summaryrefslogtreecommitdiff
path: root/libbb/vfork_daemon_rexec.c
blob: cb4781a59196aa8cea497034d1a7c0db7b1b225c (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
/* vi: set sw=4 ts=4: */
/*
 * Rexec program for system have fork() as vfork() with foreground option
 *
 * Copyright (C) Vladimir N. Oleynik <dzo@simtreas.ru>
 * Copyright (C) 2003 Russ Dill <Russ.Dill@asu.edu>
 *
 * daemon() portion taken from uClibc:
 *
 * Copyright (c) 1991, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * Modified for uClibc by Erik Andersen <andersee@debian.org>
 *
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
 */

#include "busybox.h" /* uses applet tables */

/* This does a fork/exec in one call, using vfork().  Returns PID of new child,
 * -1 for failure.  Runs argv[0], searching path if that has no / in it. */
pid_t FAST_FUNC spawn(char **argv)
{
	/* Compiler should not optimize stores here */
	volatile int failed;
	pid_t pid;

	fflush_all();

	/* Be nice to nommu machines. */
	failed = 0;
	pid = vfork();
	if (pid < 0) /* error */
		return pid;
	if (!pid) { /* child */
		/* This macro is ok - it doesn't do NOEXEC/NOFORK tricks */
		BB_EXECVP(argv[0], argv);

		/* We are (maybe) sharing a stack with blocked parent,
		 * let parent know we failed and then exit to unblock parent
		 * (but don't run atexit() stuff, which would screw up parent.)
		 */
		failed = errno;
		/* mount, for example, does not want the message */
		/*bb_perror_msg("can't execute '%s'", argv[0]);*/
		_exit(111);
	}
	/* parent */
	/* Unfortunately, this is not reliable: according to standards
	 * vfork() can be equivalent to fork() and we won't see value
	 * of 'failed'.
	 * Interested party can wait on pid and learn exit code.
	 * If 111 - then it (most probably) failed to exec */
	if (failed) {
		errno = failed;
		return -1;
	}
	return pid;
}

/* Die with an error message if we can't spawn a child process. */
pid_t FAST_FUNC xspawn(char **argv)
{
	pid_t pid = spawn(argv);
	if (pid < 0)
		bb_simple_perror_msg_and_die(*argv);
	return pid;
}

#if ENABLE_FEATURE_PREFER_APPLETS
void FAST_FUNC save_nofork_data(struct nofork_save_area *save)
{
	memcpy(&save->die_jmp, &die_jmp, sizeof(die_jmp));
	save->applet_name = applet_name;
	save->xfunc_error_retval = xfunc_error_retval;
	save->option_mask32 = option_mask32;
	save->die_sleep = die_sleep;
	save->saved = 1;
}

void FAST_FUNC restore_nofork_data(struct nofork_save_area *save)
{
	memcpy(&die_jmp, &save->die_jmp, sizeof(die_jmp));
	applet_name = save->applet_name;
	xfunc_error_retval = save->xfunc_error_retval;
	option_mask32 = save->option_mask32;
	die_sleep = save->die_sleep;
}

int FAST_FUNC run_nofork_applet_prime(struct nofork_save_area *old, int applet_no, char **argv)
{
	int rc, argc;

	applet_name = APPLET_NAME(applet_no);

	xfunc_error_retval = EXIT_FAILURE;

	/* Special flag for xfunc_die(). If xfunc will "die"
	 * in NOFORK applet, xfunc_die() sees negative
	 * die_sleep and longjmp here instead. */
	die_sleep = -1;

	/* In case getopt() or getopt32() was already called:
	 * reset the libc getopt() function, which keeps internal state.
	 *
	 * BSD-derived getopt() functions require that optind be set to 1 in
	 * order to reset getopt() state.  This used to be generally accepted
	 * way of resetting getopt().  However, glibc's getopt()
	 * has additional getopt() state beyond optind, and requires that
	 * optind be set to zero to reset its state.  So the unfortunate state of
	 * affairs is that BSD-derived versions of getopt() misbehave if
	 * optind is set to 0 in order to reset getopt(), and glibc's getopt()
	 * will core dump if optind is set 1 in order to reset getopt().
	 *
	 * More modern versions of BSD require that optreset be set to 1 in
	 * order to reset getopt().  Sigh.  Standards, anyone?
	 */
#ifdef __GLIBC__
	optind = 0;
#else /* BSD style */
	optind = 1;
	/* optreset = 1; */
#endif
	/* optarg = NULL; opterr = 1; optopt = 63; - do we need this too? */
	/* (values above are what they initialized to in glibc and uclibc) */
	/* option_mask32 = 0; - not needed, no applet depends on it being 0 */

	argc = 1;
	while (argv[argc])
		argc++;

	rc = setjmp(die_jmp);
	if (!rc) {
		/* Some callers (xargs)
		 * need argv untouched because they free argv[i]! */
		char *tmp_argv[argc+1];
		memcpy(tmp_argv, argv, (argc+1) * sizeof(tmp_argv[0]));
		/* Finally we can call NOFORK applet's main() */
		rc = applet_main[applet_no](argc, tmp_argv);

	/* The whole reason behind nofork_save_area is that <applet>_main
	 * may exit non-locally! For example, in hush Ctrl-Z tries
	 * (modulo bugs) to dynamically create a child (backgrounded task)
	 * if it detects that Ctrl-Z was pressed when a NOFORK was running.
	 * Testcase: interactive "rm -i".
	 * Don't fool yourself into thinking "and <applet>_main() returns
	 * quickly here" and removing "useless" nofork_save_area code. */

	} else { /* xfunc died in NOFORK applet */
		/* in case they meant to return 0... */
		if (rc == -2222)
			rc = 0;
	}

	/* Restoring some globals */
	restore_nofork_data(old);

	/* Other globals can be simply reset to defaults */
#ifdef __GLIBC__
	optind = 0;
#else /* BSD style */
	optind = 1;
#endif

	return rc & 0xff; /* don't confuse people with "exitcodes" >255 */
}

int FAST_FUNC run_nofork_applet(int applet_no, char **argv)
{
	struct nofork_save_area old;

	/* Saving globals */
	save_nofork_data(&old);
	return run_nofork_applet_prime(&old, applet_no, argv);
}
#endif /* FEATURE_PREFER_APPLETS */

int FAST_FUNC spawn_and_wait(char **argv)
{
	int rc;
#if ENABLE_FEATURE_PREFER_APPLETS
	int a = find_applet_by_name(argv[0]);

	if (a >= 0 && (APPLET_IS_NOFORK(a)
# if BB_MMU
			|| APPLET_IS_NOEXEC(a) /* NOEXEC trick needs fork() */
# endif
	)) {
# if BB_MMU
		if (APPLET_IS_NOFORK(a))
# endif
		{
			return run_nofork_applet(a, argv);
		}
# if BB_MMU
		/* MMU only */
		/* a->noexec is true */
		rc = fork();
		if (rc) /* parent or error */
			return wait4pid(rc);
		/* child */
		xfunc_error_retval = EXIT_FAILURE;
		run_applet_no_and_exit(a, argv);
# endif
	}
#endif /* FEATURE_PREFER_APPLETS */
	rc = spawn(argv);
	return wait4pid(rc);
}

#if !BB_MMU
void FAST_FUNC re_exec(char **argv)
{
	/* high-order bit of first char in argv[0] is a hidden
	 * "we have (already) re-execed, don't do it again" flag */
	argv[0][0] |= 0x80;
	execv(bb_busybox_exec_path, argv);
	bb_perror_msg_and_die("can't execute '%s'", bb_busybox_exec_path);
}

pid_t FAST_FUNC fork_or_rexec(char **argv)
{
	pid_t pid;
	/* Maybe we are already re-execed and come here again? */
	if (re_execed)
		return 0;
	pid = xvfork();
	if (pid) /* parent */
		return pid;
	/* child - re-exec ourself */
	re_exec(argv);
}
#endif

/* Due to a #define in libbb.h on MMU systems we actually have 1 argument -
 * char **argv "vanishes" */
void FAST_FUNC bb_daemonize_or_rexec(int flags, char **argv)
{
	int fd;

	if (flags & DAEMON_CHDIR_ROOT)
		xchdir("/");

	if (flags & DAEMON_DEVNULL_STDIO) {
		close(0);
		close(1);
		close(2);
	}

	fd = open(bb_dev_null, O_RDWR);
	if (fd < 0) {
		/* NB: we can be called as bb_sanitize_stdio() from init
		 * or mdev, and there /dev/null may legitimately not (yet) exist!
		 * Do not use xopen above, but obtain _ANY_ open descriptor,
		 * even bogus one as below. */
		fd = xopen("/", O_RDONLY); /* don't believe this can fail */
	}

	while ((unsigned)fd < 2)
		fd = dup(fd); /* have 0,1,2 open at least to /dev/null */

	if (!(flags & DAEMON_ONLY_SANITIZE)) {
		if (fork_or_rexec(argv))
			exit(EXIT_SUCCESS); /* parent */
		/* if daemonizing, make sure we detach from stdio & ctty */
		setsid();
		dup2(fd, 0);
		dup2(fd, 1);
		dup2(fd, 2);
	}
	while (fd > 2) {
		close(fd--);
		if (!(flags & DAEMON_CLOSE_EXTRA_FDS))
			return;
		/* else close everything after fd#2 */
	}
}

void FAST_FUNC bb_sanitize_stdio(void)
{
	bb_daemonize_or_rexec(DAEMON_ONLY_SANITIZE, NULL);
}