qsni/qsni.c

/* Copyright (c) 2018 Albert S. <mail at quitesimple dot org>

Permission to use, copy, modify, and distribute this software for any
purpose with or without fee is hereby granted, provided that the above
copyright notice and this permission notice appear in all copies.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/

#define _GNU_SOURCE
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <linux/limits.h>
#define NET_CLS_DIR "/sys/fs/cgroup/net_cls/"
#define IPTABLES_PROFILES_DIR "/etc/qsni.d/"

//exits if we are already inside a profile.
void ensure_outside_profile()
{
	FILE *fp = fopen("/proc/self/cgroup", "r");
	if(fp == NULL)
	{
		fprintf(stderr, "Failed to open cgroup file\n");
		exit(EXIT_FAILURE);
	}
	
	char *line = NULL;
	size_t n = 0;
	while(getline(&line, &n, fp) != -1)
	{
		char *id = line;
		char *tmp = strchr(id, ':');
		if(tmp == NULL)
		{
			fprintf(stderr, "Misformated cgroups file\n");
			exit(EXIT_FAILURE);
		}
		*tmp = 0;
		++tmp;
		char *controllers = tmp;
		tmp = strchr(controllers, ':');
		if(tmp == NULL)
		{
			fprintf(stderr, "Misformated cgroups file\n");
			exit(EXIT_FAILURE);
		}
		*tmp = 0;
		++tmp;
		
		char *assigned = tmp;
		
		if(strstr(controllers, "net_cls") != NULL)
		{
			if(assigned[0] == '/' && assigned[1] != '\n')
			{
				fprintf(stderr, "already assigned to a net class, thus you can't use this binary to change that\n");
				exit(EXIT_FAILURE);
			}
		}
		line = NULL;
		n = 0;
	}
	
	fclose(fp);
	
}

void init_profile(const char *profilepath)
{
	pid_t pid = fork();
	if(pid == 0)
	{
		if(clearenv() != 0)
		{
			perror("clearenv");
			exit(EXIT_FAILURE);
		}
		
		int ret = execl(profilepath, profilepath, (char *) NULL);
		if(ret == -1)
		{
			perror("execl of child");
			exit(EXIT_FAILURE);
		}
	}
	else if(pid > 0)
	{
		int status=1;
		pid_t w = waitpid(pid, &status, 0);
		if(w == -1)
		{
			perror("waitpid");
			exit(EXIT_FAILURE);
		}
		if(! WIFEXITED(status) || WEXITSTATUS(status) != 0)
		{
			
			fprintf(stderr, "profile setup script failed\n");
			exit(EXIT_FAILURE);
		}
	}
	if(pid == -1)
	{
		perror("fork");
		exit(EXIT_FAILURE);
	}
	
}
void drop(uid_t u, gid_t g)
{
	if(setgid(g) != 0)
	{
		perror("setgid");
		exit(EXIT_FAILURE);
	}
	if(setuid(u) != 0)
	{
		perror("setuid");
		exit(EXIT_FAILURE);
	}
}

void assign_to_profile(const char *profilename)
{
	char taskspath[PATH_MAX +1];
	snprintf(taskspath, sizeof(taskspath), "%s/%s/tasks", NET_CLS_DIR, profilename);
	
	pid_t mypid = getpid();
	FILE *fp = fopen(taskspath, "a");
	if(fp == NULL)
	{
		perror("fopen");
		exit(EXIT_FAILURE);
	}
	fprintf(fp, "%ld", (long)mypid);
	fclose(fp);
}
int main(int argc, char *argv[])
{
	if(argc < 3)
	{
		fprintf(stderr, "Usage: %s profile command [arguments...]\n", argv[0]);
		exit(EXIT_FAILURE);
	}
	ensure_outside_profile();
	
	char *profilename = argv[1];

	char profilepath[PATH_MAX +1];
	snprintf(profilepath, sizeof(profilepath), "%s/%s", IPTABLES_PROFILES_DIR, profilename);
	int ret = access(profilepath, R_OK);
	if(ret != 0)
	{
		perror("check for profile path failed\n");
		exit(EXIT_FAILURE);
	}
	
	uid_t myuid = getuid();
	gid_t myguid = getgid();
	if(setuid(0) != 0)
	{
		perror("setuid");
		exit(EXIT_FAILURE);
	}
	init_profile(profilepath);
	assign_to_profile(profilename);

	drop(myuid, myguid);
	
	
	argv += 2;
	int result = execvp(argv[0], argv);
	if(result == -1)
	{
		perror("execv");
		exit(EXIT_FAILURE);

	}
	return 0;
	
	
	
}