1/* vi: set sw=4 ts=4: */
2/*
3 * CRONTAB
4 *
5 * usually setuid root, -c option only works if getuid() == geteuid()
6 *
7 * Copyright 1994 Matthew Dillon (dillon@apollo.west.oic.com)
8 * Vladimir Oleynik <dzo@simtreas.ru> (C) 2002
9 *
10 * Licensed under the GPL v2 or later, see the file LICENSE in this tarball.
11 */
12
13#include "libbb.h"
14
15#define CRONTABS        CONFIG_FEATURE_CROND_DIR "/crontabs"
16#ifndef CRONUPDATE
17#define CRONUPDATE      "cron.update"
18#endif
19
20static void edit_file(const struct passwd *pas, const char *file)
21{
22	const char *ptr;
23	int pid = xvfork();
24
25	if (pid) { /* parent */
26		wait4pid(pid);
27		return;
28	}
29
30	/* CHILD - change user and run editor */
31	/* initgroups, setgid, setuid */
32	change_identity(pas);
33	setup_environment(DEFAULT_SHELL,
34			SETUP_ENV_CHANGEENV | SETUP_ENV_TO_TMP,
35			pas);
36	ptr = getenv("VISUAL");
37	if (!ptr) {
38		ptr = getenv("EDITOR");
39		if (!ptr)
40			ptr = "vi";
41	}
42
43	BB_EXECLP(ptr, ptr, file, NULL);
44	bb_perror_msg_and_die("exec %s", ptr);
45}
46
47static int open_as_user(const struct passwd *pas, const char *file)
48{
49	pid_t pid;
50	char c;
51
52	pid = xvfork();
53	if (pid) { /* PARENT */
54		if (wait4pid(pid) == 0) {
55			/* exitcode 0: child says it can read */
56			return open(file, O_RDONLY);
57		}
58		return -1;
59	}
60
61	/* CHILD */
62	/* initgroups, setgid, setuid */
63	change_identity(pas);
64	/* We just try to read one byte. If it works, file is readable
65	 * under this user. We signal that by exiting with 0. */
66	_exit(safe_read(xopen(file, O_RDONLY), &c, 1) < 0);
67}
68
69int crontab_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
70int crontab_main(int argc UNUSED_PARAM, char **argv)
71{
72	const struct passwd *pas;
73	const char *crontab_dir = CRONTABS;
74	char *tmp_fname;
75	char *new_fname;
76	char *user_name;  /* -u USER */
77	int fd;
78	int src_fd;
79	int opt_ler;
80
81	/* file [opts]     Replace crontab from file
82	 * - [opts]        Replace crontab from stdin
83	 * -u user         User
84	 * -c dir          Crontab directory
85	 * -l              List crontab for user
86	 * -e              Edit crontab for user
87	 * -r              Delete crontab for user
88	 * bbox also supports -d == -r, but most other crontab
89	 * implementations do not. Deprecated.
90	 */
91	enum {
92		OPT_u = (1 << 0),
93		OPT_c = (1 << 1),
94		OPT_l = (1 << 2),
95		OPT_e = (1 << 3),
96		OPT_r = (1 << 4),
97		OPT_ler = OPT_l + OPT_e + OPT_r,
98	};
99
100	opt_complementary = "?1:dr"; /* max one argument; -d implies -r */
101	opt_ler = getopt32(argv, "u:c:lerd", &user_name, &crontab_dir);
102	argv += optind;
103
104	if (sanitize_env_if_suid()) { /* Clears dangerous stuff, sets PATH */
105		/* Run by non-root */
106		if (opt_ler & (OPT_u|OPT_c))
107			bb_error_msg_and_die(bb_msg_you_must_be_root);
108	}
109
110	if (opt_ler & OPT_u) {
111		pas = xgetpwnam(user_name);
112	} else {
113		pas = xgetpwuid(getuid());
114	}
115
116#define user_name DONT_USE_ME_BEYOND_THIS_POINT
117
118	/* From now on, keep only -l, -e, -r bits */
119	opt_ler &= OPT_ler;
120	if ((opt_ler - 1) & opt_ler) /* more than one bit set? */
121		bb_show_usage();
122
123	/* Read replacement file under user's UID/GID/group vector */
124	src_fd = STDIN_FILENO;
125	if (!opt_ler) { /* Replace? */
126		if (!argv[0])
127			bb_show_usage();
128		if (NOT_LONE_DASH(argv[0])) {
129			src_fd = open_as_user(pas, argv[0]);
130			if (src_fd < 0)
131				bb_error_msg_and_die("user %s cannot read %s",
132						pas->pw_name, argv[0]);
133		}
134	}
135
136	/* cd to our crontab directory */
137	xchdir(crontab_dir);
138
139	tmp_fname = NULL;
140
141	/* Handle requested operation */
142	switch (opt_ler) {
143
144	default: /* case OPT_r: Delete */
145		unlink(pas->pw_name);
146		break;
147
148	case OPT_l: /* List */
149		{
150			char *args[2] = { pas->pw_name, NULL };
151			return bb_cat(args);
152			/* list exits,
153			 * the rest go play with cron update file */
154		}
155
156	case OPT_e: /* Edit */
157		tmp_fname = xasprintf("%s.%u", crontab_dir, (unsigned)getpid());
158		/* No O_EXCL: we don't want to be stuck if earlier crontabs
159		 * were killed, leaving stale temp file behind */
160		src_fd = xopen3(tmp_fname, O_RDWR|O_CREAT|O_TRUNC, 0600);
161		fchown(src_fd, pas->pw_uid, pas->pw_gid);
162		fd = open(pas->pw_name, O_RDONLY);
163		if (fd >= 0) {
164			bb_copyfd_eof(fd, src_fd);
165			close(fd);
166			xlseek(src_fd, 0, SEEK_SET);
167		}
168		close_on_exec_on(src_fd); /* don't want editor to see this fd */
169		edit_file(pas, tmp_fname);
170		/* fall through */
171
172	case 0: /* Replace (no -l, -e, or -r were given) */
173		new_fname = xasprintf("%s.new", pas->pw_name);
174		fd = open(new_fname, O_WRONLY|O_CREAT|O_TRUNC|O_APPEND, 0600);
175		if (fd >= 0) {
176			bb_copyfd_eof(src_fd, fd);
177			close(fd);
178			xrename(new_fname, pas->pw_name);
179		} else {
180			bb_error_msg("can't create %s/%s",
181					crontab_dir, new_fname);
182		}
183		if (tmp_fname)
184			unlink(tmp_fname);
185		/*free(tmp_fname);*/
186		/*free(new_fname);*/
187
188	} /* switch */
189
190	/* Bump notification file.  Handle window where crond picks file up
191	 * before we can write our entry out.
192	 */
193	while ((fd = open(CRONUPDATE, O_WRONLY|O_CREAT|O_APPEND, 0600)) >= 0) {
194		struct stat st;
195
196		fdprintf(fd, "%s\n", pas->pw_name);
197		if (fstat(fd, &st) != 0 || st.st_nlink != 0) {
198			/*close(fd);*/
199			break;
200		}
201		/* st.st_nlink == 0:
202		 * file was deleted, maybe crond missed our notification */
203		close(fd);
204		/* loop */
205	}
206	if (fd < 0) {
207		bb_error_msg("can't append to %s/%s",
208				crontab_dir, CRONUPDATE);
209	}
210	return 0;
211}
212