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 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 2, or (at your option)
  10    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 along
  18    with this program; if not, write to the Free Software Foundation,
  19    Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
  20
  21 /* Adapted for use in GNU remove.c by Jim Meyering.  */
  22
  23 #include <config.h>
  24
  25 #include "euidaccess-stat.h"
  26
  27 #include <unistd.h>
  28
  29 #ifndef F_OK
  30 # define F_OK 0
  31 # define X_OK 1
  32 # define W_OK 2
  33 # define R_OK 4
  34 #endif
  35
  36 #include "group-member.h"
  37 #include "stat-macros.h"
  38
  39 /* Return true if the current user has permission of type MODE
  40    on the file from which stat buffer *ST was obtained, ignoring
  41    ACLs, attributes, `read-only'ness, etc...
  42    Otherwise, return false.
  43
  44    Like the reentrant version of euidaccess, but starting with
  45    a stat buffer rather than a file name.  Hence, this function
  46    never calls access or accessx, and doesn't take into account
  47    whether the file has ACLs or other attributes, or resides on
  48    a read-only file system.  */
  49
  50 bool
  51 euidaccess_stat (struct stat const *st, int mode)
  52 {
  53   uid_t euid;
  54   unsigned int granted;
  55
  56   /* Convert the mode to traditional form, clearing any bogus bits.  */
  57   if (R_OK == 4 && W_OK == 2 && X_OK == 1 && F_OK == 0)
  58     mode &= 7;
  59   else
  60     mode = ((mode & R_OK ? 4 : 0)
  61             + (mode & W_OK ? 2 : 0)
  62             + (mode & X_OK ? 1 : 0));
  63
  64   if (mode == 0)
  65     return true;                /* The file exists.  */
  66
  67   euid = geteuid ();
  68
  69   /* The super-user can read and write any file, and execute any file
  70      that anyone can execute.  */
  71   if (euid == 0 && ((mode & X_OK) == 0
  72                     || (st->st_mode & (S_IXUSR | S_IXGRP | S_IXOTH))))
  73     return true;
  74
  75   /* Convert the file's permission bits to traditional form.  */
  76   if (   S_IRUSR == (4 << 6)
  77       && S_IWUSR == (2 << 6)
  78       && S_IXUSR == (1 << 6)
  79       && S_IRGRP == (4 << 3)
  80       && S_IWGRP == (2 << 3)
  81       && S_IXGRP == (1 << 3)
  82       && S_IROTH == (4 << 0)
  83       && S_IWOTH == (2 << 0)
  84       && S_IXOTH == (1 << 0))
  85     granted = st->st_mode;
  86   else
  87     granted = (  (st->st_mode & S_IRUSR ? 4 << 6 : 0)
  88                + (st->st_mode & S_IWUSR ? 2 << 6 : 0)
  89                + (st->st_mode & S_IXUSR ? 1 << 6 : 0)
  90                + (st->st_mode & S_IRGRP ? 4 << 3 : 0)
  91                + (st->st_mode & S_IWGRP ? 2 << 3 : 0)
  92                + (st->st_mode & S_IXGRP ? 1 << 3 : 0)
  93                + (st->st_mode & S_IROTH ? 4 << 0 : 0)
  94                + (st->st_mode & S_IWOTH ? 2 << 0 : 0)
  95                + (st->st_mode & S_IXOTH ? 1 << 0 : 0));
  96
  97   if (euid == st->st_uid)
  98     granted >>= 6;
  99   else
 100     {
 101       gid_t egid = getegid ();
 102       if (egid == st->st_gid || group_member (st->st_gid))
 103         granted >>= 3;
 104     }
 105
 106   if ((mode & ~granted) == 0)
 107     return true;
 108
 109   return false;
 110 }
 111
 112
 113 #ifdef TEST
 114 # include <errno.h>
 115 # include <stdio.h>
 116 # include <stdlib.h>
 117
 118 # include "error.h"
 119 # define _(msg) msg
 120
 121 char *program_name;
 122
 123 int
 124 main (int argc, char **argv)
 125 {
 126   char *file;
 127   int mode;
 128   bool ok;
 129   struct stat st;
 130
 131   program_name = argv[0];
 132   if (argc < 3)
 133     abort ();
 134   file = argv[1];
 135   mode = atoi (argv[2]);
 136   if (lstat (file, &st) != 0)
 137     error (EXIT_FAILURE, errno, _("cannot stat %s"), file);
 138
 139   ok = euidaccess_stat (&st, mode);
 140   printf ("%s: %s\n", file, ok ? "y" : "n");
 141   exit (0);
 142 }
 143 #endif