1 files changed, 133 insertions, 0 deletions
diff --git a/lib/group-member.c b/lib/group-member.c
new file mode 100644
index 0000000..0187026
--- /dev/null
+++ b/lib/group-member.c
@@ -0,0 +1,133 @@
+/* group-member.c -- determine whether group id is in calling user's group list
+
+   Copyright (C) 1994, 1997, 1998, 2003, 2005, 2006 Free Software
+   Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 2, or (at your option)
+   any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software Foundation,
+   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
+
+#include <config.h>
+
+#include "group-member.h"
+
+#include <stdbool.h>
+#include <stdio.h>
+#include <sys/types.h>
+#include <stdlib.h>
+
+#include <unistd.h>
+
+#include "xalloc.h"
+
+struct group_info
+  {
+    int n_groups;
+    GETGROUPS_T *group;
+  };
+
+#if HAVE_GETGROUPS
+
+static void
+free_group_info (struct group_info const *g)
+{
+  free (g->group);
+}
+
+static bool
+get_group_info (struct group_info *gi)
+{
+  int n_groups;
+  int n_group_slots = getgroups (0, NULL);
+  GETGROUPS_T *group;
+
+  if (n_group_slots < 0)
+    return false;
+
+  /* Avoid xnmalloc, as it goes awry when SIZE_MAX < n_group_slots.  */
+  if (xalloc_oversized (n_group_slots, sizeof *group))
+    xalloc_die ();
+  group = xmalloc (n_group_slots * sizeof *group);
+  n_groups = getgroups (n_group_slots, group);
+
+  /* In case of error, the user loses. */
+  if (n_groups < 0)
+    {
+      free (group);
+      return false;
+    }
+
+  gi->n_groups = n_groups;
+  gi->group = group;
+
+  return true;
+}
+
+#endif /* not HAVE_GETGROUPS */
+
+/* Return non-zero if GID is one that we have in our groups list.
+   If there is no getgroups function, return non-zero if GID matches
+   either of the current or effective group IDs.  */
+
+int
+group_member (gid_t gid)
+{
+#ifndef HAVE_GETGROUPS
+  return ((gid == getgid ()) || (gid == getegid ()));
+#else
+  int i;
+  int found;
+  struct group_info gi;
+
+  if (! get_group_info (&gi))
+    return 0;
+
+  /* Search through the list looking for GID. */
+  found = 0;
+  for (i = 0; i < gi.n_groups; i++)
+    {
+      if (gid == gi.group[i])
+	{
+	  found = 1;
+	  break;
+	}
+    }
+
+  free_group_info (&gi);
+
+  return found;
+#endif /* HAVE_GETGROUPS */
+}
+
+#ifdef TEST
+
+char *program_name;
+
+int
+main (int argc, char **argv)
+{
+  int i;
+
+  program_name = argv[0];
+
+  for (i=1; i<argc; i++)
+    {
+      gid_t gid;
+
+      gid = atoi (argv[i]);
+      printf ("%d: %s\n", gid, group_member (gid) ? "yes" : "no");
+    }
+  exit (0);
+}
+
+#endif /* TEST */