lib/euidaccess.c

   1 /* euidaccess -- check if effective user id can access file
   2    Copyright (C) 1990, 1991, 1995 Free Software Foundation, Inc.
   3
   4 This file is part of the GNU C Library.
   5
   6 The GNU C Library is free software; you can redistribute it and/or
   7 modify it under the terms of the GNU Library General Public License as
   8 published by the Free Software Foundation; either version 2 of the
   9 License, or (at your option) any later version.
  10
  11 The GNU C Library is distributed in the hope that it will be useful,
  12 but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 Library General Public License for more details.
  15
  16 You should have received a copy of the GNU Library General Public
  17 License along with the GNU C Library; see the file COPYING.LIB.  If
  18 not, write to the Free Software Foundation, Inc., 59 Temple Place -
  19 Suite 330, Boston, MA 02111-1307, USA.  */
  20
  21 /* Written by David MacKenzie and Torbjorn Granlund.
  22    Adapted for GNU C library by Roland McGrath.  */
  23
  24 #if HAVE_CONFIG_H
  25 # include <config.h>
  26 #endif
  27
  28 #include <sys/types.h>
  29 #include <sys/stat.h>
  30
  31 #ifdef S_IEXEC
  32 # ifndef S_IXUSR
  33 #  define S_IXUSR S_IEXEC
  34 # endif
  35 # ifndef S_IXGRP
  36 #  define S_IXGRP (S_IEXEC >> 3)
  37 # endif
  38 # ifndef S_IXOTH
  39 #  define S_IXOTH (S_IEXEC >> 6)
  40 # endif
  41 #endif /* S_IEXEC */
  42
  43 #if defined (HAVE_UNISTD_H) || defined (_LIBC)
  44 # include <unistd.h>
  45 #endif
  46
  47 #ifdef _POSIX_VERSION
  48 # include <limits.h>
  49 # if !defined(NGROUPS_MAX) || NGROUPS_MAX < 1
  50 #  undef NGROUPS_MAX
  51 #  define NGROUPS_MAX sysconf (_SC_NGROUPS_MAX)
  52 # endif /* NGROUPS_MAX */
  53
  54 #else /* not _POSIX_VERSION */
  55 uid_t getuid ();
  56 gid_t getgid ();
  57 uid_t geteuid ();
  58 gid_t getegid ();
  59 # include <sys/param.h>
  60 # if !defined(NGROUPS_MAX) && defined(NGROUPS)
  61 #  define NGROUPS_MAX NGROUPS
  62 # endif /* not NGROUPS_MAX and NGROUPS */
  63 #endif /* not POSIX_VERSION */
  64
  65 #include <errno.h>
  66 #ifndef errno
  67 extern int errno;
  68 #endif
  69
  70 #if defined(EACCES) && !defined(EACCESS)
  71 # define EACCESS EACCES
  72 #endif
  73
  74 #ifndef F_OK
  75 # define F_OK 0
  76 # define X_OK 1
  77 # define W_OK 2
  78 # define R_OK 4
  79 #endif
  80
  81 #if !defined (S_IROTH) && defined (R_OK)
  82 # define S_IROTH R_OK
  83 #endif
  84
  85 #if !defined (S_IWOTH) && defined (W_OK)
  86 # define S_IWOTH W_OK
  87 #endif
  88
  89 #if !defined (S_IXOTH) && defined (X_OK)
  90 # define S_IXOTH X_OK
  91 #endif
  92
  93 #ifdef _LIBC
  94
  95 # define group_member __group_member
  96
  97 #else
  98
  99 /* The user's real user id. */
 100 static uid_t uid;
 101
 102 /* The user's real group id. */
 103 static gid_t gid;
 104
 105 /* The user's effective user id. */
 106 static uid_t euid;
 107
 108 /* The user's effective group id. */
 109 static gid_t egid;
 110
 111 /* Nonzero if UID, GID, EUID, and EGID have valid values. */
 112 static int have_ids = 0;
 113
 114 # if HAVE_GETGROUPS
 115 int group_member ();
 116 # else
 117 #  define group_member(gid)     0
 118 # endif
 119
 120 #endif
 121
 122
 123 /* Return 0 if the user has permission of type MODE on file PATH;
 124    otherwise, return -1 and set `errno' to EACCESS.
 125    Like access, except that it uses the effective user and group
 126    id's instead of the real ones, and it does not check for read-only
 127    filesystem, text busy, etc. */
 128
 129 int
 130 euidaccess (path, mode)
 131      const char *path;
 132      int mode;
 133 {
 134   struct stat stats;
 135   int granted;
 136
 137 #ifdef  _LIBC
 138   uid_t uid = getuid (), euid = geteuid ();
 139   gid_t gid = getgid (), egid = getegid ();
 140 #else
 141   if (have_ids == 0)
 142     {
 143       have_ids = 1;
 144       uid = getuid ();
 145       gid = getgid ();
 146       euid = geteuid ();
 147       egid = getegid ();
 148     }
 149 #endif
 150
 151   if (uid == euid && gid == egid)
 152     /* If we are not set-uid or set-gid, access does the same.  */
 153     return access (path, mode);
 154
 155   if (stat (path, &stats))
 156     return -1;
 157
 158   mode &= (X_OK | W_OK | R_OK); /* Clear any bogus bits. */
 159 #if R_OK != S_IROTH || W_OK != S_IWOTH || X_OK != S_IXOTH
 160   ?error Oops, portability assumptions incorrect.
 161 #endif
 162
 163   if (mode == F_OK)
 164     return 0;                   /* The file exists. */
 165
 166   /* The super-user can read and write any file, and execute any file
 167      that anyone can execute. */
 168   if (euid == 0 && ((mode & X_OK) == 0
 169                     || (stats.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH))))
 170     return 0;
 171
 172   if (euid == stats.st_uid)
 173     granted = (unsigned) (stats.st_mode & (mode << 6)) >> 6;
 174   else if (egid == stats.st_gid || group_member (stats.st_gid))
 175     granted = (unsigned) (stats.st_mode & (mode << 3)) >> 3;
 176   else
 177     granted = (stats.st_mode & mode);
 178   if (granted == mode)
 179     return 0;
 180   errno = EACCESS;
 181   return -1;
 182 }