Revert "Use proot instead of nix-user-chroot."

This reverts commit f24309c9d1.

default.nix

@@ -16,8 +16,10 @@ let
     inherit arx maketar;
   };
 
+  nix-user-chroot = callPackage ./nix-user-chroot.nix {};
+
   nix-bootstrap = callPackage ./nix-bootstrap.nix {
-    inherit makebootstrap;
+    inherit nix-user-chroot makebootstrap;
   };
 
 in {

nix-bootstrap.nix

@@ -1,9 +1,9 @@
-{ stdenv, writeText, proot, makebootstrap }:
+{ stdenv, writeText, nix-user-chroot, makebootstrap }:
 
 { name, target, run }:
 
   makebootstrap {
     inherit name;
-    startup = ".${proot}/bin/proot -b./nix:/nix ${target}${run}";
-    targets = [ proot target ];
+    startup = ".${nix-user-chroot}/bin/nix-user-chroot ./nix ${target}${run}";
+    targets = [ nix-user-chroot target ];
   }

nix-user-chroot.c

@@ -0,0 +1,134 @@
+#define _GNU_SOURCE
+#include <sched.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <sys/wait.h>
+#include <signal.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <string.h>
+#include <limits.h>
+#include <errno.h>
+#include <sys/mount.h>
+#include <sys/types.h>
+#include <dirent.h>
+#include <sys/stat.h>
+
+#define err_exit(format, ...) { fprintf(stderr, format ": %s\n", ##__VA_ARGS__, strerror(errno)); exit(EXIT_FAILURE); }
+
+static void usage(char *pname) {
+    fprintf(stderr, "Usage: %s <nixpath> <command>\n", pname);
+
+    exit(EXIT_FAILURE);
+}
+
+static void update_map(char *mapping, char *map_file) {
+    int fd;
+
+    fd = open(map_file, O_WRONLY);
+    if (fd < 0) {
+        err_exit("map open");
+    }
+
+    int map_len = strlen(mapping);
+    if (write(fd, mapping, map_len) != map_len) {
+        err_exit("map write");
+    }
+
+    close(fd);
+}
+
+static void add_path(const char* name, const char* rootdir) {
+    char path_buf[PATH_MAX];
+    char path_buf2[PATH_MAX];
+
+    snprintf(path_buf, sizeof(path_buf), "/%s", name);
+
+    struct stat statbuf;
+    if (stat(path_buf, &statbuf) < 0) {
+        fprintf(stderr, "Cannot stat %s: %s\n", path_buf, strerror(errno));
+        return;
+    }
+
+    snprintf(path_buf2, sizeof(path_buf2), "%s/%s", rootdir, name);
+
+    if (S_ISDIR(statbuf.st_mode)) {
+        mkdir(path_buf2, statbuf.st_mode & ~S_IFMT);
+        if (mount(path_buf, path_buf2, "none", MS_BIND | MS_REC, NULL) < 0) {
+            fprintf(stderr, "Cannot bind mount %s to %s: %s\n", path_buf, path_buf2, strerror(errno));
+        }
+    }
+}
+
+int main(int argc, char *argv[]) {
+    if (argc < 3) {
+        usage(argv[0]);
+    }
+
+    // Create skeleton root dir in temp. All dirs will be mounted here.
+    char template[] = "/tmp/nixXXXXXX";
+    char *rootdir = mkdtemp(template);
+    if (!rootdir) {
+        err_exit("mkdtemp(%s)", template);
+    }
+
+    // determine absolute directory for nix dir
+    char *nixdir = realpath(argv[1], NULL);
+    if (!nixdir) {
+        err_exit("realpath(%s)", argv[1]);
+    }
+
+    // get uid, gid before going to new namespace
+    uid_t uid = getuid();
+    gid_t gid = getgid();
+
+    // "unshare" into new namespace
+    if (unshare(CLONE_NEWNS | CLONE_NEWUSER) < 0) {
+        err_exit("unshare()");
+    }
+
+    // add necessary system stuff to rootdir namespace
+    add_path("dev", rootdir);
+    add_path("proc", rootdir);
+    add_path("sys", rootdir);
+    add_path("run", rootdir);
+    add_path("tmp", rootdir);
+    add_path("var", rootdir);
+
+    // make sure nixdir exists
+    struct stat statbuf2;
+    if (stat(nixdir, &statbuf2) < 0) {
+        err_exit("stat(%s)", nixdir);
+    }
+
+    // mount /nix to new namespace
+    char path_buf[PATH_MAX];
+    snprintf(path_buf, sizeof(path_buf), "%s/nix", rootdir);
+    mkdir(path_buf, statbuf2.st_mode & ~S_IFMT);
+    if (mount(nixdir, path_buf, "none", MS_BIND | MS_REC, NULL) < 0) {
+        err_exit("mount(%s, %s)", nixdir, path_buf);
+    }
+
+    // fixes issue #1 where writing to /proc/self/gid_map fails
+    // see user_namespaces(7) for more documentation
+    int fd_setgroups = open("/proc/self/setgroups", O_WRONLY);
+    if (fd_setgroups > 0) {
+        write(fd_setgroups, "deny", 4);
+    }
+
+    // map the original uid/gid in the new ns
+    char map_buf[1024];
+    snprintf(map_buf, sizeof(map_buf), "%d %d 1", uid, uid);
+    update_map(map_buf, "/proc/self/uid_map");
+    snprintf(map_buf, sizeof(map_buf), "%d %d 1", gid, gid);
+    update_map(map_buf, "/proc/self/gid_map");
+
+    // chroot to rootdir
+    if (chroot(rootdir) < 0) {
+        err_exit("chroot(%s)", rootdir);
+    }
+
+    // execute the command
+    execvp(argv[2], argv+2);
+    err_exit("execvp(%s)", argv[2]);
+}

nix-user-chroot.nix

@@ -0,0 +1,14 @@
+{ stdenv, fetchFromGitHub }:
+
+  stdenv.mkDerivation {
+    name = "nix-user-chroot";
+    phases = [ "buildPhase" "installPhase" "fixupPhase" ];
+    buildPhase = ''
+      cp ${./nix-user-chroot.c} nix-user-chroot.c
+      $CC nix-user-chroot.c -o nix-user-chroot
+    '';
+    installPhase = ''
+      mkdir -p $out/bin/
+      cp nix-user-chroot $out/bin/nix-user-chroot
+    '';
+  }