util-linux/nsenter.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * Mini nsenter implementation for busybox.
   4  *
   5  * Copyright (C) 2016 by Bartosz Golaszewski <bartekgola@gmail.com>
   6  *
   7  * Licensed under GPLv2 or later, see file LICENSE in this source tree.
   8  */
   9
  10 //config:config NSENTER
  11 //config:       bool "nsenter (8.6 kb)"
  12 //config:       default y
  13 //config:       select PLATFORM_LINUX
  14 //config:       help
  15 //config:         Run program with namespaces of other processes.
  16 //config:
  17 //config:config FEATURE_NSENTER_LONG_OPTS
  18 //config:       bool "Enable long options"
  19 //config:       default y
  20 //config:       depends on NSENTER && LONG_OPTS
  21 //config:       help
  22 //config:         Support long options for the nsenter applet. This makes
  23 //config:         the busybox implementation more compatible with upstream.
  24
  25 //applet:IF_NSENTER(APPLET(nsenter, BB_DIR_USR_BIN, BB_SUID_DROP))
  26
  27 //kbuild:lib-$(CONFIG_NSENTER) += nsenter.o
  28
  29 //usage:#define nsenter_trivial_usage
  30 //usage:       "[OPTIONS] [PROG [ARGS]]"
  31 //usage:#if ENABLE_FEATURE_NSENTER_LONG_OPTS
  32 //usage:#define nsenter_full_usage "\n"
  33 //usage:     "\n        -t,--target PID         Target process to get namespaces from"
  34 //usage:     "\n        -m,--mount[=FILE]       Enter mount namespace"
  35 //usage:     "\n        -u,--uts[=FILE]         Enter UTS namespace (hostname etc)"
  36 //usage:     "\n        -i,--ipc[=FILE]         Enter System V IPC namespace"
  37 //usage:     "\n        -n,--net[=FILE]         Enter network namespace"
  38 //usage:     "\n        -p,--pid[=FILE]         Enter pid namespace"
  39 //usage:     "\n        -U,--user[=FILE]        Enter user namespace"
  40 //usage:     "\n        -S,--setuid UID         Set uid in entered namespace"
  41 //usage:     "\n        -G,--setgid GID         Set gid in entered namespace"
  42 //usage:     "\n        --preserve-credentials  Don't touch uids or gids"
  43 //usage:     "\n        -r,--root[=DIR]         Set root directory"
  44 //usage:     "\n        -w,--wd[=DIR]           Set working directory"
  45 //usage:     "\n        -F,--no-fork            Don't fork before exec'ing PROG"
  46 //usage:#else
  47 //usage:#define nsenter_full_usage "\n"
  48 //usage:     "\n        -t PID          Target process to get namespaces from"
  49 //usage:     "\n        -m[FILE]        Enter mount namespace"
  50 //usage:     "\n        -u[FILE]        Enter UTS namespace (hostname etc)"
  51 //usage:     "\n        -i[FILE]        Enter System V IPC namespace"
  52 //usage:     "\n        -n[FILE]        Enter network namespace"
  53 //usage:     "\n        -p[FILE]        Enter pid namespace"
  54 //usage:     "\n        -U[FILE]        Enter user namespace"
  55 //usage:     "\n        -S UID          Set uid in entered namespace"
  56 //usage:     "\n        -G GID          Set gid in entered namespace"
  57 //usage:     "\n        -r[DIR]         Set root directory"
  58 //usage:     "\n        -w[DIR]         Set working directory"
  59 //usage:     "\n        -F              Don't fork before exec'ing PROG"
  60 //usage:#endif
  61
  62 #include <sched.h>
  63 #ifndef CLONE_NEWUTS
  64 # define CLONE_NEWUTS  0x04000000
  65 #endif
  66 #ifndef CLONE_NEWIPC
  67 # define CLONE_NEWIPC  0x08000000
  68 #endif
  69 #ifndef CLONE_NEWUSER
  70 # define CLONE_NEWUSER 0x10000000
  71 #endif
  72 #ifndef CLONE_NEWPID
  73 # define CLONE_NEWPID  0x20000000
  74 #endif
  75 #ifndef CLONE_NEWNET
  76 # define CLONE_NEWNET  0x40000000
  77 #endif
  78
  79 #include "libbb.h"
  80
  81 struct namespace_descr {
  82         int flag;               /* value passed to setns() */
  83         char ns_nsfile8[8];     /* "ns/" + namespace file in process' procfs entry */
  84 };
  85
  86 struct namespace_ctx {
  87         char *path;             /* optional path to a custom ns file */
  88         int fd;                 /* opened namespace file descriptor */
  89 };
  90
  91 enum {
  92         OPT_user        = 1 << 0,
  93         OPT_ipc         = 1 << 1,
  94         OPT_uts         = 1 << 2,
  95         OPT_network     = 1 << 3,
  96         OPT_pid         = 1 << 4,
  97         OPT_mount       = 1 << 5,
  98         OPT_target      = 1 << 6,
  99         OPT_setuid      = 1 << 7,
 100         OPT_setgid      = 1 << 8,
 101         OPT_root        = 1 << 9,
 102         OPT_wd          = 1 << 10,
 103         OPT_nofork      = 1 << 11,
 104         OPT_prescred    = (1 << 12) * ENABLE_FEATURE_NSENTER_LONG_OPTS,
 105 };
 106 enum {
 107         NS_USR_POS = 0,
 108         NS_IPC_POS,
 109         NS_UTS_POS,
 110         NS_NET_POS,
 111         NS_PID_POS,
 112         NS_MNT_POS,
 113         NS_COUNT,
 114 };
 115 /*
 116  * The order is significant in nsenter.
 117  * The user namespace comes first, so that it is entered first.
 118  * This gives an unprivileged user the potential to enter other namespaces.
 119  */
 120 static const struct namespace_descr ns_list[] = {
 121         { CLONE_NEWUSER, "ns/user", },
 122         { CLONE_NEWIPC,  "ns/ipc",  },
 123         { CLONE_NEWUTS,  "ns/uts",  },
 124         { CLONE_NEWNET,  "ns/net",  },
 125         { CLONE_NEWPID,  "ns/pid",  },
 126         { CLONE_NEWNS,   "ns/mnt",  },
 127 };
 128 /*
 129  * Upstream nsenter doesn't support the short option for --preserve-credentials
 130  */
 131 static const char opt_str[] ALIGN1 = "U::i::u::n::p::m::""t+S+G+r::w::F";
 132
 133 #if ENABLE_FEATURE_NSENTER_LONG_OPTS
 134 static const char nsenter_longopts[] ALIGN1 =
 135         "user\0"                        Optional_argument       "U"
 136         "ipc\0"                         Optional_argument       "i"
 137         "uts\0"                         Optional_argument       "u"
 138         "network\0"                     Optional_argument       "n"
 139         "pid\0"                         Optional_argument       "p"
 140         "mount\0"                       Optional_argument       "m"
 141         "target\0"                      Required_argument       "t"
 142         "setuid\0"                      Required_argument       "S"
 143         "setgid\0"                      Required_argument       "G"
 144         "root\0"                        Optional_argument       "r"
 145         "wd\0"                          Optional_argument       "w"
 146         "no-fork\0"                     No_argument             "F"
 147         "preserve-credentials\0"        No_argument             "\xff"
 148         ;
 149 #endif
 150
 151 /*
 152  * Open a file and return the new descriptor. If a full path is provided in
 153  * fs_path, then the file to which it points is opened. Otherwise (fd_path is
 154  * NULL) the routine builds a path to a procfs file using the following
 155  * template: '/proc/<target_pid>/<target_file>'.
 156  */
 157 static int open_by_path_or_target(const char *path,
 158                                   pid_t target_pid, const char *target_file)
 159 {
 160         char proc_path_buf[sizeof("/proc/%u/1234567890") + sizeof(int)*3];
 161
 162         if (!path) {
 163                 if (target_pid == 0) {
 164                         /* Example:
 165                          * "nsenter -p PROG" - neither -pFILE nor -tPID given.
 166                          */
 167                         bb_show_usage();
 168                 }
 169                 snprintf(proc_path_buf, sizeof(proc_path_buf),
 170                          "/proc/%u/%s", (unsigned)target_pid, target_file);
 171                 path = proc_path_buf;
 172         }
 173
 174         return xopen(path, O_RDONLY);
 175 }
 176
 177 int nsenter_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 178 int nsenter_main(int argc UNUSED_PARAM, char **argv)
 179 {
 180         int i;
 181         unsigned int opts;
 182         const char *root_dir_str = NULL;
 183         const char *wd_str = NULL;
 184         struct namespace_ctx ns_ctx_list[NS_COUNT];
 185         int setgroups_failed;
 186         int root_fd, wd_fd;
 187         int target_pid = 0;
 188         int uid = 0;
 189         int gid = 0;
 190
 191         memset(ns_ctx_list, 0, sizeof(ns_ctx_list));
 192
 193         IF_FEATURE_NSENTER_LONG_OPTS(applet_long_options = nsenter_longopts);
 194         opts = getopt32(argv, opt_str,
 195                         &ns_ctx_list[NS_USR_POS].path,
 196                         &ns_ctx_list[NS_IPC_POS].path,
 197                         &ns_ctx_list[NS_UTS_POS].path,
 198                         &ns_ctx_list[NS_NET_POS].path,
 199                         &ns_ctx_list[NS_PID_POS].path,
 200                         &ns_ctx_list[NS_MNT_POS].path,
 201                         &target_pid, &uid, &gid,
 202                         &root_dir_str, &wd_str
 203         );
 204         argv += optind;
 205
 206         root_fd = wd_fd = -1;
 207         if (opts & OPT_root)
 208                 root_fd = open_by_path_or_target(root_dir_str,
 209                                                  target_pid, "root");
 210         if (opts & OPT_wd)
 211                 wd_fd = open_by_path_or_target(wd_str, target_pid, "cwd");
 212
 213         for (i = 0; i < NS_COUNT; i++) {
 214                 const struct namespace_descr *ns = &ns_list[i];
 215                 struct namespace_ctx *ns_ctx = &ns_ctx_list[i];
 216
 217                 ns_ctx->fd = -1;
 218                 if (opts & (1 << i))
 219                         ns_ctx->fd = open_by_path_or_target(ns_ctx->path,
 220                                         target_pid, ns->ns_nsfile8);
 221         }
 222
 223         /*
 224          * Entering the user namespace without --preserve-credentials implies
 225          * --setuid & --setgid and clearing root's groups.
 226          */
 227         setgroups_failed = 0;
 228         if ((opts & OPT_user) && !(opts & OPT_prescred)) {
 229                 opts |= (OPT_setuid | OPT_setgid);
 230                 /*
 231                  * We call setgroups() before and after setns() and only
 232                  * bail-out if it fails twice.
 233                  */
 234                 setgroups_failed = (setgroups(0, NULL) < 0);
 235         }
 236
 237         for (i = 0; i < NS_COUNT; i++) {
 238                 const struct namespace_descr *ns = &ns_list[i];
 239                 struct namespace_ctx *ns_ctx = &ns_ctx_list[i];
 240
 241                 if (ns_ctx->fd < 0)
 242                         continue;
 243                 if (setns(ns_ctx->fd, ns->flag)) {
 244                         bb_perror_msg_and_die(
 245                                 "setns(): can't reassociate to namespace '%s'",
 246                                 ns->ns_nsfile8 + 3 /* skip over "ns/" */
 247                         );
 248                 }
 249                 close(ns_ctx->fd); /* should close fds, to not confuse exec'ed PROG */
 250                 /*ns_ctx->fd = -1;*/
 251         }
 252
 253         if (root_fd >= 0) {
 254                 if (wd_fd < 0) {
 255                         /*
 256                          * Save the current working directory if we're not
 257                          * changing it.
 258                          */
 259                         wd_fd = xopen(".", O_RDONLY);
 260                 }
 261                 xfchdir(root_fd);
 262                 xchroot(".");
 263                 close(root_fd);
 264                 /*root_fd = -1;*/
 265         }
 266
 267         if (wd_fd >= 0) {
 268                 xfchdir(wd_fd);
 269                 close(wd_fd);
 270                 /*wd_fd = -1;*/
 271         }
 272
 273         /*
 274          * Entering the pid namespace implies forking unless it's been
 275          * explicitly requested by the user not to.
 276          */
 277         if (!(opts & OPT_nofork) && (opts & OPT_pid)) {
 278                 xvfork_parent_waits_and_exits();
 279                 /* Child continues */
 280         }
 281
 282         if (opts & OPT_setgid) {
 283                 if (setgroups(0, NULL) < 0 && setgroups_failed)
 284                         bb_perror_msg_and_die("setgroups");
 285                 xsetgid(gid);
 286         }
 287         if (opts & OPT_setuid)
 288                 xsetuid(uid);
 289
 290         exec_prog_or_SHELL(argv);
 291 }