aboutsummaryrefslogtreecommitdiff
path: root/miscutils/crontab.c
blob: 38933cf4acec2852de15fe8bc2f7e2b63390342b (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
/* vi: set sw=4 ts=4: */
/*
 * CRONTAB
 *
 * usually setuid root, -c option only works if getuid() == geteuid()
 *
 * Copyright 1994 Matthew Dillon (dillon@apollo.west.oic.com)
 * Vladimir Oleynik <dzo@simtreas.ru> (C) 2002
 *
 * Licensed under the GPL v2 or later, see the file LICENSE in this tarball.
 */

#include "libbb.h"

#ifndef CRONTABS
#define CRONTABS        "/var/spool/cron/crontabs"
#endif
#ifndef CRONUPDATE
#define CRONUPDATE      "cron.update"
#endif

static void change_user(const struct passwd *pas)
{
	setenv("USER", pas->pw_name, 1);
	setenv("HOME", pas->pw_dir, 1);
	setenv("SHELL", DEFAULT_SHELL, 1);

	/* initgroups, setgid, setuid */
	change_identity(pas);

	if (chdir(pas->pw_dir) < 0) {
		bb_perror_msg("chdir(%s) by %s failed",
				pas->pw_dir, pas->pw_name);
		xchdir("/tmp");
	}
}

static void edit_file(const struct passwd *pas, const char *file)
{
	const char *ptr;
	int pid = vfork();

	if (pid < 0) /* failure */
		bb_perror_msg_and_die("vfork");
	if (pid) { /* parent */
		wait4pid(pid);
		return;
	}

	/* CHILD - change user and run editor */
	change_user(pas);
	ptr = getenv("VISUAL");
	if (!ptr) {
		ptr = getenv("EDITOR");
		if (!ptr)
			ptr = "vi";
	}

	BB_EXECLP(ptr, ptr, file, NULL);
	bb_perror_msg_and_die("exec %s", ptr);
}

static int open_as_user(const struct passwd *pas, const char *file)
{
	pid_t pid;
	char c;

	pid = vfork();
	if (pid < 0) /* ERROR */
		bb_perror_msg_and_die("vfork");
	if (pid) { /* PARENT */
		if (wait4pid(pid) == 0) {
			/* exitcode 0: child says it can read */
			return open(file, O_RDONLY);
		}
		return -1;
	}

	/* CHILD */
	/* initgroups, setgid, setuid */
	change_identity(pas);
	/* We just try to read one byte. If it works, file is readable
	 * under this user. We signal that by exiting with 0. */
	_exit(safe_read(xopen(file, O_RDONLY), &c, 1) < 0);
}

int crontab_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int crontab_main(int argc ATTRIBUTE_UNUSED, char **argv)
{
	const struct passwd *pas;
	const char *crontab_dir = CRONTABS;
	char *tmp_fname;
	char *new_fname;
	char *user_name;  /* -u USER */
	int fd;
	int src_fd;
	int opt_ler;

	/* file [opts]     Replace crontab from file
	 * - [opts]        Replace crontab from stdin
	 * -u user         User
	 * -c dir          Crontab directory
	 * -l              List crontab for user
	 * -e              Edit crontab for user
	 * -r              Delete crontab for user
	 * bbox also supports -d == -r, but most other crontab
	 * implementations do not. Deprecated.
	 */
	enum {
		OPT_u = (1 << 0),
		OPT_c = (1 << 1),
		OPT_l = (1 << 2),
		OPT_e = (1 << 3),
		OPT_r = (1 << 4),
		OPT_ler = OPT_l + OPT_e + OPT_r,
	};

	opt_complementary = "?1:dr"; /* max one argument; -d implies -r */
	opt_ler = getopt32(argv, "u:c:lerd", &user_name, &crontab_dir);
	argv += optind;

	if (sanitize_env_if_suid()) { /* Clears dangerous stuff, sets PATH */
		/* run by non-root? */
		if (opt_ler & (OPT_u|OPT_c))
			bb_error_msg_and_die("only root can use -c or -u");
	}

	if (opt_ler & OPT_u) {
		pas = getpwnam(user_name);
		if (!pas)
			bb_error_msg_and_die("user %s is not known", user_name);
	} else {
		uid_t my_uid = getuid();
		pas = getpwuid(my_uid);
		if (!pas)
			bb_perror_msg_and_die("no user record for UID %u",
					(unsigned)my_uid);
	}

#define user_name DONT_USE_ME_BEYOND_THIS_POINT

	/* From now on, keep only -l, -e, -r bits */
	opt_ler &= OPT_ler;
	if ((opt_ler - 1) & opt_ler) /* more than one bit set? */
		bb_show_usage();

	/* Read replacement file under user's UID/GID/group vector */
	src_fd = STDIN_FILENO;
	if (!opt_ler) { /* Replace? */
		if (!argv[0])
			bb_show_usage();
		if (NOT_LONE_DASH(argv[0])) {
			src_fd = open_as_user(pas, argv[0]);
			if (src_fd < 0)
				bb_error_msg_and_die("user %s cannot read %s",
						pas->pw_name, argv[0]);
		}
	}

	/* cd to our crontab directory */
	xchdir(crontab_dir);

	tmp_fname = NULL;

	/* Handle requested operation */
	switch (opt_ler) {

	default: /* case OPT_r: Delete */
		unlink(pas->pw_name);
		break;

	case OPT_l: /* List */
		{
			char *args[2] = { pas->pw_name, NULL };
			return bb_cat(args);
			/* list exits,
			 * the rest go play with cron update file */
		}

	case OPT_e: /* Edit */
		tmp_fname = xasprintf("%s.%u", crontab_dir, (unsigned)getpid());
		/* No O_EXCL: we don't want to be stuck if earlier crontabs
		 * were killed, leaving stale temp file behind */
		src_fd = xopen3(tmp_fname, O_RDWR|O_CREAT|O_TRUNC, 0600);
		fchown(src_fd, pas->pw_uid, pas->pw_gid);
		fd = open(pas->pw_name, O_RDONLY);
		if (fd >= 0) {
			bb_copyfd_eof(fd, src_fd);
			close(fd);
			xlseek(src_fd, 0, SEEK_SET);
		}
		close_on_exec_on(src_fd); /* don't want editor to see this fd */
		edit_file(pas, tmp_fname);
		/* fall through */

	case 0: /* Replace (no -l, -e, or -r were given) */
		new_fname = xasprintf("%s.new", pas->pw_name);
		fd = open(new_fname, O_WRONLY|O_CREAT|O_TRUNC|O_APPEND, 0600);
		if (fd >= 0) {
			bb_copyfd_eof(src_fd, fd);
			close(fd);
			xrename(new_fname, pas->pw_name);
		} else {
			bb_error_msg("cannot create %s/%s",
					crontab_dir, new_fname);
		}
		if (tmp_fname)
			unlink(tmp_fname);
		/*free(tmp_fname);*/
		/*free(new_fname);*/

	} /* switch */

	/* Bump notification file.  Handle window where crond picks file up
	 * before we can write our entry out.
	 */
	while ((fd = open(CRONUPDATE, O_WRONLY|O_CREAT|O_APPEND, 0600)) >= 0) {
		struct stat st;

		fdprintf(fd, "%s\n", pas->pw_name);
		if (fstat(fd, &st) != 0 || st.st_nlink != 0) {
			/*close(fd);*/
			break;
		}
		/* st.st_nlink == 0:
		 * file was deleted, maybe crond missed our notification */
		close(fd);
		/* loop */
	}
	if (fd < 0) {
		bb_error_msg("cannot append to %s/%s",
				crontab_dir, CRONUPDATE);
	}
	return 0;
}