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https://github.com/NixOS/nixpkgs.git
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Merge pull request #31182 from yegortimoshenko/chroot-user/c-rewrite
chroot-user: rewrite in C, drop CHROOTENV_EXTRA_BINDS
This commit is contained in:
Jörg Thalheim
GitHub
commit
8bdbb21f9c
3 changed files with 194 additions and 180 deletions
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@ -1,169 +0,0 @@
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#!/usr/bin/env ruby
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# Bind mounts hierarchy: from => to (relative)
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# If 'to' is nil, path will be the same
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mounts = { '/' => 'host',
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'/proc' => nil,
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'/sys' => nil,
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'/nix' => nil,
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'/tmp' => nil,
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'/var' => nil,
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'/run' => nil,
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'/dev' => nil,
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'/home' => nil,
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}
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# Propagate environment variables
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envvars = [ 'TERM',
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'DISPLAY',
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'XAUTHORITY',
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'HOME',
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'XDG_RUNTIME_DIR',
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'LANG',
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'SSL_CERT_FILE',
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'DBUS_SESSION_BUS_ADDRESS',
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]
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require 'tmpdir'
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require 'fileutils'
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require 'pathname'
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require 'set'
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require 'fiddle'
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def write_file(path, str)
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File.open(path, 'w') { |file| file.write str }
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end
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# Import C standard library and several needed calls
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$libc = Fiddle.dlopen nil
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def make_fcall(name, args, output)
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c = Fiddle::Function.new $libc[name], args, output
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lambda do |*args|
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ret = c.call *args
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raise SystemCallError.new Fiddle.last_error if ret < 0
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return ret
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end
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end
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$fork = make_fcall 'fork', [], Fiddle::TYPE_INT
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CLONE_NEWNS = 0x00020000
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CLONE_NEWUSER = 0x10000000
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$unshare = make_fcall 'unshare', [Fiddle::TYPE_INT], Fiddle::TYPE_INT
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MS_BIND = 0x1000
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MS_REC = 0x4000
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MS_SLAVE = 0x80000
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$mount = make_fcall 'mount', [Fiddle::TYPE_VOIDP,
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Fiddle::TYPE_VOIDP,
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Fiddle::TYPE_VOIDP,
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Fiddle::TYPE_LONG,
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Fiddle::TYPE_VOIDP],
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Fiddle::TYPE_INT
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# Read command line args
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abort "Usage: chrootenv program args..." unless ARGV.length >= 1
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execp = ARGV
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# Populate extra mounts
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if not ENV["CHROOTENV_EXTRA_BINDS"].nil?
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$stderr.puts "CHROOTENV_EXTRA_BINDS is discussed for deprecation."
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$stderr.puts "If you have a usecase, please drop a note in issue #16030."
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$stderr.puts "Notice that we now bind-mount host FS to '/host' and symlink all directories from it to '/' by default."
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for extra in ENV["CHROOTENV_EXTRA_BINDS"].split(':')
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paths = extra.split('=')
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if not paths.empty?
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if paths.size <= 2
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mounts[paths[0]] = paths[1]
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else
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$stderr.puts "Ignoring invalid entry in CHROOTENV_EXTRA_BINDS: #{extra}"
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end
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end
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end
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end
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# Set destination paths for mounts
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mounts = mounts.map { |k, v| [k, v.nil? ? k.sub(/^\/*/, '') : v] }.to_h
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# Create temporary directory for root and chdir
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root = Dir.mktmpdir 'chrootenv'
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# Fork process; we need this to do a proper cleanup because
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# child process will chroot into temporary directory.
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# We use imported 'fork' instead of native to overcome
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# CRuby's meddling with threads; this should be safe because
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# we don't use threads at all.
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$cpid = $fork.call
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if $cpid == 0
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# If we are root, no need to create new user namespace.
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if Process.uid == 0
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$unshare.call CLONE_NEWNS
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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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$mount.call nil, '/', nil, MS_REC | MS_SLAVE, nil
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else
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# Save user UID and GID
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uid = Process.uid
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gid = Process.gid
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# Create new mount and user namespaces
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# CLONE_NEWUSER requires a program to be non-threaded, hence
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# native fork above.
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$unshare.call CLONE_NEWNS | CLONE_NEWUSER
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# Map users and groups to the parent namespace
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begin
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# setgroups is only available since Linux 3.19
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write_file '/proc/self/setgroups', 'deny'
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rescue
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end
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write_file '/proc/self/uid_map', "#{uid} #{uid} 1"
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write_file '/proc/self/gid_map', "#{gid} #{gid} 1"
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end
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# Do rbind mounts.
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mounts.each do |from, rto|
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to = "#{root}/#{rto}"
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FileUtils.mkdir_p to
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$mount.call from, to, nil, MS_BIND | MS_REC, nil
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end
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# Don't make root private so privilege drops inside chroot are possible
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File.chmod(0755, root)
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# Chroot!
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Dir.chroot root
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Dir.chdir '/'
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# New environment
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new_env = Hash[ envvars.map { |x| [x, ENV[x]] } ]
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# Finally, exec!
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exec(new_env, *execp, close_others: true, unsetenv_others: true)
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end
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# Wait for a child. If we catch a signal, resend it to child and continue
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# waiting.
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def wait_child
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begin
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Process.wait
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# Return child's exit code
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if $?.exited?
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exit $?.exitstatus
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else
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exit 1
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end
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rescue SignalException => e
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Process.kill e.signo, $cpid
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wait_child
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end
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end
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begin
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wait_child
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ensure
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# Cleanup
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FileUtils.rm_rf root, secure: true
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end
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182
pkgs/build-support/build-fhs-userenv/chrootenv.c
Normal file
182
pkgs/build-support/build-fhs-userenv/chrootenv.c
Normal file
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@ -0,0 +1,182 @@
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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 <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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char *env_whitelist[] = {"TERM",
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"DISPLAY",
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"XAUTHORITY",
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"HOME",
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"XDG_RUNTIME_DIR",
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"LANG",
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"SSL_CERT_FILE",
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"DBUS_SESSION_BUS_ADDRESS"};
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char **env_build(char *names[], size_t len) {
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char *env, **ret = malloc((len + 1) * sizeof(char *)), **ptr = ret;
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for (size_t i = 0; i < len; i++) {
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if ((env = getenv(names[i]))) {
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if (asprintf(ptr++, "%s=%s", names[i], env) < 0)
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errorf(EX_OSERR, "asprintf");
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}
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}
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*ptr = NULL;
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return ret;
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}
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struct bind {
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char *from;
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char *to;
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};
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struct bind binds[] = {{"/", "host"}, {"/proc", "proc"}, {"/sys", "sys"},
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{"/nix", "nix"}, {"/tmp", "tmp"}, {"/var", "var"},
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{"/run", "run"}, {"/dev", "dev"}, {"/home", "home"}};
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void bind(struct bind *bind) {
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DIR *src = opendir(bind->from);
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if (src) {
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if (closedir(src) < 0)
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errorf(EX_IOERR, "closedir");
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if (mkdir(bind->to, 0755) < 0)
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errorf(EX_IOERR, "mkdir");
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if (mount(bind->from, bind->to, "bind", MS_BIND | MS_REC, NULL) < 0)
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errorf(EX_OSERR, "mount");
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} else {
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// https://github.com/NixOS/nixpkgs/issues/31104
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if (errno != ENOENT)
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errorf(EX_OSERR, "opendir");
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}
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}
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void spitf(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_rm(const char *path, const struct stat *sb, int type,
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struct FTW *ftw) {
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if (remove(path) < 0)
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errorf(EX_IOERR, "nftw_rm");
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return 0;
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}
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#define LEN(x) sizeof(x) / sizeof(*x)
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int main(int argc, char *argv[]) {
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if (argc < 2) {
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fprintf(stderr, "Usage: %s command [arguments...]\n"
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"Requires Linux kernel >= 3.19 with CONFIG_USER_NS.\n",
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argv[0]);
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exit(EX_USAGE);
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}
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char tmpl[] = "/tmp/chrootenvXXXXXX";
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char *root = mkdtemp(tmpl);
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if (root == NULL)
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errorf(EX_IOERR, "mkdtemp");
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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");
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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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errorf(EX_OSERR, "unshare() failed: You may have an old kernel or have CLONE_NEWUSER disabled by your distribution security settings.");
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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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errorf(EX_OSERR, "unshare");
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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");
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for (size_t i = 0; i < LEN(binds); i++)
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bind(&binds[i]);
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if (chroot(root) < 0)
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errorf(EX_OSERR, "chroot");
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if (chdir("/") < 0)
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errorf(EX_OSERR, "chdir");
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argv++;
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if (execvpe(*argv, argv, env_build(env_whitelist, LEN(env_whitelist))) < 0)
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errorf(EX_OSERR, "execvpe");
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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");
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if (nftw(root, nftw_rm, getdtablesize(), FTW_DEPTH | FTW_MOUNT | FTW_PHYS) < 0)
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errorf(EX_IOERR, "nftw");
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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 EX_OSERR;
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}
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@ -2,16 +2,19 @@
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let buildFHSEnv = callPackage ./env.nix { }; in
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args@{ name, runScript ? "bash", extraBindMounts ? [], extraInstallCommands ? "", meta ? {}, passthru ? {}, ... }:
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args@{ name, runScript ? "bash", extraInstallCommands ? "", meta ? {}, passthru ? {}, ... }:
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let
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env = buildFHSEnv (removeAttrs args [ "runScript" "extraBindMounts" "extraInstallCommands" "meta" "passthru" ]);
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env = buildFHSEnv (removeAttrs args [ "runScript" "extraInstallCommands" "meta" "passthru" ]);
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# Sandboxing script
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chroot-user = writeScript "chroot-user" ''
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#! ${ruby}/bin/ruby
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${builtins.readFile ./chroot-user.rb}
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'';
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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 $out";
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makeFlags = [ "chrootenv" ];
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};
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init = run: writeScript "${name}-init" ''
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#! ${stdenv.shell}
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@ -32,8 +35,7 @@ in runCommand name {
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passthru = passthru // {
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env = runCommand "${name}-shell-env" {
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shellHook = ''
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${lib.optionalString (extraBindMounts != []) ''export CHROOTENV_EXTRA_BINDS="${lib.concatStringsSep ":" extraBindMounts}:$CHROOTENV_EXTRA_BINDS"''}
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exec ${chroot-user} ${init "bash"} "$(pwd)"
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exec ${chrootenv} ${init "bash"} "$(pwd)"
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'';
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} ''
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echo >&2 ""
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@ -46,8 +48,7 @@ in runCommand name {
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mkdir -p $out/bin
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cat <<EOF >$out/bin/${name}
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#! ${stdenv.shell}
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${lib.optionalString (extraBindMounts != []) ''export CHROOTENV_EXTRA_BINDS="${lib.concatStringsSep ":" extraBindMounts}:$CHROOTENV_EXTRA_BINDS"''}
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exec ${chroot-user} ${init runScript} "\$(pwd)" "\$@"
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exec ${chrootenv} ${init runScript} "\$(pwd)" "\$@"
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EOF
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chmod +x $out/bin/${name}
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${extraInstallCommands}
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