ms-runner/starter/ns_exec.c

#include<sys/prctl.h>
#include<sys/mount.h>
#include<sys/stat.h>

static void procfs_prepare()
{
    if (mkdir("/proc", 0555) && errno != EEXIST)                                    die("Failed to mkdir /proc: %m\n");
    if (mount("proc", "/proc", "proc", 0, ""))                                      die("Failed to mount proc: %m\n");
}

#define hostname "runner"

#define put_old "oldfs"
void mnt_prepare(char* rootfs, char* shared_mountpoint) {
    char* shared_folder = NULL;
    asprintf(&shared_folder, "../%s", shared_mountpoint);
    if (mount(rootfs, rootfs, "ext4", MS_BIND,""))                                  die("failed to mount %s: %m", rootfs);
    if (chdir(rootfs))                                                              die("falied to cd:%m");
    //if (mount("/sys","sys","sysfs",0,""))                                         die("failed to mount sysfs: %m");
    //if (mount("/dev","dev","udev",0,""))                                          die("failed to mount: %m");
    if (mkdir("shared", 0777) && errno != EEXIST)                                   die("Failed to mkdir %s: %m\n", shared_mountpoint);
    if (mount(shared_folder, "shared", "ext4", MS_BIND, ""))                        die("failed to mount shared folder: %m");
    if (mkdir(put_old, 0000) && errno != EEXIST)                                    die("Failed to mkdir %s: %m\n", put_old);
    if (syscall(SYS_pivot_root, ".", put_old))                                      die("Failed to pivot_root from %s to %s: %m\n", rootfs, put_old);
    if (chdir("/"))                                                                 die("Failed to chdir to new root: %m\n");
    procfs_prepare();
    if (umount2(put_old, MNT_DETACH))                                               die("Failed to umount put_old %s: %m\n", put_old);
    if (rmdir(put_old))                                                             die("Failed to rmdir: %m");
    free(shared_folder);
}
void ro_fs(char* shared_mountpoint) {
    char* shared_folder = malloc(strlen(shared_mountpoint)+4);
    strcpy(shared_folder, "../");
    strcat(shared_folder, shared_mountpoint);
    if (mount("/", "/", "ext4", MS_REMOUNT | MS_RDONLY| MS_BIND, ""))               die("failed to mount: %m");
    if (mount(shared_mountpoint, "shared", "ext4", MS_REMOUNT | MS_BIND, ""))       die("failed to mount: %m");
    free(shared_folder);
}
#undef put_old

void await_setup(int pipe) { // wait for signal from parent
    char buf[2];
    if (read(pipe, buf, 2) != 2) die("Failed to read from pipe: %m\n");
}

static int nsrun(void* arg) {
    //die when parent dies
    if (prctl(PR_SET_PDEATHSIG, SIGKILL)) die("cannot PR_SET_PDEATHSIG for child process: %m\n");
    struct params *params = (struct params*) arg;
    await_setup(params->fd[0]);
    char cwd[PATH_MAX];
    if(getcwd(cwd, sizeof(cwd))==NULL) die("getcwd error: %m");
    if(chdir(params->shared_folder)) die("failed to chdir to shared folder: %m")
    int out_fd = open("out", O_WRONLY | O_CREAT, 0666);
    if(out_fd == -1) die("unable to open output file:%m")
    else dup2(out_fd, STDOUT_FILENO);
    int in_fd = open("in", O_RDONLY | O_CREAT, 0666);
    if(in_fd == -1) die("unable to open input file:%m")
    else dup2(in_fd, STDIN_FILENO);
    int err_fd = open("err", O_WRONLY | O_CREAT, 0666);
    if(err_fd == -1) die("unable to open error file:%m")
    else dup2(err_fd, STDERR_FILENO);
    if(chdir(cwd)) die("failed to chdir: %m");
    mnt_prepare("minrootfs", params->shared_folder);
    sethostname(hostname, sizeof(hostname));
    ro_fs(params->shared_folder);
    if(setgid(1000)) die("failed to setgid:%m");
    if(setuid(1000)) die("failed to setuid:%m");
    char** argv = params->argv;
    char* cmd = argv[0];
    char* env[]={
        "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
        "PWD=/",
        NULL,
    };
    if (execve(cmd, argv, env) == -1) die("failed to exec,%m");
    return 1;// removes warning
}