inux 系统内核空间与用户空间通信的实现与分析

在 IBM Bluemix 云平台上开发并部署您的下一个应用。

现在就开始免费试用

static struct sock *nlfd;struct{  __u32 pid;  rwlock_t lock;}user_proc;/*挂接在 netfilter 框架的 NF_IP_PRE_ROUTING 点上的函数为 get_icmp()*/static struct nf_hook_ops imp2_ops ={  .hook = get_icmp,		/*netfilter 钩子函数*/  .pf = PF_INET,  .hooknum = NF_IP_PRE_ROUTING,  .priority = NF_IP_PRI_FILTER -1,};static int __init init(void){  rwlock_init(&user_proc.lock);  /*在内核创建一个 netlink socket，并注明由 kernel_recieve() 函数接收数据    这里协议 NL_IMP2 是自定的*/  nlfd = netlink_kernel_create(NL_IMP2, kernel_receive);  if(!nlfd)    {      printk("can not create a netlink socket\n");      return -1;    }  /*向 netfilter 的 NF_IP_PRE_ROUTING 点挂接函数*/  return nf_register_hook(&imp2_ops);}static void __exit fini(void){  if(nlfd)    {      sock_release(nlfd->socket);	}  nf_unregister_hook(&imp2_ops);}module_init(init);module_exit(fini);

DECLARE_MUTEX(receive_sem);01:  static void kernel_receive(struct sock *sk, int len)02:  {03:    do04:      {05:       struct sk_buff *skb;06:        if(down_trylock(&receive_sem))07:            return;08:09:        while((skb = skb_dequeue(&sk-<receive_queue)) != NULL)10:          {11:          {12:              struct nlmsghdr *nlh = NULL;13:        if(skb-<len <= sizeof(struct nlmsghdr))14:              {15:                nlh = (struct nlmsghdr *)skb-<data;16:                if((nlh-<nlmsg_len <= sizeof(struct nlmsghdr))17:                   && (skb-<len <= nlh-<nlmsg_len))18:                  {19:                    if(nlh-<nlmsg_type == IMP2_U_PID)20:                      {21:                        write_lock_bh(&user_proc.pid);22:                        user_proc.pid = nlh-<nlmsg_pid;23:                write_unlock_bh(&user_proc.pid);24:                      }25:                    else if(nlh-<nlmsg_type == IMP2_CLOSE)26:                      {27:                        write_lock_bh(&user_proc.pid);28:               if(nlh-<nlmsg_pid == user_proc.pid) user_proc.pid = 0;29:                        write_unlock_bh(&user_proc.pid);30:                      }31:                  }32:              }33:          }34:        kfree_skb(skb);35:        }36:        up(&receive_sem);37:      }while(nlfd && nlfd-<receive_queue.qlen);38:  }

static unsigned int get_icmp(unsigned int hook,                             struct sk_buff **pskb,                             const struct net_device *in,                             const struct net_device *out,                             int (*okfn)(struct sk_buff *)){  struct iphdr *iph = (*pskb)->nh.iph;  struct packet_info info;  if(iph->protocol == IPPROTO_ICMP)	/*若传输层协议为 ICMP*/    {      read_lock_bh(&user_proc.lock);      if(user_proc.pid != 0)	    {          read_unlock_bh(&user_proc.lock);          info.src = http://www.mamicode.com/iph->saddr;	/*记录源地址*/>

static int send_to_user(struct packet_info *info){  int ret;  int size;  unsigned char *old_tail;  struct sk_buff *skb;  struct nlmsghdr *nlh;  struct packet_info *packet;  size = NLMSG_SPACE(sizeof(*info));  /*开辟一个新的套接字缓存*/  skb = alloc_skb(size, GFP_ATOMIC);  old_tail = skb->tail;  /*填写数据报相关信息*/  nlh = NLMSG_PUT(skb, 0, 0, IMP2_K_MSG, size-sizeof(*nlh));  packet = NLMSG_DATA(nlh);  memset(packet, 0, sizeof(struct packet_info));  /*传输到用户空间的数据*/  packet->src = http://www.mamicode.com/info->src;>

/*字节对齐*/#define NLMSG_ALIGN(len) ( ((len)+NLMSG_ALIGNTO-1) & ~(NLMSG_ALIGNTO-1) )/*计算包含报头的数据报长度*/#define NLMSG_LENGTH(len) ((len)+NLMSG_ALIGN(sizeof(struct nlmsghdr)))/*字节对齐后的数据报长度*/#define NLMSG_SPACE(len) NLMSG_ALIGN(NLMSG_LENGTH(len))/*填写相关报头信息，这里使用了nlmsg_failure标签，所以在程序中要定义*/#define NLMSG_PUT(skb, pid, seq, type, len) ({ if (skb_tailroom(skb) < (int)NLMSG_SPACE(len)) goto nlmsg_failure;    __nlmsg_put(skb, pid, seq, type, len); })static __inline__ struct nlmsghdr *__nlmsg_put(struct sk_buff *skb, u32 pid, u32 seq, int type, int len){	struct nlmsghdr *nlh;	int size = NLMSG_LENGTH(len);	nlh = (struct nlmsghdr*)skb_put(skb, NLMSG_ALIGN(size));	nlh->nlmsg_type = type;	nlh->nlmsg_len = size;	nlh->nlmsg_flags = 0;	nlh->nlmsg_pid = pid;	nlh->nlmsg_seq = seq;	return nlh;}/*跳过报头取实际数据*/#define NLMSG_DATA(nlh)  ((void*)(((char*)nlh) + NLMSG_LENGTH(0)))/*取 netlink 控制字段*/#define NETLINK_CB(skb)		(*(struct netlink_skb_parms*)&((skb)->cb))