lib/util/unix_privs.c

   1 /*
   2    Unix SMB/CIFS implementation.
   3
   4    gain/lose root privileges
   5
   6    Copyright (C) Andrew Tridgell 2004
   7
   8    This program is free software; you can redistribute it and/or modify
   9    it under the terms of the GNU General Public License as published by
  10    the Free Software Foundation; either version 3 of the License, or
  11    (at your option) any later version.
  12
  13    This program is distributed in the hope that it will be useful,
  14    but WITHOUT ANY WARRANTY; without even the implied warranty of
  15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16    GNU General Public License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with this program.  If not, see <http://www.gnu.org/licenses/>.
  20 */
  21
  22 #include "includes.h"
  23 #include "system/passwd.h"
  24 #include "../lib/util/unix_privs.h"
  25
  26 /**
  27  * @file
  28  * @brief Gaining/losing root privileges
  29  */
  30
  31 /*
  32   there are times when smbd needs to temporarily gain root privileges
  33   to do some operation. To do this you call root_privileges(), which
  34   returns a talloc handle. To restore your previous privileges
  35   talloc_free() this pointer.
  36
  37   Note that this call is considered successful even if it does not
  38   manage to gain root privileges, but it will call smb_abort() if it
  39   fails to restore the privileges afterwards. The logic is that
  40   failing to gain root access can be caught by whatever operation
  41   needs to be run as root failing, but failing to lose the root
  42   privileges is dangerous.
  43
  44   This also means that this code is safe to be called from completely
  45   unprivileged processes.
  46 */
  47
  48 struct saved_state {
  49         uid_t uid;
  50 };
  51
  52 static int privileges_destructor(struct saved_state *s)
  53 {
  54         if (geteuid() != s->uid &&
  55             seteuid(s->uid) != 0) {
  56                 smb_panic("Failed to restore privileges");
  57         }
  58         return 0;
  59 }
  60
  61 /**
  62  * Obtain root privileges for the current process.
  63  *
  64  * The privileges can be dropped by talloc_free()-ing the
  65  * token returned by this function
  66  */
  67 void *root_privileges(void)
  68 {
  69         struct saved_state *s;
  70         s = talloc(NULL, struct saved_state);
  71         if (!s) return NULL;
  72         s->uid = geteuid();
  73         if (s->uid != 0) {
  74                 seteuid(0);
  75         }
  76         talloc_set_destructor(s, privileges_destructor);
  77         return s;
  78 }
  79
  80 uid_t root_privileges_original_uid(void *s)
  81 {
  82         struct saved_state *saved = talloc_get_type_abort(s, struct saved_state);
  83         return saved->uid;
  84 }