1/*	$NetBSD: pidfile.c,v 1.16 2021/08/01 15:29:29 andvar Exp $	*/
2
3/*-
4 * Copyright (c) 1999, 2016 The NetBSD Foundation, Inc.
5 * All rights reserved.
6 *
7 * This code is derived from software contributed to The NetBSD Foundation
8 * by Jason R. Thorpe, Matthias Scheler, Julio Merino and Roy Marples.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 *    notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 *    notice, this list of conditions and the following disclaimer in the
17 *    documentation and/or other materials provided with the distribution.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
20 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
21 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
22 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
23 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
24 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
25 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
26 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
27 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
28 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
29 * POSSIBILITY OF SUCH DAMAGE.
30 */
31
32#include <sys/cdefs.h>
33#if defined(LIBC_SCCS) && !defined(lint)
34__RCSID("$NetBSD: pidfile.c,v 1.16 2021/08/01 15:29:29 andvar Exp $");
35#endif
36
37#include <sys/param.h>
38
39#include <errno.h>
40#include <fcntl.h>
41#include <inttypes.h>
42#include <paths.h>
43#include <stdbool.h>
44#include <stdlib.h>
45#include <stdio.h>
46#include <string.h>
47#include <unistd.h>
48#include <util.h>
49
50static pid_t pidfile_pid;
51static char pidfile_path[PATH_MAX];
52static int pidfile_fd = -1;
53
54/* Closes pidfile resources.
55 *
56 * Returns 0 on success, otherwise -1. */
57static int
58pidfile_close(void)
59{
60	int error;
61
62	pidfile_pid = 0;
63	error = close(pidfile_fd);
64	pidfile_fd = -1;
65	pidfile_path[0] = '\0';
66	return error;
67}
68
69/* Truncate, close and unlink an existent pidfile,
70 * if and only if it was created by this process.
71 * The pidfile is truncated because we may have dropped permissions
72 * or entered a chroot and thus unable to unlink it.
73 *
74 * Returns 0 on truncation success, otherwise -1. */
75int
76pidfile_clean(void)
77{
78	int error;
79
80	if (pidfile_fd == -1) {
81		errno = EBADF;
82		return -1;
83	}
84
85	if (pidfile_pid != getpid())
86		error = EPERM;
87	else if (ftruncate(pidfile_fd, 0) == -1)
88		error = errno;
89	else {
90		(void) unlink(pidfile_path);
91		error = 0;
92	}
93
94	(void) pidfile_close();
95
96	if (error != 0) {
97		errno = error;
98		return -1;
99	}
100	return 0;
101}
102
103/* atexit shim for pidfile_clean */
104static void
105pidfile_cleanup(void)
106{
107
108	pidfile_clean();
109}
110
111/* Constructs a name for a pidfile in the default location (/var/run).
112 * If 'bname' is NULL, uses the name of the current program for the name of
113 * the pidfile.
114 *
115 * Returns 0 on success, otherwise -1. */
116static int
117pidfile_varrun_path(char *path, size_t len, const char *bname)
118{
119
120	if (bname == NULL)
121		bname = getprogname();
122
123	/* _PATH_VARRUN includes trailing / */
124	if ((size_t)snprintf(path, len, "%s%s.pid", _PATH_VARRUN, bname) >= len)
125	{
126		errno = ENAMETOOLONG;
127		return -1;
128	}
129	return 0;
130}
131
132/* Returns the process ID inside path on success, otherwise -1.
133 * If no path is given, use the last pidfile path, otherwise the default one. */
134pid_t
135pidfile_read(const char *path)
136{
137	char dpath[PATH_MAX], buf[16], *eptr;
138	int fd, error;
139	ssize_t n;
140	pid_t pid;
141
142	if (path == NULL && pidfile_path[0] != '\0')
143		path = pidfile_path;
144	if (path == NULL || strchr(path, '/') == NULL) {
145		if (pidfile_varrun_path(dpath, sizeof(dpath), path) == -1)
146			return -1;
147		path = dpath;
148	}
149
150	if ((fd = open(path, O_RDONLY | O_CLOEXEC | O_NONBLOCK)) == -1)
151		return  -1;
152	n = read(fd, buf, sizeof(buf) - 1);
153	error = errno;
154	(void) close(fd);
155	if (n == -1) {
156		errno = error;
157		return -1;
158	}
159	buf[n] = '\0';
160	pid = (pid_t)strtoi(buf, &eptr, 10, 1, INT_MAX, &error);
161	if (error && !(error == ENOTSUP && *eptr == '\n')) {
162		errno = error;
163		return -1;
164	}
165	return pid;
166}
167
168/* Locks the pidfile specified by path and writes the process pid to it.
169 * The new pidfile is "registered" in the global variables pidfile_fd,
170 * pidfile_path and pidfile_pid so that any further call to pidfile_lock(3)
171 * can check if we are recreating the same file or a new one.
172 *
173 * Returns 0 on success, otherwise the pid of the process who owns the
174 * lock if it can be read, otherwise -1. */
175pid_t
176pidfile_lock(const char *path)
177{
178	char dpath[PATH_MAX];
179	static bool registered_atexit = false;
180
181	/* Register for cleanup with atexit. */
182	if (!registered_atexit) {
183		if (atexit(pidfile_cleanup) == -1)
184			return -1;
185		registered_atexit = true;
186	}
187
188	if (path == NULL || strchr(path, '/') == NULL) {
189		if (pidfile_varrun_path(dpath, sizeof(dpath), path) == -1)
190			return -1;
191		path = dpath;
192	}
193
194	/* If path has changed (no good reason), clean up the old pidfile. */
195	if (pidfile_fd != -1 && strcmp(pidfile_path, path) != 0)
196		pidfile_clean();
197
198	if (pidfile_fd == -1) {
199		pidfile_fd = open(path,
200		    O_WRONLY | O_CREAT | O_CLOEXEC | O_NONBLOCK | O_EXLOCK,
201		    0644);
202		if (pidfile_fd == -1) {
203			pid_t pid;
204
205			if (errno == EAGAIN) {
206				/* The pidfile is locked, return the process ID
207				 * it contains.
208				 * If successful, set errno to EEXIST. */
209				if ((pid = pidfile_read(path)) != -1)
210					errno = EEXIST;
211			} else
212				pid = -1;
213
214			return pid;
215		}
216		strlcpy(pidfile_path, path, sizeof(pidfile_path));
217	}
218
219	pidfile_pid = getpid();
220
221	/* Truncate the file, as we could be re-writing it.
222	 * Then write the process ID. */
223	if (ftruncate(pidfile_fd, 0) == -1 ||
224	    lseek(pidfile_fd, 0, SEEK_SET) == -1 ||
225	    dprintf(pidfile_fd, "%d\n", pidfile_pid) == -1)
226	{
227		int error = errno;
228
229		pidfile_cleanup();
230		errno = error;
231		return -1;
232	}
233
234	/* Hold the fd open to persist the lock. */
235	return 0;
236}
237
238/* The old function.
239 * Historical behaviour is that pidfile is not re-written
240 * if path has not changed.
241 *
242 * Returns 0 on success, otherwise -1.
243 * As such we have no way of knowing the process ID who owns the lock. */
244int
245pidfile(const char *path)
246{
247	pid_t pid;
248
249	pid = pidfile_lock(path);
250	return pid == 0 ? 0 : -1;
251}
252