lib/getgroups.c

   1 /* provide consistent interface to getgroups for systems that don't allow N==0
   2
   3    Copyright (C) 1996, 1999, 2003, 2006-2024 Free Software Foundation, Inc.
   4
   5    This file is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU Lesser General Public License as
   7    published by the Free Software Foundation; either version 2.1 of the
   8    License, or (at your option) any later version.
   9
  10    This file 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 Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser 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 (_GL_UNUSED int n, _GL_UNUSED GETGROUPS_T *groups)
  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 NeXTstep 3.2, getgroups (0, NULL) always fails.
  62    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
  74   if (n < 0)
  75     {
  76       errno = EINVAL;
  77       return -1;
  78     }
  79
  80   if (n != 0 || !GETGROUPS_ZERO_BUG)
  81     {
  82       int result;
  83       if (sizeof *group == sizeof *gbuf)
  84         return getgroups (n, (GETGROUPS_T *) group);
  85
  86       if (SIZE_MAX / sizeof *gbuf <= n)
  87         {
  88           errno = ENOMEM;
  89           return -1;
  90         }
  91       gbuf = malloc (n * sizeof *gbuf);
  92       if (!gbuf)
  93         return -1;
  94       result = getgroups (n, gbuf);
  95       if (0 <= result)
  96         {
  97           n = result;
  98           while (n--)
  99             group[n] = gbuf[n];
 100         }
 101       free (gbuf);
 102       return result;
 103     }
 104
 105   n = 20;
 106   while (1)
 107     {
 108       /* No need to worry about address arithmetic overflow here,
 109          since the ancient systems that we're running on have low
 110          limits on the number of secondary groups.  */
 111       gbuf = malloc (n * sizeof *gbuf);
 112       if (!gbuf)
 113         return -1;
 114       n_groups = getgroups (n, gbuf);
 115       if (n_groups == -1 ? errno != EINVAL : n_groups < n)
 116         break;
 117       free (gbuf);
 118       n *= 2;
 119     }
 120
 121   free (gbuf);
 122   return n_groups;
 123 }
 124
 125 #endif /* HAVE_GETGROUPS */