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/*
* Copyright 2016 SUSE LLC
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/* NOTE: This code comes directly from runc/libcontainer/utils/cmsg.c. */
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <unistd.h>
#include "cmsg.h"
#define error(fmt, ...) \
({ \
fprintf(stderr, "nsenter: " fmt ": %m\n", ##__VA_ARGS__); \
errno = ECOMM; \
goto err; /* return value */ \
})
/*
* Sends a file descriptor along the sockfd provided. Returns the return
* value of sendmsg(2). Any synchronisation and preparation of state
* should be done external to this (we expect the other side to be in
* recvfd() in the code).
*/
ssize_t sendfd(int sockfd, struct file_t file)
{
struct msghdr msg = {0};
struct iovec iov[1] = {0};
struct cmsghdr *cmsg;
int *fdptr;
union {
char buf[CMSG_SPACE(sizeof(file.fd))];
struct cmsghdr align;
} u;
/*
* We need to send some other data along with the ancillary data,
* otherwise the other side won't recieve any data. This is very
* well-hidden in the documentation (and only applies to
* SOCK_STREAM). See the bottom part of unix(7).
*/
iov[0].iov_base = file.name;
iov[0].iov_len = strlen(file.name) + 1;
msg.msg_name = NULL;
msg.msg_namelen = 0;
msg.msg_iov = iov;
msg.msg_iovlen = 1;
msg.msg_control = u.buf;
msg.msg_controllen = sizeof(u.buf);
cmsg = CMSG_FIRSTHDR(&msg);
cmsg->cmsg_level = SOL_SOCKET;
cmsg->cmsg_type = SCM_RIGHTS;
cmsg->cmsg_len = CMSG_LEN(sizeof(int));
fdptr = (int *) CMSG_DATA(cmsg);
memcpy(fdptr, &file.fd, sizeof(int));
return sendmsg(sockfd, &msg, 0);
}
/*
* Receives a file descriptor from the sockfd provided. Returns the file
* descriptor as sent from sendfd(). It will return the file descriptor
* or die (literally) trying. Any synchronisation and preparation of
* state should be done external to this (we expect the other side to be
* in sendfd() in the code).
*/
struct file_t recvfd(int sockfd)
{
struct msghdr msg = {0};
struct iovec iov[1] = {0};
struct cmsghdr *cmsg;
struct file_t file = {0};
int *fdptr;
int olderrno;
union {
char buf[CMSG_SPACE(sizeof(file.fd))];
struct cmsghdr align;
} u;
/* Allocate a buffer. */
/* TODO: Make this dynamic with MSG_PEEK. */
file.name = malloc(TAG_BUFFER);
if (!file.name)
error("recvfd: failed to allocate file.tag buffer\n");
/*
* We need to "recieve" the non-ancillary data even though we don't
* plan to use it at all. Otherwise, things won't work as expected.
* See unix(7) and other well-hidden documentation.
*/
iov[0].iov_base = file.name;
iov[0].iov_len = TAG_BUFFER;
msg.msg_name = NULL;
msg.msg_namelen = 0;
msg.msg_iov = iov;
msg.msg_iovlen = 1;
msg.msg_control = u.buf;
msg.msg_controllen = sizeof(u.buf);
ssize_t ret = recvmsg(sockfd, &msg, 0);
if (ret < 0)
goto err;
cmsg = CMSG_FIRSTHDR(&msg);
if (!cmsg)
error("recvfd: got NULL from CMSG_FIRSTHDR");
if (cmsg->cmsg_level != SOL_SOCKET)
error("recvfd: expected SOL_SOCKET in cmsg: %d", cmsg->cmsg_level);
if (cmsg->cmsg_type != SCM_RIGHTS)
error("recvfd: expected SCM_RIGHTS in cmsg: %d", cmsg->cmsg_type);
if (cmsg->cmsg_len != CMSG_LEN(sizeof(int)))
error("recvfd: expected correct CMSG_LEN in cmsg: %lu", cmsg->cmsg_len);
fdptr = (int *) CMSG_DATA(cmsg);
if (!fdptr || *fdptr < 0)
error("recvfd: recieved invalid pointer");
file.fd = *fdptr;
return file;
err:
olderrno = errno;
free(file.name);
errno = olderrno;
return (struct file_t){0};
}
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