Harald Welte | c6a8697 | 2019-12-16 23:14:45 +0100 | [diff] [blame] | 1 | /* (C) 2019 by Harald Welte <laforge@gnumonks.org> |
| 2 | * |
| 3 | * All Rights Reserved |
| 4 | * |
| 5 | * SPDX-License-Identifier: GPL-2.0+ |
| 6 | * |
| 7 | * This program is free software; you can redistribute it and/or modify |
| 8 | * it under the terms of the GNU General Public License as published by |
| 9 | * the Free Software Foundation; either version 2 of the License, or |
| 10 | * (at your option) any later version. |
| 11 | * |
| 12 | * This program is distributed in the hope that it will be useful, |
| 13 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 14 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 15 | * GNU General Public License for more details. |
| 16 | * |
Harald Welte | c6a8697 | 2019-12-16 23:14:45 +0100 | [diff] [blame] | 17 | */ |
| 18 | |
| 19 | #include "config.h" |
| 20 | #ifndef EMBEDDED |
| 21 | |
Harald Welte | f3cc731 | 2020-04-17 18:23:52 +0200 | [diff] [blame] | 22 | #define _GNU_SOURCE |
Harald Welte | c6a8697 | 2019-12-16 23:14:45 +0100 | [diff] [blame] | 23 | #include <unistd.h> |
| 24 | |
| 25 | #include <errno.h> |
| 26 | #include <string.h> |
| 27 | |
| 28 | #include <stdio.h> |
| 29 | #include <dirent.h> |
| 30 | #include <sys/types.h> |
Harald Welte | f3cc731 | 2020-04-17 18:23:52 +0200 | [diff] [blame] | 31 | #include <pwd.h> |
Harald Welte | c6a8697 | 2019-12-16 23:14:45 +0100 | [diff] [blame] | 32 | |
| 33 | #include <osmocom/core/logging.h> |
| 34 | #include <osmocom/core/utils.h> |
| 35 | #include <osmocom/core/exec.h> |
| 36 | |
| 37 | /*! suggested list of environment variables to pass (if they exist) to a sub-process/script */ |
| 38 | const char *osmo_environment_whitelist[] = { |
| 39 | "USER", "LOGNAME", "HOME", |
| 40 | "LANG", "LC_ALL", "LC_COLLATE", "LC_CTYPE", "LC_MESSAGES", "LC_MONETARY", "LC_NUMERIC", "LC_TIME", |
| 41 | "PATH", |
| 42 | "PWD", |
| 43 | "SHELL", |
| 44 | "TERM", |
| 45 | "TMPDIR", |
| 46 | "LD_LIBRARY_PATH", |
| 47 | "LD_PRELOAD", |
| 48 | "POSIXLY_CORRECT", |
| 49 | "HOSTALIASES", |
| 50 | "TZ", "TZDIR", |
| 51 | "TERMCAP", |
| 52 | "COLUMNS", "LINES", |
| 53 | NULL |
| 54 | }; |
| 55 | |
| 56 | static bool str_in_list(const char **list, const char *key) |
| 57 | { |
| 58 | const char **ent; |
| 59 | |
| 60 | for (ent = list; *ent; ent++) { |
| 61 | if (!strcmp(*ent, key)) |
| 62 | return true; |
| 63 | } |
| 64 | return false; |
| 65 | } |
| 66 | |
| 67 | /*! filtered a process environment by whitelist; only copying pointers, no actual strings. |
| 68 | * |
| 69 | * This function is useful if you'd like to generate an environment to pass exec*e() |
| 70 | * functions. It will create a new environment containing only those entries whose |
| 71 | * keys (as per environment convention KEY=VALUE) are contained in the whitelist. The |
| 72 | * function will not copy the actual strings, but just create a new pointer array, pointing |
| 73 | * to the same memory as the input strings. |
| 74 | * |
| 75 | * Constraints: Keys up to a maximum length of 255 characters are supported. |
| 76 | * |
Vadim Yanitskiy | 64277a0 | 2023-02-28 03:30:27 +0700 | [diff] [blame] | 77 | * \param[out] out caller-allocated array of pointers for the generated output |
Harald Welte | c6a8697 | 2019-12-16 23:14:45 +0100 | [diff] [blame] | 78 | * \param[in] out_len size of out (number of pointers) |
| 79 | * \param[in] in input environment (NULL-terminated list of pointers like **environ) |
| 80 | * \param[in] whitelist whitelist of permitted keys in environment (like **environ) |
| 81 | * \returns number of entries filled in 'out'; negtive on error */ |
| 82 | int osmo_environment_filter(char **out, size_t out_len, char **in, const char **whitelist) |
| 83 | { |
| 84 | char tmp[256]; |
| 85 | char **ent; |
| 86 | size_t out_used = 0; |
| 87 | |
| 88 | /* invalid calls */ |
| 89 | if (!out || out_len == 0 || !whitelist) |
| 90 | return -EINVAL; |
| 91 | |
| 92 | /* legal, but unusual: no input to filter should generate empty, terminated out */ |
| 93 | if (!in) { |
| 94 | out[0] = NULL; |
| 95 | return 1; |
| 96 | } |
| 97 | |
| 98 | /* iterate over input entries */ |
| 99 | for (ent = in; *ent; ent++) { |
| 100 | char *eq = strchr(*ent, '='); |
| 101 | unsigned long eq_pos; |
| 102 | if (!eq) { |
| 103 | /* no '=' in string, skip it */ |
| 104 | continue; |
| 105 | } |
| 106 | eq_pos = eq - *ent; |
| 107 | if (eq_pos >= ARRAY_SIZE(tmp)) |
| 108 | continue; |
| 109 | strncpy(tmp, *ent, eq_pos); |
| 110 | tmp[eq_pos] = '\0'; |
| 111 | if (str_in_list(whitelist, tmp)) { |
| 112 | if (out_used == out_len-1) |
| 113 | break; |
| 114 | /* append to output */ |
| 115 | out[out_used++] = *ent; |
| 116 | } |
| 117 | } |
| 118 | OSMO_ASSERT(out_used < out_len); |
| 119 | out[out_used++] = NULL; |
| 120 | return out_used; |
| 121 | } |
| 122 | |
| 123 | /*! append one environment to another; only copying pointers, not actual strings. |
| 124 | * |
| 125 | * This function is useful if you'd like to append soem entries to an environment |
| 126 | * befoer passing it to exec*e() functions. |
| 127 | * |
| 128 | * It will append all entries from 'in' to the environment in 'out', as long as |
| 129 | * 'out' has space (determined by 'out_len'). |
| 130 | * |
| 131 | * Constraints: If the same key exists in 'out' and 'in', duplicate keys are |
| 132 | * generated. It is a simple append, without any duplicate checks. |
| 133 | * |
Vadim Yanitskiy | 64277a0 | 2023-02-28 03:30:27 +0700 | [diff] [blame] | 134 | * \param[out] out caller-allocated array of pointers for the generated output |
Harald Welte | c6a8697 | 2019-12-16 23:14:45 +0100 | [diff] [blame] | 135 | * \param[in] out_len size of out (number of pointers) |
| 136 | * \param[in] in input environment (NULL-terminated list of pointers like **environ) |
| 137 | * \returns number of entries filled in 'out'; negative on error */ |
| 138 | int osmo_environment_append(char **out, size_t out_len, char **in) |
| 139 | { |
| 140 | size_t out_used = 0; |
| 141 | |
| 142 | if (!out || out_len == 0) |
| 143 | return -EINVAL; |
| 144 | |
| 145 | /* seek to end of existing output */ |
| 146 | for (out_used = 0; out[out_used]; out_used++) {} |
| 147 | |
| 148 | if (!in) { |
| 149 | if (out_used == 0) |
| 150 | out[out_used++] = NULL; |
| 151 | return out_used; |
| 152 | } |
| 153 | |
| 154 | for (; *in && out_used < out_len-1; in++) |
| 155 | out[out_used++] = *in; |
| 156 | |
| 157 | OSMO_ASSERT(out_used < out_len); |
| 158 | out[out_used++] = NULL; |
| 159 | |
| 160 | return out_used; |
| 161 | } |
| 162 | |
| 163 | /* Iterate over files in /proc/self/fd and close all above lst_fd_to_keep */ |
| 164 | int osmo_close_all_fds_above(int last_fd_to_keep) |
| 165 | { |
| 166 | struct dirent *ent; |
| 167 | DIR *dir; |
| 168 | int rc; |
| 169 | |
| 170 | dir = opendir("/proc/self/fd"); |
| 171 | if (!dir) { |
| 172 | LOGP(DLGLOBAL, LOGL_ERROR, "Cannot open /proc/self/fd: %s\n", strerror(errno)); |
| 173 | return -ENODEV; |
| 174 | } |
| 175 | |
| 176 | while ((ent = readdir(dir))) { |
| 177 | int fd = atoi(ent->d_name); |
| 178 | if (fd <= last_fd_to_keep) |
| 179 | continue; |
| 180 | if (fd == dirfd(dir)) |
| 181 | continue; |
| 182 | rc = close(fd); |
| 183 | if (rc) |
| 184 | LOGP(DLGLOBAL, LOGL_ERROR, "Error closing fd=%d: %s\n", fd, strerror(errno)); |
| 185 | } |
| 186 | closedir(dir); |
| 187 | return 0; |
| 188 | } |
| 189 | |
| 190 | /* Seems like POSIX has no header file for this, and even glibc + __USE_GNU doesn't help */ |
| 191 | extern char **environ; |
| 192 | |
Harald Welte | f3cc731 | 2020-04-17 18:23:52 +0200 | [diff] [blame] | 193 | /*! call an external shell command as 'user' without waiting for it. |
Harald Welte | c6a8697 | 2019-12-16 23:14:45 +0100 | [diff] [blame] | 194 | * |
| 195 | * This mimics the behavior of system(3), with the following differences: |
| 196 | * - it doesn't wait for completion of the child process |
| 197 | * - it closes all non-stdio file descriptors by iterating /proc/self/fd |
| 198 | * - it constructs a reduced environment where only whitelisted keys survive |
| 199 | * - it (optionally) appends additional variables to the environment |
Harald Welte | f3cc731 | 2020-04-17 18:23:52 +0200 | [diff] [blame] | 200 | * - it (optionally) changes the user ID to that of 'user' (requires execution as root) |
Harald Welte | c6a8697 | 2019-12-16 23:14:45 +0100 | [diff] [blame] | 201 | * |
| 202 | * \param[in] command the shell command to be executed, see system(3) |
| 203 | * \param[in] env_whitelist A white-list of keys for environment variables |
| 204 | * \param[in] addl_env any additional environment variables to be appended |
Harald Welte | f3cc731 | 2020-04-17 18:23:52 +0200 | [diff] [blame] | 205 | * \param[in] user name of the user to which we should switch before executing the command |
Harald Welte | c6a8697 | 2019-12-16 23:14:45 +0100 | [diff] [blame] | 206 | * \returns PID of generated child process; negative on error |
| 207 | */ |
Harald Welte | f3cc731 | 2020-04-17 18:23:52 +0200 | [diff] [blame] | 208 | int osmo_system_nowait2(const char *command, const char **env_whitelist, char **addl_env, const char *user) |
Harald Welte | c6a8697 | 2019-12-16 23:14:45 +0100 | [diff] [blame] | 209 | { |
Philipp Maier | 6a90c72 | 2020-04-20 11:08:29 +0200 | [diff] [blame] | 210 | struct passwd _pw; |
| 211 | struct passwd *pw = NULL; |
Harald Welte | f3cc731 | 2020-04-17 18:23:52 +0200 | [diff] [blame] | 212 | int getpw_buflen = sysconf(_SC_GETPW_R_SIZE_MAX); |
Harald Welte | c6a8697 | 2019-12-16 23:14:45 +0100 | [diff] [blame] | 213 | int rc; |
| 214 | |
Harald Welte | f3cc731 | 2020-04-17 18:23:52 +0200 | [diff] [blame] | 215 | if (user) { |
| 216 | char buf[getpw_buflen]; |
| 217 | getpwnam_r(user, &_pw, buf, sizeof(buf), &pw); |
| 218 | if (!pw) |
| 219 | return -EINVAL; |
| 220 | } |
| 221 | |
Harald Welte | c6a8697 | 2019-12-16 23:14:45 +0100 | [diff] [blame] | 222 | rc = fork(); |
| 223 | if (rc == 0) { |
| 224 | /* we are in the child */ |
| 225 | char *new_env[1024]; |
| 226 | |
| 227 | /* close all file descriptors above stdio */ |
| 228 | osmo_close_all_fds_above(2); |
| 229 | |
Vadim Yanitskiy | d419f65 | 2020-02-09 04:44:35 +0700 | [diff] [blame] | 230 | /* man execle: "an array of pointers *must* be terminated by a null pointer" */ |
| 231 | new_env[0] = NULL; |
| 232 | |
Harald Welte | c6a8697 | 2019-12-16 23:14:45 +0100 | [diff] [blame] | 233 | /* build the new environment */ |
Vadim Yanitskiy | 979c3b7 | 2020-02-09 05:06:12 +0700 | [diff] [blame] | 234 | if (env_whitelist) { |
| 235 | rc = osmo_environment_filter(new_env, ARRAY_SIZE(new_env), environ, env_whitelist); |
| 236 | if (rc < 0) |
| 237 | return rc; |
| 238 | } |
| 239 | if (addl_env) { |
| 240 | rc = osmo_environment_append(new_env, ARRAY_SIZE(new_env), addl_env); |
| 241 | if (rc < 0) |
| 242 | return rc; |
| 243 | } |
Harald Welte | c6a8697 | 2019-12-16 23:14:45 +0100 | [diff] [blame] | 244 | |
Harald Welte | f3cc731 | 2020-04-17 18:23:52 +0200 | [diff] [blame] | 245 | /* drop privileges */ |
| 246 | if (pw) { |
| 247 | if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0) { |
| 248 | perror("setresgid() during privilege drop"); |
| 249 | exit(1); |
| 250 | } |
| 251 | |
| 252 | if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0) { |
| 253 | perror("setresuid() during privilege drop"); |
| 254 | exit(1); |
| 255 | } |
| 256 | |
| 257 | } |
| 258 | |
Harald Welte | c6a8697 | 2019-12-16 23:14:45 +0100 | [diff] [blame] | 259 | /* if we want to behave like system(3), we must go via the shell */ |
| 260 | execle("/bin/sh", "sh", "-c", command, (char *) NULL, new_env); |
| 261 | /* only reached in case of error */ |
| 262 | LOGP(DLGLOBAL, LOGL_ERROR, "Error executing command '%s' after fork: %s\n", |
| 263 | command, strerror(errno)); |
| 264 | return -EIO; |
| 265 | } else { |
| 266 | /* we are in the parent */ |
| 267 | return rc; |
| 268 | } |
| 269 | } |
| 270 | |
Harald Welte | f3cc731 | 2020-04-17 18:23:52 +0200 | [diff] [blame] | 271 | /*! call an external shell command without waiting for it. |
| 272 | * |
| 273 | * This mimics the behavior of system(3), with the following differences: |
| 274 | * - it doesn't wait for completion of the child process |
| 275 | * - it closes all non-stdio file descriptors by iterating /proc/self/fd |
| 276 | * - it constructs a reduced environment where only whitelisted keys survive |
| 277 | * - it (optionally) appends additional variables to the environment |
| 278 | * |
| 279 | * \param[in] command the shell command to be executed, see system(3) |
| 280 | * \param[in] env_whitelist A white-list of keys for environment variables |
| 281 | * \param[in] addl_env any additional environment variables to be appended |
| 282 | * \returns PID of generated child process; negative on error |
| 283 | */ |
| 284 | int osmo_system_nowait(const char *command, const char **env_whitelist, char **addl_env) |
| 285 | { |
| 286 | return osmo_system_nowait2(command, env_whitelist, addl_env, NULL); |
| 287 | } |
| 288 | |
| 289 | |
Harald Welte | c6a8697 | 2019-12-16 23:14:45 +0100 | [diff] [blame] | 290 | #endif /* EMBEDDED */ |