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/* Copyright 2009 SPARTA, Inc. All rights reserved
* Use is subject to license terms specified in the COPYING file
* distributed with the Net-SNMP package.
*/
/*
* This is merely a wrapper around stdin/out for sshd to call. It
* simply passes traffic to the running snmpd through a unix domain
* socket after first passing any needed SSH Domain information.
*/
#include <net-snmp/net-snmp-config.h>
#ifdef HAVE_SYS_PARAM_H
#include <sys/param.h>
#endif
#ifdef HAVE_SYS_SOCKET_H
#include <sys/socket.h>
#endif
#if HAVE_SYS_UN_H
#include <sys/un.h>
#endif
#include <sys/select.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
#include <stdio.h>
#ifndef MAXPATHLEN
#warning no system max path length detected
#define MAXPATHLEN 2048
#endif
#define DEFAULT_SOCK_PATH "/var/net-snmp/sshdomainsocket"
#define NETSNMP_SSHTOSNMP_VERSION_NUMBER 1
/*
* Extra debugging output for, um, debugging.
*/
#undef DEBUGGING
#define DEBUG(x) deb(x)
#ifdef DEBUGGING
FILE *debf = NULL;
static void
deb(const char *string) {
if (NULL == debf) {
debf = fopen("/tmp/sshtosnmp.log", "a");
}
if (NULL != debf) {
fprintf(debf, "%s\n", string);
fflush(debf);
}
}
#else /* !DEBUGGING */
NETSNMP_STATIC_INLINE void
deb(const char *string) { }
#endif /* DEBUGGING code */
int
main(int argc, char **argv) {
int sock;
struct sockaddr_un addr;
u_char buf[4096];
size_t buf_len = sizeof(buf);
int rc = 0, pktsize = 0;
fd_set read_set;
DEBUG("----------\nstarting up");
/* Open a connection to the UNIX domain socket or fail */
addr.sun_family = AF_UNIX;
snprintf(addr.sun_path, sizeof(addr.sun_path), "%s",
argc > 1 ? argv[1] : DEFAULT_SOCK_PATH);
sock = socket(PF_UNIX, SOCK_STREAM, 0);
DEBUG("created socket");
if (sock <= 0) {
exit(1);
}
/* set the SO_PASSCRED option so we can pass uid */
/* XXX: according to the unix(1) manual this shouldn't be needed
on the sending side? */
{
int one = 1;
setsockopt(sock, SOL_SOCKET, SO_PASSCRED, (void *) &one,
sizeof(one));
}
if (connect(sock, (struct sockaddr *) &addr,
sizeof(struct sockaddr_un)) != 0) {
DEBUG("FAIL CONNECT");
exit(1);
}
DEBUG("opened socket");
/*
* we are running as the user that ssh authenticated us as, and this
* is the name/uid that the agent needs for processing as a SNMPv3
* security name. So this is the only thing needed to pass to the
* agent.
*/
/* version 1 of our internal ssh to snmp wrapper is just a single
byte version number and indicates we're also passing unix
socket credentials containing our user id */
/* In case of future changes, we'll pass a version number first */
buf[0] = NETSNMP_SSHTOSNMP_VERSION_NUMBER;
buf_len = 1;
/* send the prelim message and the credentials together using sendmsg() */
{
struct msghdr m;
/*
* Ancillary data buffer, wrapped in a union in order to ensure it is
* suitably aligned.
*/
union {
char buf[CMSG_SPACE(sizeof(struct ucred))];
struct cmsghdr cm;
} cmsg;
struct ucred *const ouruser = (void *)CMSG_DATA(&cmsg.cm);
struct iovec iov = { buf, buf_len };
/* Make sure that even padding fields get initialized.*/
memset(&cmsg, 0, sizeof(cmsg));
memset(&m, 0, sizeof(m));
/* set up the message header */
cmsg.cm.cmsg_len = sizeof(cmsg);
cmsg.cm.cmsg_level = SOL_SOCKET;
cmsg.cm.cmsg_type = SCM_CREDENTIALS;
ouruser->uid = getuid();
ouruser->gid = getgid();
ouruser->pid = getpid();
m.msg_iov = &iov;
m.msg_iovlen = 1;
m.msg_control = &cmsg;
m.msg_controllen = sizeof(cmsg);
m.msg_flags = 0;
DEBUG("sending to sock");
rc = sendmsg(sock, &m, MSG_NOSIGNAL|MSG_DONTWAIT);
if (rc < 0) {
fprintf(stderr, "failed to send startup message\n");
DEBUG("failed to send startup message\n");
exit(1);
}
}
DEBUG("sent name");
/* now we just send and receive from both the socket and stdin/stdout */
while(1) {
/* read from stdin and the socket */
FD_ZERO(&read_set);
FD_SET(sock, &read_set);
FD_SET(STDIN_FILENO, &read_set);
/* blocking without a timeout be fine fine */
select(sock+1, &read_set, NULL, NULL, NULL);
if (FD_ISSET(STDIN_FILENO, &read_set)) {
/* read from stdin to get stuff from sshd to send to the agent */
DEBUG("data from stdin");
rc = read(STDIN_FILENO, buf, sizeof(buf));
if (rc <= 0) {
/* end-of-file */
#ifndef HAVE_CLOSESOCKET
rc = close(sock);
#else
rc = closesocket(sock);
#endif
exit(0);
}
DEBUG("read from stdin");
/* send it up the pipe */
pktsize = rc;
rc = -1;
while (rc < 0) {
DEBUG("sending to socket");
rc = sendto(sock, buf, pktsize, 0, NULL, 0);
DEBUG("back from sendto");
if (rc < 0)
DEBUG("sentto failed");
if (rc < 0 && errno != EINTR) {
break;
}
}
if (rc > 0)
DEBUG("sent to socket");
else
DEBUG("failed to send to socket!!");
}
if (FD_ISSET(sock, &read_set)) {
/* read from the socket and send to to stdout which goes to sshd */
DEBUG("data on unix socket");
rc = -1;
while (rc < 0) {
rc = recvfrom(sock, buf, sizeof(buf), 0, NULL, NULL);
if (rc < 0 && errno != EINTR) {
close(sock);
exit(0);
}
}
DEBUG("read from socket");
pktsize = rc;
rc = write(STDOUT_FILENO, buf, pktsize);
/* XXX: check that counts match */
if (rc > 0) {
DEBUG("wrote to stdout");
} else {
DEBUG("failed to write to stdout");
}
}
}
}
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