1 /* Check if effective user id can access file
2 Copyright (C) 1990-2023 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19 /* Written by David MacKenzie and Torbjorn Granlund.
20 Adapted for GNU C library by Roland McGrath. */
21
22 #ifdef HAVE_CONFIG_H
23 # include <config.h>
24 #endif
25
26 #include <sys/types.h>
27 #include <sys/stat.h>
28
29 #ifdef S_IEXEC
30 # ifndef S_IXUSR
31 # define S_IXUSR S_IEXEC
32 # endif
33 # ifndef S_IXGRP
34 # define S_IXGRP (S_IEXEC >> 3)
35 # endif
36 # ifndef S_IXOTH
37 # define S_IXOTH (S_IEXEC >> 6)
38 # endif
39 #endif /* S_IEXEC */
40
41 #if defined HAVE_UNISTD_H || defined _LIBC
42 # include <unistd.h>
43 #endif
44
45 #ifndef _POSIX_VERSION
46 uid_t getuid ();
47 gid_t getgid ();
48 uid_t geteuid ();
49 gid_t getegid ();
50 #endif /* not POSIX_VERSION */
51
52 #include <errno.h>
53 #ifndef errno
54 extern int errno;
55 #endif
56 #ifndef __set_errno
57 # define __set_errno(val) errno = (val)
58 #endif
59
60 #if defined EACCES && !defined EACCESS
61 # define EACCESS EACCES
62 #endif
63
64 #ifndef F_OK
65 # define F_OK 0
66 # define X_OK 1
67 # define W_OK 2
68 # define R_OK 4
69 #endif
70
71 #if !defined S_IROTH && defined R_OK
72 # define S_IROTH R_OK
73 #endif
74 #if !defined S_IWOTH && defined W_OK
75 # define S_IWOTH W_OK
76 #endif
77 #if !defined S_IXOTH && defined X_OK
78 # define S_IXOTH X_OK
79 #endif
80
81
82 #ifdef _LIBC
83
84 # define group_member __group_member
85 # define euidaccess __euidaccess
86
87 #else
88
89 /* The user's real user id. */
90 static uid_t uid;
91
92 /* The user's real group id. */
93 static gid_t gid;
94
95 /* The user's effective user id. */
96 static uid_t euid;
97
98 /* The user's effective group id. */
99 static gid_t egid;
100
101 /* Nonzero if UID, GID, EUID, and EGID have valid values. */
102 static int have_ids;
103
104 # ifdef HAVE_GETGROUPS
105 int group_member ();
106 # else
107 # define group_member(gid) 0
108 # endif
109
110 #endif
111
112
113 /* Return 0 if the user has permission of type MODE on file PATH;
114 otherwise, return -1 and set `errno' to EACCESS.
115 Like access, except that it uses the effective user and group
116 id's instead of the real ones, and it does not check for read-only
117 filesystem, text busy, etc. */
118
119 int
120 euidaccess (const char *path, int mode)
121 {
122 struct __stat64_t64 stats;
123 int granted;
124
125 #ifdef _LIBC
126 uid_t euid;
127 gid_t egid;
128 #else
129 if (have_ids == 0)
130 {
131 have_ids = 1;
132 uid = getuid ();
133 gid = getgid ();
134 euid = geteuid ();
135 egid = getegid ();
136 }
137
138 if (uid == euid && gid == egid)
139 /* If we are not set-uid or set-gid, access does the same. */
140 return access (path, mode);
141 #endif
142
143 if (__stat64_time64 (path, &stats))
144 return -1;
145
146 mode &= (X_OK | W_OK | R_OK); /* Clear any bogus bits. */
147 #if R_OK != S_IROTH || W_OK != S_IWOTH || X_OK != S_IXOTH
148 ?error Oops, portability assumptions incorrect.
149 #endif
150
151 if (mode == F_OK)
152 return 0; /* The file exists. */
153
154 #ifdef _LIBC
155 /* Now we need the IDs. */
156 euid = __geteuid ();
157 egid = __getegid ();
158
159 if (__getuid () == euid && __getgid () == egid)
160 /* If we are not set-uid or set-gid, access does the same. */
161 return __access (path, mode);
162 #endif
163
164 /* The super-user can read and write any file, and execute any file
165 that anyone can execute. */
166 if (euid == 0 && ((mode & X_OK) == 0
167 || (stats.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH))))
168 return 0;
169
170 if (euid == stats.st_uid)
171 granted = (unsigned int) (stats.st_mode & (mode << 6)) >> 6;
172 else if (egid == stats.st_gid || group_member (stats.st_gid))
173 granted = (unsigned int) (stats.st_mode & (mode << 3)) >> 3;
174 else
175 granted = (stats.st_mode & mode);
176 /* XXX Add support for ACLs. */
177 if (granted == mode)
178 return 0;
179 __set_errno (EACCESS);
180 return -1;
181 }
182 #undef euidaccess
183 #undef eaccess
184 #ifdef weak_alias
185 weak_alias (__euidaccess, euidaccess)
186 weak_alias (__euidaccess, eaccess)
187 #endif
188
189 #ifdef TEST
190 # include <stdio.h>
191 # include <errno.h>
192 # include "error.h"
193
194 char *program_name;
195
196 int
197 main (int argc, char **argv)
198 {
199 char *file;
200 int mode;
201 int err;
202
203 program_name = argv[0];
204 if (argc < 3)
205 abort ();
206 file = argv[1];
207 mode = atoi (argv[2]);
208
209 err = euidaccess (file, mode);
210 printf ("%d\n", err);
211 if (err != 0)
212 error (0, errno, "%s", file);
213 exit (0);
214 }
215 #endif