bus-proxy: beef up policy enforcement

- actually return permission errors to clients

- use the right ucreds field

- fix error paths when we cannot keep track of locally acquired names
  due to OOM

- avoid unnecessary global variables

- log when the policy denies access

- enforce correct policy rule order

- always request all the metadata its we need to make decisions

4 files changed, 452 insertions, 284 deletions

diff --git a/src/bus-proxyd/bus-policy.c b/src/bus-proxyd/bus-policy.c
index d543bf9af4..3cfe9befb2 100644
--- a/src/bus-proxyd/bus-policy.c
+++ b/src/bus-proxyd/bus-policy.c
@@ -593,14 +593,29 @@ static int file_load(Policy *p, const char *path) {
 }
 
 enum {
+        DENY,
         ALLOW,
         DUNNO,
-        DENY,
 };
 
+static const char *verdict_to_string(int v) {
+        switch (v) {
+
+        case DENY:
+                return "DENY";
+        case ALLOW:
+                return "ALLOW";
+        case DUNNO:
+                return "DUNNO";
+        }
+
+        return NULL;
+}
+
 struct policy_check_filter {
         PolicyItemClass class;
-        const struct ucred *ucred;
+        uid_t uid;
+        gid_t gid;
         int message_type;
         const char *name;
         const char *interface;
@@ -656,17 +671,15 @@ static int check_policy_item(PolicyItem *i, const struct policy_check_filter *fi
                 break;
 
         case POLICY_ITEM_USER:
-                assert(filter->ucred);
-
-                if ((streq_ptr(i->name, "*") || (i->uid_valid && i->uid == filter->ucred->uid)))
-                        return is_permissive(i);
+                if (filter->uid != (uid_t) -1)
+                        if ((streq_ptr(i->name, "*") || (i->uid_valid && i->uid == filter->uid)))
+                                return is_permissive(i);
                 break;
 
         case POLICY_ITEM_GROUP:
-                assert(filter->ucred);
-
-                if ((streq_ptr(i->name, "*") || (i->gid_valid && i->gid == filter->ucred->gid)))
-                        return is_permissive(i);
+                if (filter->gid != (gid_t) -1)
+                        if ((streq_ptr(i->name, "*") || (i->gid_valid && i->gid == filter->gid)))
+                                return is_permissive(i);
                 break;
 
         case POLICY_ITEM_IGNORE:
@@ -680,29 +693,31 @@ static int check_policy_item(PolicyItem *i, const struct policy_check_filter *fi
 static int check_policy_items(PolicyItem *items, const struct policy_check_filter *filter) {
 
         PolicyItem *i;
-        int r, ret = DUNNO;
+        int verdict = DUNNO;
 
         assert(filter);
 
         /* Check all policies in a set - a broader one might be followed by a more specific one,
          * and the order of rules in policy definitions matters */
         LIST_FOREACH(items, i, items) {
+                int v;
+
                 if (i->class != filter->class &&
                     !(i->class == POLICY_ITEM_OWN_PREFIX && filter->class == POLICY_ITEM_OWN))
                         continue;
 
-                r = check_policy_item(i, filter);
-                if (r != DUNNO)
-                        ret = r;
+                v = check_policy_item(i, filter);
+                if (v != DUNNO)
+                        verdict = v;
         }
 
-        return ret;
+        return verdict;
 }
 
 static int policy_check(Policy *p, const struct policy_check_filter *filter) {
 
         PolicyItem *items;
-        int r;
+        int verdict, v;
 
         assert(p);
         assert(filter);
@@ -712,68 +727,96 @@ static int policy_check(Policy *p, const struct policy_check_filter *filter) {
         /*
          * The policy check is implemented by the following logic:
          *
-         * 1. Check mandatory items. If the message matches any of these, it is decisive.
-         * 2. See if the passed ucred match against the user/group hashmaps. A matching entry is also decisive.
-         * 3. Consult the defaults if non of the above matched with a more specific rule.
-         * 4. If the message isn't caught be the defaults either, reject it.
+         *  1. Check default items
+         *  2. Check group items
+         *  3. Check user items
+         *  4. Check mandatory items
+         *
+         *  Later rules override earlier rules.
          */
 
-        r = check_policy_items(p->mandatory_items, filter);
-        if (r != DUNNO)
-                return r;
+        verdict = check_policy_items(p->default_items, filter);
 
-        if (filter->ucred) {
-                items = hashmap_get(p->user_items, UINT32_TO_PTR(filter->ucred->uid));
+        if (filter->gid != (gid_t) -1) {
+                items = hashmap_get(p->group_items, UINT32_TO_PTR(filter->gid));
                 if (items) {
-                        r = check_policy_items(items, filter);
-                        if (r != DUNNO)
-                                return r;
+                        v = check_policy_items(items, filter);
+                        if (v != DUNNO)
+                                verdict = v;
                 }
+        }
 
-                items = hashmap_get(p->group_items, UINT32_TO_PTR(filter->ucred->gid));
+        if (filter->uid != (uid_t) -1) {
+                items = hashmap_get(p->user_items, UINT32_TO_PTR(filter->uid));
                 if (items) {
-                        r = check_policy_items(items, filter);
-                        if (r != DUNNO)
-                                return r;
+                        v = check_policy_items(items, filter);
+                        if (v != DUNNO)
+                                verdict = v;
                 }
         }
 
-        return check_policy_items(p->default_items, filter);
+        v = check_policy_items(p->mandatory_items, filter);
+        if (v != DUNNO)
+                verdict = v;
+
+        return verdict;
 }
 
-bool policy_check_own(Policy *p, const struct ucred *ucred, const char *name) {
+bool policy_check_own(Policy *p, uid_t uid, gid_t gid, const char *name) {
 
         struct policy_check_filter filter = {
                 .class = POLICY_ITEM_OWN,
-                .ucred = ucred,
+                .uid   = uid,
+                .gid   = gid,
                 .name  = name,
         };
 
-        return policy_check(p, &filter) == ALLOW;
+        int verdict;
+
+        assert(p);
+        assert(name);
+
+        verdict = policy_check(p, &filter);
+
+        log_full(LOG_AUTH | (verdict != ALLOW ? LOG_WARNING : LOG_DEBUG),
+                 "Ownership permission check for uid=" UID_FMT " gid=" GID_FMT" name=%s: %s",
+                 uid, gid, strna(name), strna(verdict_to_string(verdict)));
+
+        return verdict == ALLOW;
 }
 
-bool policy_check_hello(Policy *p, const struct ucred *ucred) {
+bool policy_check_hello(Policy *p, uid_t uid, gid_t gid) {
 
         struct policy_check_filter filter = {
-                .ucred  = ucred,
+                .uid = uid,
+                .gid = gid,
         };
-        int user, group;
+        int verdict;
+
+        assert(p);
 
         filter.class = POLICY_ITEM_USER;
-        user = policy_check(p, &filter);
-        if (user == DENY)
-                return false;
+        verdict = policy_check(p, &filter);
+
+        if (verdict != DENY) {
+                int v;
 
-        filter.class = POLICY_ITEM_GROUP;
-        group = policy_check(p, &filter);
-        if (group == DENY)
-                return false;
+                filter.class = POLICY_ITEM_GROUP;
+                v = policy_check(p, &filter);
+                if (v != DUNNO)
+                        verdict = v;
+        }
 
-        return !(user == DUNNO && group == DUNNO);
+        log_full(LOG_AUTH | (verdict != ALLOW ? LOG_WARNING : LOG_DEBUG),
+                 "Hello permission check for uid=" UID_FMT " gid=" GID_FMT": %s",
+                 uid, gid, strna(verdict_to_string(verdict)));
+
+        return verdict == ALLOW;
 }
 
 bool policy_check_recv(Policy *p,
-                       const struct ucred *ucred,
+                       uid_t uid,
+                       gid_t gid,
                        int message_type,
                        const char *name,
                        const char *path,
@@ -782,7 +825,8 @@ bool policy_check_recv(Policy *p,
 
         struct policy_check_filter filter = {
                 .class        = POLICY_ITEM_RECV,
-                .ucred        = ucred,
+                .uid          = uid,
+                .gid          = gid,
                 .message_type = message_type,
                 .name         = name,
                 .interface    = interface,
@@ -790,11 +834,22 @@ bool policy_check_recv(Policy *p,
                 .member       = member,
         };
 
-        return policy_check(p, &filter) == ALLOW;
+        int verdict;
+
+        assert(p);
+
+        verdict = policy_check(p, &filter);
+
+        log_full(LOG_AUTH | (verdict != ALLOW ? LOG_WARNING : LOG_DEBUG),
+                 "Recieve permission check for uid=" UID_FMT " gid=" GID_FMT" message=%s name=%s interface=%s path=%s member=%s: %s",
+                 uid, gid, bus_message_type_to_string(message_type), strna(name), strna(path), strna(interface), strna(member), strna(verdict_to_string(verdict)));
+
+        return verdict == ALLOW;
 }
 
 bool policy_check_send(Policy *p,
-                       const struct ucred *ucred,
+                       uid_t uid,
+                       gid_t gid,
                        int message_type,
                        const char *name,
                        const char *path,
@@ -803,7 +858,8 @@ bool policy_check_send(Policy *p,
 
         struct policy_check_filter filter = {
                 .class        = POLICY_ITEM_SEND,
-                .ucred        = ucred,
+                .uid          = uid,
+                .gid          = gid,
                 .message_type = message_type,
                 .name         = name,
                 .interface    = interface,
@@ -811,7 +867,17 @@ bool policy_check_send(Policy *p,
                 .member       = member,
         };
 
-        return policy_check(p, &filter) == ALLOW;
+        int verdict;
+
+        assert(p);
+
+        verdict = policy_check(p, &filter);
+
+        log_full(LOG_AUTH | (verdict != ALLOW ? LOG_WARNING : LOG_DEBUG),
+                 "Send permission check for uid=" UID_FMT " gid=" GID_FMT" message=%s name=%s interface=%s path=%s member=%s: %s",
+                 uid, gid, bus_message_type_to_string(message_type), strna(name), strna(path), strna(interface), strna(member), strna(verdict_to_string(verdict)));
+
+        return verdict == ALLOW;
 }
 
 int policy_load(Policy *p, char **files) {
@@ -939,6 +1005,7 @@ static void dump_items(PolicyItem *items, const char *prefix) {
                         printf("%sGroup: %s (%d)\n",
                                prefix, strna(group), i->gid);
                 }
+                printf("%s-\n", prefix);
         }
 }
 
diff --git a/src/bus-proxyd/bus-policy.h b/src/bus-proxyd/bus-policy.h
index 64fe1ffac5..933a53ceb5 100644
--- a/src/bus-proxyd/bus-policy.h
+++ b/src/bus-proxyd/bus-policy.h
@@ -76,17 +76,19 @@ typedef struct Policy {
 int policy_load(Policy *p, char **files);
 void policy_free(Policy *p);
 
-bool policy_check_own(Policy *p, const struct ucred *ucred, const char *name);
-bool policy_check_hello(Policy *p, const struct ucred *ucred);
+bool policy_check_own(Policy *p, uid_t uid, gid_t gid, const char *name);
+bool policy_check_hello(Policy *p, uid_t uid, gid_t gid);
 bool policy_check_recv(Policy *p,
-                       const struct ucred *ucred,
+                       uid_t uid,
+                       gid_t gid,
                        int message_type,
                        const char *name,
                        const char *path,
                        const char *interface,
                        const char *member);
 bool policy_check_send(Policy *p,
-                       const struct ucred *ucred,
+                       uid_t uid,
+                       gid_t gid,
                        int message_type,
                        const char *name,
                        const char *path,
diff --git a/src/bus-proxyd/bus-proxyd.c b/src/bus-proxyd/bus-proxyd.c
index 4df2fb10af..50ffd0ac16 100644
--- a/src/bus-proxyd/bus-proxyd.c
+++ b/src/bus-proxyd/bus-proxyd.c
@@ -51,8 +51,6 @@ static char *arg_command_line_buffer = NULL;
 static bool arg_drop_privileges = false;
 static char **arg_configuration = NULL;
 
-static Hashmap *names_hash = NULL;
-
 static int help(void) {
 
         printf("%s [OPTIONS...]\n\n"
@@ -442,95 +440,7 @@ static int get_creds_by_message(sd_bus *bus, sd_bus_message *m, uint64_t mask, s
         return get_creds_by_name(bus, name, mask, _creds, error);
 }
 
-static int process_policy(sd_bus *a, sd_bus *b, sd_bus_message *m, Policy *policy, const struct ucred *ucred) {
-        int r;
-        char **name;
-        char **names_strv;
-        bool granted = false;
-        Iterator i;
-
-        assert(a);
-        assert(b);
-        assert(m);
-
-        if (!policy)
-                return 0;
-
-        if (b->is_kernel) {
-
-                /* The message came from the kernel, and is sent to our legacy client. */
-                r = sd_bus_creds_get_well_known_names(&m->creds, &names_strv);
-                if (r < 0)
-                        return r;
-
-                STRV_FOREACH(name, names_strv) {
-                        if (policy_check_send(policy, ucred, m->header->type, *name, m->path, m->interface, m->member)) {
-                                r = free_and_strdup(&m->destination_ptr, *name);
-                                if (r < 0)
-                                        break;
-
-                                granted = true;
-                                break;
-                        }
-                }
-
-                if (r < 0)
-                        return r;
-
-                if (!granted)
-                        return -EPERM;
-
-                granted = false;
-
-                HASHMAP_FOREACH(name, names_hash, i) {
-                        if (policy_check_recv(policy, ucred, m->header->type, *name, m->path, m->interface, m->member))
-                                return 0;
-                }
-
-                return -EPERM;
-        } else {
-                sd_bus_creds *bus_creds;
-
-                /* The message came from the legacy client, and is sent to kdbus. */
-                r = sd_bus_get_name_creds(a, m->destination, SD_BUS_CREDS_WELL_KNOWN_NAMES, &bus_creds);
-                if (r < 0)
-                        return r;
-
-                STRV_FOREACH(name, names_strv) {
-                        if (policy_check_send(policy, ucred, m->header->type, *name, m->path, m->interface, m->member)) {
-                                r = free_and_strdup(&m->destination_ptr, *name);
-                                if (r < 0)
-                                        break;
-
-                                r = bus_kernel_parse_unique_name(m->sender, &m->verify_destination_id);
-                                if (r < 0)
-                                        break;
-
-                                granted = true;
-                                break;
-                        }
-                }
-
-                if (r < 0)
-                        return r;
-
-                if (!granted)
-                        return -EPERM;
-
-                granted = false;
-
-                HASHMAP_FOREACH(name, names_hash, i) {
-                        if (policy_check_recv(policy, ucred, m->header->type, *name, m->path, m->interface, m->member))
-                                return 0;
-                }
-
-                return -EPERM;
-        }
-
-        return 0;
-}
-
-static int process_driver(sd_bus *a, sd_bus *b, sd_bus_message *m, Policy *policy, const struct ucred *ucred) {
+static int process_driver(sd_bus *a, sd_bus *b, sd_bus_message *m, Policy *policy, const struct ucred *ucred, Set *owned_names) {
         int r;
 
         assert(a);
@@ -883,7 +793,7 @@ static int process_driver(sd_bus *a, sd_bus *b, sd_bus_message *m, Policy *polic
                         return synthetic_reply_method_errno(m, r, NULL);
                 }
 
-                hashmap_remove(names_hash, name);
+                set_remove(owned_names, (char*) name);
 
                 return synthetic_reply_method_return(m, "u", BUS_NAME_RELEASED);
 
@@ -909,7 +819,7 @@ static int process_driver(sd_bus *a, sd_bus *b, sd_bus_message *m, Policy *polic
                 if (r < 0)
                         return synthetic_reply_method_errno(m, r, NULL);
 
-                if (policy && !policy_check_own(policy, ucred, name))
+                if (policy && !policy_check_own(policy, ucred->uid, ucred->gid, name))
                         return synthetic_reply_method_errno(m, -EPERM, NULL);
 
                 if ((flags & ~(BUS_NAME_ALLOW_REPLACEMENT|BUS_NAME_REPLACE_EXISTING|BUS_NAME_DO_NOT_QUEUE)) != 0)
@@ -923,21 +833,24 @@ static int process_driver(sd_bus *a, sd_bus *b, sd_bus_message *m, Policy *polic
                 if (!(flags & BUS_NAME_DO_NOT_QUEUE))
                         param |= SD_BUS_NAME_QUEUE;
 
+                r = set_put_strdup(owned_names, name);
+                if (r < 0)
+                        return synthetic_reply_method_errno(m, r, NULL);
+
                 r = sd_bus_request_name(a, name, param);
                 if (r < 0) {
-                        if (r == -EEXIST)
-                                return synthetic_reply_method_return(m, "u", BUS_NAME_EXISTS);
                         if (r == -EALREADY)
                                 return synthetic_reply_method_return(m, "u", BUS_NAME_ALREADY_OWNER);
+
+                        set_remove(owned_names, (char*) name);
+
+                        if (r == -EEXIST)
+                                return synthetic_reply_method_return(m, "u", BUS_NAME_EXISTS);
                         return synthetic_reply_method_errno(m, r, NULL);
                 }
 
                 in_queue = (r == 0);
 
-                r = hashmap_put(names_hash, name, NULL);
-                if (r < 0)
-                        return synthetic_reply_method_errno(m, r, NULL);
-
                 if (in_queue)
                         return synthetic_reply_method_return(m, "u", BUS_NAME_IN_QUEUE);
 
@@ -1049,7 +962,166 @@ static int process_driver(sd_bus *a, sd_bus *b, sd_bus_message *m, Policy *polic
         }
 }
 
-static int process_hello(sd_bus *a, sd_bus *b, sd_bus_message *m, Policy *policy, const struct ucred *ucred, bool *got_hello) {
+static int process_policy(sd_bus *from, sd_bus *to, sd_bus_message *m, Policy *policy, const struct ucred *our_ucred, Set *owned_names) {
+        int r;
+
+        assert(from);
+        assert(to);
+        assert(m);
+
+        if (!policy)
+                return 0;
+
+        if (from->is_kernel) {
+                uid_t sender_uid = (uid_t) -1;
+                gid_t sender_gid = (gid_t) -1;
+                char **sender_names = NULL;
+                bool granted = false;
+
+                /* Driver messages are always OK */
+                if (streq_ptr(m->sender, "org.freedesktop.DBus"))
+                        return 0;
+
+                /* The message came from the kernel, and is sent to our legacy client. */
+                r = sd_bus_creds_get_well_known_names(&m->creds, &sender_names);
+                if (r < 0)
+                        return r;
+
+                (void) sd_bus_creds_get_uid(&m->creds, &sender_uid);
+                (void) sd_bus_creds_get_gid(&m->creds, &sender_gid);
+
+                /* First check whether the sender can send the message to our name */
+                if (set_isempty(owned_names)) {
+                        if (policy_check_send(policy, sender_uid, sender_gid, m->header->type, NULL, m->path, m->interface, m->member))
+                                granted = true;
+                } else {
+                        Iterator i;
+                        char *n;
+
+                        SET_FOREACH(n, owned_names, i)
+                                if (policy_check_send(policy, sender_uid, sender_gid, m->header->type, n, m->path, m->interface, m->member)) {
+                                        granted = true;
+                                        break;
+                                }
+                }
+
+                if (granted) {
+                        /* Then check whether us, the recipient can recieve from the sender's name */
+                        if (strv_isempty(sender_names)) {
+                                if (policy_check_recv(policy, our_ucred->uid, our_ucred->gid, m->header->type, NULL, m->path, m->interface, m->member))
+                                        return 0;
+                        } else {
+                                char **n;
+
+                                STRV_FOREACH(n, sender_names) {
+                                        if (policy_check_recv(policy, our_ucred->uid, our_ucred->gid, m->header->type, *n, m->path, m->interface, m->member))
+                                                return 0;
+                                }
+                        }
+                }
+
+                /* Return an error back to the caller */
+                if (m->header->type == SD_BUS_MESSAGE_METHOD_CALL)
+                        return sd_bus_reply_method_errorf(m, SD_BUS_ERROR_ACCESS_DENIED, "Access prohibited by XML receiver policy.");
+
+                /* Return 1, indicating that the message shall not be processed any further */
+                return 1;
+        }
+
+        if (to->is_kernel) {
+                _cleanup_bus_creds_unref_ sd_bus_creds *destination_creds = NULL;
+                uid_t destination_uid = (uid_t) -1;
+                gid_t destination_gid = (gid_t) -1;
+                const char *destination_unique = NULL;
+                char **destination_names = NULL;
+                bool granted = false;
+
+                /* Driver messages are always OK */
+                if (streq_ptr(m->destination, "org.freedesktop.DBus"))
+                        return 0;
+
+                /* The message came from the legacy client, and is sent to kdbus. */
+                if (m->destination) {
+                        r = sd_bus_get_name_creds(to, m->destination,
+                                                  SD_BUS_CREDS_WELL_KNOWN_NAMES|SD_BUS_CREDS_UNIQUE_NAME|
+                                                  SD_BUS_CREDS_UID|SD_BUS_CREDS_GID|SD_BUS_CREDS_PID, &destination_creds);
+                        if (r < 0)
+                                return r;
+
+                        r = sd_bus_creds_get_well_known_names(destination_creds, &destination_names);
+                        if (r < 0)
+                                return r;
+
+                        r = sd_bus_creds_get_unique_name(destination_creds, &destination_unique);
+                        if (r < 0)
+                                return r;
+
+                        (void) sd_bus_creds_get_uid(destination_creds, &destination_uid);
+                        (void) sd_bus_creds_get_gid(destination_creds, &destination_gid);
+                }
+
+                /* First check if we, the sender can send to this name */
+                if (strv_isempty(destination_names)) {
+                        if (policy_check_send(policy, our_ucred->uid, our_ucred->gid, m->header->type, NULL, m->path, m->interface, m->member))
+                                granted = true;
+                } else {
+                        char **n;
+
+                        STRV_FOREACH(n, destination_names) {
+                                if (policy_check_send(policy, our_ucred->uid, our_ucred->gid, m->header->type, *n, m->path, m->interface, m->member)) {
+
+                                        /* If we made a receiver decision,
+                                           then remember which name's policy
+                                           we used, and to which unique ID it
+                                           mapped when we made the
+                                           decision. Then, let's pass this to
+                                           the kernel when sending the
+                                           message, so that it refuses the
+                                           operation should the name and
+                                           unique ID not map to each other
+                                           anymore. */
+
+                                        r = free_and_strdup(&m->destination_ptr, *n);
+                                        if (r < 0)
+                                                return r;
+
+                                        r = bus_kernel_parse_unique_name(destination_unique, &m->verify_destination_id);
+                                        if (r < 0)
+                                                break;
+
+                                        granted = true;
+                                        break;
+                                }
+                        }
+                }
+
+                /* Then check if the recipient can receive from our name */
+                if (granted) {
+                        if (set_isempty(owned_names)) {
+                                if (policy_check_recv(policy, destination_uid, destination_gid, m->header->type, NULL, m->path, m->interface, m->member))
+                                        return 0;
+                        } else {
+                                Iterator i;
+                                char *n;
+
+                                SET_FOREACH(n, owned_names, i)
+                                        if (policy_check_recv(policy, destination_uid, destination_gid, m->header->type, n, m->path, m->interface, m->member))
+                                                return 0;
+                        }
+                }
+
+                /* Return an error back to the caller */
+                if (m->header->type == SD_BUS_MESSAGE_METHOD_CALL)
+                        return sd_bus_reply_method_errorf(m, SD_BUS_ERROR_ACCESS_DENIED, "Access prohibited by XML sender policy.");
+
+                /* Return 1, indicating that the message shall not be processed any further */
+                return 1;
+        }
+
+        return 0;
+}
+
+static int process_hello(sd_bus *a, sd_bus *b, sd_bus_message *m, bool *got_hello) {
         _cleanup_bus_message_unref_ sd_bus_message *n = NULL;
         bool is_hello;
         int r;
@@ -1081,11 +1153,6 @@ static int process_hello(sd_bus *a, sd_bus *b, sd_bus_message *m, Policy *policy
                 return -EIO;
         }
 
-        if (policy && !policy_check_hello(policy, ucred)) {
-                log_error("Policy denied HELLO");
-                return -EPERM;
-        }
-
         *got_hello = true;
 
         if (!a->is_kernel)
@@ -1192,7 +1259,6 @@ static int patch_sender(sd_bus *a, sd_bus_message *m) {
 
 int main(int argc, char *argv[]) {
 
-        _cleanup_bus_creds_unref_ sd_bus_creds *bus_creds = NULL;
         _cleanup_bus_close_unref_ sd_bus *a = NULL, *b = NULL;
         sd_id128_t server_id;
         int r, in_fd, out_fd;
@@ -1200,7 +1266,8 @@ int main(int argc, char *argv[]) {
         bool is_unix;
         struct ucred ucred = {};
         _cleanup_free_ char *peersec = NULL;
-        Policy policy = {};
+        Policy policy_buffer = {}, *policy = NULL;
+        _cleanup_set_free_free_ Set *owned_names = NULL;
 
         log_set_target(LOG_TARGET_JOURNAL_OR_KMSG);
         log_parse_environment();
@@ -1210,14 +1277,6 @@ int main(int argc, char *argv[]) {
         if (r <= 0)
                 goto finish;
 
-        r = policy_load(&policy, arg_configuration);
-        if (r < 0) {
-                log_error("Failed to load policy: %s", strerror(-r));
-                goto finish;
-        }
-
-        /* policy_dump(&policy); */
-
         r = sd_listen_fds(0);
         if (r == 0) {
                 in_fd = STDIN_FILENO;
@@ -1255,8 +1314,8 @@ int main(int argc, char *argv[]) {
                         goto finish;
         }
 
-        names_hash = hashmap_new(&string_hash_ops);
-        if (!names_hash) {
+        owned_names = set_new(&string_hash_ops);
+        if (!owned_names) {
                 log_oom();
                 goto finish;
         }
@@ -1285,6 +1344,12 @@ int main(int argc, char *argv[]) {
                 goto finish;
         }
 
+        r = sd_bus_negotiate_creds(a, true, SD_BUS_CREDS_UID|SD_BUS_CREDS_PID|SD_BUS_CREDS_GID|SD_BUS_CREDS_SELINUX_CONTEXT);
+        if (r < 0) {
+                log_error("Failed to set credential negotiation: %s", strerror(-r));
+                goto finish;
+        }
+
         if (ucred.pid > 0) {
                 a->fake_pids.pid = ucred.pid;
                 a->fake_pids_valid = true;
@@ -1319,10 +1384,41 @@ int main(int argc, char *argv[]) {
                 goto finish;
         }
 
-        r = sd_bus_get_owner_creds(a, SD_BUS_CREDS_UID, &bus_creds);
-        if (r < 0) {
-                log_error("Failed to get bus creds: %s", strerror(-r));
-                goto finish;
+        if (a->is_kernel) {
+                _cleanup_bus_creds_unref_ sd_bus_creds *bus_creds = NULL;
+                uid_t bus_uid;
+
+                r = sd_bus_get_owner_creds(a, SD_BUS_CREDS_UID, &bus_creds);
+                if (r < 0) {
+                        log_error("Failed to get bus creds: %s", strerror(-r));
+                        goto finish;
+                }
+
+                r = sd_bus_creds_get_uid(bus_creds, &bus_uid);
+                if (r < 0) {
+                        log_error("Failed to get bus owner UID: %s", strerror(-r));
+                        goto finish;
+                }
+
+                if (bus_uid == 0) {
+                        /* We only enforce the old XML policy on
+                         * kernel busses owned by root users. */
+
+                        r = policy_load(&policy_buffer, arg_configuration);
+                        if (r < 0) {
+                                log_error("Failed to load policy: %s", strerror(-r));
+                                goto finish;
+                        }
+
+                        if (!policy_check_hello(&policy_buffer, ucred.uid, ucred.gid)) {
+                                log_error("Policy denied connection");
+                                r = -EPERM;
+                                goto finish;
+                        }
+
+                        policy_dump(&policy_buffer);
+                        policy = &policy_buffer;
+                }
         }
 
         r = sd_bus_new(&b);
@@ -1349,6 +1445,12 @@ int main(int argc, char *argv[]) {
                 goto finish;
         }
 
+        r = sd_bus_negotiate_creds(b, true, SD_BUS_CREDS_UID|SD_BUS_CREDS_PID|SD_BUS_CREDS_GID|SD_BUS_CREDS_SELINUX_CONTEXT);
+        if (r < 0) {
+                log_error("Failed to set credential negotiation: %s", strerror(-r));
+                goto finish;
+        }
+
         r = sd_bus_set_anonymous(b, true);
         if (r < 0) {
                 log_error("Failed to set anonymous authentication: %s", strerror(-r));
@@ -1428,6 +1530,8 @@ int main(int argc, char *argv[]) {
                 int k;
 
                 if (got_hello) {
+                        /* Read messages from bus, to pass them on to our client */
+
                         r = sd_bus_process(a, &m);
                         if (r < 0) {
                                 /* treat 'connection reset by peer' as clean exit condition */
@@ -1440,6 +1544,8 @@ int main(int argc, char *argv[]) {
                         }
 
                         if (m) {
+                                bool processed = false;
+
                                 /* We officially got EOF, let's quit */
                                 if (sd_bus_message_is_signal(m, "org.freedesktop.DBus.Local", "Disconnected")) {
                                         r = 0;
@@ -1455,16 +1561,31 @@ int main(int argc, char *argv[]) {
 
                                 patch_sender(a, m);
 
-                                k = sd_bus_send(b, m, NULL);
-                                if (k < 0) {
-                                        if (k == -ECONNRESET)
-                                                r = 0;
-                                        else {
+                                if (policy) {
+                                        k = process_policy(a, b, m, policy, &ucred, owned_names);
+                                        if (k < 0) {
                                                 r = k;
-                                                log_error("Failed to send message: %s", strerror(-r));
+                                                log_error("Failed to process policy: %s", strerror(-r));
+                                                goto finish;
+                                        } else if (k > 0) {
+                                                r = 1;
+                                                processed = true;
                                         }
+                                }
 
-                                        goto finish;
+                                if (!processed) {
+                                        k = sd_bus_send(b, m, NULL);
+                                        if (k < 0) {
+                                                if (k == -ECONNRESET)
+                                                        r = 0;
+                                                else {
+                                                        r = k;
+                                                        log_error("Failed to send message to client: %s", strerror(-r));
+                                                }
+
+                                                goto finish;
+                                        } else
+                                                r = 1;
                                 }
                         }
 
@@ -1472,6 +1593,7 @@ int main(int argc, char *argv[]) {
                                 continue;
                 }
 
+                /* Read messages from our client, to pass them on to the bus */
                 r = sd_bus_process(b, &m);
                 if (r < 0) {
                         /* treat 'connection reset by peer' as clean exit condition */
@@ -1484,15 +1606,7 @@ int main(int argc, char *argv[]) {
                 }
 
                 if (m) {
-                        Policy *p = NULL;
-                        uid_t uid;
-
-                        assert_se(sd_bus_creds_get_uid(bus_creds, &uid) == 0);
-
-/*
-                        if (uid == 0 || uid != ucred.uid)
-                                p = &policy;
-*/
+                        bool processed = false;
 
                         /* We officially got EOF, let's quit */
                         if (sd_bus_message_is_signal(m, "org.freedesktop.DBus.Local", "Disconnected")) {
@@ -1500,53 +1614,61 @@ int main(int argc, char *argv[]) {
                                 goto finish;
                         }
 
-                        k = process_hello(a, b, m, p, &ucred, &got_hello);
+                        k = process_hello(a, b, m, &got_hello);
                         if (k < 0) {
                                 r = k;
                                 log_error("Failed to process HELLO: %s", strerror(-r));
                                 goto finish;
+                        } else if (k > 0) {
+                                processed = true;
+                                r = 1;
                         }
 
-                        if (k > 0)
-                                r = k;
-                        else {
-                                k = process_driver(a, b, m, p, &ucred);
+                        if (!processed) {
+                                k = process_driver(a, b, m, policy, &ucred, owned_names);
                                 if (k < 0) {
                                         r = k;
                                         log_error("Failed to process driver calls: %s", strerror(-r));
                                         goto finish;
+                                } else if (k > 0) {
+                                        processed = true;
+                                        r = 1;
                                 }
 
-                                if (k > 0)
-                                        r = k;
-                                else {
-                                        bool retry;
-
-                                        do {
-                                                retry = false;
+                                if (!processed) {
 
-                                                k = process_policy(a, b, m, p, &ucred);
-                                                if (k < 0) {
-                                                        r = k;
-                                                        log_error("Failed to process policy: %s", strerror(-r));
-                                                        goto finish;
+                                        for (;;) {
+                                                if (policy) {
+                                                        k = process_policy(b, a, m, policy, &ucred, owned_names);
+                                                        if (k < 0) {
+                                                                r = k;
+                                                                log_error("Failed to process policy: %s", strerror(-r));
+                                                                goto finish;
+                                                        } else if (k > 0) {
+                                                                processed = true;
+                                                                r = 1;
+                                                                break;
+                                                        }
                                                 }
 
                                                 k = sd_bus_send(a, m, NULL);
                                                 if (k < 0) {
-                                                        if (k == -ECONNRESET)
+                                                        if (k == -EREMCHG)
+                                                                /* The name database changed since the policy check, hence let's check again */
+                                                                continue;
+                                                        else if (k == -ECONNRESET)
                                                                 r = 0;
-                                                        else if (k == -EREMCHG)
-                                                                retry = true;
                                                         else {
                                                                 r = k;
-                                                                log_error("Failed to send message: %s", strerror(-r));
+                                                                log_error("Failed to send message to bus: %s", strerror(-r));
                                                         }
 
-                                                        if (!retry)
-                                                                goto finish;
-                                                }
-                                        } while (retry);
+                                                        goto finish;
+                                                } else
+                                                        r = 1;
+
+                                                break;
+                                        }
                                 }
                         }
                 }
@@ -1620,9 +1742,8 @@ finish:
                   "STOPPING=1\n"
                   "STATUS=Shutting down.");
 
-        policy_free(&policy);
+        policy_free(&policy_buffer);
         strv_free(arg_configuration);
-        hashmap_free(names_hash);
         free(arg_address);
 
         return r < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
diff --git a/src/bus-proxyd/test-bus-policy.c b/src/bus-proxyd/test-bus-policy.c
index 1c1d1ef9ed..91ab33da4a 100644
--- a/src/bus-proxyd/test-bus-policy.c
+++ b/src/bus-proxyd/test-bus-policy.c
@@ -62,41 +62,29 @@ static int test_policy_load(Policy *p, const char *name)
 int main(int argc, char *argv[]) {
 
         Policy p = {};
-        struct ucred ucred = {};
 
         /* Ownership tests */
         assert_se(test_policy_load(&p, "ownerships.conf") == 0);
 
-        ucred.uid = 0;
-        assert_se(policy_check_own(&p, &ucred, "org.test.test1") == true);
-        ucred.uid = 1;
-        assert_se(policy_check_own(&p, &ucred, "org.test.test1") == true);
+        assert_se(policy_check_own(&p, 0, 0, "org.test.test1") == true);
+        assert_se(policy_check_own(&p, 1, 0, "org.test.test1") == true);
 
-        ucred.uid = 0;
-        assert_se(policy_check_own(&p, &ucred, "org.test.test2") == true);
-        ucred.uid = 1;
-        assert_se(policy_check_own(&p, &ucred, "org.test.test2") == false);
+        assert_se(policy_check_own(&p, 0, 0, "org.test.test2") == true);
+        assert_se(policy_check_own(&p, 1, 0, "org.test.test2") == false);
 
-        ucred.uid = 0;
-        assert_se(policy_check_own(&p, &ucred, "org.test.test3") == false);
-        ucred.uid = 1;
-        assert_se(policy_check_own(&p, &ucred, "org.test.test3") == false);
+        assert_se(policy_check_own(&p, 0, 0, "org.test.test3") == false);
+        assert_se(policy_check_own(&p, 1, 0, "org.test.test3") == false);
 
-        ucred.uid = 0;
-        assert_se(policy_check_own(&p, &ucred, "org.test.test4") == false);
-        ucred.uid = 1;
-        assert_se(policy_check_own(&p, &ucred, "org.test.test4") == true);
+        assert_se(policy_check_own(&p, 0, 0, "org.test.test4") == false);
+        assert_se(policy_check_own(&p, 1, 0, "org.test.test4") == true);
 
         policy_free(&p);
 
         /* Signaltest */
         assert_se(test_policy_load(&p, "signals.conf") == 0);
 
-        ucred.uid = 0;
-        assert_se(policy_check_send(&p, &ucred, SD_BUS_MESSAGE_SIGNAL, "bli.bla.blubb", NULL, "/an/object/path", NULL) == true);
-
-        ucred.uid = 1;
-        assert_se(policy_check_send(&p, &ucred, SD_BUS_MESSAGE_SIGNAL, "bli.bla.blubb", NULL, "/an/object/path", NULL) == false);
+        assert_se(policy_check_send(&p, 0, 0, SD_BUS_MESSAGE_SIGNAL, "bli.bla.blubb", NULL, "/an/object/path", NULL) == true);
+        assert_se(policy_check_send(&p, 1, 0, SD_BUS_MESSAGE_SIGNAL, "bli.bla.blubb", NULL, "/an/object/path", NULL) == false);
 
         policy_free(&p);
 
@@ -104,14 +92,12 @@ int main(int argc, char *argv[]) {
         assert_se(test_policy_load(&p, "methods.conf") == 0);
         policy_dump(&p);
 
-        ucred.uid = 0;
-
-        assert_se(policy_check_send(&p, &ucred, SD_BUS_MESSAGE_METHOD_CALL, "org.test.test1", "/an/object/path", "bli.bla.blubb", "Member") == false);
-        assert_se(policy_check_send(&p, &ucred, SD_BUS_MESSAGE_METHOD_CALL, "org.test.test1", "/an/object/path", "bli.bla.blubb", "Member") == false);
-        assert_se(policy_check_send(&p, &ucred, SD_BUS_MESSAGE_METHOD_CALL, "org.test.test1", "/an/object/path", "org.test.int1", "Member") == true);
-        assert_se(policy_check_send(&p, &ucred, SD_BUS_MESSAGE_METHOD_CALL, "org.test.test1", "/an/object/path", "org.test.int2", "Member") == true);
+        assert_se(policy_check_send(&p, 0, 0, SD_BUS_MESSAGE_METHOD_CALL, "org.test.test1", "/an/object/path", "bli.bla.blubb", "Member") == false);
+        assert_se(policy_check_send(&p, 0, 0, SD_BUS_MESSAGE_METHOD_CALL, "org.test.test1", "/an/object/path", "bli.bla.blubb", "Member") == false);
+        assert_se(policy_check_send(&p, 0, 0, SD_BUS_MESSAGE_METHOD_CALL, "org.test.test1", "/an/object/path", "org.test.int1", "Member") == true);
+        assert_se(policy_check_send(&p, 0, 0, SD_BUS_MESSAGE_METHOD_CALL, "org.test.test1", "/an/object/path", "org.test.int2", "Member") == true);
 
-        assert_se(policy_check_recv(&p, &ucred, SD_BUS_MESSAGE_METHOD_CALL, "org.test.test3", "/an/object/path", "org.test.int3", "Member111") == true);
+        assert_se(policy_check_recv(&p, 0, 0, SD_BUS_MESSAGE_METHOD_CALL, "org.test.test3", "/an/object/path", "org.test.int3", "Member111") == true);
 
         policy_free(&p);
 
@@ -119,15 +105,9 @@ int main(int argc, char *argv[]) {
         assert_se(test_policy_load(&p, "hello.conf") == 0);
         policy_dump(&p);
 
-        ucred.uid = 0;
-        assert_se(policy_check_hello(&p, &ucred) == true);
-
-        ucred.uid = 1;
-        assert_se(policy_check_hello(&p, &ucred) == false);
-
-        ucred.uid = 0;
-        ucred.gid = 1;
-        assert_se(policy_check_hello(&p, &ucred) == false);
+        assert_se(policy_check_hello(&p, 0, 0) == true);
+        assert_se(policy_check_hello(&p, 1, 0) == false);
+        assert_se(policy_check_hello(&p, 0, 1) == false);
 
         policy_free(&p);
 
@@ -136,14 +116,14 @@ int main(int argc, char *argv[]) {
         assert_se(test_policy_load(&p, "check-own-rules.conf") >= 0);
         policy_dump(&p);
 
-        assert_se(policy_check_own(&p, &ucred, "org.freedesktop") == false);
-        assert_se(policy_check_own(&p, &ucred, "org.freedesktop.ManySystem") == false);
-        assert_se(policy_check_own(&p, &ucred, "org.freedesktop.ManySystems") == true);
-        assert_se(policy_check_own(&p, &ucred, "org.freedesktop.ManySystems.foo") == true);
-        assert_se(policy_check_own(&p, &ucred, "org.freedesktop.ManySystems.foo.bar") == true);
-        assert_se(policy_check_own(&p, &ucred, "org.freedesktop.ManySystems2") == false);
-        assert_se(policy_check_own(&p, &ucred, "org.freedesktop.ManySystems2.foo") == false);
-        assert_se(policy_check_own(&p, &ucred, "org.freedesktop.ManySystems2.foo.bar") == false);
+        assert_se(policy_check_own(&p, 0, 0, "org.freedesktop") == false);
+        assert_se(policy_check_own(&p, 0, 0, "org.freedesktop.ManySystem") == false);
+        assert_se(policy_check_own(&p, 0, 0, "org.freedesktop.ManySystems") == true);
+        assert_se(policy_check_own(&p, 0, 0, "org.freedesktop.ManySystems.foo") == true);
+        assert_se(policy_check_own(&p, 0, 0, "org.freedesktop.ManySystems.foo.bar") == true);
+        assert_se(policy_check_own(&p, 0, 0, "org.freedesktop.ManySystems2") == false);
+        assert_se(policy_check_own(&p, 0, 0, "org.freedesktop.ManySystems2.foo") == false);
+        assert_se(policy_check_own(&p, 0, 0, "org.freedesktop.ManySystems2.foo.bar") == false);
 
         policy_free(&p);
 
@@ -158,23 +138,21 @@ int main(int argc, char *argv[]) {
         assert_se(test_policy_load(&p, "test.conf") >= 0);
         policy_dump(&p);
 
-        ucred.uid = 0;
-        assert_se(policy_check_own(&p, &ucred, "org.foo.FooService") == true);
-        assert_se(policy_check_own(&p, &ucred, "org.foo.FooService2") == false);
-        assert_se(policy_check_send(&p, &ucred, SD_BUS_MESSAGE_METHOD_CALL, "org.test.test1", "/an/object/path", "org.test.int2", "Member") == false);
-        assert_se(policy_check_send(&p, &ucred, SD_BUS_MESSAGE_METHOD_CALL, "org.test.test1", "/an/object/path", "org.foo.FooBroadcastInterface", "Member") == true);
-        assert_se(policy_check_recv(&p, &ucred, SD_BUS_MESSAGE_METHOD_CALL, "org.foo.FooService", "/an/object/path", "org.foo.FooBroadcastInterface", "Member") == true);
-        assert_se(policy_check_recv(&p, &ucred, SD_BUS_MESSAGE_METHOD_CALL, "org.foo.FooService", "/an/object/path", "org.foo.FooBroadcastInterface2", "Member") == false);
-        assert_se(policy_check_recv(&p, &ucred, SD_BUS_MESSAGE_METHOD_CALL, "org.foo.FooService2", "/an/object/path", "org.foo.FooBroadcastInterface", "Member") == false);
-
-        ucred.uid = 100;
-        assert_se(policy_check_own(&p, &ucred, "org.foo.FooService") == false);
-        assert_se(policy_check_own(&p, &ucred, "org.foo.FooService2") == false);
-        assert_se(policy_check_send(&p, &ucred, SD_BUS_MESSAGE_METHOD_CALL, "org.test.test1", "/an/object/path", "org.test.int2", "Member") == false);
-        assert_se(policy_check_send(&p, &ucred, SD_BUS_MESSAGE_METHOD_CALL, "org.test.test1", "/an/object/path", "org.foo.FooBroadcastInterface", "Member") == false);
-        assert_se(policy_check_recv(&p, &ucred, SD_BUS_MESSAGE_METHOD_CALL, "org.foo.FooService", "/an/object/path", "org.foo.FooBroadcastInterface", "Member") == true);
-        assert_se(policy_check_recv(&p, &ucred, SD_BUS_MESSAGE_METHOD_CALL, "org.foo.FooService", "/an/object/path", "org.foo.FooBroadcastInterface2", "Member") == false);
-        assert_se(policy_check_recv(&p, &ucred, SD_BUS_MESSAGE_METHOD_CALL, "org.foo.FooService2", "/an/object/path", "org.foo.FooBroadcastInterface", "Member") == false);
+        assert_se(policy_check_own(&p, 0, 0, "org.foo.FooService") == true);
+        assert_se(policy_check_own(&p, 0, 0, "org.foo.FooService2") == false);
+        assert_se(policy_check_send(&p, 0, 0, SD_BUS_MESSAGE_METHOD_CALL, "org.test.test1", "/an/object/path", "org.test.int2", "Member") == false);
+        assert_se(policy_check_send(&p, 0, 0, SD_BUS_MESSAGE_METHOD_CALL, "org.test.test1", "/an/object/path", "org.foo.FooBroadcastInterface", "Member") == true);
+        assert_se(policy_check_recv(&p, 0, 0, SD_BUS_MESSAGE_METHOD_CALL, "org.foo.FooService", "/an/object/path", "org.foo.FooBroadcastInterface", "Member") == true);
+        assert_se(policy_check_recv(&p, 0, 0, SD_BUS_MESSAGE_METHOD_CALL, "org.foo.FooService", "/an/object/path", "org.foo.FooBroadcastInterface2", "Member") == false);
+        assert_se(policy_check_recv(&p, 0, 0, SD_BUS_MESSAGE_METHOD_CALL, "org.foo.FooService2", "/an/object/path", "org.foo.FooBroadcastInterface", "Member") == false);
+
+        assert_se(policy_check_own(&p, 100, 0, "org.foo.FooService") == false);
+        assert_se(policy_check_own(&p, 100, 0, "org.foo.FooService2") == false);
+        assert_se(policy_check_send(&p, 100, 0, SD_BUS_MESSAGE_METHOD_CALL, "org.test.test1", "/an/object/path", "org.test.int2", "Member") == false);
+        assert_se(policy_check_send(&p, 100, 0, SD_BUS_MESSAGE_METHOD_CALL, "org.test.test1", "/an/object/path", "org.foo.FooBroadcastInterface", "Member") == false);
+        assert_se(policy_check_recv(&p, 100, 0, SD_BUS_MESSAGE_METHOD_CALL, "org.foo.FooService", "/an/object/path", "org.foo.FooBroadcastInterface", "Member") == true);
+        assert_se(policy_check_recv(&p, 100, 0, SD_BUS_MESSAGE_METHOD_CALL, "org.foo.FooService", "/an/object/path", "org.foo.FooBroadcastInterface2", "Member") == false);
+        assert_se(policy_check_recv(&p, 100, 0, SD_BUS_MESSAGE_METHOD_CALL, "org.foo.FooService2", "/an/object/path", "org.foo.FooBroadcastInterface", "Member") == false);
 
         policy_free(&p);