/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- * selinux.c SELinux security checks for D-Bus * * Author: Matthew Rickard * * SPDX-License-Identifier: AFL-2.1 OR GPL-2.0-or-later * * Licensed under the Academic Free License version 2.1 * * 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 of the License, 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 #include #include #ifndef DBUS_WIN #include #endif #include "selinux.h" #include "audit.h" #include "services.h" #include "policy.h" #include "utils.h" #include "config-parser.h" #ifdef HAVE_ERRNO_H #include #endif #ifdef HAVE_SELINUX #include #include #include #include #include #include #include #include #include #include #include #include #endif /* HAVE_SELINUX */ #ifdef HAVE_LIBAUDIT #include #endif /* HAVE_LIBAUDIT */ #define BUS_SID_FROM_SELINUX(sid) ((BusSELinuxID*) (sid)) #define SELINUX_SID_FROM_BUS(sid) ((security_id_t) (sid)) #ifdef HAVE_SELINUX /* Store the value telling us if SELinux is enabled in the kernel. */ static dbus_bool_t selinux_enabled = FALSE; /* Store an avc_entry_ref to speed AVC decisions. */ static struct avc_entry_ref aeref; /* Store the avc netlink fd. */ static int avc_netlink_fd = -1; /* Watch to listen for SELinux status changes via netlink. */ static DBusWatch *avc_netlink_watch_obj = NULL; static DBusLoop *avc_netlink_loop_obj = NULL; /* Store the SID of the bus itself to use as the default. */ static security_id_t bus_sid = SECSID_WILD; /* Prototypes for AVC callback functions. */ static int log_callback (int type, const char *fmt, ...) _DBUS_GNUC_PRINTF (2, 3); static int log_audit_callback (void *data, security_class_t class, char *buf, size_t bufleft); #endif /* HAVE_SELINUX */ /** * Log callback to log denial messages from the AVC. * This is used in avc_init. Logs to both standard * error and syslogd. * * @param fmt the format string * @param variable argument list */ #ifdef HAVE_SELINUX static int log_callback (int type, const char *fmt, ...) { va_list ap; #ifdef HAVE_LIBAUDIT int audit_fd, audit_type; #endif va_start(ap, fmt); #ifdef HAVE_LIBAUDIT audit_fd = bus_audit_get_fd (); if (audit_fd >= 0) { /* This should really be a DBusString, but DBusString allocates * memory dynamically; before switching it, we need to check with * SELinux people that it would be OK for this to fall back to * syslog if OOM, like the equivalent AppArmor code does. */ char buf[PATH_MAX*2]; switch (type) { case SELINUX_AVC: audit_type = AUDIT_USER_AVC; break; #if defined(SELINUX_POLICYLOAD) && defined(AUDIT_USER_MAC_POLICY_LOAD) case SELINUX_POLICYLOAD: audit_type = AUDIT_USER_MAC_POLICY_LOAD; break; #endif #if defined(SELINUX_SETENFORCE) && defined(AUDIT_USER_MAC_STATUS) case SELINUX_SETENFORCE: audit_type = AUDIT_USER_MAC_STATUS; break; #endif default: /* Not auditable */ audit_type = 0; break; } if (audit_type > 0) { /* FIXME: need to change this to show real user */ vsnprintf(buf, sizeof(buf), fmt, ap); audit_log_user_avc_message(audit_fd, audit_type, buf, NULL, NULL, NULL, getuid()); goto out; } } #endif /* HAVE_LIBAUDIT */ vsyslog (LOG_USER | LOG_INFO, fmt, ap); #ifdef HAVE_LIBAUDIT out: #endif va_end(ap); return 0; } /** * On a policy reload we need to reparse the SELinux configuration file, since * this could have changed. Send a SIGHUP to reload all configs. */ static int policy_reload_callback (int seqno) { _dbus_verbose ("SELinux policy reload callback called, sending SIGHUP\n"); return raise (SIGHUP); } /** * Log any auxiliary data */ static int log_audit_callback (void *data, security_class_t class, char *buf, size_t bufleft) { DBusString *audmsg = data; if (bufleft > (size_t) _dbus_string_get_length(audmsg)) { _dbus_string_copy_to_buffer_with_nul (audmsg, buf, bufleft); } else { DBusString s; _dbus_string_init_const(&s, "Buffer too small for audit message"); if (bufleft > (size_t) _dbus_string_get_length(&s)) _dbus_string_copy_to_buffer_with_nul (&s, buf, bufleft); } return 0; } static dbus_bool_t handle_avc_netlink_watch (DBusWatch *passed_watch, unsigned int flags, void *data) { if (avc_netlink_check_nb () < 0) { _dbus_warn ("Failed to check the netlink socket for pending messages and process them: %s", _dbus_strerror (errno)); return FALSE; } return TRUE; } #endif /* HAVE_SELINUX */ /** * Return whether or not SELinux is enabled; must be * called after bus_selinux_init. */ dbus_bool_t bus_selinux_enabled (void) { #ifdef HAVE_SELINUX return selinux_enabled; #else return FALSE; #endif /* HAVE_SELINUX */ } BusSELinuxID* bus_selinux_get_self (void) { #ifdef HAVE_SELINUX if(bus_selinux_enabled ()) return BUS_SID_FROM_SELINUX (bus_sid); else return NULL; #else return NULL; #endif /* HAVE_SELINUX */ } /** * Do early initialization; determine whether SELinux is enabled. */ dbus_bool_t bus_selinux_pre_init (void) { #ifdef HAVE_SELINUX int r; _dbus_assert (bus_sid == SECSID_WILD); /* Determine if we are running an SELinux kernel. */ r = is_selinux_enabled (); if (r < 0) { _dbus_warn ("Could not tell if SELinux is enabled: %s", _dbus_strerror (errno)); return FALSE; } selinux_enabled = r != 0; return TRUE; #else return TRUE; #endif } /** * Establish dynamic object class and permission mapping and * initialize the user space access vector cache (AVC) for D-Bus and set up * logging callbacks. */ dbus_bool_t bus_selinux_full_init (BusContext *context, DBusError *error) { #ifdef HAVE_SELINUX char *bus_context; _dbus_assert (bus_sid == SECSID_WILD); if (!selinux_enabled) { _dbus_verbose ("SELinux not enabled in this kernel.\n"); return TRUE; } _dbus_verbose ("SELinux is enabled in this kernel.\n"); avc_entry_ref_init (&aeref); if (avc_open (NULL, 0) < 0) { dbus_set_error (error, DBUS_ERROR_FAILED, "Failed to start Access Vector Cache (AVC): %s", _dbus_strerror (errno)); return FALSE; } else { _dbus_verbose ("Access Vector Cache (AVC) started.\n"); } avc_netlink_fd = avc_netlink_acquire_fd (); if (avc_netlink_fd < 0) { dbus_set_error (error, DBUS_ERROR_FAILED, "Cannot acquire AVC netlink fd: %s", _dbus_strerror (errno)); goto error; } _dbus_fd_set_close_on_exec (avc_netlink_fd); avc_netlink_loop_obj = bus_context_get_loop (context); /* avc_netlink_loop_obj is a global variable */ _dbus_loop_ref (avc_netlink_loop_obj); avc_netlink_watch_obj = _dbus_watch_new (avc_netlink_fd, DBUS_WATCH_READABLE, TRUE, handle_avc_netlink_watch, NULL, NULL); if (avc_netlink_watch_obj == NULL) { BUS_SET_OOM (error); goto error; } if (!_dbus_loop_add_watch (avc_netlink_loop_obj, avc_netlink_watch_obj)) { _dbus_watch_invalidate (avc_netlink_watch_obj); _dbus_clear_watch (&avc_netlink_watch_obj); avc_netlink_watch_obj = NULL; BUS_SET_OOM (error); goto error; } selinux_set_callback (SELINUX_CB_POLICYLOAD, (union selinux_callback) policy_reload_callback); selinux_set_callback (SELINUX_CB_AUDIT, (union selinux_callback) log_audit_callback); selinux_set_callback (SELINUX_CB_LOG, (union selinux_callback) log_callback); bus_context = NULL; bus_sid = SECSID_WILD; if (getcon (&bus_context) < 0) { dbus_set_error (error, DBUS_ERROR_FAILED, "Error getting context of bus: %s", _dbus_strerror (errno)); goto error; } if (avc_context_to_sid (bus_context, &bus_sid) < 0) { dbus_set_error (error, DBUS_ERROR_FAILED, "Error getting SID from bus context: %s", _dbus_strerror (errno)); freecon (bus_context); goto error; } freecon (bus_context); return TRUE; error: if (avc_netlink_watch_obj) { _dbus_loop_remove_watch (avc_netlink_loop_obj, avc_netlink_watch_obj); _dbus_watch_invalidate (avc_netlink_watch_obj); _dbus_clear_watch (&avc_netlink_watch_obj); } _dbus_clear_loop (&avc_netlink_loop_obj); if (avc_netlink_fd >= 0) { avc_netlink_release_fd (); avc_netlink_fd = -1; } avc_destroy (); _DBUS_ASSERT_ERROR_IS_SET (error); return FALSE; #endif /* HAVE_SELINUX */ return TRUE; } /** * Determine if the SELinux security policy allows the given sender * security context to go to the given recipient security context. * This function determines if the requested permissions are to be * granted from the connection to the message bus or to another * optionally supplied security identifier (e.g. for a service * context). Currently these permissions are either send_msg or * acquire_svc in the dbus class. * * @param sender_sid source security context * @param override_sid is the target security context. If SECSID_WILD this will * use the context of the bus itself (e.g. the default). * @param target_class is the target security class. * @param requested is the requested permissions. * @returns #TRUE if security policy allows the send. */ #ifdef HAVE_SELINUX static dbus_bool_t bus_selinux_check (BusSELinuxID *sender_sid, BusSELinuxID *override_sid, const char *target_class, const char *requested, DBusString *auxdata) { int saved_errno; security_class_t security_class; access_vector_t requested_access; if (!selinux_enabled) return TRUE; security_class = string_to_security_class (target_class); if (security_class == 0) { saved_errno = errno; log_callback (SELINUX_ERROR, "Unknown class %s", target_class); if (security_deny_unknown () == 0) { return TRUE; } _dbus_verbose ("Unknown class %s\n", target_class); errno = saved_errno; return FALSE; } requested_access = string_to_av_perm (security_class, requested); if (requested_access == 0) { saved_errno = errno; log_callback (SELINUX_ERROR, "Unknown permission %s for class %s", requested, target_class); if (security_deny_unknown () == 0) { return TRUE; } _dbus_verbose ("Unknown permission %s for class %s\n", requested, target_class); errno = saved_errno; return FALSE; } /* Make the security check. AVC checks enforcing mode here as well. */ if (avc_has_perm (SELINUX_SID_FROM_BUS (sender_sid), override_sid ? SELINUX_SID_FROM_BUS (override_sid) : bus_sid, security_class, requested_access, &aeref, auxdata) < 0) { switch (errno) { case EACCES: _dbus_verbose ("SELinux denying due to security policy.\n"); return FALSE; case EINVAL: _dbus_verbose ("SELinux denying due to invalid security context.\n"); return FALSE; default: _dbus_verbose ("SELinux denying due to: %s\n", _dbus_strerror (errno)); return FALSE; } } else return TRUE; } #endif /* HAVE_SELINUX */ /** * Returns true if the given connection can acquire a service, * assuming the given security ID is needed for that service. * * @param connection connection that wants to own the service * @param service_sid the SID of the service from the table * @returns #TRUE if acquire is permitted. */ dbus_bool_t bus_selinux_allows_acquire_service (DBusConnection *connection, BusSELinuxID *service_sid, const char *service_name, DBusError *error) { #ifdef HAVE_SELINUX BusSELinuxID *connection_sid; unsigned long spid; DBusString auxdata; dbus_bool_t ret; if (!selinux_enabled) return TRUE; connection_sid = bus_connection_get_selinux_id (connection); if (!dbus_connection_get_unix_process_id (connection, &spid)) spid = 0; if (!_dbus_string_init (&auxdata)) goto oom; if (!_dbus_string_append (&auxdata, "service=")) goto oom; if (!_dbus_string_append (&auxdata, service_name)) goto oom; if (spid) { if (!_dbus_string_append_printf (&auxdata, " spid=%lu", spid)) goto oom; } ret = bus_selinux_check (connection_sid, service_sid, "dbus", "acquire_svc", &auxdata); _dbus_string_free (&auxdata); return ret; oom: _dbus_string_free (&auxdata); BUS_SET_OOM (error); return FALSE; #else return TRUE; #endif /* HAVE_SELINUX */ } /** * Check if SELinux security controls allow the message to be sent to a * particular connection based on the security context of the sender and * that of the receiver. The destination connection need not be the * addressed recipient, it could be an "eavesdropper" * * @param sender the sender of the message. * @param proposed_recipient the connection the message is to be sent to. * @returns whether to allow the send */ dbus_bool_t bus_selinux_allows_send (DBusConnection *sender, DBusConnection *proposed_recipient, const char *msgtype, const char *interface, const char *member, const char *error_name, const char *destination, BusActivationEntry *activation_entry, DBusError *error) { #ifdef HAVE_SELINUX BusSELinuxID *recipient_sid; BusSELinuxID *sender_sid; unsigned long spid, tpid; DBusString auxdata; dbus_bool_t ret; dbus_bool_t string_alloced; if (!selinux_enabled) return TRUE; /* We do not mediate activation attempts yet. */ if (activation_entry) return TRUE; if (!sender || !dbus_connection_get_unix_process_id (sender, &spid)) spid = 0; if (!proposed_recipient || !dbus_connection_get_unix_process_id (proposed_recipient, &tpid)) tpid = 0; string_alloced = FALSE; if (!_dbus_string_init (&auxdata)) goto oom; string_alloced = TRUE; if (!_dbus_string_append (&auxdata, "msgtype=")) goto oom; if (!_dbus_string_append (&auxdata, msgtype)) goto oom; if (interface) { if (!_dbus_string_append (&auxdata, " interface=")) goto oom; if (!_dbus_string_append (&auxdata, interface)) goto oom; } if (member) { if (!_dbus_string_append (&auxdata, " member=")) goto oom; if (!_dbus_string_append (&auxdata, member)) goto oom; } if (error_name) { if (!_dbus_string_append (&auxdata, " error_name=")) goto oom; if (!_dbus_string_append (&auxdata, error_name)) goto oom; } if (destination) { if (!_dbus_string_append (&auxdata, " dest=")) goto oom; if (!_dbus_string_append (&auxdata, destination)) goto oom; } if (spid) { if (!_dbus_string_append_printf (&auxdata, " spid=%lu", spid)) goto oom; } if (tpid) { if (!_dbus_string_append_printf (&auxdata, " tpid=%lu", tpid)) goto oom; } sender_sid = bus_connection_get_selinux_id (sender); /* A NULL proposed_recipient with no activation entry means the bus itself. */ if (proposed_recipient) recipient_sid = bus_connection_get_selinux_id (proposed_recipient); else recipient_sid = BUS_SID_FROM_SELINUX (bus_sid); ret = bus_selinux_check (sender_sid, recipient_sid, "dbus", "send_msg", &auxdata); _dbus_string_free (&auxdata); return ret; oom: if (string_alloced) _dbus_string_free (&auxdata); BUS_SET_OOM (error); return FALSE; #else return TRUE; #endif /* HAVE_SELINUX */ } dbus_bool_t bus_selinux_append_context (DBusMessage *message, BusSELinuxID *sid, DBusError *error) { #ifdef HAVE_SELINUX char *context; if (avc_sid_to_context (SELINUX_SID_FROM_BUS (sid), &context) < 0) { if (errno == ENOMEM) BUS_SET_OOM (error); else dbus_set_error (error, DBUS_ERROR_FAILED, "Error getting context from SID: %s\n", _dbus_strerror (errno)); return FALSE; } if (!dbus_message_append_args (message, DBUS_TYPE_ARRAY, DBUS_TYPE_BYTE, &context, strlen (context), DBUS_TYPE_INVALID)) { _DBUS_SET_OOM (error); return FALSE; } freecon (context); return TRUE; #else return TRUE; #endif } /** * Gets the security context of a connection to the bus. It is up to * the caller to freecon() when they are done. * * @param connection the connection to get the context of. * @param con the location to store the security context. * @returns #TRUE if context is successfully obtained. */ #ifdef HAVE_SELINUX static dbus_bool_t bus_connection_read_selinux_context (DBusConnection *connection, char **con) { int fd; if (!selinux_enabled) return FALSE; _dbus_assert (connection != NULL); if (!dbus_connection_get_unix_fd (connection, &fd)) { _dbus_verbose ("Failed to get file descriptor of socket.\n"); return FALSE; } if (getpeercon (fd, con) < 0) { _dbus_verbose ("Error getting context of socket peer: %s\n", _dbus_strerror (errno)); return FALSE; } _dbus_verbose ("Successfully read connection context.\n"); return TRUE; } #endif /* HAVE_SELINUX */ /** * Read the SELinux ID from the connection. * * @param connection the connection to read from * @returns the SID if successfully determined, #NULL otherwise. */ BusSELinuxID* bus_selinux_init_connection_id (DBusConnection *connection, DBusError *error) { #ifdef HAVE_SELINUX char *con; security_id_t sid; if (!selinux_enabled) return NULL; if (!bus_connection_read_selinux_context (connection, &con)) { dbus_set_error (error, DBUS_ERROR_FAILED, "Failed to read an SELinux context from connection"); _dbus_verbose ("Error getting peer context.\n"); return NULL; } _dbus_verbose ("Converting context to SID to store on connection\n"); if (avc_context_to_sid (con, &sid) < 0) { if (errno == ENOMEM) BUS_SET_OOM (error); else dbus_set_error (error, DBUS_ERROR_FAILED, "Error getting SID from context \"%s\": %s\n", con, _dbus_strerror (errno)); _dbus_warn ("Error getting SID from context \"%s\": %s", con, _dbus_strerror (errno)); freecon (con); return NULL; } freecon (con); return BUS_SID_FROM_SELINUX (sid); #else return NULL; #endif /* HAVE_SELINUX */ } /** * Creates a new table mapping service names to security ID. * A security ID is a "compiled" security context, a security * context is just a string. * * @returns the new table or #NULL if no memory */ DBusHashTable* bus_selinux_id_table_new (void) { return _dbus_hash_table_new (DBUS_HASH_STRING, (DBusFreeFunction) dbus_free, NULL); } /** * Hashes a service name and service context into the service SID * table as a string and a SID. * * @param service_name is the name of the service. * @param service_context is the context of the service. * @param service_table is the table to hash them into. * @return #FALSE if not enough memory */ dbus_bool_t bus_selinux_id_table_insert (DBusHashTable *service_table, const char *service_name, const char *service_context) { #ifdef HAVE_SELINUX dbus_bool_t retval; security_id_t sid; char *key; if (!selinux_enabled) return TRUE; sid = SECSID_WILD; retval = FALSE; key = _dbus_strdup (service_name); if (key == NULL) return retval; if (avc_context_to_sid ((char *) service_context, &sid) < 0) { if (errno == ENOMEM) { dbus_free (key); return FALSE; } _dbus_warn ("Error getting SID from context \"%s\": %s", (char *) service_context, _dbus_strerror (errno)); goto out; } if (!_dbus_hash_table_insert_string (service_table, key, BUS_SID_FROM_SELINUX (sid))) goto out; _dbus_verbose ("Parsed \tservice: %s \n\t\tcontext: %s\n", key, sid->ctx); /* These are owned by the hash, so clear them to avoid unref */ key = NULL; sid = SECSID_WILD; retval = TRUE; out: if (key) dbus_free (key); return retval; #else return TRUE; #endif /* HAVE_SELINUX */ } /** * Find the security identifier associated with a particular service * name. Return a pointer to this SID, or #NULL/SECSID_WILD if the * service is not found in the hash table. This should be nearly a * constant time operation. If SELinux support is not available, * always return NULL. * * @param service_table the hash table to check for service name. * @param service_name the name of the service to look for. * @returns the SELinux ID associated with the service */ BusSELinuxID* bus_selinux_id_table_lookup (DBusHashTable *service_table, const DBusString *service_name) { #ifdef HAVE_SELINUX security_id_t sid; sid = SECSID_WILD; /* default context */ if (!selinux_enabled) return NULL; _dbus_verbose ("Looking up service SID for %s\n", _dbus_string_get_const_data (service_name)); sid = _dbus_hash_table_lookup_string (service_table, _dbus_string_get_const_data (service_name)); if (sid == SECSID_WILD) _dbus_verbose ("Service %s not found\n", _dbus_string_get_const_data (service_name)); else _dbus_verbose ("Service %s found\n", _dbus_string_get_const_data (service_name)); return BUS_SID_FROM_SELINUX (sid); #endif /* HAVE_SELINUX */ return NULL; } /** * Get the SELinux policy root. This is used to find the D-Bus * specific config file within the policy. */ const char * bus_selinux_get_policy_root (void) { #ifdef HAVE_SELINUX return selinux_policy_root (); #else return NULL; #endif /* HAVE_SELINUX */ } /** * For debugging: Print out the current hash table of service SIDs. */ void bus_selinux_id_table_print (DBusHashTable *service_table) { #if defined (DBUS_ENABLE_VERBOSE_MODE) && defined (HAVE_SELINUX) DBusHashIter iter; if (!selinux_enabled) return; _dbus_verbose ("Service SID Table:\n"); _dbus_hash_iter_init (service_table, &iter); while (_dbus_hash_iter_next (&iter)) { const char *key = _dbus_hash_iter_get_string_key (&iter); security_id_t sid = _dbus_hash_iter_get_value (&iter); _dbus_verbose ("The key is %s\n", key); _dbus_verbose ("The context is %s\n", sid->ctx); } #endif /* DBUS_ENABLE_VERBOSE_MODE && HAVE_SELINUX */ } /** * Print out some AVC statistics. */ #ifdef HAVE_SELINUX static void bus_avc_print_stats (void) { #ifdef DBUS_ENABLE_VERBOSE_MODE struct avc_cache_stats cstats; if (!selinux_enabled) return; _dbus_verbose ("AVC Statistics:\n"); avc_cache_stats (&cstats); avc_av_stats (); _dbus_verbose ("AVC Cache Statistics:\n"); _dbus_verbose ("Entry lookups: %d\n", cstats.entry_lookups); _dbus_verbose ("Entry hits: %d\n", cstats.entry_hits); _dbus_verbose ("Entry misses %d\n", cstats.entry_misses); _dbus_verbose ("Entry discards: %d\n", cstats.entry_discards); _dbus_verbose ("CAV lookups: %d\n", cstats.cav_lookups); _dbus_verbose ("CAV hits: %d\n", cstats.cav_hits); _dbus_verbose ("CAV probes: %d\n", cstats.cav_probes); _dbus_verbose ("CAV misses: %d\n", cstats.cav_misses); #endif /* DBUS_ENABLE_VERBOSE_MODE */ } #endif /* HAVE_SELINUX */ /** * Destroy the AVC before we terminate. */ void bus_selinux_shutdown (void) { #ifdef HAVE_SELINUX if (!selinux_enabled) return; _dbus_verbose ("AVC shutdown\n"); if (avc_netlink_watch_obj) { _dbus_loop_remove_watch (avc_netlink_loop_obj, avc_netlink_watch_obj); _dbus_watch_invalidate (avc_netlink_watch_obj); _dbus_clear_watch (&avc_netlink_watch_obj); } _dbus_clear_loop (&avc_netlink_loop_obj); if (avc_netlink_fd >= 0) { avc_netlink_release_fd (); avc_netlink_fd = -1; } if (bus_sid != SECSID_WILD) { bus_sid = SECSID_WILD; bus_avc_print_stats (); avc_destroy (); } #endif /* HAVE_SELINUX */ }