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2b7948ef90
Previously, the hash table indexed by uid (or gid) took ownership of the single reference to the heap-allocated struct, and the hash table indexed by username (or group name) had a borrowed pointer to the same struct that exists in the other hash table. However, this can break down if you have two or more distinct usernames that share a numeric identifier. This is generally a bad idea, because the user-space model in such situations does not match the kernel-space reality, and in particular there is no effective kernel-level security boundary between such users, but it is sometimes done anyway. In this case, when the second username is looked up in the userdb, it overwrites (replaces) the entry in the hash table that is indexed by uid, freeing the DBusUserInfo. This results in both the key and the value in the hash table that is indexed by username becoming dangling pointers (use-after-free), leading to undefined behaviour, which is certainly not what we want to see when doing access control. An equivalent situation can occur with groups, in the rare case where a numeric group ID has two names (although I have not heard of this being done in practice). Solve this by reference-counting the data structure. There are up to three references in practice: one held temporarily while the lookup function is populating and storing it, one held by the hash table that is indexed by uid, and one held by the hash table that is indexed by name. Closes: dbus#305 Signed-off-by: Simon McVittie <smcv@collabora.com>
121 lines
5.2 KiB
C
121 lines
5.2 KiB
C
/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
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/* dbus-userdb.h User database abstraction
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*
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* Copyright (C) 2003 Red Hat, Inc.
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*
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* Licensed under the Academic Free License version 2.1
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*
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*/
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#ifndef DBUS_USERDB_H
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#define DBUS_USERDB_H
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#include <dbus/dbus-sysdeps-unix.h>
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#ifdef DBUS_WIN
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#error "Don't include this on Windows"
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#endif
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DBUS_BEGIN_DECLS
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typedef struct DBusUserDatabase DBusUserDatabase;
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#ifdef DBUS_USERDB_INCLUDES_PRIVATE
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#include <dbus/dbus-hash.h>
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/**
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* Internals of DBusUserDatabase
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*/
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struct DBusUserDatabase
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{
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int refcount; /**< Reference count */
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DBusHashTable *users; /**< Users in the database by UID */
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DBusHashTable *groups; /**< Groups in the database by GID */
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DBusHashTable *users_by_name; /**< Users in the database by name */
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DBusHashTable *groups_by_name; /**< Groups in the database by name */
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};
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DBusUserDatabase* _dbus_user_database_new (void);
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DBusUserDatabase* _dbus_user_database_ref (DBusUserDatabase *db);
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void _dbus_user_database_flush (DBusUserDatabase *db);
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void _dbus_user_database_unref (DBusUserDatabase *db);
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DBUS_PRIVATE_EXPORT
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dbus_bool_t _dbus_user_database_get_uid (DBusUserDatabase *db,
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dbus_uid_t uid,
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const DBusUserInfo **info,
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DBusError *error);
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DBUS_PRIVATE_EXPORT
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dbus_bool_t _dbus_user_database_get_username (DBusUserDatabase *db,
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const DBusString *username,
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const DBusUserInfo **info,
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DBusError *error);
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DBUS_PRIVATE_EXPORT
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const DBusUserInfo *_dbus_user_database_lookup (DBusUserDatabase *db,
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dbus_uid_t uid,
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const DBusString *username,
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DBusError *error);
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DBUS_PRIVATE_EXPORT
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const DBusGroupInfo* _dbus_user_database_lookup_group (DBusUserDatabase *db,
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dbus_gid_t gid,
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const DBusString *groupname,
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DBusError *error);
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void _dbus_user_info_unref (DBusUserInfo *info);
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DBUS_PRIVATE_EXPORT
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void _dbus_group_info_unref (DBusGroupInfo *info);
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#endif /* DBUS_USERDB_INCLUDES_PRIVATE */
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DBUS_PRIVATE_EXPORT
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DBusUserDatabase* _dbus_user_database_get_system (void);
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DBUS_PRIVATE_EXPORT _DBUS_WARN_UNUSED_RESULT
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dbus_bool_t _dbus_user_database_lock_system (void);
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DBUS_PRIVATE_EXPORT
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void _dbus_user_database_unlock_system (void);
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void _dbus_user_database_flush_system (void);
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dbus_bool_t _dbus_get_user_id (const DBusString *username,
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dbus_uid_t *uid);
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dbus_bool_t _dbus_get_group_id (const DBusString *group_name,
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dbus_gid_t *gid);
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DBUS_PRIVATE_EXPORT
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dbus_bool_t _dbus_get_user_id_and_primary_group (const DBusString *username,
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dbus_uid_t *uid_p,
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dbus_gid_t *gid_p);
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dbus_bool_t _dbus_groups_from_uid (dbus_uid_t uid,
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dbus_gid_t **group_ids,
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int *n_group_ids);
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DBUS_PRIVATE_EXPORT
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dbus_bool_t _dbus_is_console_user (dbus_uid_t uid,
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DBusError *error);
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DBUS_PRIVATE_EXPORT
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dbus_bool_t _dbus_is_a_number (const DBusString *str,
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unsigned long *num);
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DBUS_PRIVATE_EXPORT
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dbus_bool_t _dbus_username_from_current_process (const DBusString **username);
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DBUS_PRIVATE_EXPORT
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dbus_bool_t _dbus_homedir_from_current_process (const DBusString **homedir);
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dbus_bool_t _dbus_homedir_from_uid (dbus_uid_t uid,
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DBusString *homedir);
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DBUS_END_DECLS
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#endif /* DBUS_USERDB_H */
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