1 /* euidaccess -- check if effective user id can access file
2
3 Copyright (C) 1990-1991, 1995, 1998, 2000, 2003-2006, 2008-2023 Free
4 Software Foundation, Inc.
5
6 This file is part of the GNU C Library.
7
8 This file is free software: you can redistribute it and/or modify
9 it under the terms of the GNU Lesser General Public License as
10 published by the Free Software Foundation; either version 2.1 of the
11 License, or (at your option) any later version.
12
13 This file is distributed in the hope that it will be useful,
14 but WITHOUT ANY WARRANTY; without even the implied warranty of
15 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 GNU Lesser General Public License for more details.
17
18 You should have received a copy of the GNU Lesser General Public License
19 along with this program. If not, see <https://www.gnu.org/licenses/>. */
20
21 /* Written by David MacKenzie and Torbjorn Granlund.
22 Adapted for GNU C library by Roland McGrath. */
23
24 #ifndef _LIBC
25 # include <config.h>
26 #endif
27
28 #include <fcntl.h>
29 #include <sys/types.h>
30 #include <sys/stat.h>
31 #include <unistd.h>
32 #if defined _WIN32 && ! defined __CYGWIN__
33 # include <io.h>
34 #else
35 # include "root-uid.h"
36 #endif
37
38 #if HAVE_LIBGEN_H
39 # include <libgen.h>
40 #endif
41
42 #include <errno.h>
43 #ifndef __set_errno
44 # define __set_errno(val) errno = (val)
45 #endif
46
47 #if defined EACCES && !defined EACCESS
48 # define EACCESS EACCES
49 #endif
50
51 #ifndef F_OK
52 # define F_OK 0
53 # define X_OK 1
54 # define W_OK 2
55 # define R_OK 4
56 #endif
57
58
59 #ifdef _LIBC
60
61 # define access __access
62 # define getuid __getuid
63 # define getgid __getgid
64 # define geteuid __geteuid
65 # define getegid __getegid
66 # define group_member __group_member
67 # define euidaccess __euidaccess
68 # undef stat
69 # define stat stat64
70
71 #endif
72
73 /* Return 0 if the user has permission of type MODE on FILE;
74 otherwise, return -1 and set 'errno'.
75 Like access, except that it uses the effective user and group
76 id's instead of the real ones, and it does not always check for read-only
77 file system, text busy, etc. */
78
79 int
80 euidaccess (const char *file, int mode)
81 {
82 #if HAVE_FACCESSAT /* glibc, AIX 7, Solaris 11, Cygwin 1.7 */
83 return faccessat (AT_FDCWD, file, mode, AT_EACCESS);
84 #elif defined EFF_ONLY_OK /* IRIX, OSF/1, Interix */
85 return access (file, mode | EFF_ONLY_OK);
86 #elif defined ACC_SELF /* AIX */
87 return accessx (file, mode, ACC_SELF);
88 #elif HAVE_EACCESS /* FreeBSD */
89 return eaccess (file, mode);
90 #elif defined _WIN32 && ! defined __CYGWIN__ /* mingw */
91 return _access (file, mode);
92 #else /* Mac OS X, NetBSD, OpenBSD, HP-UX, Solaris, Cygwin, BeOS */
93
94 uid_t uid = getuid ();
95 gid_t gid = getgid ();
96 uid_t euid = geteuid ();
97 gid_t egid = getegid ();
98 struct stat stats;
99
100 # if HAVE_DECL_SETREGID && PREFER_NONREENTRANT_EUIDACCESS
101
102 /* Define PREFER_NONREENTRANT_EUIDACCESS if you prefer euidaccess to
103 return the correct result even if this would make it
104 nonreentrant. Define this only if your entire application is
105 safe even if the uid or gid might temporarily change. If your
106 application uses signal handlers or threads it is probably not
107 safe. */
108
109 if (mode == F_OK)
110 {
111 int result = stat (file, &stats);
112 return result != 0 && errno == EOVERFLOW ? 0 : result;
113 }
114 else
115 {
116 int result;
117 int saved_errno;
118
119 if (uid != euid)
120 setreuid (euid, uid);
121 if (gid != egid)
122 setregid (egid, gid);
123
124 result = access (file, mode);
125 saved_errno = errno;
126
127 /* Restore them. */
128 if (uid != euid)
129 setreuid (uid, euid);
130 if (gid != egid)
131 setregid (gid, egid);
132
133 errno = saved_errno;
134 return result;
135 }
136
137 # else
138
139 /* The following code assumes the traditional Unix model, and is not
140 correct on systems that have ACLs or the like. However, it's
141 better than nothing, and it is reentrant. */
142
143 unsigned int granted;
144 if (uid == euid && gid == egid)
145 /* If we are not set-uid or set-gid, access does the same. */
146 return access (file, mode);
147
148 if (stat (file, &stats) == -1)
149 return mode == F_OK && errno == EOVERFLOW ? 0 : -1;
150
151 /* The super-user can read and write any file, and execute any file
152 that anyone can execute. */
153 if (euid == ROOT_UID
154 && ((mode & X_OK) == 0
155 || (stats.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH))))
156 return 0;
157
158 /* Convert the mode to traditional form, clearing any bogus bits. */
159 if (R_OK == 4 && W_OK == 2 && X_OK == 1 && F_OK == 0)
160 mode &= 7;
161 else
162 mode = ((mode & R_OK ? 4 : 0)
163 + (mode & W_OK ? 2 : 0)
164 + (mode & X_OK ? 1 : 0));
165
166 if (mode == 0)
167 return 0; /* The file exists. */
168
169 /* Convert the file's permission bits to traditional form. */
170 if (S_IRUSR == (4 << 6) && S_IWUSR == (2 << 6) && S_IXUSR == (1 << 6)
171 && S_IRGRP == (4 << 3) && S_IWGRP == (2 << 3) && S_IXGRP == (1 << 3)
172 && S_IROTH == (4 << 0) && S_IWOTH == (2 << 0) && S_IXOTH == (1 << 0))
173 granted = stats.st_mode;
174 else
175 granted = ((stats.st_mode & S_IRUSR ? 4 << 6 : 0)
176 + (stats.st_mode & S_IWUSR ? 2 << 6 : 0)
177 + (stats.st_mode & S_IXUSR ? 1 << 6 : 0)
178 + (stats.st_mode & S_IRGRP ? 4 << 3 : 0)
179 + (stats.st_mode & S_IWGRP ? 2 << 3 : 0)
180 + (stats.st_mode & S_IXGRP ? 1 << 3 : 0)
181 + (stats.st_mode & S_IROTH ? 4 << 0 : 0)
182 + (stats.st_mode & S_IWOTH ? 2 << 0 : 0)
183 + (stats.st_mode & S_IXOTH ? 1 << 0 : 0));
184
185 if (euid == stats.st_uid)
186 granted >>= 6;
187 else if (egid == stats.st_gid || group_member (stats.st_gid))
188 granted >>= 3;
189
190 if ((mode & ~granted) == 0)
191 return 0;
192 __set_errno (EACCESS);
193 return -1;
194
195 # endif
196 #endif
197 }
198 #undef euidaccess
199 #ifdef weak_alias
200 weak_alias (__euidaccess, euidaccess)
201 #endif
202
203 #ifdef TEST
204 # include <error.h>
205 # include <stdio.h>
206 # include <stdlib.h>
207
208 int
209 main (int argc, char **argv)
210 {
211 char *file;
212 int mode;
213 int err;
214
215 if (argc < 3)
216 abort ();
217 file = argv[1];
218 mode = atoi (argv[2]);
219
220 err = euidaccess (file, mode);
221 printf ("%d\n", err);
222 if (err != 0)
223 error (0, errno, "%s", file);
224 exit (0);
225 }
226 #endif