uucplock.c revision 1.21 
1/*	$OpenBSD: uucplock.c,v 1.21 2019/07/03 03:24:04 deraadt Exp $	*/
2/*
3 * Copyright (c) 1988, 1993
4 *	The Regents of the University of California.  All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 *    notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 *    notice, this list of conditions and the following disclaimer in the
13 *    documentation and/or other materials provided with the distribution.
14 * 3. Neither the name of the University nor the names of its contributors
15 *    may be used to endorse or promote products derived from this software
16 *    without specific prior written permission.
17 *
18 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
19 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
20 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
21 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
22 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
23 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
24 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
25 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
26 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
27 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
28 * SUCH DAMAGE.
29 *
30 *
31 */
32
33#include <sys/types.h>
34#include <dirent.h>
35#include <errno.h>
36#include <fcntl.h>
37#include <unistd.h>
38#include <signal.h>
39#include <stdio.h>
40#include <stdlib.h>
41#include <paths.h>
42#include <string.h>
43#include "util.h"
44
45#define MAXTRIES 5
46
47#define LOCKTMP "LCKTMP..%ld"
48#define LOCKFMT "LCK..%s"
49
50#define GORET(level, val) { err = errno; uuerr = (val); \
51			    goto __CONCAT(ret, level); }
52
53/* Forward declarations */
54static int put_pid(int fd, pid_t pid);
55static pid_t get_pid(int fd,int *err);
56
57/*
58 * uucp style locking routines
59 */
60int
61uu_lock(const char *ttyname)
62{
63	char lckname[sizeof(_PATH_UUCPLOCK) + MAXNAMLEN],
64	     lcktmpname[sizeof(_PATH_UUCPLOCK) + MAXNAMLEN];
65	int fd, tmpfd, i, err, uuerr;
66	pid_t pid, pid_old;
67
68	pid = getpid();
69	(void)snprintf(lcktmpname, sizeof(lcktmpname), _PATH_UUCPLOCK LOCKTMP,
70	    (long)pid);
71	(void)snprintf(lckname, sizeof(lckname), _PATH_UUCPLOCK LOCKFMT,
72	    ttyname);
73	tmpfd = open(lcktmpname, O_CREAT|O_TRUNC|O_WRONLY|O_CLOEXEC, 0664);
74	if (tmpfd == -1)
75		GORET(0, UU_LOCK_CREAT_ERR);
76
77	for (i = 0; i < MAXTRIES; i++) {
78		if (link(lcktmpname, lckname) == -1) {
79			if (errno != EEXIST)
80				GORET(1, UU_LOCK_LINK_ERR);
81			/*
82			 * file is already locked
83			 * check to see if the process holding the lock
84			 * still exists
85			 */
86			if ((fd = open(lckname, O_RDONLY | O_CLOEXEC)) == -1)
87				GORET(1, UU_LOCK_OPEN_ERR);
88
89			if ((pid_old = get_pid(fd, &err)) == -1)
90				GORET(2, UU_LOCK_READ_ERR);
91
92			close(fd);
93
94			if (kill(pid_old, 0) == 0 || errno != ESRCH)
95				GORET(1, UU_LOCK_INUSE);
96			/*
97			 * The process that locked the file isn't running, so
98			 * we'll lock it ourselves
99			 */
100			(void)unlink(lckname);
101		} else {
102			if (!put_pid(tmpfd, pid))
103				GORET(3, UU_LOCK_WRITE_ERR);
104			break;
105		}
106	}
107	GORET(1, (i >= MAXTRIES) ? UU_LOCK_TRY_ERR : UU_LOCK_OK);
108
109ret3:
110	(void)unlink(lckname);
111	goto ret1;
112ret2:
113	(void)close(fd);
114ret1:
115	(void)close(tmpfd);
116	(void)unlink(lcktmpname);
117ret0:
118	errno = err;
119	return uuerr;
120}
121
122int
123uu_lock_txfr(const char *ttyname, pid_t pid)
124{
125	char lckname[sizeof(_PATH_UUCPLOCK) + MAXNAMLEN];
126	int fd, err, ret;
127
128	snprintf(lckname, sizeof(lckname), _PATH_UUCPLOCK LOCKFMT, ttyname);
129
130	if ((fd = open(lckname, O_RDWR | O_CLOEXEC)) == -1)
131		return UU_LOCK_OWNER_ERR;
132	if (get_pid(fd, &err) != getpid())
133		ret = UU_LOCK_OWNER_ERR;
134	else {
135		lseek(fd, 0, SEEK_SET);
136		ret = put_pid(fd, pid) ? UU_LOCK_OK : UU_LOCK_WRITE_ERR;
137	}
138
139	close(fd);
140	return ret;
141}
142
143int
144uu_unlock(const char *ttyname)
145{
146	char tbuf[sizeof(_PATH_UUCPLOCK) + MAXNAMLEN];
147
148	(void)snprintf(tbuf, sizeof(tbuf), _PATH_UUCPLOCK LOCKFMT, ttyname);
149	return unlink(tbuf);
150}
151
152const char *
153uu_lockerr(int uu_lockresult)
154{
155	static char errbuf[128];
156	const char *err;
157
158	switch (uu_lockresult) {
159	case UU_LOCK_INUSE:
160		return "device in use";
161	case UU_LOCK_OK:
162		return "";
163	case UU_LOCK_OPEN_ERR:
164		err = "open error";
165		break;
166	case UU_LOCK_READ_ERR:
167		err = "read error";
168		break;
169	case UU_LOCK_CREAT_ERR:
170		err = "creat error";
171		break;
172	case UU_LOCK_WRITE_ERR:
173		err = "write error";
174		break;
175	case UU_LOCK_LINK_ERR:
176		err = "link error";
177		break;
178	case UU_LOCK_TRY_ERR:
179		err = "too many tries";
180		break;
181	case UU_LOCK_OWNER_ERR:
182		err = "not locking process";
183		break;
184	default:
185		err = "undefined error";
186		break;
187	}
188
189	(void)snprintf(errbuf, sizeof(errbuf), "%s: %s", err, strerror(errno));
190	return errbuf;
191}
192
193static int
194put_pid(int fd, pid_t pid)
195{
196	char buf[32];
197	int len;
198
199	len = snprintf(buf, sizeof buf, "%10ld\n", (long)pid);
200	if (len < 0 || len >= sizeof buf)
201		return 0;
202
203	if (write(fd, buf, len) != len)
204		return 0;
205
206	/* We don't mind too much if ftruncate() fails - see get_pid */
207	ftruncate(fd, (off_t)len);
208	return 1;
209}
210
211static pid_t
212get_pid(int fd, int *err)
213{
214	ssize_t bytes_read;
215	char buf[32];
216	pid_t pid;
217
218	bytes_read = read(fd, buf, sizeof (buf) - 1);
219	if (bytes_read > 0) {
220		buf[bytes_read] = '\0';
221		pid = (pid_t)strtoul(buf, (char **) NULL, 10);
222	} else {
223		pid = -1;
224		*err = bytes_read ? errno : EINVAL;
225	}
226	return pid;
227}
228