1 /* vi: set sw=4 ts=4: */
2 /*
3 * Rexec program for system have fork() as vfork() with foreground option
4 *
5 * Copyright (C) Vladimir N. Oleynik <dzo@simtreas.ru>
6 * Copyright (C) 2003 Russ Dill <Russ.Dill@asu.edu>
7 *
8 * daemon() portion taken from uClibc:
9 *
10 * Copyright (c) 1991, 1993
11 * The Regents of the University of California. All rights reserved.
12 *
13 * Modified for uClibc by Erik Andersen <andersee@debian.org>
14 *
15 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
16 */
17
18 #include "busybox.h" /* uses applet tables */
19
20 /* This does a fork/exec in one call, using vfork(). Returns PID of new child,
21 * -1 for failure. Runs argv[0], searching path if that has no / in it. */
spawn(char ** argv)22 pid_t FAST_FUNC spawn(char **argv)
23 {
24 /* Compiler should not optimize stores here */
25 volatile int failed;
26 pid_t pid;
27
28 fflush_all();
29
30 /* Be nice to nommu machines. */
31 failed = 0;
32 pid = vfork();
33 if (pid < 0) /* error */
34 return pid;
35 if (!pid) { /* child */
36 /* This macro is ok - it doesn't do NOEXEC/NOFORK tricks */
37 BB_EXECVP(argv[0], argv);
38
39 /* We are (maybe) sharing a stack with blocked parent,
40 * let parent know we failed and then exit to unblock parent
41 * (but don't run atexit() stuff, which would screw up parent.)
42 */
43 failed = errno;
44 /* mount, for example, does not want the message */
45 /*bb_perror_msg("can't execute '%s'", argv[0]);*/
46 _exit(111);
47 }
48 /* parent */
49 /* Unfortunately, this is not reliable: according to standards
50 * vfork() can be equivalent to fork() and we won't see value
51 * of 'failed'.
52 * Interested party can wait on pid and learn exit code.
53 * If 111 - then it (most probably) failed to exec */
54 if (failed) {
55 safe_waitpid(pid, NULL, 0); /* prevent zombie */
56 errno = failed;
57 return -1;
58 }
59 return pid;
60 }
61
62 /* Die with an error message if we can't spawn a child process. */
xspawn(char ** argv)63 pid_t FAST_FUNC xspawn(char **argv)
64 {
65 pid_t pid = spawn(argv);
66 if (pid < 0)
67 bb_simple_perror_msg_and_die(*argv);
68 return pid;
69 }
70
71 #if ENABLE_FEATURE_PREFER_APPLETS \
72 || ENABLE_FEATURE_SH_NOFORK
73 static jmp_buf die_jmp;
jump(void)74 static void jump(void)
75 {
76 /* Special case. We arrive here if NOFORK applet
77 * calls xfunc, which then decides to die.
78 * We don't die, but jump instead back to caller.
79 * NOFORK applets still cannot carelessly call xfuncs:
80 * p = xmalloc(10);
81 * q = xmalloc(10); // BUG! if this dies, we leak p!
82 */
83 /* | 0x100 allows to pass zero exitcode (longjmp can't pass 0).
84 * This works because exitcodes are bytes,
85 * run_nofork_applet() ensures that by "& 0xff" */
86 longjmp(die_jmp, xfunc_error_retval | 0x100);
87 }
88
89 struct nofork_save_area {
90 jmp_buf die_jmp;
91 void (*die_func)(void);
92 const char *applet_name;
93 uint32_t option_mask32;
94 uint8_t xfunc_error_retval;
95 };
save_nofork_data(struct nofork_save_area * save)96 static void save_nofork_data(struct nofork_save_area *save)
97 {
98 memcpy(&save->die_jmp, &die_jmp, sizeof(die_jmp));
99 save->die_func = die_func;
100 save->applet_name = applet_name;
101 save->option_mask32 = option_mask32;
102 save->xfunc_error_retval = xfunc_error_retval;
103 }
restore_nofork_data(struct nofork_save_area * save)104 static void restore_nofork_data(struct nofork_save_area *save)
105 {
106 memcpy(&die_jmp, &save->die_jmp, sizeof(die_jmp));
107 die_func = save->die_func;
108 applet_name = save->applet_name;
109 option_mask32 = save->option_mask32;
110 xfunc_error_retval = save->xfunc_error_retval;
111 }
112
run_nofork_applet(int applet_no,char ** argv)113 int FAST_FUNC run_nofork_applet(int applet_no, char **argv)
114 {
115 int rc, argc;
116 struct nofork_save_area old;
117
118 save_nofork_data(&old);
119
120 xfunc_error_retval = EXIT_FAILURE;
121
122 /* In case getopt() or getopt32() was already called:
123 * reset the libc getopt() function, which keeps internal state.
124 *
125 * BSD-derived getopt() functions require that optind be set to 1 in
126 * order to reset getopt() state. This used to be generally accepted
127 * way of resetting getopt(). However, glibc's getopt()
128 * has additional getopt() state beyond optind, and requires that
129 * optind be set to zero to reset its state. So the unfortunate state of
130 * affairs is that BSD-derived versions of getopt() misbehave if
131 * optind is set to 0 in order to reset getopt(), and glibc's getopt()
132 * will core dump if optind is set 1 in order to reset getopt().
133 *
134 * More modern versions of BSD require that optreset be set to 1 in
135 * order to reset getopt(). Sigh. Standards, anyone?
136 */
137 #ifdef __GLIBC__
138 optind = 0;
139 #else /* BSD style */
140 optind = 1;
141 /* optreset = 1; */
142 #endif
143 /* optarg = NULL; opterr = 1; optopt = 63; - do we need this too? */
144 /* (values above are what they initialized to in glibc and uclibc) */
145 /* option_mask32 = 0; - not needed, no applet depends on it being 0 */
146
147 argc = 1;
148 while (argv[argc])
149 argc++;
150
151 /* If xfunc "dies" in NOFORK applet, die_func longjmp's here instead */
152 die_func = jump;
153 rc = setjmp(die_jmp);
154 if (!rc) {
155 /* Some callers (xargs)
156 * need argv untouched because they free argv[i]! */
157 char *tmp_argv[argc+1];
158 memcpy(tmp_argv, argv, (argc+1) * sizeof(tmp_argv[0]));
159 applet_name = tmp_argv[0];
160 /* Finally we can call NOFORK applet's main() */
161 rc = applet_main[applet_no](argc, tmp_argv);
162 } else {
163 /* xfunc died in NOFORK applet */
164 }
165
166 /* Restoring some globals */
167 restore_nofork_data(&old);
168
169 /* Other globals can be simply reset to defaults */
170 #ifdef __GLIBC__
171 optind = 0;
172 #else /* BSD style */
173 optind = 1;
174 #endif
175
176 return rc & 0xff; /* don't confuse people with "exitcodes" >255 */
177 }
178 #endif /* FEATURE_PREFER_APPLETS || FEATURE_SH_NOFORK */
179
spawn_and_wait(char ** argv)180 int FAST_FUNC spawn_and_wait(char **argv)
181 {
182 int rc;
183 #if ENABLE_FEATURE_PREFER_APPLETS
184 int a = find_applet_by_name(argv[0]);
185
186 if (a >= 0 && (APPLET_IS_NOFORK(a)
187 # if BB_MMU
188 || APPLET_IS_NOEXEC(a) /* NOEXEC trick needs fork() */
189 # endif
190 )) {
191 # if BB_MMU
192 if (APPLET_IS_NOFORK(a))
193 # endif
194 {
195 return run_nofork_applet(a, argv);
196 }
197 # if BB_MMU
198 /* MMU only */
199 /* a->noexec is true */
200 rc = fork();
201 if (rc) /* parent or error */
202 return wait4pid(rc);
203 /* child */
204 xfunc_error_retval = EXIT_FAILURE;
205 run_applet_no_and_exit(a, argv);
206 # endif
207 }
208 #endif /* FEATURE_PREFER_APPLETS */
209 rc = spawn(argv);
210 return wait4pid(rc);
211 }
212
213 #if !BB_MMU
re_exec(char ** argv)214 void FAST_FUNC re_exec(char **argv)
215 {
216 /* high-order bit of first char in argv[0] is a hidden
217 * "we have (already) re-execed, don't do it again" flag */
218 argv[0][0] |= 0x80;
219 execv(bb_busybox_exec_path, argv);
220 bb_perror_msg_and_die("can't execute '%s'", bb_busybox_exec_path);
221 }
222
fork_or_rexec(char ** argv)223 pid_t FAST_FUNC fork_or_rexec(char **argv)
224 {
225 pid_t pid;
226 /* Maybe we are already re-execed and come here again? */
227 if (re_execed)
228 return 0;
229 pid = xvfork();
230 if (pid) /* parent */
231 return pid;
232 /* child - re-exec ourself */
233 re_exec(argv);
234 }
235 #endif
236
237 /* Due to a #define in libbb.h on MMU systems we actually have 1 argument -
238 * char **argv "vanishes" */
bb_daemonize_or_rexec(int flags,char ** argv)239 void FAST_FUNC bb_daemonize_or_rexec(int flags, char **argv)
240 {
241 int fd;
242
243 if (flags & DAEMON_CHDIR_ROOT)
244 xchdir("/");
245
246 if (flags & DAEMON_DEVNULL_STDIO) {
247 close(0);
248 close(1);
249 close(2);
250 }
251
252 fd = open(bb_dev_null, O_RDWR);
253 if (fd < 0) {
254 /* NB: we can be called as bb_sanitize_stdio() from init
255 * or mdev, and there /dev/null may legitimately not (yet) exist!
256 * Do not use xopen above, but obtain _ANY_ open descriptor,
257 * even bogus one as below. */
258 fd = xopen("/", O_RDONLY); /* don't believe this can fail */
259 }
260
261 while ((unsigned)fd < 2)
262 fd = dup(fd); /* have 0,1,2 open at least to /dev/null */
263
264 if (!(flags & DAEMON_ONLY_SANITIZE)) {
265 if (fork_or_rexec(argv))
266 exit(EXIT_SUCCESS); /* parent */
267 /* if daemonizing, detach from stdio & ctty */
268 setsid();
269 dup2(fd, 0);
270 dup2(fd, 1);
271 dup2(fd, 2);
272 if (flags & DAEMON_DOUBLE_FORK) {
273 /* On Linux, session leader can acquire ctty
274 * unknowingly, by opening a tty.
275 * Prevent this: stop being a session leader.
276 */
277 if (fork_or_rexec(argv))
278 exit(EXIT_SUCCESS); /* parent */
279 }
280 }
281 while (fd > 2) {
282 close(fd--);
283 if (!(flags & DAEMON_CLOSE_EXTRA_FDS))
284 return;
285 /* else close everything after fd#2 */
286 }
287 }
288
bb_sanitize_stdio(void)289 void FAST_FUNC bb_sanitize_stdio(void)
290 {
291 bb_daemonize_or_rexec(DAEMON_ONLY_SANITIZE, NULL);
292 }
293