diff options
Diffstat (limited to 'conmon/cmsg.c')
| -rw-r--r-- | conmon/cmsg.c | 149 |
1 files changed, 149 insertions, 0 deletions
diff --git a/conmon/cmsg.c b/conmon/cmsg.c new file mode 100644 index 000000000..c44db2ef1 --- /dev/null +++ b/conmon/cmsg.c @@ -0,0 +1,149 @@ +/* + * 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}; +} |