1 /* $NetBSD: shm.c,v 1.3 2015/07/08 07:14:38 martin Exp $ */
2
3 /*-
4 * Copyright (c) 2013 The NetBSD Foundation, Inc.
5 * All rights reserved.
6 *
7 * This code is derived from software contributed to The NetBSD Foundation
8 * by Mindaugas Rasiukevicius.
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 /*
33 * Interface for POSIX shared memory objects.
34 */
35
36 #include <sys/cdefs.h>
37 __RCSID("$NetBSD: shm.c,v 1.3 2015/07/08 07:14:38 martin Exp $");
38
39 #include <sys/mman.h>
40 #include <sys/mount.h>
41 #include <sys/stat.h>
42
43 #include <stdio.h>
44 #include <stdbool.h>
45 #include <string.h>
46 #include <unistd.h>
47 #include <fcntl.h>
48 #include <errno.h>
49 #include <limits.h>
50
51 /*
52 * Shared memory objects are supported using tmpfs.
53 */
54 #define SHMFS_DIR_PATH "/var/shm"
55 #define SHMFS_DIR_MODE (S_ISVTX | S_IRWXU | S_IRWXG | S_IRWXO)
56 #define SHMFS_OBJ_PREFIX ".shmobj_"
57
58 #define MOUNT_SHMFS MOUNT_TMPFS
59
60 static bool shm_ok = false;
61
62 static bool
_shm_check_fs(void)63 _shm_check_fs(void)
64 {
65 int fd;
66 struct statvfs sv;
67 struct stat st;
68
69 fd = open(SHMFS_DIR_PATH, O_DIRECTORY|O_RDONLY);
70 if (fd == -1)
71 return false;
72
73 if (fstatvfs1(fd, &sv, ST_NOWAIT) == -1)
74 goto out;
75
76 if (strncmp(sv.f_fstypename, MOUNT_SHMFS, sizeof(sv.f_fstypename)))
77 goto out;
78
79 if (fstat(fd, &st) == -1)
80 goto out;
81
82 if ((st.st_mode & SHMFS_DIR_MODE) != SHMFS_DIR_MODE)
83 goto out;
84
85 shm_ok = true;
86
87 out:
88 close(fd);
89 return shm_ok;
90 }
91
92 static bool
_shm_get_path(char * buf,size_t len,const char * name)93 _shm_get_path(char *buf, size_t len, const char *name)
94 {
95 int ret;
96
97 if (__predict_false(!shm_ok) && !_shm_check_fs()) {
98 errno = ENOTSUP;
99 return false;
100 }
101
102 /*
103 * As per POSIX: the name should begin with a slash character.
104 * We may disallow other slashes (implementation-defined behaviour).
105 */
106 if (*name++ != '/' || strchr(name, '/') != NULL) {
107 errno = EINVAL;
108 return false;
109 }
110
111 ret = snprintf(buf, len, SHMFS_DIR_PATH "/" SHMFS_OBJ_PREFIX "%s",
112 name);
113
114 if ((size_t)ret >= len) {
115 errno = ENAMETOOLONG;
116 return false;
117 }
118 return ret != -1;
119 }
120
121 int
shm_open(const char * name,int oflag,mode_t mode)122 shm_open(const char *name, int oflag, mode_t mode)
123 {
124 char path[PATH_MAX];
125
126 if (!_shm_get_path(path, sizeof(path), name)) {
127 return -1;
128 }
129 return open(path, oflag | O_CLOEXEC | O_NOFOLLOW, mode);
130 }
131
132 int
shm_unlink(const char * name)133 shm_unlink(const char *name)
134 {
135 char path[PATH_MAX];
136
137 if (!_shm_get_path(path, sizeof(path), name)) {
138 return -1;
139 }
140 return unlink(path);
141 }
142