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/*
* Process/Thread Start Monitor
* Copyright (C) 2011 Philip J. Turmel <philip@turmel.org>
*
* Inspired by a blog entry by Scott James Remnant:
* http://netsplit.com/2011/02/09/the-proc-connector-and-socket-filters/
*
* Maintained at http://github.com/pturmel/startmon
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, version 2.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*/

#define _GNU_SOURCE
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <getopt.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/uio.h>
#include <linux/netlink.h>
#include <linux/connector.h>
#include <linux/cn_proc.h>

void usage(char *arg0) {
fprintf(stderr, "Usage:\n %s [-eft] [--exec] [--fork] [--thread]\n\n"
"Specify at least '--exec' or '--fork'\n",
arg0);
exit(1);
}

const char my_short_opts[] = "efht";
struct option my_long_opts[] = {
{"exec", 0, NULL, 'e'},
{"fork", 0, NULL, 'f'},
{"help", 0, NULL, 'h'},
{"thread", 0, NULL, 't'},
{}
};

int execflag = 0;
int forkflag = 0;
int threadflag = 0;

char procname[50];
char cmdlinebuf[4096];
ssize_t bytes;

char *get_cmdline(pid_t id) {
int fd;
ssize_t remain;
char *c;

sprintf(procname, "/proc/%d/cmdline", id);
fd = open(procname, O_RDONLY);
if (fd != -1) {
bytes = read(fd, cmdlinebuf, 4096);
close(fd);
for (c=cmdlinebuf, remain=bytes; remain>0; c++, remain--)
if (*c < 32)
*c = ' ';
*c = 0;
} else
bytes = sprintf(cmdlinebuf, "<N/A>");
return cmdlinebuf;
}

/* Given a single connection message, evaluate and process
* the enclosed proc message.
*/
void dispatch_nl_cn(struct cn_msg *hdr) {
if (hdr->id.idx != CN_IDX_PROC || hdr->id.val != CN_VAL_PROC)
return;
struct proc_event *pe = (struct proc_event *)hdr->data;
switch (pe->what) {
case PROC_EVENT_FORK:
if (!forkflag)
break;
if (pe->event_data.fork.child_pid == pe->event_data.fork.child_tgid) {
/* Regular fork, parent process is the originator */
printf("Fork %d %d %s\n",
pe->event_data.fork.parent_pid,
pe->event_data.fork.child_pid,
get_cmdline(pe->event_data.fork.child_tgid));
} else {
/* Thread fork, thread group leader is the originator */
if (threadflag)
printf("Thread %d %d %s\n",
pe->event_data.fork.child_tgid,
pe->event_data.fork.child_pid,
get_cmdline(pe->event_data.fork.child_tgid));
}
break;
case PROC_EVENT_EXEC:
if (!execflag)
break;
if (pe->event_data.exec.process_pid == pe->event_data.exec.process_tgid) {
/* Thread group leader did an exec */
printf("Exec - %d %s\n",
pe->event_data.exec.process_pid,
get_cmdline(pe->event_data.exec.process_tgid));
} else {
/* Subordinate thread did an exec */
if (threadflag)
printf("Exec %d %d %s\n",
pe->event_data.exec.process_tgid,
pe->event_data.exec.process_pid,
get_cmdline(pe->event_data.exec.process_tgid));
}
break;
}
}

/* Given a single netlink message, evaluate and process the
* enclosed container message.
*/
void dispatch_nl(struct nlmsghdr *nlhdr) {
switch (nlhdr->nlmsg_type) {
case NLMSG_ERROR:
case NLMSG_NOOP:
return;
case NLMSG_OVERRUN:
printf("overrun\n");
return;
default:
dispatch_nl_cn(NLMSG_DATA(nlhdr));
}
}

int main(int argc, char **argv) {
int opt, longidx, nlsock, rc;
struct sockaddr_nl nladdr = {AF_NETLINK};
socklen_t nlalen;
pid_t mypid;
ssize_t bcount;
char *called;
void *rcvbuf;

/* Isolate the base name of the program as invoked. */
called = strrchr(argv[0], '/');
if (!called)
called = argv[0];

/* Parse the given options, looking for the filtering mode. */
while ((opt = getopt_long(argc, argv, my_short_opts, my_long_opts, &longidx)) != -1) {
switch (opt) {
case 'e':
execflag = 1;
break;
case 'f':
forkflag = 1;
break;
case 't':
threadflag = 1;
break;
default:
if (opt != 'h')
fprintf(stderr, "%s: Invalid option '%c' !\n", called, opt);
usage(called);
}
}

/* If no filtering mode, bail out. */
if (!(execflag || forkflag)) {
fprintf(stderr, "%s: Missing required mode option!\n", called);
usage(called);
}

/* Create the netlink socket */
nlsock = socket(PF_NETLINK, SOCK_DGRAM | SOCK_CLOEXEC, NETLINK_CONNECTOR);
if (nlsock == -1) {
perror("Unable to open a netlink socket!");
exit(1);
}

/* Attach to the process connector group */
{
nladdr.nl_pid = mypid = getpid();
nladdr.nl_groups = CN_IDX_PROC;
if (bind(nlsock, (struct sockaddr *)&nladdr, sizeof(nladdr))) {
perror("Unable to bind to the process connector!");
exit(1);
}
}

/* Request the process messages */
{
enum proc_cn_mcast_op cnop = PROC_CN_MCAST_LISTEN;
struct cn_msg cnmsg = {{CN_IDX_PROC, CN_VAL_PROC}, 0, 0, sizeof(cnop), 0};
struct nlmsghdr nlmsg = {NLMSG_LENGTH(sizeof cnmsg + sizeof cnop), NLMSG_DONE};
char padding[16];
struct iovec iov[4] = {
{&nlmsg, sizeof(nlmsg)},
{padding, NLMSG_LENGTH(0) - sizeof(nlmsg)},
{&cnmsg, sizeof(cnmsg)},
{&cnop, sizeof(cnop)}
};
nlmsg.nlmsg_pid = mypid;
if ((bcount = writev(nlsock, iov, 4)) == -1) {
perror("Unable to listen to the process connector!");
exit(1);
}
}

/* Receive messages forever ... */
rcvbuf = malloc(4096+CONNECTOR_MAX_MSG_SIZE);
if (!rcvbuf) {
perror("Unable to allocate a receive buffer!");
exit(1);
}
setbuf(stdout, NULL);
while (1) {
nlalen = sizeof(nladdr);
bcount = recvfrom(nlsock, rcvbuf, 4096+CONNECTOR_MAX_MSG_SIZE,
0, (struct sockaddr *)&nladdr, &nlalen);
if (nladdr.nl_pid == 0) {
struct nlmsghdr *hdr = rcvbuf;
for (hdr=rcvbuf; NLMSG_OK(hdr, bcount); hdr=NLMSG_NEXT(hdr, bcount))
dispatch_nl(hdr);
}
}
}
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