nss/nss_action.c

   1 /* NSS actions, elements in a nsswitch.conf configuration line.
   2    Copyright (c) 2020-2021 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library 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 GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <nsswitch.h>
  20
  21 #include <string.h>
  22 #include <libc-lock.h>
  23
  24 /* Maintain a global list of NSS action lists.  Since most databases
  25    use the same list of actions, this list is usually short.
  26    Deduplication in __nss_action_allocate ensures that the list does
  27    not grow without bounds.  */
  28
  29 struct nss_action_list_wrapper
  30 {
  31   /* The next element of the list.  */
  32   struct nss_action_list_wrapper *next;
  33
  34   /* Number of elements in the list (excluding the terminator).  */
  35   size_t count;
  36
  37   /* NULL-terminated list of actions.  */
  38   struct nss_action actions[];
  39 };
  40
  41 /* Toplevel list of allocated NSS action lists.  */
  42 static struct nss_action_list_wrapper *nss_actions;
  43
  44 /* Lock covers the nss_actions list.  */
  45 __libc_lock_define (static, nss_actions_lock);
  46
  47 /* Returns true if the actions are equal (same module, same actions
  48    array).  */
  49 static bool
  50 actions_equal (const struct nss_action *a, const struct nss_action *b)
  51 {
  52   return a->module == b->module && a->action_bits == b->action_bits;
  53 }
  54
  55
  56 /* Returns true if COUNT actions at A and B are equal (according to
  57    actions_equal above). Caller must ensure that either A or B have at
  58    least COUNT actions.  */
  59 static bool
  60 action_lists_equal (const struct nss_action *a, const struct nss_action *b,
  61                     size_t count)
  62 {
  63   for (size_t i = 0; i < count; ++i)
  64     if (!actions_equal (a + i, b + i))
  65       return false;
  66   return true;
  67 }
  68
  69 /* Returns a pre-allocated action list for COUNT actions at ACTIONS,
  70    or NULL if no such list exists.  */
  71 static nss_action_list
  72 find_allocated (struct nss_action *actions, size_t count)
  73 {
  74   for (struct nss_action_list_wrapper *p = nss_actions; p != NULL; p = p->next)
  75     if (p->count == count && action_lists_equal (p->actions, actions, count))
  76       return p->actions;
  77   return NULL;
  78 }
  79
  80 nss_action_list
  81 __nss_action_allocate (struct nss_action *actions, size_t count)
  82 {
  83   nss_action_list result = NULL;
  84   __libc_lock_lock (nss_actions_lock);
  85
  86   result = find_allocated (actions, count);
  87   if (result == NULL)
  88     {
  89       struct nss_action_list_wrapper *wrapper
  90         = malloc (sizeof (*wrapper) + sizeof (*actions) * count);
  91       if (wrapper != NULL)
  92         {
  93           wrapper->next = nss_actions;
  94           wrapper->count = count;
  95           memcpy (wrapper->actions, actions, sizeof (*actions) * count);
  96           nss_actions = wrapper;
  97           result = wrapper->actions;
  98         }
  99     }
 100
 101   __libc_lock_unlock (nss_actions_lock);
 102   return result;
 103 }
 104
 105 void __libc_freeres_fn_section
 106 __nss_action_freeres (void)
 107 {
 108   struct nss_action_list_wrapper *current = nss_actions;
 109   while (current != NULL)
 110     {
 111       struct nss_action_list_wrapper *next = current->next;
 112       free (current);
 113       current = next;
 114     }
 115   nss_actions = NULL;
 116 }