LXR toybox/toys/other/nsenter.c

   1/* nsenter.c - Enter existing namespaces
   2 *
   3 * Copyright 2014 Andy Lutomirski <luto@amacapital.net>
   4 *
   5 * See http://man7.org/linux/man-pages/man1/nsenter.1.html
   6 *
   7 * unshare.c - run command in new context
   8 *
   9 * Copyright 2011 Rob Landley <rob@landley.net>
  10 *
  11 * See http://man7.org/linux/man-pages/man1/unshare.1.html
  12 *
  13
  14// Note: flags go in same order (right to left) for shared subset
  15USE_NSENTER(NEWTOY(nsenter, "<1F(no-fork)t#<1(target)i:(ipc);m:(mount);n:(net);p:(pid);u:(uts);U:(user);", TOYFLAG_USR|TOYFLAG_BIN))
  16USE_UNSHARE(NEWTOY(unshare, "<1^f(fork);r(map-root-user);i:(ipc);m:(mount);n:(net);p:(pid);u:(uts);U:(user);", TOYFLAG_USR|TOYFLAG_BIN))
  17
  18config UNSHARE
  19  bool "unshare"
  20  default y
  21  depends on TOYBOX_CONTAINER
  22  help
  23    usage: unshare [-imnpuUr] COMMAND...
  24
  25    Create new container namespace(s) for this process and its children, so
  26    some attribute is not shared with the parent process.
  27
  28    -f  Fork command in the background (--fork)
  29    -i  SysV IPC (message queues, semaphores, shared memory) (--ipc)
  30    -m  Mount/unmount tree (--mount)
  31    -n  Network address, sockets, routing, iptables (--net)
  32    -p  Process IDs and init (--pid)
  33    -r  Become root (map current euid/egid to 0/0, implies -U) (--map-root-user)
  34    -u  Host and domain names (--uts)
  35    -U  UIDs, GIDs, capabilities (--user)
  36
  37    A namespace allows a set of processes to have a different view of the
  38    system than other sets of processes.
  39
  40config NSENTER
  41  bool "nsenter"
  42  depends on TOYBOX_CONTAINER
  43  default y
  44  help
  45    usage: nsenter [-t pid] [-F] [-i] [-m] [-n] [-p] [-u] [-U] COMMAND...
  46
  47    Run COMMAND in an existing (set of) namespace(s).
  48
  49    -t  PID to take namespaces from    (--target)
  50    -F  don't fork, even if -p is used (--no-fork)
  51
  52    The namespaces to switch are:
  53
  54    -i  SysV IPC: message queues, semaphores, shared memory (--ipc)
  55    -m  Mount/unmount tree (--mount)
  56    -n  Network address, sockets, routing, iptables (--net)
  57    -p  Process IDs and init, will fork unless -F is used (--pid)
  58    -u  Host and domain names (--uts)
  59    -U  UIDs, GIDs, capabilities (--user)
  60
  61    If -t isn't specified, each namespace argument must provide a path
  62    to a namespace file, ala "-i=/proc/$PID/ns/ipc"
  63*/
  64
  65#define FOR_nsenter
  66#include "toys.h"
  67#include <sys/syscall.h>
  68#include <linux/sched.h>
  69
  70#define unshare(flags) syscall(SYS_unshare, flags)
  71#define setns(fd, nstype) syscall(SYS_setns, fd, nstype)
  72
  73GLOBALS(
  74  char *Uupnmi[6];
  75  long t;
  76)
  77
  78// Code that must run in unshare's flag context
  79#define CLEANUP_nsenter
  80#define FOR_unshare
  81#include <generated/flags.h>
  82
  83static void write_ugid_map(char *map, unsigned eugid)
  84{
  85  int bytes = sprintf(toybuf, "0 %u 1", eugid), fd = xopen(map, O_WRONLY);
  86
  87  xwrite(fd, toybuf, bytes);
  88  xclose(fd);
  89}
  90
  91static void handle_r(int euid, int egid)
  92{
  93  int fd;
  94
  95  if ((fd = open("/proc/self/setgroups", O_WRONLY)) >= 0) {
  96    xwrite(fd, "deny", 4);
  97    close(fd);
  98  }
  99
 100  write_ugid_map("/proc/self/uid_map", euid);
 101  write_ugid_map("/proc/self/gid_map", egid);
 102}
 103
 104static int test_r()
 105{
 106  return toys.optflags & FLAG_r;
 107}
 108
 109static int test_f()
 110{
 111  return toys.optflags & FLAG_f;
 112}
 113
 114// Shift back to the context GLOBALS lives in (I.E. matching the filename).
 115#define CLEANUP_unshare
 116#define FOR_nsenter
 117#include <generated/flags.h>
 118
 119void unshare_main(void)
 120{
 121  unsigned flags[]={CLONE_NEWUSER, CLONE_NEWUTS, CLONE_NEWPID, CLONE_NEWNET,
 122                    CLONE_NEWNS, CLONE_NEWIPC}, f = 0;
 123  int i, fd;
 124
 125  // Create new namespace(s)?
 126  if (CFG_UNSHARE && *toys.which->name=='u') {
 127    // For -r, we have to save our original [ug]id before calling unshare()
 128    int euid = geteuid(), egid = getegid();
 129
 130    // unshare -U does not imply -r, so we cannot use [+rU]
 131    if (test_r()) toys.optflags |= FLAG_U;
 132
 133    for (i = 0; i<ARRAY_LEN(flags); i++)
 134      if (toys.optflags & (1<<i)) f |= flags[i];
 135
 136    if (unshare(f)) perror_exit(0);
 137    if (test_r()) handle_r(euid, egid);
 138
 139    if (test_f()) {
 140      toys.exitval = xrun(toys.optargs);
 141
 142      return;
 143    }
 144  // Bind to existing namespace(s)?
 145  } else if (CFG_NSENTER) {
 146    char *nsnames = "user\0uts\0pid\0net\0mnt\0ipc";
 147
 148    for (i = 0; i<ARRAY_LEN(flags); i++) {
 149      char *filename = TT.Uupnmi[i];
 150
 151      if (toys.optflags & (1<<i)) {
 152        if (!filename || !*filename) {
 153          if (!(toys.optflags & FLAG_t)) error_exit("need -t or =filename");
 154          sprintf(toybuf, "/proc/%ld/ns/%s", TT.t, nsnames);
 155          filename = toybuf;
 156        }
 157
 158        if (setns(fd = xopenro(filename), flags[i])) perror_exit("setns");
 159        close(fd);
 160      }
 161      nsnames += strlen(nsnames)+1;
 162    }
 163
 164    if ((toys.optflags & FLAG_p) && !(toys.optflags & FLAG_F)) {
 165      toys.exitval = xrun(toys.optargs);
 166
 167      return;
 168    }
 169  }
 170
 171  xexec(toys.optargs);
 172}
 173
 174void nsenter_main(void)
 175{
 176  unshare_main();
 177}
 178