写一个通过NETLINK新增SA的C代码

以下是一个通过NETLINK新增Security Association（SA）的C代码示例：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <sys/socket.h>
#include <linux/netlink.h>
#include <linux/xfrm.h>

#define SA_PAYLOAD_SIZE 1024

int main(int argc, char *argv[]) {
    int nl_sock, ret;
    char payload[SA_PAYLOAD_SIZE];
    struct nlmsghdr *nlh;
    struct xfrm_usersa_info *usa;
    struct sockaddr_nl sa_nl;

    // Create NETLINK socket
    nl_sock = socket(AF_NETLINK, SOCK_RAW, NETLINK_XFRM);
    if (nl_sock < 0) {
        perror("socket");
        exit(EXIT_FAILURE);
    }

    // Initialize sockaddr_nl structure
    memset(&sa_nl, 0, sizeof(sa_nl));
    sa_nl.nl_family = AF_NETLINK;

    // Bind socket to NETLINK_XFRM protocol
    ret = bind(nl_sock, (struct sockaddr *)&sa_nl, sizeof(sa_nl));
    if (ret < 0) {
        perror("bind");
        close(nl_sock);
        exit(EXIT_FAILURE);
    }

    // Allocate memory for NETLINK message header and payload
    nlh = (struct nlmsghdr *)malloc(NLMSG_SPACE(sizeof(struct xfrm_usersa_info)));
    usa = (struct xfrm_usersa_info *)NLMSG_DATA(nlh);

    // Fill in xfrm_usersa_info structure
    usa->family = AF_INET;
    usa->proto = IPPROTO_ESP;
    usa->mode = XFRM_MODE_TUNNEL;
    usa->flags = XFRM_STATE_ESN | XFRM_STATE_DECAP_DSCP;
    usa->spi = 0x12345678;
    usa->reqid = 0xabcdef;
    usa->replay_window = 32;
    usa->saddr.a4 = inet_addr("192.168.1.1");
    usa->id.daddr.a4 = inet_addr("10.0.0.1");
    usa->encap_family = AF_INET;
    usa->encap_type = XFRM_ENCAP_ESPINUDP;
    usa->enckey_len = 16;
    memcpy(usa->enckey, "0123456789abcdef", usa->enckey_len);
    usa->authkey_len = 20;
    memcpy(usa->authkey, "0123456789abcdefghijklmnopq", usa->authkey_len);

    // Fill in NETLINK message header
    nlh->nlmsg_len = NLMSG_LENGTH(sizeof(struct xfrm_usersa_info));
    nlh->nlmsg_type = XFRM_MSG_NEWSA;
    nlh->nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK;
    nlh->nlmsg_seq = 0;
    nlh->nlmsg_pid = getpid();

    // Send message to kernel
    ret = send(nl_sock, nlh, nlh->nlmsg_len, 0);
    if (ret < 0) {
        perror("send");
        close(nl_sock);
        free(nlh);
        exit(EXIT_FAILURE);
    }

    // Receive response from kernel
    ret = recv(nl_sock, payload, SA_PAYLOAD_SIZE, 0);
    if (ret < 0) {
        perror("recv");
        close(nl_sock);
        free(nlh);
        exit(EXIT_FAILURE);
    }

    // Parse response message
    nlh = (struct nlmsghdr *)payload;
    if (nlh->nlmsg_type == NLMSG_ERROR) {
        struct nlmsgerr *err = (struct nlmsgerr *)NLMSG_DATA(nlh);
        if (err->error != 0) {
            fprintf(stderr, "Error: %s\n", strerror(-err->error));
            close(nl_sock);
            free(nlh);
            exit(EXIT_FAILURE);
        }
    }

    // Clean up
    close(nl_sock);
    free(nlh);

    return 0;
}

这个程序创建了一个NETLINK_XFRM套接字，并使用它向内核发送一个XFRM_MSG_NEWSA消息，以添加一个新的SA。在这个示例中，新的SA是一个ESP隧道，使用IP地址192.168.1.1和10.0.0.1作为源和目的地，使用16字节的AES-128加密密钥和20字节的HMAC-SHA1认证密钥，使用32个包的重放窗口，SPI值为0x12345678，请求ID为0xabcdef，以及ESN和解码DSCP标志设置。程序还等待内核的响应，以检查是否有任何错误发生