Linux内核中的IPSEC实现(6)

quhr 发表于 2011-12-21 08:43

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<div><br>8. 安全协议</div>
<div><br>与IPSEC相关的安全协议是AH(51)和ESP(50), IPSEC使用这两个协议对普通数据包进行封装, AH只认证不加密,
ESP既加密又认证, 当ESP和AH同时使用时, 一般都是先进行ESP封装, 再进行AH封装, 因为AH是对整个IP包进行验证的,
而ESP只验证负载部分.</div>
<div><br>在IPV4下的AH和ESP的协议实现在net/ipv4/ah4.c和net/ipv4/esp4.c中,
每个协议实现实际是要完成两个结构: struct net_protocol和struct xfrm_type,
前者用于处理接收的该协议类型的IP包, 后者则是IPSEC协议处理.</div>
<div><br>8.1 AH</div>
<div><br>8.1.1 初始化</div>
<div><br>/* net/ipv4/ah4.c */<br>static int __init ah4_init(void)<br>{<br>// 登记AH协议的xfrm协议处理结构<br> if (xfrm_register_type(&ah_type, AF_INET) < 0) {<br>  printk(KERN_INFO "ip ah init: can't add xfrm type\n");<br>  return -EAGAIN;<br> }<br>// 登记AH协议到IP协议<br> if (inet_add_protocol(&ah4_protocol, IPPROTO_AH) < 0) {<br>  printk(KERN_INFO "ip ah init: can't add protocol\n");<br>  xfrm_unregister_type(&ah_type, AF_INET);<br>  return -EAGAIN;<br> }<br> return 0;<br>}</div>
<div><br>8.1.2 IPV4下的AH协议处理结构</div>
<div><br>// AH协议处理结构, 接收到IPV4包后, 系统根据IP头中的protocol字段选择相应的上层协议处理<br>// 函数, 当IP协议号是51时, 数据包将调用该结构的handler处理函数:<br>static struct net_protocol ah4_protocol = {<br> .handler = xfrm4_rcv,<br> .err_handler = ah4_err,<br> .no_policy = 1,<br>};</div>
<div>AH协议结构的handler函数为xfrm4_rcv, 在net/ipv4/xfrm4_input.c 中定义, 在上一篇中进行了介绍.</div>
<div><br>// 错误处理, 收到ICMP错误包时的处理情况, 此时的skb包是ICMP包<br>static void ah4_err(struct sk_buff *skb, u32 info)<br>{<br>// 应用层, data指向ICMP错误包里的内部IP头<br> struct iphdr *iph = (struct iphdr*)skb->data;<br>// AH头<br> struct ip_auth_hdr *ah = (struct ip_auth_hdr*)(skb->data+(iph->ihl<<2));<br> struct xfrm_state *x;<br>// ICMP错误类型检查, 本处理函数只处理"目的不可达"和"需要分片"两种错误<br> if (skb->h.icmph->type != ICMP_DEST_UNREACH ||<br>     skb->h.icmph->code != ICMP_FRAG_NEEDED)<br>  return;<br>// 重新查找SA<br> x = xfrm_state_lookup((xfrm_address_t *)&iph->daddr, ah->spi, IPPROTO_AH, AF_INET);<br> if (!x)<br>  return;<br> printk(KERN_DEBUG "pmtu discovery on SA AH/%08x/%08x\n",<br>        ntohl(ah->spi), ntohl(iph->daddr));<br> xfrm_state_put(x);<br>}</div>
<div><br>8.1.3 AH4协议的IPSEC处理结构</div>
<div><br>// AH4的xfrm协议处理结构<br>static struct xfrm_type ah_type =<br>{<br> .description = "AH4",<br> .owner  = THIS_MODULE,<br> .proto       = IPPROTO_AH,<br>// 状态初始化<br> .init_state = ah_init_state,<br>// 协议释放<br> .destructor = ah_destroy,<br>// 协议输入<br> .input  = ah_input,<br>// 协议输出<br> .output  = ah_output<br>};<br>结构的重点是input和ouput函数</div>
<div><br>8.1.3.1 状态初始化</div>
<div>ah_data数据结构:</div>
<div>/* include/net/ah.h */</div>
<div>struct ah_data<br>{<br>// 密钥指针<br> u8   *key;<br>// 密钥长度<br> int   key_len;<br>// 工作初始化向量<br> u8   *work_icv;<br>// 初始化向量完整长度<br> int   icv_full_len;<br>// 初始化向量截断长度<br> int   icv_trunc_len;<br>// HASH算法<br> struct crypto_hash *tfm;<br>};</div>
<div><br>// 该函数被xfrm状态(SA)初始化函数xfrm_init_state调用<br>// 用来生成SA中所用的AH数据处理结构相关信息<br>static int ah_init_state(struct xfrm_state *x)<br>{<br> struct ah_data *ahp = NULL;<br> struct xfrm_algo_desc *aalg_desc;<br> struct crypto_hash *tfm;</div>
<div>// 对AH协议的SA, 认证算法是必须的, 否则就没法进行AH认证了<br> if (!x->aalg)<br>  goto error;</div>
<div> /* null auth can use a zero length key */<br>// 认证算法密钥长度要大于512<br> if (x->aalg->alg_key_len > 512)<br>  goto error;</div>
<div>// 如果要进行UDP封装(进行NAT穿越), 错误, 因为AH是不支持NAT的<br> if (x->encap)<br>  goto error;</div>
<div>// 分配ah_data数据结构空间<br> ahp = kzalloc(sizeof(*ahp), GFP_KERNEL);<br> if (ahp == NULL)<br>  return -ENOMEM;</div>
<div>// 设置AH数据结构的密钥和长度<br> ahp->key = x->aalg->alg_key;<br> ahp->key_len = (x->aalg->alg_key_len+7)/8;<br>// 分配认证算法HASH结构指针并赋值给AH数据结构<br>// 算法是固定相同的, 但在每个应用使用算法时的上下文是不同的, 该结构就是描述具体应用<br>// 时的相关处理的上下文数据的<br> tfm = crypto_alloc_hash(x->aalg->alg_name, 0, CRYPTO_ALG_ASYNC);<br> if (IS_ERR(tfm))<br>  goto error;</div>
<div> ahp->tfm = tfm;<br>// 设置认证算法密钥<br> if (crypto_hash_setkey(tfm, ahp->key, ahp->key_len))<br>  goto error;<br> <br> /*<br>  * Lookup the algorithm description maintained by xfrm_algo,<br>  * verify crypto transform properties, and store information<br>  * we need for AH processing.  This lookup cannot fail here<br>  * after a successful crypto_alloc_hash().<br>  */<br>// 分配算法描述结构<br> aalg_desc = xfrm_aalg_get_byname(x->aalg->alg_name, 0);<br> BUG_ON(!aalg_desc);</div>
<div> if (aalg_desc->uinfo.auth.icv_fullbits/8 !=<br>     crypto_hash_digestsize(tfm)) {<br>  printk(KERN_INFO "AH: %s digestsize %u != %hu\n",<br>         x->aalg->alg_name, crypto_hash_digestsize(tfm),<br>         aalg_desc->uinfo.auth.icv_fullbits/8);<br>  goto error;<br> }<br>// AH数据结构的初始化向量的总长和截断长度的赋值 <br> ahp->icv_full_len = aalg_desc->uinfo.auth.icv_fullbits/8;<br> ahp->icv_trunc_len = aalg_desc->uinfo.auth.icv_truncbits/8;<br> <br> BUG_ON(ahp->icv_trunc_len > MAX_AH_AUTH_LEN);</div>
<div>// 分配初始化向量空间, 没对其赋值, 其初始值就是随机值, 这也是初始化向量所需要的<br> ahp->work_icv = kmalloc(ahp->icv_full_len, GFP_KERNEL);<br> if (!ahp->work_icv)<br>  goto error;<br>// AH类型SA中AH头长度: ip_auth_hdr结构和初始化向量长度, 按8字节对齐 <br>// 反映在AH封装操作时要将数据包增加的长度<br> x->props.header_len = XFRM_ALIGN8(sizeof(struct ip_auth_hdr) + ahp->icv_trunc_len);<br>// 如果是通道模式, 增加IP头长度<br> if (x->props.mode == XFRM_MODE_TUNNEL)<br>  x->props.header_len += sizeof(struct iphdr);<br>// SA数据指向AH数据结构<br> x->data = ahp;</div>
<div> return 0;</div>
<div>error:<br> if (ahp) {<br>  kfree(ahp->work_icv);<br>  crypto_free_hash(ahp->tfm);<br>  kfree(ahp);<br> }<br> return -EINVAL;<br>}</div>
<div><br>8.1.3.2 协议释放</div>
<div>// 该函数被xfrm状态(SA)释放函数xfrm_state_gc_destroy()调用<br>static void ah_destroy(struct xfrm_state *x)<br>{<br> struct ah_data *ahp = x->data;</div>
<div> if (!ahp)<br>  return;<br>// 释放初始化向量空间<br> kfree(ahp->work_icv);<br> ahp->work_icv = NULL;<br>// 算法描述释放<br> crypto_free_hash(ahp->tfm);<br> ahp->tfm = NULL;<br>// AH数据结构释放<br> kfree(ahp);<br>}</div>
<div><br>8.1.3.3 协议输入</div>
<div><br>// 接收数据处理, 在xfrm4_rcv_encap()函数中调用<br>// 进行AH认证, 剥离AH头<br>static int ah_input(struct xfrm_state *x, struct sk_buff *skb)<br>{<br> int ah_hlen;<br> int ihl;<br> int err = -EINVAL;<br> struct iphdr *iph;<br> struct ip_auth_hdr *ah;<br> struct ah_data *ahp;<br>// IP头备份空间<br> char work_buf;</div>
<div>// skb数据包要准备留出AH头空间<br> if (!pskb_may_pull(skb, sizeof(struct ip_auth_hdr)))<br>  goto out;<br>// IP上层数据为AH数据<br> ah = (struct ip_auth_hdr*)skb->data;<br>// SA相关的AH处理数据<br> ahp = x->data;<br> ah_hlen = (ah->hdrlen + 2) << 2;<br>// AH头部长度合法性检查<br> if (ah_hlen != XFRM_ALIGN8(sizeof(struct ip_auth_hdr) + ahp->icv_full_len) &&<br>     ah_hlen != XFRM_ALIGN8(sizeof(struct ip_auth_hdr) + ahp->icv_trunc_len)) <br>  goto out;</div>
<div>// skb数据包要准备留出实际AH头空间<br> if (!pskb_may_pull(skb, ah_hlen))<br>  goto out;</div>
<div> /* We are going to _remove_ AH header to keep sockets happy,<br>  * so... Later this can change. */<br>// 对于clone的包要复制成独立包<br> if (skb_cloned(skb) &&<br>     pskb_expand_head(skb, 0, 0, GFP_ATOMIC))<br>  goto out;</div>
<div> skb->ip_summed = CHECKSUM_NONE;<br>// 可能包已经进行了复制, 所以对ah重新赋值<br> ah = (struct ip_auth_hdr*)skb->data;<br> iph = skb->nh.iph;<br>// IP头长度<br> ihl = skb->data - skb->nh.raw;<br>// 备份外部IP头数据<br> memcpy(work_buf, iph, ihl);</div>
<div>// 将IP头中的一些参数清零, 这些参数不进行认证<br> iph->ttl = 0;<br> iph->tos = 0;<br> iph->frag_off = 0;<br> iph->check = 0;<br>// IP头长度超过20字节时,处理IP选项参数<br> if (ihl > sizeof(*iph)) {<br>  u32 dummy;<br>  if (ip_clear_mutable_options(iph, &dummy))<br>   goto out;<br> }<br>        {<br>// 认证数据缓冲区<br>  u8 auth_data;<br>// 拷贝数据包中的认证数据到缓冲区<br>  memcpy(auth_data, ah->auth_data, ahp->icv_trunc_len);<br>// 包括IP头部分数据<br>  skb_push(skb, ihl);<br>// 计算认证值是否匹配, 非0表示出错<br>  err = ah_mac_digest(ahp, skb, ah->auth_data);<br>// 认证失败返回错误<br>  if (err)<br>   goto out;<br>  err = -EINVAL;<br>// 复制一定长度的认证数据作为初始化向量<br>  if (memcmp(ahp->work_icv, auth_data, ahp->icv_trunc_len)) {<br>   x->stats.integrity_failed++;<br>   goto out;<br>  }<br> }<br>// 将备份的IP头缓冲区中的协议改为AH内部包裹的协议<br> ((struct iphdr*)work_buf)->protocol = ah->nexthdr;<br>// 将原来IP头数据拷贝到原来AH头后面作为新IP头<br> skb->h.raw = memcpy(skb->nh.raw += ah_hlen, work_buf, ihl);<br>// skb包缩减原来的IP头和AH头, 以新IP头作为数据开始<br> __skb_pull(skb, ah_hlen + ihl);</div>
<div> return 0;</div>
<div>out:<br> return err;<br>}</div>
<div><br>8.1.3.4 协议输出</div>
<div><br>// 发送数据处理, 在xfrm4_output_one()中调用<br>// 计算AH认证值, 添加AH头<br>static int ah_output(struct xfrm_state *x, struct sk_buff *skb)<br>{<br> int err;<br> struct iphdr *iph, *top_iph;<br> struct ip_auth_hdr *ah;<br> struct ah_data *ahp;<br>// 临时IP头缓冲区, 最大IP头60字节<br> union {<br>  struct iphdr iph;<br>  char   buf;<br> } tmp_iph;</div>
<div>// 当前的IP头将作为最外部IP头<br> top_iph = skb->nh.iph;<br>// 临时IP头,用于临时保存IP头内部分字段数据<br> iph = &tmp_iph.iph;</div>
<div>// 将当前IP头中不进行认证的字段数据复制到临时IP头<br> iph->tos = top_iph->tos;<br> iph->ttl = top_iph->ttl;<br> iph->frag_off = top_iph->frag_off;<br>// 如果有IP选项, 处理IP选项<br> if (top_iph->ihl != 5) {<br>  iph->daddr = top_iph->daddr;<br>  memcpy(iph+1, top_iph+1, top_iph->ihl*4 - sizeof(struct iphdr));<br>  err = ip_clear_mutable_options(top_iph, &top_iph->daddr);<br>  if (err)<br>   goto error;<br> }<br>// AH头定位在外部IP头后面, skb缓冲中已经预留出AH头的数据部分了, <br>// 这是通过mode->output函数预留的, 通常调用type->output前要调用mode->oputput<br> ah = (struct ip_auth_hdr *)((char *)top_iph+top_iph->ihl*4);<br>// AH中的下一个头用原来的外部IP头中的协议<br> ah->nexthdr = top_iph->protocol;<br>// 将外部IP头的不进行认证计算的部分字段清零<br> top_iph->tos = 0;<br> top_iph->tot_len = htons(skb->len);<br> top_iph->frag_off = 0;<br> top_iph->ttl = 0;<br>// IP协议改为AH<br> top_iph->protocol = IPPROTO_AH;<br> top_iph->check = 0;</div>
<div>// AH数据处理结构<br> ahp = x->data;<br>// AH头长度对齐<br> ah->hdrlen  = (XFRM_ALIGN8(sizeof(struct ip_auth_hdr) + <br>       ahp->icv_trunc_len) >> 2) - 2;<br>// AH头参数赋值<br> ah->reserved = 0;<br>// SPI值<br> ah->spi = x->id.spi;<br>// 序列号<br> ah->seq_no = htonl(++x->replay.oseq);<br>// 通知防止重放攻击处理, 更新序列号<br> xfrm_aevent_doreplay(x);<br>// 对skb进行AH认证值的计算<br> err = ah_mac_digest(ahp, skb, ah->auth_data);<br> if (err)<br>  goto error;<br>// 赋值初始化向量值到认证数据部分<br> memcpy(ah->auth_data, ahp->work_icv, ahp->icv_trunc_len);</div>
<div>// 恢复原来IP头的的不认证部分的值<br> top_iph->tos = iph->tos;<br> top_iph->ttl = iph->ttl;<br> top_iph->frag_off = iph->frag_off;<br> if (top_iph->ihl != 5) {<br>  top_iph->daddr = iph->daddr;<br>  memcpy(top_iph+1, iph+1, top_iph->ihl*4 - sizeof(struct iphdr));<br> }<br>// 重新计算IP头的认证值<br> ip_send_check(top_iph);</div>
<div> err = 0;</div>
<div>error:<br> return err;<br>}</div>
<div> </div>
<div>8.2 ESP</div>
<div><br>8.2.1 初始化</div>
<div><br>/* net/ipv4/esp4.c */</div>
<div>static int __init esp4_init(void)<br>{<br>// 登记ESP协议的xfrm协议处理结构<br> if (xfrm_register_type(&esp_type, AF_INET) < 0) {<br>  printk(KERN_INFO "ip esp init: can't add xfrm type\n");<br>  return -EAGAIN;<br> }<br>// 登记ESP协议到IP协议<br> if (inet_add_protocol(&esp4_protocol, IPPROTO_ESP) < 0) {<br>  printk(KERN_INFO "ip esp init: can't add protocol\n");<br>  xfrm_unregister_type(&esp_type, AF_INET);<br>  return -EAGAIN;<br> }<br> return 0;<br>}</div>
<div><br>8.2.2 IPV4下的ESP协议处理结构</div>
<div><br>// ESP协议处理结构, 接收到IPV4包后, 系统根据IP头中的protocol<br>// 字段选择相应的上层协议处理函数, 当IP协议号是50时, 数据包将<br>// 调用该结构的handler处理函数:<br>static struct net_protocol esp4_protocol = {<br> .handler = xfrm4_rcv,<br> .err_handler = esp4_err,<br> .no_policy = 1,<br>};</div>
<div><br>ESP协议结构的handler函数也是xfrm4_rcv, 在net/ipv4/xfrm4_input.c 中定义, <br>在上一篇中进行了介绍.</div>
<div><br>// 错误处理, 收到ICMP错误包时的处理情况, 此时的skb包是ICMP包<br>static void esp4_err(struct sk_buff *skb, u32 info)<br>{<br>// 应用层, data指向ICMP错误包里的内部IP头<br> struct iphdr *iph = (struct iphdr*)skb->data;<br>// ESP头<br> struct ip_esp_hdr *esph = (struct ip_esp_hdr*)(skb->data+(iph->ihl<<2));<br> struct xfrm_state *x;</div>
<div>// ICMP错误类型检查, 本处理函数只处理"目的不可达"和"需要分片"两种错误<br> if (skb->h.icmph->type != ICMP_DEST_UNREACH ||<br>     skb->h.icmph->code != ICMP_FRAG_NEEDED)<br>  return;</div>
<div>// 重新查找SA<br> x = xfrm_state_lookup((xfrm_address_t *)&iph->daddr, esph->spi, IPPROTO_ESP, AF_INET);<br> if (!x)<br>  return;<br> NETDEBUG(KERN_DEBUG "pmtu discovery on SA ESP/%08x/%08x\n",<br>   ntohl(esph->spi), ntohl(iph->daddr));<br> xfrm_state_put(x);<br>}</div>
<div><br>8.2.3 ESP4协议的IPSEC处理结构</div>
<div><br>static struct xfrm_type esp_type =<br>{<br> .description = "ESP4",<br> .owner  = THIS_MODULE,<br> .proto       = IPPROTO_ESP,<br>// 状态初始化<br> .init_state = esp_init_state,<br>// 协议释放<br> .destructor = esp_destroy,<br>// 计算最大长度<br> .get_max_size = esp4_get_max_size,<br>// 协议输入<br> .input  = esp_input,<br>// 协议输出<br> .output  = esp_output<br>};</div>
<div><br>8.2.3.1 状态初始化</div>
<div>esp_data数据结构:</div>
<div>/* include/net/esp.h */</div>
<div>struct esp_data<br>{<br> struct scatterlist  sgbuf;</div>
<div> /* Confidentiality */<br>// 加密使用的相关数据<br> struct {<br>// 密钥<br>  u8   *key;  /* Key */<br>// 密钥长度<br>  int   key_len; /* Key length */<br>// 填充长度<br>  int   padlen;  /* 0..255 */<br>  /* ivlen is offset from enc_data, where encrypted data start.<br>   * It is logically different of crypto_tfm_alg_ivsize(tfm).<br>   * We assume that it is either zero (no ivec), or<br>   * >= crypto_tfm_alg_ivsize(tfm). */<br>// 初始化向量长度<br>  int   ivlen;<br>// 初始化向量是否初始化标志<br>  int   ivinitted;<br>// 初始化向量<br>  u8   *ivec;  /* ivec buffer */<br>// 加密算法<br>  struct crypto_blkcipher *tfm;  /* crypto handle */<br> } conf;</div>
<div> /* Integrity. It is active when icv_full_len != 0 */<br>// 认证使用的相关数据<br> struct {<br>// 密钥<br>  u8   *key;  /* Key */<br>// 密钥长度<br>  int   key_len; /* Length of the key */<br>// 初始化向量<br>  u8   *work_icv;<br>// 初始化向量全长<br>  int   icv_full_len;<br>// 初始化向量截断长度<br>  int   icv_trunc_len;<br>// 初始化向量更新函数, 好象没用<br>  void   (*icv)(struct esp_data*,<br>                                 struct sk_buff *skb,<br>                                 int offset, int len, u8 *icv);<br>// HASH算法<br>  struct crypto_hash *tfm;<br> } auth;<br>};</div>
<div>// ESP的esp_data数据结构初始化<br>static int esp_init_state(struct xfrm_state *x)<br>{<br> struct esp_data *esp = NULL;<br> struct crypto_blkcipher *tfm;</div>
<div> /* null auth and encryption can have zero length keys */<br>// 如果有认证算法, 密钥至少512, ESP的认证处理是可选的, 但在实际中都会使用认证<br> if (x->aalg) {<br>  if (x->aalg->alg_key_len > 512)<br>   goto error;<br> }<br>// ESP加密算法是必须的<br> if (x->ealg == NULL)<br>  goto error;</div>
<div>// 分配esp_data数据结构空间<br> esp = kzalloc(sizeof(*esp), GFP_KERNEL);<br> if (esp == NULL)<br>  return -ENOMEM;<br>// 如果定义了认证算法, 初始化认证算法参数, 和AH类似<br> if (x->aalg) {<br>  struct xfrm_algo_desc *aalg_desc;<br>  struct crypto_hash *hash;<br>// 认证密钥和长度设置<br>  esp->auth.key = x->aalg->alg_key;<br>  esp->auth.key_len = (x->aalg->alg_key_len+7)/8;<br>// 分配HASH算法的实现<br>  hash = crypto_alloc_hash(x->aalg->alg_name, 0,<br>      CRYPTO_ALG_ASYNC);<br>  if (IS_ERR(hash))<br>   goto error;</div>
<div>  esp->auth.tfm = hash;<br>// 设置HASH算法密钥<br>  if (crypto_hash_setkey(hash, esp->auth.key, esp->auth.key_len))<br>   goto error;<br>// 找到算法描述<br>  aalg_desc = xfrm_aalg_get_byname(x->aalg->alg_name, 0);<br>  BUG_ON(!aalg_desc);<br>// 检查算法初始化向量长度合法性<br>  if (aalg_desc->uinfo.auth.icv_fullbits/8 !=<br>      crypto_hash_digestsize(hash)) {<br>   NETDEBUG(KERN_INFO "ESP: %s digestsize %u != %hu\n",<br>     x->aalg->alg_name,<br>     crypto_hash_digestsize(hash),<br>     aalg_desc->uinfo.auth.icv_fullbits/8);<br>   goto error;<br>  }<br>// 初始化向量的全长和截断长度<br>  esp->auth.icv_full_len = aalg_desc->uinfo.auth.icv_fullbits/8;<br>  esp->auth.icv_trunc_len = aalg_desc->uinfo.auth.icv_truncbits/8;<br>// 分配全长度的初始化向量空间<br>  esp->auth.work_icv = kmalloc(esp->auth.icv_full_len, GFP_KERNEL);<br>  if (!esp->auth.work_icv)<br>   goto error;<br> }</div>
<div>// 初始化加密算法相关参数, ESP使用的加密算法都是对称块加密算法, 不可能用非对称算法的<br>// 加密密钥<br> esp->conf.key = x->ealg->alg_key;<br>// 加密密钥长度<br> esp->conf.key_len = (x->ealg->alg_key_len+7)/8;<br>// 分配加密算法的具体实现结构<br> tfm = crypto_alloc_blkcipher(x->ealg->alg_name, 0, CRYPTO_ALG_ASYNC);<br> if (IS_ERR(tfm))<br>  goto error;<br> esp->conf.tfm = tfm;<br>// 初始化向量大小<br> esp->conf.ivlen = crypto_blkcipher_ivsize(tfm);<br>// 填充数据长度初始化为0<br> esp->conf.padlen = 0;<br>// 初始化向量长度非0, 分配具体的初始化向量空间<br> if (esp->conf.ivlen) {<br>  esp->conf.ivec = kmalloc(esp->conf.ivlen, GFP_KERNEL);<br>  if (unlikely(esp->conf.ivec == NULL))<br>   goto error;<br>  esp->conf.ivinitted = 0;<br> }<br>// 设置加密算法密钥<br> if (crypto_blkcipher_setkey(tfm, esp->conf.key, esp->conf.key_len))<br>  goto error;<br>// 定义SA中ESP头部长度: ESP头加初始化向量长度<br>// 反映在ESP封装操作时要将数据包增加的长度<br> x->props.header_len = sizeof(struct ip_esp_hdr) + esp->conf.ivlen;<br>// 如果是通道模式, 还需要增加IP头长度<br> if (x->props.mode == XFRM_MODE_TUNNEL)<br>  x->props.header_len += sizeof(struct iphdr);<br>// 如果要进行UDP封装<br> if (x->encap) {<br>  struct xfrm_encap_tmpl *encap = x->encap;</div>
<div>  switch (encap->encap_type) {<br>  default:<br>   goto error;<br>  case UDP_ENCAP_ESPINUDP:<br>// 该类型封装增加UDP头长度<br>   x->props.header_len += sizeof(struct udphdr);<br>   break;<br>  case UDP_ENCAP_ESPINUDP_NON_IKE:<br>// 该类型封装增加UDP头长度外加加8字节<br>   x->props.header_len += sizeof(struct udphdr) + 2 * sizeof(u32);<br>   break;<br>  }<br> }<br>// 将esp_data作为SA的data指针<br> x->data = esp;<br>// 追踪长度, 最大增加长度和当前的计算的增加长度的差值,在路由时会用到<br>// 对于AH, 由于没有定义get_max_size(), 该值位0<br> x->props.trailer_len = esp4_get_max_size(x, 0) - x->props.header_len;<br> return 0;</div>
<div>error:<br> x->data = esp;<br> esp_destroy(x);<br> x->data = NULL;<br> return -EINVAL;<br>}</div>
<div><br>8.2.3.2 协议释放</div>
<div><br>// 该函数被xfrm状态(SA)释放函数xfrm_state_gc_destroy()调用<br>static void esp_destroy(struct xfrm_state *x)<br>{<br> struct esp_data *esp = x->data;</div>
<div> if (!esp)<br>  return;<br>// 释放加密算法<br> crypto_free_blkcipher(esp->conf.tfm);<br> esp->conf.tfm = NULL;<br>// 释放加密初始化向量<br> kfree(esp->conf.ivec);<br> esp->conf.ivec = NULL;<br>// 释放认证算法<br> crypto_free_hash(esp->auth.tfm);<br> esp->auth.tfm = NULL;<br>// 释放认证初始化向量<br> kfree(esp->auth.work_icv);<br> esp->auth.work_icv = NULL;<br>// 释放esp_data<br> kfree(esp);<br>}</div>
<div><br>8.2.3.3 计算最大长度</div>
<div><br>// 在xfrm_state_mtu()函数中调用, 计算最大增加的数据长度<br>// AH中没有该函数, 增加的长度使用x->props.header_len<br>static u32 esp4_get_max_size(struct xfrm_state *x, int mtu)<br>{<br> struct esp_data *esp = x->data;<br>// 加密块长度, 按4字节对齐<br> u32 blksize = ALIGN(crypto_blkcipher_blocksize(esp->conf.tfm), 4);<br> int enclen = 0;</div>
<div> switch (x->props.mode) {<br> case XFRM_MODE_TUNNEL:<br>// 通道模式下的MTU, 按加密块大小对齐, +2是要包括2字节数据长度<br>  mtu = ALIGN(mtu +2, blksize);<br>  break;<br> default:<br> case XFRM_MODE_TRANSPORT:<br>  /* The worst case */<br>// 传输模式下, MTU先按4字节对齐, 再加块长度减4<br>  mtu = ALIGN(mtu + 2, 4) + blksize - 4;<br>  break;<br> case XFRM_MODE_BEET:<br>   /* The worst case. */<br>  enclen = IPV4_BEET_PHMAXLEN;<br>  mtu = ALIGN(mtu + enclen + 2, blksize);<br>  break;<br> }<br>// 如果加密算法中定义了填充长度, MTU也要按填充长度对齐<br> if (esp->conf.padlen)<br>  mtu = ALIGN(mtu, esp->conf.padlen);<br>// 返回MTU加提议中需要增加的头部长度和认证初始化向量的截断长度<br>// enclen只在BEET模式下非0, 在通道和传输模式下都是0<br> return mtu + x->props.header_len + esp->auth.icv_trunc_len - enclen;<br>}</div>
<div> </div>
<div>8.2.3.4 协议输入</div>
<div><br>struct scatterlist结构说明:</div>
<div>/* include/asm-i386/scatterlist.h */</div>
<div>struct scatterlist {<br>    struct page  *page;<br>    unsigned int offset;<br>    dma_addr_t  dma_address;<br>    unsigned int length;<br>};</div>
<div><br>/*<br> * Note: detecting truncated vs. non-truncated authentication data is very<br> * expensive, so we only support truncated data, which is the recommended<br> * and common case.<br> */<br>// 接收数据处理, 在xfrm4_rcv_encap()函数中调用<br>// 进行ESP认证解密, 剥离ESP头, 解密成普通数据包, 数据包长度减少<br>// 输入的数据包是ESP包<br>static int esp_input(struct xfrm_state *x, struct sk_buff *skb)<br>{<br> struct iphdr *iph;<br> struct ip_esp_hdr *esph;<br> struct esp_data *esp = x->data;<br> struct crypto_blkcipher *tfm = esp->conf.tfm;<br> struct blkcipher_desc desc = { .tfm = tfm };<br> struct sk_buff *trailer;<br> int blksize = ALIGN(crypto_blkcipher_blocksize(tfm), 4);<br>// 认证初始化向量截断长度<br> int alen = esp->auth.icv_trunc_len;<br>// 需要加密的数据长度: 总长减ESP头, 加密初始化向量长度, 认证初始化向量长度<br> int elen = skb->len - sizeof(struct ip_esp_hdr) - esp->conf.ivlen - alen;<br> int nfrags;<br> int ihl;<br> u8 nexthdr;<br> struct scatterlist *sg;<br> int padlen;<br> int err;</div>
<div>// 在skb头留出ESP头的空间<br> if (!pskb_may_pull(skb, sizeof(struct ip_esp_hdr)))<br>  goto out;</div>
<div>// 检查需要加密的数据长度, 必须大于0而且按块大小对齐的<br> if (elen <= 0 || (elen & (blksize-1)))<br>  goto out;</div>
<div> /* If integrity check is required, do this. */<br>// 认证计算处理<br> if (esp->auth.icv_full_len) {<br>  u8 sum;<br>// 计算认证值, 认证值保存在esp_data结构中<br>  err = esp_mac_digest(esp, skb, 0, skb->len - alen);<br>  if (err)<br>   goto out;</div>
<div>// 将skb中的认证初始化向量部分数据拷贝到缓冲区sum中<br>  if (skb_copy_bits(skb, skb->len - alen, sum, alen))<br>   BUG();<br>// 比较sum中的向量值和认证算法结构中的向量值是否匹配, 数据包正常情况下应该是相同的<br>  if (unlikely(memcmp(esp->auth.work_icv, sum, alen))) {<br>   x->stats.integrity_failed++;<br>   goto out;<br>  }<br> }<br>// 使数据包是可写的<br> if ((nfrags = skb_cow_data(skb, 0, &trailer)) < 0)<br>  goto out;</div>
<div> skb->ip_summed = CHECKSUM_NONE;<br>// 定位在数据包中的ESP头位置, 为当前的data位置<br> esph = (struct ip_esp_hdr*)skb->data;</div>
<div> /* Get ivec. This can be wrong, check against another impls. */<br>// 设置加密算法的初始化向量<br> if (esp->conf.ivlen)<br>  crypto_blkcipher_set_iv(tfm, esph->enc_data, esp->conf.ivlen);</div>
<div> sg = &esp->sgbuf;</div>
<div> if (unlikely(nfrags > ESP_NUM_FAST_SG)) {<br>  sg = kmalloc(sizeof(struct scatterlist)*nfrags, GFP_ATOMIC);<br>  if (!sg)<br>   goto out;<br> }<br> skb_to_sgvec(skb, sg, sizeof(struct ip_esp_hdr) + esp->conf.ivlen, elen);<br>// 解密操作, 返回非0表示失败<br> err = crypto_blkcipher_decrypt(&desc, sg, sg, elen);<br> if (unlikely(sg != &esp->sgbuf))<br>  kfree(sg);<br>// 解密失败返回<br> if (unlikely(err))<br>  return err;<br>// 拷贝两字节数据<br> if (skb_copy_bits(skb, skb->len-alen-2, nexthdr, 2))<br>  BUG();</div>
<div> padlen = nexthdr;<br> if (padlen+2 >= elen)<br>  goto out;</div>
<div> /* ... check padding bits here. Silly. :-) */ <br>// 新的IP头<br> iph = skb->nh.iph;<br> ihl = iph->ihl * 4;<br>// 如果是NAT穿越情况, 进行一些处理<br> if (x->encap) {<br>// xfrm封装模板<br>  struct xfrm_encap_tmpl *encap = x->encap;<br>// 定位UDP数据头位置, 在IP头之后<br>  struct udphdr *uh = (void *)(skb->nh.raw + ihl);</div>
<div>  /*<br>   * 1) if the NAT-T peer's IP or port changed then<br>   *    advertize the change to the keying daemon.<br>   *    This is an inbound SA, so just compare<br>   *    SRC ports.<br>   */<br>// 如果IP头源地址和SA提议中的源地址不同或源端口不同<br>  if (iph->saddr != x->props.saddr.a4 ||<br>      uh->source != encap->encap_sport) {<br>   xfrm_address_t ipaddr;<br>// 保存当前IP头源地址<br>   ipaddr.a4 = iph->saddr;<br>// 进行NAT通知回调处理<br>   km_new_mapping(x, &ipaddr, uh->source);<br>    <br>   /* XXX: perhaps add an extra<br>    * policy check here, to see<br>    * if we should allow or<br>    * reject a packet from a<br>    * different source<br>    * address/port.<br>    */<br>  }<br> <br>  /*<br>   * 2) ignore UDP/TCP checksums in case<br>   *    of NAT-T in Transport Mode, or<br>   *    perform other post-processing fixes<br>   *    as per draft-ietf-ipsec-udp-encaps-06,<br>   *    section 3.1.2<br>   */<br>// 如果是传输模式或BEET模式, 设置不需要计算校验和<br>  if (x->props.mode == XFRM_MODE_TRANSPORT ||<br>      x->props.mode == XFRM_MODE_BEET)<br>   skb->ip_summed = CHECKSUM_UNNECESSARY;<br> }<br>// 新IP头中协议<br> iph->protocol = nexthdr;<br>// 缩减skb数据包长度<br> pskb_trim(skb, skb->len - alen - padlen - 2);<br>// 重新定位IP上层数据头位置<br> skb->h.raw = __skb_pull(skb, sizeof(*esph) + esp->conf.ivlen) - ihl;</div>
<div> return 0;</div>
<div>out:<br> return -EINVAL;<br>}</div>
<div><br>8.2.3.4 协议输出</div>
<div><br>// 发送数据处理, 在xfrm4_output_one()中调用<br>// 添加ESP头, 对数据包进行加密和认证处理, 数据包长度扩大<br>// 在NAT穿越情况下会封装为UDP数据<br>static int esp_output(struct xfrm_state *x, struct sk_buff *skb)<br>{<br> int err;<br> struct iphdr *top_iph;<br> struct ip_esp_hdr *esph;<br> struct crypto_blkcipher *tfm;<br> struct blkcipher_desc desc;<br> struct esp_data *esp;<br> struct sk_buff *trailer;<br> int blksize;<br> int clen;<br> int alen;<br> int nfrags;</div>
<div> /* Strip IP+ESP header. */<br>// 缩减skb数据, 减去IP头和ESP头, 剩下的数据就是要进行加密和认证的部分<br> __skb_pull(skb, skb->h.raw - skb->data);<br> /* Now skb is pure payload to encrypt */</div>
<div> err = -ENOMEM;</div>
<div> /* Round to block size */<br>// 加密块的初始值<br> clen = skb->len;</div>
<div>// 获取SA的esp_data数据结构<br> esp = x->data;<br>// 认证初始化向量截断长度<br> alen = esp->auth.icv_trunc_len;<br>// 加密算法<br> tfm = esp->conf.tfm;<br>// 给块加密算法描述结构赋值<br> desc.tfm = tfm;<br> desc.flags = 0;<br>// 每个加密块大小<br> blksize = ALIGN(crypto_blkcipher_blocksize(tfm), 4);<br>// 对齐要加密的数据总长<br> clen = ALIGN(clen + 2, blksize);<br>// 如果要考虑填充, 继续对齐<br> if (esp->conf.padlen)<br>  clen = ALIGN(clen, esp->conf.padlen);</div>
<div>// 使数据包可写<br> if ((nfrags = skb_cow_data(skb, clen-skb->len+alen, &trailer)) < 0)<br>  goto error;</div>
<div> /* Fill padding... */<br>// 长度对齐后填充多余长度部分内容<br> do {<br>  int i;<br>  for (i=0; i<clen-skb->len - 2; i++)<br>   *(u8*)(trailer->tail + i) = i+1;<br> } while (0);<br>// 最后两字节表示填充数据的长度<br> *(u8*)(trailer->tail + clen-skb->len - 2) = (clen - skb->len)-2;<br> pskb_put(skb, trailer, clen - skb->len);<br>// 在将IP头部分扩展回来<br> __skb_push(skb, skb->data - skb->nh.raw);<br>// 现在的IP头作为外部IP头<br> top_iph = skb->nh.iph;<br>// esp头跟在IP头后<br> esph = (struct ip_esp_hdr *)(skb->nh.raw + top_iph->ihl*4);<br>// 数据总长增加认证部分长度<br> top_iph->tot_len = htons(skb->len + alen);<br> *(u8*)(trailer->tail - 1) = top_iph->protocol;</div>
<div> /* this is non-NULL only with UDP Encapsulation */<br> if (x->encap) {<br>// NAT穿越情况下要将数据封装为UDP包<br>  struct xfrm_encap_tmpl *encap = x->encap;<br>  struct udphdr *uh;<br>  u32 *udpdata32;<br>// IP头后改为UDP头<br>  uh = (struct udphdr *)esph;<br>// 填充UDP头参数, 源端口, 目的端口, UDP数据长度<br>  uh->source = encap->encap_sport;<br>  uh->dest = encap->encap_dport;<br>  uh->len = htons(skb->len + alen - top_iph->ihl*4);<br>// 校验和为0, 表示不需要计算校验和, ESP本身就进行认证了<br>  uh->check = 0;</div>
<div>  switch (encap->encap_type) {<br>  default:<br>  case UDP_ENCAP_ESPINUDP:<br>// 在该模式下ESP头跟在UDP头后面<br>   esph = (struct ip_esp_hdr *)(uh + 1);<br>   break;<br>  case UDP_ENCAP_ESPINUDP_NON_IKE:<br>// 在该模式下ESP头跟在UDP头后面8字节处<br>   udpdata32 = (u32 *)(uh + 1);<br>   udpdata32 = udpdata32 = 0;<br>   esph = (struct ip_esp_hdr *)(udpdata32 + 2);<br>   break;<br>  }<br>// 外部IP头协议是UDP<br>  top_iph->protocol = IPPROTO_UDP;<br> } else<br>// 非NAT穿越情况下, 外部IP头中的协议是ESP<br>  top_iph->protocol = IPPROTO_ESP;</div>
<div>// 填充ESP头中的SPI和序列号<br> esph->spi = x->id.spi;<br> esph->seq_no = htonl(++x->replay.oseq);<br>// 序列号更新通知回调<br> xfrm_aevent_doreplay(x);</div>
<div>// 如果加密初始化向量长度非零, 设置加密算法中的初始化向量<br> if (esp->conf.ivlen) {<br>  if (unlikely(!esp->conf.ivinitted)) {<br>   get_random_bytes(esp->conf.ivec, esp->conf.ivlen);<br>   esp->conf.ivinitted = 1;<br>  }<br>  crypto_blkcipher_set_iv(tfm, esp->conf.ivec, esp->conf.ivlen);<br> }<br>// 加密操作<br> do {<br>  struct scatterlist *sg = &esp->sgbuf;</div>
<div>  if (unlikely(nfrags > ESP_NUM_FAST_SG)) {<br>   sg = kmalloc(sizeof(struct scatterlist)*nfrags, GFP_ATOMIC);<br>   if (!sg)<br>    goto error;<br>  }<br>  skb_to_sgvec(skb, sg, esph->enc_data+esp->conf.ivlen-skb->data, clen);<br>// 对数据加密<br>  err = crypto_blkcipher_encrypt(&desc, sg, sg, clen);<br>  if (unlikely(sg != &esp->sgbuf))<br>   kfree(sg);<br> } while (0);</div>
<div> if (unlikely(err))<br>  goto error;<br>// 将加密算法初始化向量拷贝到数据包<br> if (esp->conf.ivlen) {<br>  memcpy(esph->enc_data, esp->conf.ivec, esp->conf.ivlen);<br>  crypto_blkcipher_get_iv(tfm, esp->conf.ivec, esp->conf.ivlen);<br> }<br>// 认证计算, 计算出HASH值并拷贝到数据包中<br> if (esp->auth.icv_full_len) {<br>  err = esp_mac_digest(esp, skb, (u8 *)esph - skb->data,<br>         sizeof(*esph) + esp->conf.ivlen + clen);<br>  memcpy(pskb_put(skb, trailer, alen), esp->auth.work_icv, alen);<br> }<br>// 重新计算外部IP头校验和<br> ip_send_check(top_iph);</div>
<div>error:<br> return err;<br>}</div>
<div> </div>
<div>...... 待续 ......</div>

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Linux内核中的IPSEC实现(6)