fsuid test

fsuid.c

#include <errno.h>
#include <fcntl.h>
#include <pthread.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/syscall.h>

#define PARENTFILE ".parentfile"
#define CHILDFILE  ".childfile"
#define gettid() syscall(SYS_gettid)

pthread_mutex_t kid1mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t  kid1cond  = PTHREAD_COND_INITIALIZER;
pthread_mutex_t kid2mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t  kid2cond  = PTHREAD_COND_INITIALIZER;

void *
kid1func (void *notused)
{
	int fd;

	(void)pthread_mutex_lock(&kid1mutex);

	printf("kid1 (%d) setting fsuid to 9876\n",gettid());
	(void)setfsuid(9876);

	printf("kid1 (%d) creating %s\n",gettid(),CHILDFILE);
	fd = open(CHILDFILE,O_RDWR|O_CREAT|O_EXCL,0600);
	if (fd >= 0) {
		printf("file created OK\n");
		close(fd);
	}
	else {
		perror("child create");
	}

	(void)pthread_cond_signal(&kid1cond);
	(void)pthread_mutex_unlock(&kid1mutex);
	return NULL;
}

void *
kid2func (void *notused)
{
	int fd;

	(void)pthread_mutex_lock(&kid2mutex);

	printf("kid2 (%d) trying to open %s\n",gettid(),PARENTFILE);
	fd = open(PARENTFILE,O_RDWR);
	if (fd >= 0) {
		printf("file opened, setfsuid must be per-thread\n");
		close(fd);
	}
	else {
		printf("open failed (%d), setfsuid must be per-process\n",
		       errno);
	}

	(void)pthread_cond_signal(&kid2cond);
	(void)pthread_mutex_unlock(&kid2mutex);
	return NULL;
}

int
main (int argc, char **argv)
{
	int       fd;
	pthread_t kid1;
	pthread_t kid2;

	fd = open(PARENTFILE,O_RDWR|O_CREAT|O_EXCL,0600);
	if (fd < 0) {
		perror("parent create");
		return !0;
	}

	(void)pthread_mutex_lock(&kid1mutex);
	(void)pthread_create(&kid1,NULL,kid1func,NULL);
	(void)pthread_mutex_lock(&kid2mutex);
	(void)pthread_create(&kid2,NULL,kid2func,NULL);

	printf("parent waking first child\n");
	(void)pthread_cond_wait(&kid1cond,&kid1mutex);
	(void)pthread_mutex_unlock(&kid1mutex);

	printf("parent waking second child\n");
	(void)pthread_cond_wait(&kid2cond,&kid2mutex);
	(void)pthread_mutex_unlock(&kid2mutex);

	printf("test complete\n");
	(void)pthread_join(kid1,NULL);
	(void)pthread_join(kid2,NULL);
	return 0;
}

From http://pl.atyp.us/hekafs.org/files/fsuid.c