summaryrefslogtreecommitdiff
path: root/libbb/vfork_daemon_rexec.c
blob: 78f3c4ad462f0d3400e457f4b3b21edd09d34962 (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
/* 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 tarball for details.
 */

#include <paths.h>
#include "busybox.h" /* for struct bb_applet */

/* 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 spawn(char **argv)
{
	/* Compiler should not optimize stores here */
	volatile int failed;
	pid_t pid;

// Ain't it a good place to fflush(NULL)?

	/* 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;
		_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 xspawn(char **argv)
{
	pid_t pid = spawn(argv);
	if (pid < 0)
		bb_perror_msg_and_die("%s", *argv);
	return pid;
}

// Wait for the specified child PID to exit, returning child's error return.
int wait4pid(int pid)
{
	int status;

	if (pid <= 0) {
		/*errno = ECHILD; -- wrong. */
		/* we expect errno to be already set from failed [v]fork/exec */
		return -1;
	}
	if (waitpid(pid, &status, 0) == -1)
		return -1;
	if (WIFEXITED(status))
		return WEXITSTATUS(status);
	if (WIFSIGNALED(status))
		return WTERMSIG(status) + 1000;
	return 0;
}

int wait_nohang(int *wstat)
{
	return waitpid(-1, wstat, WNOHANG);
}

int wait_pid(int *wstat, int pid)
{
	int r;

	do
		r = waitpid(pid, wstat, 0);
	while ((r == -1) && (errno == EINTR));
	return r;
}

int run_nofork_applet(const struct bb_applet *a, char **argv)
{
	int rc, argc;

	/* Save some shared globals */
	const struct bb_applet *old_a = current_applet;
	int old_x = xfunc_error_retval;
	uint32_t old_m = option_mask32;
	int old_sleep = die_sleep;

	current_applet = a;
	applet_name = a->name;
	xfunc_error_retval = EXIT_FAILURE;
	/*option_mask32 = 0; - not needed */
	/* 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;

	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 = a->main(argc, tmp_argv);
	} else { /* xfunc died in NOFORK applet */
		/* in case they meant to return 0... */
		if (rc == -111)
			rc = 0;
	}

	/* Restoring globals */
	current_applet = old_a;
	applet_name = old_a->name;
	xfunc_error_retval = old_x;
	option_mask32 = old_m;
	die_sleep = old_sleep;
	return rc;
}

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

	if (a && (a->nofork
#if BB_MMU
		 || a->noexec /* NOEXEC trick needs fork() */
#endif
	)) {
#if BB_MMU
		if (a->nofork)
#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;
		current_applet = a;
		run_current_applet_and_exit(argv);
#endif
	}
#endif /* FEATURE_PREFER_APPLETS */
	rc = spawn(argv);
	return wait4pid(rc);
}


#if !BB_MMU
void forkexit_or_rexec(char **argv)
{
	pid_t pid;
	/* Maybe we are already re-execed and come here again? */
	if (re_execed)
		return;

	pid = vfork();
	if (pid < 0) /* wtf? */
		bb_perror_msg_and_die("vfork");
	if (pid) /* parent */
		exit(0);
	/* child - re-exec ourself */
	/* high-order bit of first char in argv[0] is a hidden
	 * "we have (alrealy) re-execed, don't do it again" flag */
	argv[0][0] |= 0x80;
	execv(CONFIG_BUSYBOX_EXEC_PATH, argv);
	bb_perror_msg_and_die("exec %s", CONFIG_BUSYBOX_EXEC_PATH);
}
#else
/* Dance around (void)...*/
#undef forkexit_or_rexec
void forkexit_or_rexec(void)
{
	pid_t pid;
	pid = fork();
	if (pid < 0) /* wtf? */
		bb_perror_msg_and_die("fork");
	if (pid) /* parent */
		exit(0);
	/* child */
}
#define forkexit_or_rexec(argv) forkexit_or_rexec()
#endif

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

	fd = xopen(bb_dev_null, O_RDWR);

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

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

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

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

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