Advanced Programming in UNIX Environment Episode 110

最新推荐文章于 2025-08-22 12:07:00 发布

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最新推荐文章于 2025-08-22 12:07:00 发布

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分类专栏： Advanced Programming in the Unix Environment 文章标签： unix

本文链接：https://blog.youkuaiyun.com/myfather103/article/details/80495170

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该博客介绍了如何在UNIX域套接字中使用C语言实现发送文件描述符和凭证的功能。代码展示了如何利用`socat`宏定义以及`struct cmsghdr`、`struct ucred`等数据结构来封装和传递这些信息。通过示例函数`send_fd`，可以看到如何将一个文件描述符和相关凭证附加到消息控制块中，然后使用`sendmsg`函数进行发送。

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#include "aupe.h"
#include <sys/socket.h>

#if defined(SCM_CREDS)
#define CREDSTRUCT cmsgcred
#define SCM_CREDTYPE SCM_CREDS
#elif defined(SCM_CREDENTIALS)
#define CREDSTRUCT ucred
#define SCM_CREDTYPE SCM_CREDENTIALS
#else
#error passing credentials is unsupported!
#endif

#define RIGHTSLEN CMSG_LEN(sizeof(int))
#define CREDSLEN CMSG_LEN(sizeof(struct CREDSTRUCT))
#define CONTROLLEN (RIGHTSLEN+CREDSLEN)

static struct cmsghdr *cmptr=NULL;

int send_fd(int fd, int fd_to_send)
{
    struct CREDSTRUCT *credp;
    struct cmsghdr *cmp;
    struct iovec iov[1];
    struct msghdr msg;
    char buf[2];

    iov[0].iov_base=buf;
    iov[0].iov_len=2;
    msg.msg_iov=iov;
    msg.msg_iovlen=1;
    msg.msg_name=NULL;
    msg.msg_namelen=0;
    msg.msg_flags=0;
    if(fd_to_send<0)
    {
        msg.msg_control=NULL;
        msg.msg_controllen=0;
        buf[1]=-fd_to_send;
        if(buf[1]==0)
            buf[1]=1;
    }
    else
    {
        if(cmptr==NULL&&(cmptr=malloc(CONTROLLEN))==NULL)
            return -1;
        msg.msg_control=cmptr;
        msg.msg_controllen=CONTROLLEN;
        cmp=cmptr;
        cmp->cmsg_level=SOL_SOCKET;
        cmp->cmsg_type=SCM_RIGHTS;
        cmp->cmsg_len=RIGHTLEN;
        *(int *)CMSG_DATA(cmp)=fd_to_send;
        cmp->cmsg_level=SOL_SCOKET;
        cmp->cmsg_type=SCM_CREDTYPE;
        cmp->cmsg_len=CREDSLEN;
        credp=(struct CREDSTRUCT *)CMSG_DATA(cmp);
#if defined(SCM_CREDENTIALS)
        credp->uid=geteuid();
        credp->gid=getegid();
        credp->pid=getpid();
#endif
        buf[1]=0;
    }
    buf[0]=0;
    if(sendmsg(fd, &msg,0)!=2)
        return -1;
    return 0;
}

Sending credentials over UNIX domain sockets