summaryrefslogtreecommitdiff
path: root/libbb/vfork_daemon_rexec.c
blob: 50ecea762ead413e48d4c3d27dacb08ae5982aa9 (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
283
/* 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 */
#include "NUM_APPLETS.h"

/* 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) {
		safe_waitpid(pid, NULL, 0); /* prevent zombie */
		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 \
 || ENABLE_FEATURE_SH_NOFORK
static jmp_buf die_jmp;
static void jump(void)
{
	/* Special case. We arrive here if NOFORK applet
	 * calls xfunc, which then decides to die.
	 * We don't die, but jump instead back to caller.
	 * NOFORK applets still cannot carelessly call xfuncs:
	 * p = xmalloc(10);
	 * q = xmalloc(10); // BUG! if this dies, we leak p!
	 */
	/* | 0x100 allows to pass zero exitcode (longjmp can't pass 0).
	 * This works because exitcodes are bytes,
	 * run_nofork_applet() ensures that by "& 0xff" */
	longjmp(die_jmp, xfunc_error_retval | 0x100);
}

struct nofork_save_area {
	jmp_buf die_jmp;
	void (*die_func)(void);
	const char *applet_name;
	uint32_t option_mask32;
	smallint logmode;
	uint8_t xfunc_error_retval;
};
static void save_nofork_data(struct nofork_save_area *save)
{
	memcpy(&save->die_jmp, &die_jmp, sizeof(die_jmp));
	save->die_func = die_func;
	save->applet_name = applet_name;
	save->option_mask32 = option_mask32;
	save->logmode = logmode;
	save->xfunc_error_retval = xfunc_error_retval;
}
static void restore_nofork_data(struct nofork_save_area *save)
{
	memcpy(&die_jmp, &save->die_jmp, sizeof(die_jmp));
	die_func = save->die_func;
	applet_name = save->applet_name;
	option_mask32 = save->option_mask32;
	logmode = save->logmode;
	xfunc_error_retval = save->xfunc_error_retval;
}

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

	save_nofork_data(&old);

	logmode = LOGMODE_STDIO;
	xfunc_error_retval = EXIT_FAILURE;
	/* In case getopt() or getopt32() was already called:
	 * reset the libc getopt() function, which keeps internal state.
	 */
	GETOPT_RESET();

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

	/* If xfunc "dies" in NOFORK applet, die_func longjmp's here instead */
	die_func = jump;
	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]));
		applet_name = tmp_argv[0];
		/* Finally we can call NOFORK applet's main() */
		rc = applet_main[applet_no](argc, tmp_argv);
		/* Important for shells: `which CMD` was failing */
		fflush_all();
	} else {
		/* xfunc died in NOFORK applet */
	}

	/* Restoring some globals */
	restore_nofork_data(&old);
	/* Other globals can be simply reset to defaults */
	GETOPT_RESET();

	return rc & 0xff; /* don't confuse people with "exitcodes" >255 */
}
#endif /* FEATURE_PREFER_APPLETS || FEATURE_SH_NOFORK */

int FAST_FUNC spawn_and_wait(char **argv)
{
	int rc;
#if ENABLE_FEATURE_PREFER_APPLETS && (NUM_APPLETS > 1)
	int a = find_applet_by_name(argv[0]);

	if (a >= 0) {
		if (APPLET_IS_NOFORK(a))
			return run_nofork_applet(a, argv);
# if BB_MMU /* NOEXEC needs fork(), thus this is done only on MMU machines: */
		if (APPLET_IS_NOEXEC(a)) {
			fflush_all();
			rc = fork();
			if (rc) /* parent or error */
				return wait4pid(rc);

			/* child */
//TODO: prctl(PR_SET_NAME, (long)argv[0], 0, 0, 0);? [think pidof, pgrep, pkill]
//Rewrite /proc/PID/cmdline? (need to save argv0 and length at init for this to work!)
			/* reset some state and run without execing */

			/* msg_eol = "\n"; - no caller needs this reinited yet */
			logmode = LOGMODE_STDIO;
			/* die_func = NULL; - needed if the caller is a shell,
			 * init, or a NOFORK applet. But none of those call us
			 * as of yet (and that should probably always stay true).
			 */
			/* xfunc_error_retval and applet_name are init by: */
			run_applet_no_and_exit(a, argv[0], 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;

	/* fflush_all(); ? - so far all callers had no buffered output to flush */

	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)) {

		/* fflush_all(); - add it in fork_or_rexec() if necessary */

		if (fork_or_rexec(argv))
			_exit(EXIT_SUCCESS); /* parent */
		/* if daemonizing, detach from stdio & ctty */
		setsid();
		dup2(fd, 0);
		dup2(fd, 1);
		dup2(fd, 2);
		if (flags & DAEMON_DOUBLE_FORK) {
			/* On Linux, session leader can acquire ctty
			 * unknowingly, by opening a tty.
			 * Prevent this: stop being a session leader.
			 */
			if (fork_or_rexec(argv))
				_exit(EXIT_SUCCESS); /* parent */
		}
	}
	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);
}