lib/getgroups.c

   1 /* provide consistent interface to getgroups for systems that don't allow N==0
   2
   3    Copyright (C) 1996, 1999, 2003, 2006-2017 Free Software Foundation, Inc.
   4
   5    This program is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 3 of the License, or
   8    (at your option) any later version.
   9
  10    This program 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
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  17
  18 /* written by Jim Meyering */
  19
  20 #include <config.h>
  21
  22 #include <unistd.h>
  23
  24 #include <errno.h>
  25 #include <stdlib.h>
  26 #include <stdint.h>
  27
  28 #if !HAVE_GETGROUPS
  29
  30 /* Provide a stub that fails with ENOSYS, since there is no group
  31    information available on mingw.  */
  32 int
  33 getgroups (int n _GL_UNUSED, GETGROUPS_T *groups _GL_UNUSED)
  34 {
  35   errno = ENOSYS;
  36   return -1;
  37 }
  38
  39 #else /* HAVE_GETGROUPS */
  40
  41 # undef getgroups
  42 # ifndef GETGROUPS_ZERO_BUG
  43 #  define GETGROUPS_ZERO_BUG 0
  44 # endif
  45
  46 /* On OS X 10.6 and later, use the usual getgroups, not the one
  47    supplied when _DARWIN_C_SOURCE is defined.  _DARWIN_C_SOURCE is
  48    normally defined, since it means "conform to POSIX, but add
  49    non-POSIX extensions even if that violates the POSIX namespace
  50    rules", which is what we normally want.  But with getgroups there
  51    is an inconsistency, and _DARWIN_C_SOURCE means "change getgroups()
  52    so that it no longer works right".  The BUGS section of compat(5)
  53    says that the behavior is dubious if you compile different sections
  54    of a program with different _DARWIN_C_SOURCE settings, so fix only
  55    the offending symbol.  */
  56 # ifdef __APPLE__
  57 int posix_getgroups (int, gid_t []) __asm ("_getgroups");
  58 #  define getgroups posix_getgroups
  59 # endif
  60
  61 /* On at least Ultrix 4.3 and NextStep 3.2, getgroups (0, NULL) always
  62    fails.  On other systems, it returns the number of supplemental
  63    groups for the process.  This function handles that special case
  64    and lets the system-provided function handle all others.  However,
  65    it can fail with ENOMEM if memory is tight.  It is unspecified
  66    whether the effective group id is included in the list.  */
  67
  68 int
  69 rpl_getgroups (int n, gid_t *group)
  70 {
  71   int n_groups;
  72   GETGROUPS_T *gbuf;
  73   int saved_errno;
  74
  75   if (n < 0)
  76     {
  77       errno = EINVAL;
  78       return -1;
  79     }
  80
  81   if (n != 0 || !GETGROUPS_ZERO_BUG)
  82     {
  83       int result;
  84       if (sizeof *group == sizeof *gbuf)
  85         return getgroups (n, (GETGROUPS_T *) group);
  86
  87       if (SIZE_MAX / sizeof *gbuf <= n)
  88         {
  89           errno = ENOMEM;
  90           return -1;
  91         }
  92       gbuf = malloc (n * sizeof *gbuf);
  93       if (!gbuf)
  94         return -1;
  95       result = getgroups (n, gbuf);
  96       if (0 <= result)
  97         {
  98           n = result;
  99           while (n--)
 100             group[n] = gbuf[n];
 101         }
 102       saved_errno = errno;
 103       free (gbuf);
 104       errno = saved_errno;
 105       return result;
 106     }
 107
 108   n = 20;
 109   while (1)
 110     {
 111       /* No need to worry about address arithmetic overflow here,
 112          since the ancient systems that we're running on have low
 113          limits on the number of secondary groups.  */
 114       gbuf = malloc (n * sizeof *gbuf);
 115       if (!gbuf)
 116         return -1;
 117       n_groups = getgroups (n, gbuf);
 118       if (n_groups == -1 ? errno != EINVAL : n_groups < n)
 119         break;
 120       free (gbuf);
 121       n *= 2;
 122     }
 123
 124   saved_errno = errno;
 125   free (gbuf);
 126   errno = saved_errno;
 127
 128   return n_groups;
 129 }
 130
 131 #endif /* HAVE_GETGROUPS */