chrootenv: rewrite on top of GLib
Changes:
* doesn't handle root user separately
* doesn't chdir("/") which makes using it seamless
* only bind mounts, doesn't symlink (i.e. files)
Incidentally, fixes #33106.
It's about two times shorter than the previous version, and much
easier to read/follow through. It uses GLib quite heavily, along with
RAII (available in GCC/Clang).
This commit is contained in:
Yegor Timoshenko
parent
25b35f4ffb
commit
4b1cf5afb8
@ -1,238 +0,0 @@
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#define _GNU_SOURCE
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#include <errno.h>
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#include <error.h>
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#define errorf(status, fmt, ...) \
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error_at_line(status, errno, __FILE__, __LINE__, fmt, ##__VA_ARGS__)
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#include <dirent.h>
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#include <ftw.h>
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#include <sched.h>
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#include <stdarg.h>
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#include <stdbool.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sysexits.h>
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#include <unistd.h>
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#include <sys/mount.h>
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#include <sys/stat.h>
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#include <sys/wait.h>
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#define LEN(x) (sizeof(x) / sizeof(*x))
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// TODO: fill together with @abbradar when he gets better
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const char *environ_blacklist[] = {};
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void environ_blacklist_filter() {
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for (size_t i = 0; i < LEN(environ_blacklist); i++) {
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if (unsetenv(environ_blacklist[i]) < 0)
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errorf(EX_OSERR, "unsetenv(%s)", environ_blacklist[i]);
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}
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}
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void bind(const char *from, const char *to) {
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if (mkdir(to, 0755) < 0)
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errorf(EX_IOERR, "mkdir(%s)", to);
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if (mount(from, to, "bind", MS_BIND | MS_REC, NULL) < 0)
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errorf(EX_OSERR, "mount(%s, %s)", from, to);
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}
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const char *bind_blacklist[] = {".", "..", "bin", "etc", "host", "usr"};
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bool str_contains(const char *needle, const char **haystack, size_t len) {
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for (size_t i = 0; i < len; i++) {
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if (!strcmp(needle, haystack[i]))
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return true;
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}
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return false;
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}
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bool is_dir(const char *path) {
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struct stat buf;
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if (stat(path, &buf) < 0)
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errorf(EX_IOERR, "stat(%s)", path);
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return S_ISDIR(buf.st_mode);
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}
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void bind_to_cwd(const char *prefix) {
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DIR *prefix_dir = opendir(prefix);
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if (prefix_dir == NULL)
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errorf(EX_IOERR, "opendir(%s)", prefix);
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struct dirent *prefix_dirent;
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while (prefix_dirent = readdir(prefix_dir)) {
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if (str_contains(prefix_dirent->d_name, bind_blacklist,
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LEN(bind_blacklist)))
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continue;
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char *prefix_dirent_path;
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if (asprintf(&prefix_dirent_path, "%s%s", prefix, prefix_dirent->d_name) <
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0)
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errorf(EX_IOERR, "asprintf");
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if (is_dir(prefix_dirent_path)) {
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bind(prefix_dirent_path, prefix_dirent->d_name);
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} else {
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char *host_target;
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if (asprintf(&host_target, "host/%s", prefix_dirent->d_name) < 0)
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errorf(EX_IOERR, "asprintf");
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if (symlink(host_target, prefix_dirent->d_name) < 0)
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errorf(EX_IOERR, "symlink(%s, %s)", host_target, prefix_dirent->d_name);
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free(host_target);
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}
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free(prefix_dirent_path);
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}
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bind(prefix, "host");
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if (closedir(prefix_dir) < 0)
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errorf(EX_IOERR, "closedir(%s)", prefix);
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}
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void spitf(const char *path, char *fmt, ...) {
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va_list args;
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va_start(args, fmt);
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FILE *f = fopen(path, "w");
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if (f == NULL)
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errorf(EX_IOERR, "spitf(%s): fopen", path);
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if (vfprintf(f, fmt, args) < 0)
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errorf(EX_IOERR, "spitf(%s): vfprintf", path);
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if (fclose(f) < 0)
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errorf(EX_IOERR, "spitf(%s): fclose", path);
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}
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int nftw_remove(const char *path, const struct stat *sb, int type,
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struct FTW *ftw) {
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return remove(path);
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}
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#define REQUIREMENTS \
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"Requires Linux version >= 3.19 built with CONFIG_USER_NS option.\n"
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int main(int argc, char *argv[]) {
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const char *self = *argv++;
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if (argc < 2) {
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fprintf(stderr, "Usage: %s command [arguments...]\n" REQUIREMENTS, self);
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exit(EX_USAGE);
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}
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if (getenv("NIX_CHROOTENV") != NULL) {
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fputs("Can't create chrootenv inside chrootenv!\n", stderr);
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exit(EX_USAGE);
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}
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if (setenv("NIX_CHROOTENV", "1", false) < 0)
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errorf(EX_OSERR, "setenv(NIX_CHROOTENV, 1)");
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const char *temp = getenv("TMPDIR");
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if (temp == NULL)
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temp = "/tmp";
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char *root;
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if (asprintf(&root, "%s/chrootenvXXXXXX", temp) < 0)
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errorf(EX_IOERR, "asprintf");
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root = mkdtemp(root);
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if (root == NULL)
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errorf(EX_IOERR, "mkdtemp(%s)", root);
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// Don't make root private so that privilege drops inside chroot are possible:
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if (chmod(root, 0755) < 0)
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errorf(EX_IOERR, "chmod(%s, 0755)", root);
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pid_t cpid = fork();
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if (cpid < 0)
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errorf(EX_OSERR, "fork");
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if (cpid == 0) {
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uid_t uid = getuid();
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gid_t gid = getgid();
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// If we are root, no need to create new user namespace.
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if (uid == 0) {
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if (unshare(CLONE_NEWNS) < 0) {
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fputs(REQUIREMENTS, stderr);
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errorf(EX_OSERR, "unshare");
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}
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// Mark all mounted filesystems as slave so changes
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// don't propagate to the parent mount namespace.
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if (mount(NULL, "/", NULL, MS_REC | MS_SLAVE, NULL) < 0)
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errorf(EX_OSERR, "mount");
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} else {
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// Create new mount and user namespaces. CLONE_NEWUSER
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// requires a program to be non-threaded.
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if (unshare(CLONE_NEWNS | CLONE_NEWUSER) < 0) {
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fputs(access("/proc/sys/kernel/unprivileged_userns_clone", F_OK)
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? REQUIREMENTS
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: "Run: sudo sysctl -w kernel.unprivileged_userns_clone=1\n",
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stderr);
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errorf(EX_OSERR, "unshare");
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}
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// Map users and groups to the parent namespace.
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// setgroups is only available since Linux 3.19:
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spitf("/proc/self/setgroups", "deny");
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spitf("/proc/self/uid_map", "%d %d 1", uid, uid);
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spitf("/proc/self/gid_map", "%d %d 1", gid, gid);
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}
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if (chdir(root) < 0)
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errorf(EX_IOERR, "chdir(%s)", root);
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bind_to_cwd("/");
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if (chroot(root) < 0)
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errorf(EX_OSERR, "chroot(%s)", root);
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if (chdir("/") < 0)
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errorf(EX_IOERR, "chdir(/)");
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environ_blacklist_filter();
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if (execvp(*argv, argv) < 0)
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errorf(EX_OSERR, "execvp(%s)", *argv);
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}
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int status;
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if (waitpid(cpid, &status, 0) < 0)
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errorf(EX_OSERR, "waitpid(%d)", cpid);
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if (nftw(root, nftw_remove, getdtablesize(),
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FTW_DEPTH | FTW_MOUNT | FTW_PHYS) < 0)
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errorf(EX_IOERR, "nftw(%s)", root);
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free(root);
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if (WIFEXITED(status)) {
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return WEXITSTATUS(status);
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} else if (WIFSIGNALED(status)) {
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kill(getpid(), WTERMSIG(status));
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}
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return EX_OSERR;
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}
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139
pkgs/build-support/build-fhs-userenv/chrootenv/chrootenv.c
Normal file
139
pkgs/build-support/build-fhs-userenv/chrootenv/chrootenv.c
Normal file
@ -0,0 +1,139 @@
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#define _GNU_SOURCE
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#include <glib.h>
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#include <glib/gstdio.h>
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#include <errno.h>
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#include <sched.h>
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#include <unistd.h>
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#define fail(s, err) g_error("%s: %s: %s", __func__, s, g_strerror(err))
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#define fail_if(expr) \
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if (expr) \
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fail(#expr, errno);
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#include <ftw.h>
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#include <sys/mount.h>
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#include <sys/stat.h>
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#include <sys/types.h>
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#include <sys/wait.h>
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const gchar *bind_blacklist[] = {"bin", "etc", "host", "usr", NULL};
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void bind_mount(const gchar *source, const gchar *target) {
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fail_if(g_mkdir(target, 0755));
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fail_if(mount(source, target, "bind", MS_BIND | MS_REC, NULL));
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}
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void bind_mount_host(const gchar *host, const gchar *guest) {
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g_autofree gchar *point = g_build_filename(guest, "host", NULL);
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bind_mount(host, point);
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}
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void bind_mount_item(const gchar *host, const gchar *guest, const gchar *name) {
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g_autofree gchar *source = g_build_filename(host, name, NULL);
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g_autofree gchar *target = g_build_filename(guest, name, NULL);
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if (G_LIKELY(g_file_test(source, G_FILE_TEST_IS_DIR)))
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bind_mount(source, target);
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}
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void bind(const gchar *host, const gchar *guest) {
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g_autoptr(GError) err = NULL;
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g_autoptr(GDir) dir = g_dir_open(host, 0, &err);
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if (err != NULL)
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fail("g_dir_open", errno);
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const gchar *item;
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while (item = g_dir_read_name(dir))
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if (!g_strv_contains(bind_blacklist, item))
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bind_mount_item(host, guest, item);
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bind_mount_host(host, guest);
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}
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void spit(const char *path, char *fmt, ...) {
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va_list args;
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va_start(args, fmt);
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FILE *f = g_fopen(path, "w");
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if (f == NULL)
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fail("g_fopen", errno);
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g_vfprintf(f, fmt, args);
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fclose(f);
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}
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int nftw_remove(const char *path, const struct stat *sb, int type,
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struct FTW *ftw) {
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return remove(path);
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}
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int main(gint argc, gchar **argv) {
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const gchar *self = *argv++;
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if (argc < 2) {
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g_message("%s command [arguments...]", self);
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return 1;
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}
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if (g_getenv("NIX_CHROOTENV"))
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g_warning("chrootenv doesn't stack!");
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else
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g_setenv("NIX_CHROOTENV", "", TRUE);
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g_autofree gchar *prefix =
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g_build_filename(g_get_tmp_dir(), "chrootenvXXXXXX", NULL);
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fail_if(!g_mkdtemp_full(prefix, 0755));
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pid_t cpid = fork();
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if (cpid < 0)
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fail("fork", errno);
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else if (cpid == 0) {
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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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int unshare_errno = errno;
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g_message("Requires Linux version >= 3.19 built with CONFIG_USER_NS");
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if (g_file_test("/proc/sys/kernel/unprivileged_userns_clone",
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G_FILE_TEST_EXISTS))
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g_message("Run: sudo sysctl -w kernel.unprivileged_userns_clone=1");
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fail("unshare", unshare_errno);
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}
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spit("/proc/self/setgroups", "deny");
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spit("/proc/self/uid_map", "%d %d 1", uid, uid);
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spit("/proc/self/gid_map", "%d %d 1", gid, gid);
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bind("/", prefix);
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fail_if(chroot(prefix));
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fail_if(execvp(*argv, argv));
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}
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else {
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int status;
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fail_if(waitpid(cpid, &status, 0) != cpid);
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fail_if(nftw(prefix, nftw_remove, getdtablesize(),
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FTW_DEPTH | FTW_MOUNT | FTW_PHYS));
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if (WIFEXITED(status))
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return WEXITSTATUS(status);
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else if (WIFSIGNALED(status))
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kill(getpid(), WTERMSIG(status));
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return 1;
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}
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}
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19
pkgs/build-support/build-fhs-userenv/chrootenv/default.nix
Normal file
19
pkgs/build-support/build-fhs-userenv/chrootenv/default.nix
Normal file
@ -0,0 +1,19 @@
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{ stdenv, pkgconfig, glib }:
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stdenv.mkDerivation {
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name = "chrootenv";
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nativeBuildInputs = [ pkgconfig ];
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buildInputs = [ glib ];
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buildCommand = ''
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cc ${./chrootenv.c} $(pkg-config --cflags --libs glib-2.0) -o $out
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'';
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meta = with stdenv.lib; {
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description = "Setup mount/user namespace for FHS emulation";
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license = licenses.free;
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maintainers = with maintainers; [ yegortimoshenko ];
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platforms = platforms.linux;
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};
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}
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@ -1,4 +1,4 @@
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{ callPackage, runCommand, lib, writeScript, stdenv, coreutils, ruby }:
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{ callPackage, runCommand, lib, writeScript, stdenv, coreutils }:
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let buildFHSEnv = callPackage ./env.nix { }; in
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@ -7,14 +7,7 @@ args@{ name, runScript ? "bash", extraInstallCommands ? "", meta ? {}, passthru
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let
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env = buildFHSEnv (removeAttrs args [ "runScript" "extraInstallCommands" "meta" "passthru" ]);
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chrootenv = stdenv.mkDerivation {
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name = "chrootenv";
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unpackPhase = "cp ${./chrootenv.c} chrootenv.c";
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installPhase = "cp chrootenv $out";
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makeFlags = [ "chrootenv" ];
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};
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chrootenv = callPackage ./chrootenv {};
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init = run: writeScript "${name}-init" ''
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#! ${stdenv.shell}
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Block a user