1 /* $OpenBSD: shm_open.c,v 1.9 2017/09/10 18:20:00 guenther Exp $ */
2 /*
3 * Copyright (c) 2013 Ted Unangst <tedu@openbsd.org>
4 *
5 * Permission to use, copy, modify, and distribute this software for any
6 * purpose with or without fee is hereby granted, provided that the above
7 * copyright notice and this permission notice appear in all copies.
8 *
9 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
10 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
11 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
12 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
13 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
14 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
15 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
16 */
17 #include <sys/types.h>
18 #include <sys/mman.h>
19 #include <sys/stat.h>
20
21 #include <errno.h>
22 #include <fcntl.h>
23 #include <limits.h>
24 #include <sha2.h>
25 #include <stdio.h>
26 #include <stdlib.h>
27 #include <string.h>
28 #include <unistd.h>
29
30 /* SHA256_DIGEST_STRING_LENGTH includes nul */
31 /* "/tmp/" + sha256 + ".shm" */
32 #define SHM_PATH_SIZE (5 + SHA256_DIGEST_STRING_LENGTH + 4)
33
34 /* O_CLOEXEC and O_NOFOLLOW are extensions to POSIX */
35 #define OK_FLAGS (O_CREAT | O_EXCL | O_TRUNC | O_CLOEXEC | O_NOFOLLOW)
36
37 static void
makeshmpath(const char * origpath,char * shmpath,size_t len)38 makeshmpath(const char *origpath, char *shmpath, size_t len)
39 {
40 char buf[SHA256_DIGEST_STRING_LENGTH];
41
42 SHA256Data(origpath, strlen(origpath), buf);
43 snprintf(shmpath, len, "/tmp/%s.shm", buf);
44 }
45
46 int
shm_open(const char * path,int flags,mode_t mode)47 shm_open(const char *path, int flags, mode_t mode)
48 {
49 char shmpath[SHM_PATH_SIZE];
50 struct stat sb;
51 int fd;
52
53 if (((flags & O_ACCMODE) != O_RDONLY && (flags & O_ACCMODE) != O_RDWR)
54 || (flags & ~(O_ACCMODE | OK_FLAGS))) {
55 errno = EINVAL;
56 return -1;
57 }
58
59 flags |= O_CLOEXEC | O_NOFOLLOW;
60 mode = mode & 0600;
61
62 makeshmpath(path, shmpath, sizeof(shmpath));
63
64 fd = HIDDEN(open)(shmpath, flags, mode);
65 if (fd == -1)
66 return -1;
67 if (fstat(fd, &sb) == -1 || !S_ISREG(sb.st_mode)) {
68 HIDDEN(close)(fd);
69 errno = EINVAL;
70 return -1;
71 }
72 if (sb.st_uid != geteuid()) {
73 HIDDEN(close)(fd);
74 errno = EPERM;
75 return -1;
76 }
77 return fd;
78 }
79 DEF_WEAK(shm_open);
80
81 int
shm_unlink(const char * path)82 shm_unlink(const char *path)
83 {
84 char shmpath[SHM_PATH_SIZE];
85
86 makeshmpath(path, shmpath, sizeof(shmpath));
87 return unlink(shmpath);
88 }
89
90 int
shm_mkstemp(char * template)91 shm_mkstemp(char *template)
92 {
93 size_t templatelen;
94 char *t;
95 int i, fd;
96
97 templatelen = strlen(template);
98 t = malloc(templatelen + 1);
99 if (!t)
100 return -1;
101 t[templatelen] = '\0';
102
103 fd = -1;
104 for (i = 0; i < INT_MAX; i++) {
105 memcpy(t, template, templatelen);
106 if (!_mktemp(t))
107 break;
108 fd = shm_open(t, O_RDWR | O_EXCL | O_CREAT, 0600);
109 if (fd != -1) {
110 memcpy(template, t, templatelen);
111 break;
112 }
113 }
114
115 free(t);
116 return fd;
117 }
118
119