howto Enter into chroot environment from C? - c

Question

what i am try to do is to get my program to enter chroot environment and do some commands and then exit.
For Example
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#define ChRoot "sudo chroot \"/\" /usr/bin/env -i HOME=/root TERM=\"$TERM\" PATH=/bin:/usr/bin:/sbin:/usr/sbin:/bin /bin/bash --login +h"
void func1(){
//enter the chroot environment
char line[130]; FILE *fp;
fp = popen(ChRoot, "r");
while(fgets( line, sizeof line, fp)){
printf ("%s\n",line);
}
pclose(fp);
}
void func2(){
//run a command in the chroot environment
char line[130]; FILE *fp;
fp = popen("ls", "r");
while(fgets( line, sizeof line, fp)){
printf ("%s\n",line);
}
pclose(fp);
}
int main() {
func1();
func2();
return 0;
}
the problem with this code is, it will get me in the chroot environment however it will not fire func2 until i exit form the chroot environment. What i need is to get my code to do func1 and then func2 in chroot environment and then exit.I know what i am doing in my code is horribly wrong, however, i hope i could get some directions .
Any help would be much appreciated.

Answer 1

If you're in C and you want to enter a chroot you can do so directly using the chroot() function:
#include <stdio.h>
#include <unistd.h>
int main(void) {
FILE *f;
/* chroot */
chdir("/tmp");
if (chroot("/tmp") != 0) {
perror("chroot /tmp");
return 1;
}
/* do something after chrooting */
f = fopen("/etc/passwd", "r");
if (f == NULL) {
perror("/etc/passwd");
return 1;
} else {
char buf[100];
while (fgets(buf, sizeof(buf), f)) {
printf("%s", buf);
}
}
return 0;
}
Note that if you don't set the current directory before chrooting it's possible to break out of the chroot.

Answer 2

There is a chroot system call that does what you want. In fact, the chroot command-line utility itself uses this first and then spawns a shell.