/* -*- mode: C; c-file-style: "gnu" -*- * selinux.c SELinux security checks for D-BUS * * Author: Matthew Rickard * * 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., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA * */ #include #include #include "selinux.h" #include "services.h" #include "policy.h" #include "utils.h" #include "config-parser.h" #ifdef HAVE_SELINUX #include #include #include #include #include #include #include #include #include #endif /* HAVE_SELINUX */ #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 SID of the bus itself to use as the default. */ static security_id_t bus_sid = SECSID_WILD; /* Thread to listen for SELinux status changes via netlink. */ static pthread_t avc_notify_thread; /* Prototypes for AVC callback functions. */ static void log_callback (const char *fmt, ...); static void log_audit_callback (void *data, security_class_t class, char *buf, size_t bufleft); static void *avc_create_thread (void (*run) (void)); static void avc_stop_thread (void *thread); static void *avc_alloc_lock (void); static void avc_get_lock (void *lock); static void avc_release_lock (void *lock); static void avc_free_lock (void *lock); /* AVC callback structures for use in avc_init. */ static const struct avc_memory_callback mem_cb = { .func_malloc = dbus_malloc, .func_free = dbus_free }; static const struct avc_log_callback log_cb = { .func_log = log_callback, .func_audit = log_audit_callback }; static const struct avc_thread_callback thread_cb = { .func_create_thread = avc_create_thread, .func_stop_thread = avc_stop_thread }; static const struct avc_lock_callback lock_cb = { .func_alloc_lock = avc_alloc_lock, .func_get_lock = avc_get_lock, .func_release_lock = avc_release_lock, .func_free_lock = avc_free_lock }; #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 void log_callback (const char *fmt, ...) { va_list ap; va_start(ap, fmt); vsyslog (LOG_INFO, fmt, ap); va_end(ap); } /** * 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 (u_int32_t event, security_id_t ssid, security_id_t tsid, security_class_t tclass, access_vector_t perms, access_vector_t *out_retained) { if (event == AVC_CALLBACK_RESET) return raise (SIGHUP); return 0; } /** * Log any auxiliary data */ static void log_audit_callback (void *data, security_class_t class, char *buf, size_t bufleft) { DBusString *audmsg = data; _dbus_string_copy_to_buffer (audmsg, buf, bufleft); } /** * Create thread to notify the AVC of enforcing and policy reload * changes via netlink. * * @param run the thread run function * @return pointer to the thread */ static void * avc_create_thread (void (*run) (void)) { int rc; rc = pthread_create (&avc_notify_thread, NULL, (void *(*) (void *)) run, NULL); if (rc != 0) { _dbus_warn ("Failed to start AVC thread: %s\n", _dbus_strerror (rc)); exit (1); } return &avc_notify_thread; } /* Stop AVC netlink thread. */ static void avc_stop_thread (void *thread) { pthread_cancel (*(pthread_t *) thread); } /* Allocate a new AVC lock. */ static void * avc_alloc_lock (void) { pthread_mutex_t *avc_mutex; avc_mutex = dbus_new (pthread_mutex_t, 1); if (avc_mutex == NULL) { _dbus_warn ("Could not create mutex: %s\n", _dbus_strerror (errno)); exit (1); } pthread_mutex_init (avc_mutex, NULL); return avc_mutex; } /* Acquire an AVC lock. */ static void avc_get_lock (void *lock) { pthread_mutex_lock (lock); } /* Release an AVC lock. */ static void avc_release_lock (void *lock) { pthread_mutex_unlock (lock); } /* Free an AVC lock. */ static void avc_free_lock (void *lock) { pthread_mutex_destroy (lock); dbus_free (lock); } #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 */ } /** * 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\n", _dbus_strerror (errno)); return FALSE; } selinux_enabled = r != 0; return TRUE; #else return TRUE; #endif } /** * Initialize the user space access vector cache (AVC) for D-BUS and set up * logging callbacks. */ dbus_bool_t bus_selinux_full_init (void) { #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_init ("avc", &mem_cb, &log_cb, &thread_cb, &lock_cb) < 0) { _dbus_warn ("Failed to start Access Vector Cache (AVC).\n"); return FALSE; } else { openlog ("dbus", LOG_PERROR, LOG_USER); _dbus_verbose ("Access Vector Cache (AVC) started.\n"); } if (avc_add_callback (policy_reload_callback, AVC_CALLBACK_RESET, NULL, NULL, 0, 0) < 0) { _dbus_warn ("Failed to add policy reload callback: %s\n", _dbus_strerror (errno)); avc_destroy (); return FALSE; } bus_context = NULL; bus_sid = SECSID_WILD; if (getcon (&bus_context) < 0) { _dbus_verbose ("Error getting context of bus: %s\n", _dbus_strerror (errno)); return FALSE; } if (avc_context_to_sid (bus_context, &bus_sid) < 0) { _dbus_verbose ("Error getting SID from bus context: %s\n", _dbus_strerror (errno)); freecon (bus_context); return FALSE; } freecon (bus_context); return TRUE; #else return TRUE; #endif /* HAVE_SELINUX */ } /** * Decrement SID reference count. * * @param sid the SID to decrement */ void bus_selinux_id_unref (BusSELinuxID *sid) { #ifdef HAVE_SELINUX if (!selinux_enabled) return; _dbus_assert (sid != NULL); sidput (SELINUX_SID_FROM_BUS (sid)); #endif /* HAVE_SELINUX */ } void bus_selinux_id_ref (BusSELinuxID *sid) { #ifdef HAVE_SELINUX if (!selinux_enabled) return; _dbus_assert (sid != NULL); sidget (SELINUX_SID_FROM_BUS (sid)); #endif /* HAVE_SELINUX */ } /** * 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, security_class_t target_class, access_vector_t requested, DBusString *auxdata) { if (!selinux_enabled) return TRUE; /* 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) : SELINUX_SID_FROM_BUS (bus_sid), target_class, requested, &aeref, auxdata) < 0) { _dbus_verbose ("SELinux denying due to security policy.\n"); 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 (&auxdata, " spid=")) goto oom; if (!_dbus_string_append_uint (&auxdata, spid)) goto oom; } ret = bus_selinux_check (connection_sid, service_sid, SECCLASS_DBUS, 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, 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; 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 (&auxdata, " spid=")) goto oom; if (!_dbus_string_append_uint (&auxdata, spid)) goto oom; } if (tpid) { if (!_dbus_string_append (&auxdata, " tpid=")) goto oom; if (!_dbus_string_append_uint (&auxdata, tpid)) goto oom; } sender_sid = bus_connection_get_selinux_id (sender); /* A NULL proposed_recipient 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, SECCLASS_DBUS, 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\n", con, _dbus_strerror (errno)); freecon (con); return NULL; } freecon (con); return BUS_SID_FROM_SELINUX (sid); #else return NULL; #endif /* HAVE_SELINUX */ } /** * Function for freeing hash table data. These SIDs * should no longer be referenced. */ static void bus_selinux_id_table_free_value (BusSELinuxID *sid) { #ifdef HAVE_SELINUX /* NULL sometimes due to how DBusHashTable works */ if (sid) bus_selinux_id_unref (sid); #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, (DBusFreeFunction) bus_selinux_id_table_free_value); } /** * 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) return FALSE; _dbus_warn ("Error getting SID from context \"%s\": %s\n", (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 (sid != SECSID_WILD) sidput (sid); 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) { #ifdef DBUS_ENABLE_VERBOSE_MODE #ifdef 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); _dbus_verbose ("The refcount is %d\n", sid->refcnt); } #endif /* HAVE_SELINUX */ #endif /* DBUS_ENABLE_VERBOSE_MODE */ } #ifdef DBUS_ENABLE_VERBOSE_MODE #ifdef HAVE_SELINUX /** * Print out some AVC statistics. */ static void bus_avc_print_stats (void) { 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 /* HAVE_SELINUX */ #endif /* DBUS_ENABLE_VERBOSE_MODE */ /** * Destroy the AVC before we terminate. */ void bus_selinux_shutdown (void) { #ifdef HAVE_SELINUX if (!selinux_enabled) return; _dbus_verbose ("AVC shutdown\n"); if (bus_sid != SECSID_WILD) { sidput (bus_sid); bus_sid = SECSID_WILD; #ifdef DBUS_ENABLE_VERBOSE_MODE bus_avc_print_stats (); #endif /* DBUS_ENABLE_VERBOSE_MODE */ avc_destroy (); } #endif /* HAVE_SELINUX */ }