1/* Test for access to file, relative to open directory. Linux version.
2 Copyright (C) 2006-2020 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#include <errno.h>
20#include <fcntl.h>
21#include <stddef.h>
22#include <stdio.h>
23#include <string.h>
24#include <unistd.h>
25#include <sys/types.h>
26#include <alloca.h>
27#include <sysdep.h>
28
29
30int
31faccessat (int fd, const char *file, int mode, int flag)
32{
33 if (flag & ~(AT_SYMLINK_NOFOLLOW | AT_EACCESS))
34 return INLINE_SYSCALL_ERROR_RETURN_VALUE (EINVAL);
35
36 if ((flag == 0 || ((flag & ~AT_EACCESS) == 0 && ! __libc_enable_secure)))
37 return INLINE_SYSCALL (faccessat, 3, fd, file, mode);
38
39 struct stat64 stats;
40 if (__fxstatat64 (_STAT_VER, fd, file, &stats, flag & AT_SYMLINK_NOFOLLOW))
41 return -1;
42
43 mode &= (X_OK | W_OK | R_OK); /* Clear any bogus bits. */
44#if R_OK != S_IROTH || W_OK != S_IWOTH || X_OK != S_IXOTH
45# error Oops, portability assumptions incorrect.
46#endif
47
48 if (mode == F_OK)
49 return 0; /* The file exists. */
50
51 uid_t uid = (flag & AT_EACCESS) ? __geteuid () : __getuid ();
52
53 /* The super-user can read and write any file, and execute any file
54 that anyone can execute. */
55 if (uid == 0 && ((mode & X_OK) == 0
56 || (stats.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH))))
57 return 0;
58
59 int granted = (uid == stats.st_uid
60 ? (unsigned int) (stats.st_mode & (mode << 6)) >> 6
61 : (stats.st_gid == ((flag & AT_EACCESS)
62 ? __getegid () : __getgid ())
63 || __group_member (stats.st_gid))
64 ? (unsigned int) (stats.st_mode & (mode << 3)) >> 3
65 : (stats.st_mode & mode));
66
67 if (granted == mode)
68 return 0;
69
70 return INLINE_SYSCALL_ERROR_RETURN_VALUE (EACCES);
71}
72