lib/euidaccess-stat.c

   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 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 #ifndef F_OK
  29 # define F_OK 0
  30 # define X_OK 1
  31 # define W_OK 2
  32 # define R_OK 4
  33 #endif
  34
  35 #include "group-member.h"
  36 #include "stat-macros.h"
  37
  38 /* Return true if the current user has permission of type MODE
  39    on the file from which stat buffer *ST was obtained, ignoring
  40    ACLs, attributes, `read-only'ness, etc...
  41    Otherwise, return false.
  42
  43    Like the reentrant version of euidaccess, but starting with
  44    a stat buffer rather than a file name.  Hence, this function
  45    never calls access or accessx, and doesn't take into account
  46    whether the file has ACLs or other attributes, or resides on
  47    a read-only file system.  */
  48
  49 bool
  50 euidaccess_stat (struct stat const *st, int mode)
  51 {
  52   uid_t euid;
  53   unsigned int granted;
  54
  55   /* Convert the mode to traditional form, clearing any bogus bits.  */
  56   if (R_OK == 4 && W_OK == 2 && X_OK == 1 && F_OK == 0)
  57     mode &= 7;
  58   else
  59     mode = ((mode & R_OK ? 4 : 0)
  60             + (mode & W_OK ? 2 : 0)
  61             + (mode & X_OK ? 1 : 0));
  62
  63   if (mode == 0)
  64     return true;                /* The file exists.  */
  65
  66   euid = geteuid ();
  67
  68   /* The super-user can read and write any file, and execute any file
  69      that anyone can execute.  */
  70   if (euid == 0 && ((mode & X_OK) == 0
  71                     || (st->st_mode & (S_IXUSR | S_IXGRP | S_IXOTH))))
  72     return true;
  73
  74   /* Convert the file's permission bits to traditional form.  */
  75   if (   S_IRUSR == (4 << 6)
  76       && S_IWUSR == (2 << 6)
  77       && S_IXUSR == (1 << 6)
  78       && S_IRGRP == (4 << 3)
  79       && S_IWGRP == (2 << 3)
  80       && S_IXGRP == (1 << 3)
  81       && S_IROTH == (4 << 0)
  82       && S_IWOTH == (2 << 0)
  83       && S_IXOTH == (1 << 0))
  84     granted = st->st_mode;
  85   else
  86     granted = (  (st->st_mode & S_IRUSR ? 4 << 6 : 0)
  87                + (st->st_mode & S_IWUSR ? 2 << 6 : 0)
  88                + (st->st_mode & S_IXUSR ? 1 << 6 : 0)
  89                + (st->st_mode & S_IRGRP ? 4 << 3 : 0)
  90                + (st->st_mode & S_IWGRP ? 2 << 3 : 0)
  91                + (st->st_mode & S_IXGRP ? 1 << 3 : 0)
  92                + (st->st_mode & S_IROTH ? 4 << 0 : 0)
  93                + (st->st_mode & S_IWOTH ? 2 << 0 : 0)
  94                + (st->st_mode & S_IXOTH ? 1 << 0 : 0));
  95
  96   if (euid == st->st_uid)
  97     granted >>= 6;
  98   else
  99     {
 100       gid_t egid = getegid ();
 101       if (egid == st->st_gid || group_member (st->st_gid))
 102         granted >>= 3;
 103     }
 104
 105   if ((mode & ~granted) == 0)
 106     return true;
 107
 108   return false;
 109 }
 110
 111
 112 #ifdef TEST
 113 # include <errno.h>
 114 # include <stdio.h>
 115 # include <stdlib.h>
 116
 117 # include "error.h"
 118 # define _(msg) msg
 119
 120 char *program_name;
 121
 122 int
 123 main (int argc, char **argv)
 124 {
 125   char *file;
 126   int mode;
 127   bool ok;
 128   struct stat st;
 129
 130   program_name = argv[0];
 131   if (argc < 3)
 132     abort ();
 133   file = argv[1];
 134   mode = atoi (argv[2]);
 135   if (lstat (file, &st) != 0)
 136     error (EXIT_FAILURE, errno, _("cannot stat %s"), file);
 137
 138   ok = euidaccess_stat (&st, mode);
 139   printf ("%s: %s\n", file, ok ? "y" : "n");
 140   exit (0);
 141 }
 142 #endif