1/* euidaccess-stat -- check if effective user id can access lstat'd file
2   This function is probably useful only for choosing whether to issue
3   a prompt in an implementation of POSIX-specified rm.
4
5   Copyright (C) 2005-2006, 2009-2010 Free Software Foundation, Inc.
6
7   This program is free software: you can redistribute it and/or modify
8   it under the terms of the GNU General Public License as published by
9   the Free Software Foundation, either version 3 of the License, or
10   (at your option) any later version.
11
12   This program is distributed in the hope that it will be useful,
13   but WITHOUT ANY WARRANTY; without even the implied warranty of
14   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
15   GNU General Public License for more details.
16
17   You should have received a copy of the GNU General Public License
18   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
19
20/* Adapted for use in GNU remove.c by Jim Meyering.  */
21
22#include <config.h>
23
24#include "euidaccess-stat.h"
25
26#include <unistd.h>
27
28#include "group-member.h"
29#include "stat-macros.h"
30
31/* Return true if the current user has permission of type MODE
32   on the file from which stat buffer *ST was obtained, ignoring
33   ACLs, attributes, `read-only'ness, etc...
34   Otherwise, return false.
35
36   Like the reentrant version of euidaccess, but starting with
37   a stat buffer rather than a file name.  Hence, this function
38   never calls access or accessx, and doesn't take into account
39   whether the file has ACLs or other attributes, or resides on
40   a read-only file system.  */
41
42bool
43euidaccess_stat (struct stat const *st, int mode)
44{
45  uid_t euid;
46  unsigned int granted;
47
48  /* Convert the mode to traditional form, clearing any bogus bits.  */
49  if (R_OK == 4 && W_OK == 2 && X_OK == 1 && F_OK == 0)
50    mode &= 7;
51  else
52    mode = ((mode & R_OK ? 4 : 0)
53            + (mode & W_OK ? 2 : 0)
54            + (mode & X_OK ? 1 : 0));
55
56  if (mode == 0)
57    return true;		/* The file exists.  */
58
59  euid = geteuid ();
60
61  /* The super-user can read and write any file, and execute any file
62     that anyone can execute.  */
63  if (euid == 0 && ((mode & X_OK) == 0
64                    || (st->st_mode & (S_IXUSR | S_IXGRP | S_IXOTH))))
65    return true;
66
67  /* Convert the file's permission bits to traditional form.  */
68  if (   S_IRUSR == (4 << 6)
69      && S_IWUSR == (2 << 6)
70      && S_IXUSR == (1 << 6)
71      && S_IRGRP == (4 << 3)
72      && S_IWGRP == (2 << 3)
73      && S_IXGRP == (1 << 3)
74      && S_IROTH == (4 << 0)
75      && S_IWOTH == (2 << 0)
76      && S_IXOTH == (1 << 0))
77    granted = st->st_mode;
78  else
79    granted = (  (st->st_mode & S_IRUSR ? 4 << 6 : 0)
80               + (st->st_mode & S_IWUSR ? 2 << 6 : 0)
81               + (st->st_mode & S_IXUSR ? 1 << 6 : 0)
82               + (st->st_mode & S_IRGRP ? 4 << 3 : 0)
83               + (st->st_mode & S_IWGRP ? 2 << 3 : 0)
84               + (st->st_mode & S_IXGRP ? 1 << 3 : 0)
85               + (st->st_mode & S_IROTH ? 4 << 0 : 0)
86               + (st->st_mode & S_IWOTH ? 2 << 0 : 0)
87               + (st->st_mode & S_IXOTH ? 1 << 0 : 0));
88
89  if (euid == st->st_uid)
90    granted >>= 6;
91  else
92    {
93      gid_t egid = getegid ();
94      if (egid == st->st_gid || group_member (st->st_gid))
95        granted >>= 3;
96    }
97
98  if ((mode & ~granted) == 0)
99    return true;
100
101  return false;
102}
103
104
105#ifdef TEST
106# include <errno.h>
107# include <stdio.h>
108# include <stdlib.h>
109
110# include "error.h"
111# define _(msg) msg
112
113char *program_name;
114
115int
116main (int argc, char **argv)
117{
118  char *file;
119  int mode;
120  bool ok;
121  struct stat st;
122
123  program_name = argv[0];
124  if (argc < 3)
125    abort ();
126  file = argv[1];
127  mode = atoi (argv[2]);
128  if (lstat (file, &st) != 0)
129    error (EXIT_FAILURE, errno, _("cannot stat %s"), file);
130
131  ok = euidaccess_stat (&st, mode);
132  printf ("%s: %s\n", file, ok ? "y" : "n");
133  return 0;
134}
135#endif
136