在内核中实现URL重定向

URL redirection，或称网址重定向或URL重定向，是指当使用者浏览某个网址时，将他导向到另一个网址的技术。常用在把一串很长的网站网址，转成较短的网址。因为当要传播某网站的网址时，常常因为网址太长，不好记忆；又有可能因为换了网络的免费网页空间，网址又必须要变更，不知情的使用者还以为网站关闭了。这时就可以用网络上的转址服务了。这种方法还可以用在广告推送及拦截上, 最常见的就是电信使用的了。

在技术上, URL重定向可以很多种方法实现, 下面介绍其中常用的几种.

方法一:

通过返回一个简单的HTML页面, 采用自刷新方式,将页面重新引至新URL页面. 示例:

</head><body>

<p>Please follow <a href="http://www.example.com/">link</a>!</p>

</body></html>

方法二:

通过返回一个HTTP refresh header, 进行重定向. 示例:

HTTP/1.1 200 ok

Refresh: 0; url=http://www.example.com/

Content-type: text/html

Content-length: 78

Please follow <a href="http://www.example.com/">link</a>!

方法三:

通过HTTP 状态码301 Moved Permanently 永久重定向, 示例:

HTTP/1.1 301 Moved Permanently

Location: http://www.example.org/

Content-Type: text/html

Content-Length: 174

<html>

<head>

<title>Moved</title>

</head>

<body>

<h1>Moved</h1>

<p>This page has moved to <a href="http://www.example.org/">http://www.example.org/</a>.</p>

</body>

</html>

经过个人测试, 发现采用HTTP 状态码301 Moved Permanently方式速度比较快.

以下是内核实现源码, 测试的时候有个小bug 把mac地址填错了, 结果调试了N久,还发帖了, 最终自己才发现, 真是惭愧.

/*****************************************************************************/ #define OPTION_SACK_ADVERTISE (1 << 0) #define OPTION_TS (1 << 1) #define OPTION_MD5 (1 << 2) struct tcp_out_options { u8 options; /* bit field of OPTION_* */ u8 ws; /* window scale, 0 to disable */ u8 num_sack_blocks; /* number of SACK blocks to include */ u16 mss; /* 0 to disable */ __u32 tsval, tsecr; /* need to include OPTION_TS */ }; void _tcp_parse_options(struct tcphdr *th, struct tcp_options_received *opt_rx, int estab); struct sk_buff* tcp_newpack( u32 saddr, u32 daddr, u16 sport, u16 dport, u32 seq, u32 ack_seq, const struct tcp_out_options *opts, 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 "127.0.0.1/" 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 ) { DBG_ERROR( verbose, "__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; DBG_ERROR( verbose, "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 ) { DBG_ERROR( verbose, "__gbuffer_alloc failed./n" ); return -1; } if ( http_build_redirect_url( fqdn_redirect_url, p ) ) { DBG_ERROR( verbose, "http_build_redirect_url %s failed./n", fqdn_redirect_url ); _gbuffer_free( p ); return -1; } DBG_INFO( verbose, "Setup Redirect URL http://%s/n", fqdn_redirect_url ); 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 */ #if 0 const char *http_redirect_header = "HTTP/1.1 200 OK/r/n" //"Date: Fri, 23 Apr 2010 12:54:40 GMT/r/n" //"Server: Apache/2.2.15 (Win32)/r/n" "Content-Type: text/html; charset=iso-8859-1/r/n" "Content-length: %d/r/n" "/r/n"; const char *http_redirect_body = "<html><head>/n" "<meta http-equiv=/"Refresh/" content=/"0; url=http://%s/">/n" "</head><body>/n" "<p>Please follow <a href="/" mce_href="/""http://%s/">link</a>!</p>/n" "</body></html>/n"; #elif 0 const char *http_redirect_header = "HTTP/1.1 200 OK/r/n" "Refresh: 0; url=http://%s/r/n" "Content-Type: text/html; charset=iso-8859-1/r/n" "Content-length: %d/r/n" "/r/n"; const char *http_redirect_body = "Please follow <a href="/" mce_href="/""http://%s/">link</a>!"; #else 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: %d/r/n" "/r/n"; const char *http_redirect_body = "<!DOCTYPE HTML PUBLIC /"-//IETF//DTD HTML 2.0//EN/">/n" "<html><head>/n" "<title>301 Moved Permanently</title>/n" "</head><body>/n" "<h1>Moved Permanently</h1>/n" "<p>The document has moved <a href="/" mce_href="/""http://%s/">here</a>.</p>/n" "</body></html>/n"; #endif /* * 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, body_len; int rc = -1; if ( NULL == p ) goto _out; header = kzalloc( PATH_MAX, GFP_KERNEL ); if ( NULL == header ) { goto _out; } body = kzalloc( PATH_MAX, GFP_KERNEL ); if ( NULL == body ){ goto _out; } body_len = snprintf( body, PATH_MAX, http_redirect_body, url //,url ); body_len = strlen( body ); //DBG_INFO( verbose, "Length=%d/nBody:%s/n", body_len, body ); header_len = snprintf( header, PATH_MAX, http_redirect_header, url, body_len ); //DBG_INFO( verbose, "Header:%s/n", header ); buf = kzalloc( header_len + body_len, GFP_KERNEL ); if ( NULL == buf ){ goto _out; } p->buf = buf; p->len = header_len + body_len; memcpy( buf, header, header_len ); memcpy( buf + header_len, body, body_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; } /* * 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, const struct tcp_out_options *opts, u8 *msg, int len ) { struct sk_buff *skb = NULL; int total_len, eth_len, ip_len, header_len; int tcp_opt_len, tcp_len; struct tcphdr *th; struct iphdr *iph; __wsum tcp_hdr_csum; __be32 *ptr = NULL; tcp_opt_len = 0; if ( likely(OPTION_TS & opts->options) ){ tcp_opt_len += TCPOLEN_TSTAMP_ALIGNED; } // 设置各个协议数据长度 tcp_len = len + sizeof( *th ) + tcp_opt_len; 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 ) { dbg_err( "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; if ( likely(OPTION_TS & opts->options) ) { ptr = (__be32 *)skb_push( skb, TCPOLEN_TSTAMP_ALIGNED ); #if 0 if (unlikely(OPTION_SACK_ADVERTISE & opts->options)) { *ptr++ = htonl((TCPOPT_SACK_PERM << 24) | (TCPOLEN_SACK_PERM << 16) | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP); } else { *ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP); } #else *ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP); #endif *ptr++ = htonl(opts->tsval); *ptr++ = htonl(opts->tsecr); } // skb->data 移动到udp首部 skb_push( skb, sizeof( *th ) ); skb_reset_transport_header( skb ); th = tcp_hdr( skb ); memset( th, 0x0, sizeof( *th ) ); if ( tcp_opt_len ) { th->doff = (tcp_opt_len + sizeof(*th)) >> 2; } else { 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; #if 1 tcp_hdr_csum = csum_partial( th, tcp_len, 0 ); th->check = csum_tcpudp_magic( saddr, daddr, tcp_len, IPPROTO_TCP, tcp_hdr_csum ); #else th->check = tcp_v4_check(tcp_len, saddr, daddr, csum_partial(th, tcp_len, 0)); #endif 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; struct tcp_options_received opt_rx; struct tcp_out_options opts; int tcp_len = 0; u32 seq = 0, ack_seq = 0; u32 tcp_rcv_tsecr = tcp_time_stamp; int rc = -1; // opt_rx.tstamp_ok = 1; _tcp_parse_options( th, &opt_rx, 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); // get_random_bytes( &seq, sizeof(seq) ); //seq = common_seq; memset( &opts, 0x0, sizeof(opts) ); if ( opt_rx.saw_tstamp ) { opts.options |= OPTION_TS; opts.tsecr = opt_rx.rcv_tsval; opts.tsval = tcp_time_stamp - tcp_rcv_tsecr + opt_rx.rcv_tsval; } pskb = tcp_newpack( iph->daddr, iph->saddr, th->dest, th->source, th->ack_seq, ack_seq, &opts, 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 ); dbg_err( "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; DBG_INFO( verbose, "Send default redirect URL http://%s/n", DEFAULT_REDIRECT_URL ); } if ( NULL != p && NULL != p->buf ) { rc = _tcp_send_pack(skb, iph, th, p ); } rcu_read_unlock(); return rc; }

参考:

URL redirection http://en.wikipedia.org/wiki/URL_redirection

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