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https://github.com/lucabrunox/nix-user-chroot.git
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3
Makefile
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3
Makefile
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nix-user-chroot: main.c
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gcc -o nix-user-chroot main.c
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6
README.md
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6
README.md
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Run nix as user in a lightweight chrooted container.
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1. Create an empty directory somewhere, `$DIR`
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2. Run `nix-user-chroot $DIR bash`
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You can now install nix under /nix as user.
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119
main.c
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119
main.c
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#define _GNU_SOURCE
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#include <sched.h>
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#include <unistd.h>
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#include <stdlib.h>
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#include <sys/wait.h>
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#include <signal.h>
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#include <fcntl.h>
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#include <stdio.h>
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#include <string.h>
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#include <limits.h>
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#include <errno.h>
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#include <sys/mount.h>
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#include <sys/types.h>
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#include <dirent.h>
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#include <sys/stat.h>
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#define err_exit(msg) { perror(msg); exit(EXIT_FAILURE); }
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static void usage(char *pname) {
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fprintf(stderr, "Usage: %s <rootdir> <command>\n", pname);
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exit(EXIT_FAILURE);
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}
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static void update_map(char *mapping, char *map_file) {
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int fd;
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fd = open(map_file, O_WRONLY);
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if (fd < 0) {
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err_exit("map open");
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}
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int map_len = strlen(mapping);
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if (write(fd, mapping, map_len) != map_len) {
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err_exit("map write");
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}
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close(fd);
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}
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int main(int argc, char *argv[]) {
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char map_buf[1024];
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char path_buf[PATH_MAX];
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char path_buf2[PATH_MAX];
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char cwd[PATH_MAX];
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if (argc < 3) {
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usage(argv[0]);
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}
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char *rootdir = realpath(argv[1], NULL);
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if (!rootdir) {
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err_exit("realpath");
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}
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uid_t uid = getuid();
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gid_t gid = getgid();
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if (unshare (CLONE_NEWNS | CLONE_NEWUSER) < 0) {
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err_exit("unshare");
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}
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// bind mount all / stuff into rootdir
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DIR* d = opendir("/");
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if (!d) {
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err_exit("open /");
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}
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struct dirent *ent;
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while ((ent = readdir(d))) {
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// do not bind mount an existing nix installation
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if (!strcmp (ent->d_name, ".") || !strcmp (ent->d_name, "..") ||
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!strcmp (ent->d_name, "nix")) {
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continue;
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}
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snprintf(path_buf, sizeof(path_buf), "/%s", ent->d_name);
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struct stat statbuf;
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if (lstat(path_buf, &statbuf) < 0) {
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fprintf(stderr, "Cannot stat %s: %s\n", path_buf,
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strerror(errno));
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continue;
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}
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snprintf(path_buf2, sizeof(path_buf2), "%s/%s", rootdir,
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ent->d_name);
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if (S_ISDIR(statbuf.st_mode)) {
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mkdir(path_buf2, statbuf.st_mode & ~S_IFMT);
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if (mount(path_buf, path_buf2, "none", MS_BIND | MS_REC,
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NULL) < 0) {
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fprintf(stderr, "Cannot bind mount %s to %s: %s\n",
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path_buf, path_buf2, strerror(errno));
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}
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}
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}
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// map the original uid/gid in the new ns
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snprintf(map_buf, sizeof(map_buf), "%d %d 1", uid, uid);
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update_map(map_buf, "/proc/self/uid_map");
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snprintf(map_buf, sizeof(map_buf), "%d %d 1", gid, gid);
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update_map(map_buf, "/proc/self/gid_map");
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if (!getcwd(cwd, PATH_MAX)) {
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err_exit("getcwd");
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}
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chdir("/");
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if (chroot (rootdir) < 0) {
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err_exit("chroot");
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}
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chdir(cwd);
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// execute the command
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execvp(argv[2], argv+2);
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err_exit("execvp");
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}
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