用户层通过socket使用XFRM_MSG_GETSA如果获取xfrm_algo_auth信息的C代码示例

以下是使用socket获取xfrm_algo_auth信息的C代码示例：

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

#define NETLINK_XFRM 27
#define XFRM_MSG_GETSA 18

int main() {
    struct sockaddr_nl nladdr;
    struct nlmsghdr *nlh;
    struct xfrm_usersa_info *info;
    struct msghdr msg;
    struct iovec iov;
    char buffer[4096];
    int sock, len;

    // 创建socket
    sock = socket(AF_NETLINK, SOCK_RAW, NETLINK_XFRM);
    if (sock < 0) {
        perror("socket");
        exit(EXIT_FAILURE);
    }

    // 绑定本地地址
    memset(&nladdr, 0, sizeof(nladdr));
    nladdr.nl_family = AF_NETLINK;
    nladdr.nl_pid = getpid();
    nladdr.nl_groups = 0;
    if (bind(sock, (struct sockaddr *)&nladdr, sizeof(nladdr)) < 0) {
        perror("bind");
        exit(EXIT_FAILURE);
    }

    // 构造请求消息
    nlh = (struct nlmsghdr *)buffer;
    nlh->nlmsg_len = NLMSG_LENGTH(sizeof(*info));
    nlh->nlmsg_type = XFRM_MSG_GETSA;
    nlh->nlmsg_flags = NLM_F_REQUEST | NLM_F_DUMP;
    nlh->nlmsg_seq = 0;
    nlh->nlmsg_pid = getpid();
    info = (struct xfrm_usersa_info *)NLMSG_DATA(nlh);
    memset(info, 0, sizeof(*info));
    info->info.type = XFRM_USERSA_INFO;
    info->saddr.a4 = htonl(INADDR_LOOPBACK); // 指定源地址
    info->id.daddr.a4 = htonl(INADDR_LOOPBACK); // 指定目的地址

    // 发送请求消息
    iov.iov_base = (void *)nlh;
    iov.iov_len = nlh->nlmsg_len;
    msg.msg_name = (void *)&nladdr;
    msg.msg_namelen = sizeof(nladdr);
    msg.msg_iov = &iov;
    msg.msg_iovlen = 1;
    if (sendmsg(sock, &msg, 0) < 0) {
        perror("sendmsg");
        exit(EXIT_FAILURE);
    }

    // 接收响应消息
    iov.iov_base = buffer;
    iov.iov_len = sizeof(buffer);
    msg.msg_name = (void *)&nladdr;
    msg.msg_namelen = sizeof(nladdr);
    msg.msg_iov = &iov;
    msg.msg_iovlen = 1;
    len = recvmsg(sock, &msg, 0);
    if (len < 0) {
        perror("recvmsg");
        exit(EXIT_FAILURE);
    }

    // 解析响应消息
    nlh = (struct nlmsghdr *)buffer;
    while (NLMSG_OK(nlh, len)) {
        if (nlh->nlmsg_type == NLMSG_DONE) {
            break;
        }
        if (nlh->nlmsg_type == NLMSG_ERROR) {
            perror("NLMSG_ERROR");
            exit(EXIT_FAILURE);
        }
        if (nlh->nlmsg_type == XFRM_MSG_NEWSA) {
            info = (struct xfrm_usersa_info *)NLMSG_DATA(nlh);
            if (info->id.proto == IPPROTO_ESP) { // 只处理ESP协议
                struct xfrm_algo *a;
                for (a = info->aalgos; a; a = a->next) {
                    if (a->alg_key_len == 16 && a->alg_iv_len == 8) { // 只处理AES-CBC-128算法
                        printf("ESP AES-CBC-128 authentication algorithm: %s\n", a->alg_name);
                    }
                }
            }
        }
        nlh = NLMSG_NEXT(nlh, len);
    }

    // 关闭socket
    close(sock);
    return 0;
}

该示例程序使用NETLINK_XFRM协议的socket，通过XFRM_MSG_GETSA消息获取系统中所有安全关联，并从中筛选出ESP协议的安全关联，进一步获取其使用的AES-CBC-128算法的认证信息