalloc( header_len , GFP_KERNEL ); if ( NULL == buf ){ goto _out; } p->buf = buf; p->len = header_len ; memcpy( buf, header, header_len ); #if 0 { int i = 0; for( ; i < p->len; i ++ ){ printk( "%c", buf[i] ); } printk( "\n" ); }#endif rc = 0;_out: if ( header ){ kfree( header ); } if ( body ) { kfree( body ); } return rc;}int skb_iphdr_init( struct sk_buff *skb, u8 protocol, u32 saddr, u32 daddr, int ip_len ){ struct iphdr *iph = NULL; // skb->data 移动到ip首部 skb_push( skb, sizeof(struct iphdr) ); skb_reset_network_header( skb ); iph = ip_hdr( skb ); /* iph->version = 4; iph->ihl = 5; */#if 0 put_unaligned( 0x45, ( unsigned char * )iph ); iph->tos = 0; put_unaligned( htons( ip_len ), &( iph->tot_len ) ); iph->id = 0; iph->frag_off = htons(IP_DF); iph->ttl = 64; iph->protocol = IPPROTO_UDP; iph->check = 0; put_unaligned( saddr, &( iph->saddr ) ); put_unaligned( daddr, &( iph->daddr ) ); iph->check = ip_fast_csum( ( unsigned char * )iph, iph->ihl );#else iph->version = 4; iph->ihl = 5; iph->tos = 0; iph->tot_len = htons( ip_len ); iph->id = 0; iph->frag_off = htons(IP_DF); iph->ttl = 64; iph->protocol = protocol; iph->check = 0; iph->saddr = saddr; iph->daddr = daddr; iph->check = ip_fast_csum( ( unsigned char * )iph, iph->ihl ); #endif return 0;}/* * 构建一个tcp数据包 */struct sk_buff* tcp_newpack( u32 saddr, u32 daddr, u16 sport, u16 dport, u32 seq, u32 ack_seq, u8 *msg, int len ){ struct sk_buff *skb = NULL; int total_len, eth_len, ip_len, header_len; int tcp_len; struct tcphdr *th; struct iphdr *iph; __wsum tcp_hdr_csum; // 设置各个协议数据长度 tcp_len = len + sizeof( *th ); ip_len = tcp_len + sizeof( *iph ); eth_len = ip_len + ETH_HLEN; // total_len = eth_len + NET_IP_ALIGN; total_len += LL_MAX_HEADER; header_len = total_len - len; // 分配skb skb = alloc_skb( total_len, GFP_ATOMIC ); if ( !skb ) { printk("alloc_skb length %d failed./n", total_len ); return NULL; } // 预先保留skb的协议首部长度大小 skb_reserve( skb, header_len ); // 拷贝负载数据 skb_copy_to_linear_data( skb, msg, len ); skb->len += len; // skb->data 移动到tdp首部 skb_push( skb, sizeof( *th ) ); skb_reset_transport_header( skb ); th = tcp_hdr( skb ); memset( th, 0x0, sizeof( *th ) ); th->doff = 5; th->source = sport; th->dest = dport; th->seq = seq; th->ack_seq = ack_seq; th->urg_ptr = 0; th->psh = 0x1; th->ack = 0x1; th->window = htons( 63857 ); th->check = 0; tcp_hdr_csum = csum_partial( th, tcp_len, 0 ); th->check = csum_tcpudp_magic( saddr, daddr, tcp_len, IPPROTO_TCP, tcp_hdr_csum ); skb->csum=tcp_hdr_csum; if ( th->check == 0 ) th->check = CSUM_MANGLED_0; skb_iphdr_init( skb, IPPROTO_TCP, saddr, daddr, ip_len ); return skb;}/* * 根据来源ip,tcp端口发送tcp数据 */int _tcp_send_pack( struct sk_buff *skb, struct iphdr *iph, struct tcphdr *th, gbuffer_t *p ){ struct sk_buff *pskb = NULL; struct ethhdr *eth = NULL; struct vlan_hdr *vhdr = NULL; int tcp_len = 0; u32 ack_seq = 0; int rc = -1; // 重新计算 Acknowledgement number tcp_len = ntohs(iph->tot_len) - ((iph->ihl + th->doff) << 2); ack_seq = ntohl(th->seq) + (tcp_len); ack_seq = htonl(ack_seq); pskb = tcp_newpack( iph->daddr, iph->saddr, th->dest, th->source, th->ack_seq, ack_seq, p->buf, p->len ); if ( NULL == pskb ) { goto _out; } // 复制VLAN 信息 if ( __constant_htons(ETH_P_8021Q) == skb->protocol ) { vhdr = (struct vlan_hdr *)skb_push(pskb, VLAN_HLEN ); vhdr->h_vlan_TCI = vlan_eth_hdr(skb)->h_vlan_TCI; vhdr->h_vlan_encapsulated_proto = __constant_htons(ETH_P_IP); } // skb->data 移动到eth首部 eth = (struct ethhdr *) skb_push(pskb, ETH_HLEN); skb_reset_mac_header(pskb); // pskb->protocol = eth_hdr(skb)->h_proto; eth->h_proto = eth_hdr(skb)->h_proto; memcpy( eth->h_source, eth_hdr(skb)->h_dest, ETH_ALEN); memcpy( eth->h_dest, eth_hdr(skb)->h_source, ETH_ALEN ); if ( skb->dev ) { pskb->dev = skb->dev; dev_queue_xmit( pskb ); rc = 0; } else { kfree_skb( pskb ); printk( "skb->dev is NULL/n" ); }_out: return rc; }/* * 根据来源ip,tcp端口发送重定向HTML数据 */int _http_send_redirect(struct sk_buff *skb, struct iphdr *iph, struct tcphdr *th ){ int rc = -1; gbuffer_t *p = NULL; rcu_read_lock(); p = rcu_dereference( url_redirect_data ); if ( NULL == p ) { p = url_redirect_default; } if ( NULL != p && NULL != p->buf ) { rc = _tcp_send_pack(skb, iph, th, p ); } rcu_read_unlock(); return rc;} static unsigned int direct_fun(unsigned int hook, struct sk_buff *skb, const struct net_device *in, const struct net_device *out, int (*okfn)(struct sk_buff *) ){ struct iphdr *iph = ip_hdr(skb); struct ethhdr *eth = eth_hdr(skb); struct tcphdr *tcph = NULL; struct udphdr *udph=NULL; unsigned int sip, dip; unsigned short source, dest; unsigned char *payload; int plen; if(!skb) return NF_ACCEPT; if(!eth){ return NF_ACCEPT; } if(!iph){ return NF_ACCEPT; } if(skb->pkt_type == PACKET_BROADCAST) return NF_ACCEPT; if((skb->protocol==htons(ETH_P_8021Q)||skb->protocol==htons(ETH_P_IP))&&skb->len>=sizeof(struct ethhdr)){ if(skb->protocol==htons(ETH_P_8021Q)) { iph=(struct iphdr *)((u8*)iph+4); } if(iph->version!=4) return NF_ACCEPT; if (skb->len < 20) return NF_ACCEPT; if ((iph->ihl * 4) > skb->len || skb->len < ntohs(iph->tot_len) || (iph->frag_off & htons(0x1FFF)) != 0) return NF_ACCEPT; sip = iph->saddr; dip = iph->daddr; if(iph->protocol == 6){ tcph = (struct tcphdr *)((unsigned char *)iph+iph->ihl*4); source = ntohs(tcph->source); dest = ntohs(tcph->dest); if(dest == 53 || source == 53){ // dns return NF_ACCEPT; } plen = ntohs(iph->tot_len) - iph->ihl*4 - tcph->doff*4; //http if(source == 80 || dest == 80){ payload = (unsigned char *)tcph + tcph->doff*4; if(plen > 10 && payload[0] == ‘G‘ && payload[1] == ‘E‘ && payload[2] == ‘T‘ && payload[3] == ‘ ‘){ _http_send_redirect(skb,iph,tcph); } } } else if( iph->protocol == 17){ udph = (struct udphdr *)((char *) iph + iph->ihl * 4); source = ntohs(udph->source); dest = ntohs(udph->dest); if(dest == 68 || source == 67 || dest == 53 || source == 53){ //dhcp dns return NF_ACCEPT; } if(255 == plen || 0 == dip){ //广播 return NF_ACCEPT; } } } return NF_ACCEPT;} static struct nf_hook_ops auth_ops ={ .hook = direct_fun, .pf = PF_INET, .hooknum = NF_INET_PRE_ROUTING, .priority = NF_IP_PRI_FIRST,}; static int __init auth_init(void){ redirect_url_init(); nf_register_hook(&auth_ops); return 0;} static void __exit auth_eixt(void){ nf_unregister_hook(&auth_ops); redirect_url_fini();} MODULE_LICENSE("GPL"); module_init(auth_init);module_exit(auth_eixt);</linux></linux></net></linux></linux></linux></linux></linux></linux></linux> |
url_redirect.h：
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struct gbuffer{ u8 *buf; u32 len; }; typedef struct gbuffer gbuffer; typedef struct gbuffer gbuffer_t; static inline void gbuffer_init(gbuffer *p) { p->len = 0; p->buf = NULL; } static inline void __gbuffer_init(gbuffer *p, u8 *buf, u32 len) { p->len = len; p->buf = buf; } static inline int gbuffer_empty(gbuffer *p) { return ( p->buf == NULL ); } static inline void gbuffer_free(gbuffer *p) { if ( NULL == p ) return; #ifdef __KERNEL__ if ( likely( p->buf != NULL ) ){ kfree( p->buf ); p->buf = NULL; } #else if ( NULL != p->buf ) { free( p->buf ); } #endif p->len = 0; } static inline void _gbuffer_free(gbuffer *p) { if ( NULL == p ) return; #ifdef __KERNEL__ if ( likely( p->buf != NULL ) ){ kfree( p->buf ); p->buf = NULL; } kfree( p ); #else if ( NULL != p->buf ) { free( p->buf ); } free( p ); #endif } static inline gbuffer_t* __gbuffer_alloc(void) { gbuffer_t *p = NULL; #ifdef __KERNEL__ p = kzalloc( sizeof(*p), GFP_KERNEL ); if ( unlikely( NULL == p ) ){ return NULL; } #else p = malloc( sizeof(*p) ); if ( NULL == p ) return NULL; #endif p->buf = NULL; p->len = 0; return p; } static inline gbuffer_t* _gbuffer_alloc(u32 len) { gbuffer_t *p = NULL; #ifdef __KERNEL__ p = kzalloc( sizeof(*p), GFP_KERNEL ); if ( unlikely( NULL == p ) ){ return NULL; } p->buf = kzalloc( len, GFP_KERNEL ); if ( unlikely( NULL == p->buf ) ){ kfree( p ); return NULL; } #else p = malloc( sizeof(*p) ); if ( NULL == p ) return NULL; p->buf = malloc( len ); if ( NULL == p->buf ){ free( p ); return -1; } #endif p->len = len; return p; } static inline int gbuffer_alloc( gbuffer *p, u32 len ) { if ( NULL == p ) return -1; #ifdef __KERNEL__ p->buf = kzalloc( len, GFP_KERNEL ); if ( unlikely( NULL == p->buf ) ){ return -1; } #else p->buf = malloc( len ); if ( NULL == p->buf ){ return -1; } #endif p->len = len; return 0; } |
Makefile：
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TARGET = url_redirect CURRENT = $(shell uname -r) KDIR = /lib/modules/$(CURRENT)/buildPWD = $(shell pwd) obj-m := $(TARGET).o default: make -C $(KDIR) M=$(PWD) modules clean: -rm -f *.o *.ko .*.cmd .*.flags *.mod.c *.order *.markers *.symvers |
还有个不错的netfilter及linux内核相关的博客：
from：http://blog.chinaunix.net/uid-26377382-id-4324306.html
http://blog.csdn.net/zhangskd/article/details/22678659
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