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