bus-proxy: extract proxy into Proxy object

Move all the proxy code into a "struct Proxy" object that can be used
from multiple binaries.

We now dropped SMACK as we have to refactor it to work properly. We can
introduce it later on.

1 files changed, 859 insertions, 0 deletions

diff --git a/src/bus-proxyd/proxy.c b/src/bus-proxyd/proxy.c
new file mode 100644
index 0000000000..744b11da5c
--- /dev/null
+++ b/src/bus-proxyd/proxy.c
@@ -0,0 +1,859 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+/***
+  This file is part of systemd.
+
+  Copyright 2010 Lennart Poettering
+  Copyright 2013 Daniel Mack
+  Copyright 2014 Kay Sievers
+  Copyright 2014 David Herrmann
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd 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
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <sys/types.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <string.h>
+#include <errno.h>
+#include <sys/poll.h>
+#include <stddef.h>
+#include <getopt.h>
+
+#include "log.h"
+#include "util.h"
+#include "socket-util.h"
+#include "sd-daemon.h"
+#include "sd-bus.h"
+#include "bus-internal.h"
+#include "bus-message.h"
+#include "bus-util.h"
+#include "build.h"
+#include "strv.h"
+#include "def.h"
+#include "capability.h"
+#include "bus-control.h"
+#include "smack-util.h"
+#include "set.h"
+#include "bus-xml-policy.h"
+#include "driver.h"
+#include "proxy.h"
+#include "synthesize.h"
+
+static int proxy_create_dest(Proxy *p, const char *dest, const char *local_sec, bool negotiate_fds) {
+        _cleanup_bus_close_unref_ sd_bus *b = NULL;
+        int r;
+
+        r = sd_bus_new(&b);
+        if (r < 0)
+                return log_error_errno(r, "Failed to allocate bus: %m");
+
+        r = sd_bus_set_description(b, "sd-proxy");
+        if (r < 0)
+                return log_error_errno(r, "Failed to set bus name: %m");
+
+        r = sd_bus_set_address(b, dest);
+        if (r < 0)
+                return log_error_errno(r, "Failed to set address to connect to: %m");
+
+        r = sd_bus_negotiate_fds(b, negotiate_fds);
+        if (r < 0)
+                return log_error_errno(r, "Failed to set FD negotiation: %m");
+
+        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)
+                return log_error_errno(r, "Failed to set credential negotiation: %m");
+
+        if (p->local_creds.pid > 0) {
+                b->fake_pids.pid = p->local_creds.pid;
+                b->fake_pids_valid = true;
+
+                b->fake_creds.uid = p->local_creds.uid;
+                b->fake_creds.euid = UID_INVALID;
+                b->fake_creds.suid = UID_INVALID;
+                b->fake_creds.fsuid = UID_INVALID;
+                b->fake_creds.gid = p->local_creds.gid;
+                b->fake_creds.egid = GID_INVALID;
+                b->fake_creds.sgid = GID_INVALID;
+                b->fake_creds.fsgid = GID_INVALID;
+                b->fake_creds_valid = true;
+        }
+
+        if (local_sec) {
+                b->fake_label = strdup(local_sec);
+                if (!b->fake_label)
+                        return log_oom();
+        }
+
+        b->manual_peer_interface = true;
+
+        r = sd_bus_start(b);
+        if (r < 0)
+                return log_error_errno(r, "Failed to start bus client: %m");
+
+        p->dest_bus = b;
+        b = NULL;
+        return 0;
+}
+
+static int proxy_create_local(Proxy *p, int in_fd, int out_fd, bool negotiate_fds) {
+        _cleanup_bus_close_unref_ sd_bus *b = NULL;
+        sd_id128_t server_id;
+        int r;
+
+        r = sd_bus_new(&b);
+        if (r < 0)
+                return log_error_errno(r, "Failed to allocate bus: %m");
+
+        r = sd_bus_set_fd(b, in_fd, out_fd);
+        if (r < 0)
+                return log_error_errno(r, "Failed to set fds: %m");
+
+        r = sd_bus_get_bus_id(p->dest_bus, &server_id);
+        if (r < 0)
+                return log_error_errno(r, "Failed to get server ID: %m");
+
+        r = sd_bus_set_server(b, 1, server_id);
+        if (r < 0)
+                return log_error_errno(r, "Failed to set server mode: %m");
+
+        r = sd_bus_negotiate_fds(b, negotiate_fds);
+        if (r < 0)
+                return log_error_errno(r, "Failed to set FD negotiation: %m");
+
+        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)
+                return log_error_errno(r, "Failed to set credential negotiation: %m");
+
+        r = sd_bus_set_anonymous(b, true);
+        if (r < 0)
+                return log_error_errno(r, "Failed to set anonymous authentication: %m");
+
+        b->manual_peer_interface = true;
+
+        r = sd_bus_start(b);
+        if (r < 0)
+                return log_error_errno(r, "Failed to start bus client: %m");
+
+        p->local_bus = b;
+        b = NULL;
+        return 0;
+}
+
+static int proxy_prepare_matches(Proxy *p) {
+        _cleanup_free_ char *match = NULL;
+        const char *unique;
+        int r;
+
+        if (!p->dest_bus->is_kernel)
+                return 0;
+
+        r = sd_bus_get_unique_name(p->dest_bus, &unique);
+        if (r < 0)
+                return log_error_errno(r, "Failed to get unique name: %m");
+
+        match = strjoin("type='signal',"
+                        "sender='org.freedesktop.DBus',"
+                        "path='/org/freedesktop/DBus',"
+                        "interface='org.freedesktop.DBus',"
+                        "member='NameOwnerChanged',"
+                        "arg1='",
+                        unique,
+                        "'",
+                        NULL);
+        if (!match)
+                return log_oom();
+
+        r = sd_bus_add_match(p->dest_bus, NULL, match, NULL, NULL);
+        if (r < 0)
+                return log_error_errno(r, "Failed to add match for NameLost: %m");
+
+        free(match);
+        match = strjoin("type='signal',"
+                        "sender='org.freedesktop.DBus',"
+                        "path='/org/freedesktop/DBus',"
+                        "interface='org.freedesktop.DBus',"
+                        "member='NameOwnerChanged',"
+                        "arg2='",
+                        unique,
+                        "'",
+                        NULL);
+        if (!match)
+                return log_oom();
+
+        r = sd_bus_add_match(p->dest_bus, NULL, match, NULL, NULL);
+        if (r < 0)
+                return log_error_errno(r, "Failed to add match for NameAcquired: %m");
+
+        return 0;
+}
+
+int proxy_new(Proxy **out, int in_fd, int out_fd, const char *dest) {
+        _cleanup_(proxy_freep) Proxy *p = NULL;
+        _cleanup_free_ char *local_sec = NULL;
+        bool is_unix;
+        int r;
+
+        p = new0(Proxy, 1);
+        if (!p)
+                return log_oom();
+
+        p->local_in = in_fd;
+        p->local_out = out_fd;
+
+        p->owned_names = set_new(&string_hash_ops);
+        if (!p->owned_names)
+                return log_oom();
+
+        is_unix = sd_is_socket(in_fd, AF_UNIX, 0, 0) > 0 &&
+                  sd_is_socket(out_fd, AF_UNIX, 0, 0) > 0;
+
+        if (is_unix) {
+                (void) getpeercred(in_fd, &p->local_creds);
+                (void) getpeersec(in_fd, &local_sec);
+        }
+
+        r = proxy_create_dest(p, dest, local_sec, is_unix);
+        if (r < 0)
+                return r;
+
+        r = proxy_create_local(p, in_fd, out_fd, is_unix);
+        if (r < 0)
+                return r;
+
+        r = proxy_prepare_matches(p);
+        if (r < 0)
+                return r;
+
+        *out = p;
+        p = NULL;
+        return 0;
+}
+
+Proxy *proxy_free(Proxy *p) {
+        if (!p)
+                return NULL;
+
+        sd_bus_close_unrefp(&p->local_bus);
+        sd_bus_close_unrefp(&p->dest_bus);
+        set_free_free(p->owned_names);
+        free(p);
+
+        return NULL;
+}
+
+int proxy_load_policy(Proxy *p, char **configuration) {
+        _cleanup_strv_free_ char **strv = NULL;
+        int r;
+
+        assert(p);
+
+        /* no need to load legacy policy if destination is not kdbus */
+        if (!p->dest_bus->is_kernel)
+                return 0;
+
+        if (!configuration) {
+                const char *scope;
+
+                r = sd_bus_get_scope(p->dest_bus, &scope);
+                if (r < 0)
+                        return log_error_errno(r, "Couldn't determine bus scope: %m");
+
+                if (streq(scope, "system"))
+                        strv = strv_new("/etc/dbus-1/system.conf",
+                                        "/etc/dbus-1/system.d/",
+                                        "/etc/dbus-1/system-local.conf",
+                                        NULL);
+                else if (streq(scope, "user"))
+                        strv = strv_new("/etc/dbus-1/session.conf",
+                                        "/etc/dbus-1/session.d/",
+                                        "/etc/dbus-1/session-local.conf",
+                                        NULL);
+                else
+                        return log_error("Unknown scope %s, don't know which policy to load. Refusing.", scope);
+
+                if (!strv)
+                        return log_oom();
+
+                configuration = strv;
+        }
+
+        r = policy_load(&p->policy_buffer, configuration);
+        if (r < 0)
+                return log_error_errno(r, "Failed to load policy: %m");
+
+        p->policy = &p->policy_buffer;
+        /* policy_dump(p->policy); */
+
+        return 0;
+}
+
+int proxy_hello_policy(Proxy *p, uid_t original_uid) {
+        assert(p);
+
+        if (!p->policy)
+                return 0;
+
+        if (p->local_creds.uid == original_uid)
+                log_debug("Permitting access, since bus owner matches bus client.");
+        else if (policy_check_hello(p->policy, p->local_creds.uid, p->local_creds.gid))
+                log_debug("Permitting access due to XML policy.");
+        else
+                return log_error_errno(EPERM, "Policy denied connection.");
+
+        return 0;
+}
+
+static int proxy_wait(Proxy *p) {
+        uint64_t timeout_dest, timeout_local, t;
+        int events_dest, events_local, fd;
+        struct timespec _ts, *ts;
+        struct pollfd *pollfd;
+        int r;
+
+        assert(p);
+
+        fd = sd_bus_get_fd(p->dest_bus);
+        if (fd < 0)
+                return log_error_errno(fd, "Failed to get fd: %m");
+
+        events_dest = sd_bus_get_events(p->dest_bus);
+        if (events_dest < 0)
+                return log_error_errno(events_dest, "Failed to get events mask: %m");
+
+        r = sd_bus_get_timeout(p->dest_bus, &timeout_dest);
+        if (r < 0)
+                return log_error_errno(r, "Failed to get timeout: %m");
+
+        events_local = sd_bus_get_events(p->local_bus);
+        if (events_local < 0)
+                return log_error_errno(events_local, "Failed to get events mask: %m");
+
+        r = sd_bus_get_timeout(p->local_bus, &timeout_local);
+        if (r < 0)
+                return log_error_errno(r, "Failed to get timeout: %m");
+
+        t = timeout_dest;
+        if (t == (uint64_t) -1 || (timeout_local != (uint64_t) -1 && timeout_local < timeout_dest))
+                t = timeout_local;
+
+        if (t == (uint64_t) -1)
+                ts = NULL;
+        else {
+                usec_t nw;
+
+                nw = now(CLOCK_MONOTONIC);
+                if (t > nw)
+                        t -= nw;
+                else
+                        t = 0;
+
+                ts = timespec_store(&_ts, t);
+        }
+
+        pollfd = (struct pollfd[3]) {
+                { .fd = fd,           .events = events_dest,            },
+                { .fd = p->local_in,  .events = events_local & POLLIN,  },
+                { .fd = p->local_out, .events = events_local & POLLOUT, },
+        };
+
+        r = ppoll(pollfd, 3, ts, NULL);
+        if (r < 0)
+                return log_error_errno(errno, "ppoll() failed: %m");
+
+        return 0;
+}
+
+static int handle_policy_error(sd_bus_message *m, int r) {
+        if (r == -ESRCH || r == -ENXIO)
+                return synthetic_reply_method_errorf(m, SD_BUS_ERROR_NAME_HAS_NO_OWNER, "Name %s is currently not owned by anyone.", m->destination);
+
+        return r;
+}
+
+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;
+
+        /*
+         * dbus-1 distinguishes expected and non-expected replies by tracking
+         * method-calls and timeouts. By default, DENY rules are *NEVER* applied
+         * on expected replies, unless explicitly specified. But we dont track
+         * method-calls, thus, we cannot know whether a reply is expected.
+         * Fortunately, the kdbus forbids non-expected replies, so we can safely
+         * ignore any policy on those and let the kernel deal with it.
+         *
+         * TODO: To be correct, we should only ignore policy-tags that are
+         * applied on non-expected replies. However, so far we don't parse those
+         * tags so we let everything pass. I haven't seen a DENY policy tag on
+         * expected-replies, ever, so don't bother..
+         */
+        if (m->reply_cookie > 0)
+                return 0;
+
+        if (from->is_kernel) {
+                uid_t sender_uid = UID_INVALID;
+                gid_t sender_gid = GID_INVALID;
+                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. */
+                sd_bus_creds_get_well_known_names(&m->creds, &sender_names);
+
+                (void) sd_bus_creds_get_uid(&m->creds, &sender_uid);
+                (void) sd_bus_creds_get_gid(&m->creds, &sender_gid);
+
+                if (sender_uid == UID_INVALID || sender_gid == GID_INVALID) {
+                        _cleanup_bus_creds_unref_ sd_bus_creds *sender_creds = NULL;
+
+                        /* If the message came from another legacy
+                         * client, then the message creds will be
+                         * missing, simply because on legacy clients
+                         * per-message creds were unknown. In this
+                         * case, query the creds of the peer
+                         * instead. */
+
+                        r = bus_get_name_creds_kdbus(from, m->sender, SD_BUS_CREDS_UID|SD_BUS_CREDS_GID, true, &sender_creds);
+                        if (r < 0)
+                                return handle_policy_error(m, r);
+
+                        (void) sd_bus_creds_get_uid(sender_creds, &sender_uid);
+                        (void) sd_bus_creds_get_gid(sender_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, false))
+                                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, false)) {
+                                        granted = true;
+                                        break;
+                                }
+                }
+
+                if (granted) {
+                        /* Then check whether us (the recipient) can receive 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, false))
+                                        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, false))
+                                                return 0;
+                                }
+                        }
+                }
+
+                /* Return an error back to the caller */
+                if (m->header->type == SD_BUS_MESSAGE_METHOD_CALL)
+                        return synthetic_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_INVALID;
+                gid_t destination_gid = GID_INVALID;
+                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 = bus_get_name_creds_kdbus(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,
+                                                     true, &destination_creds);
+                        if (r < 0)
+                                return handle_policy_error(m, r);
+
+                        r = sd_bus_creds_get_unique_name(destination_creds, &destination_unique);
+                        if (r < 0)
+                                return handle_policy_error(m, r);
+
+                        sd_bus_creds_get_well_known_names(destination_creds, &destination_names);
+
+                        (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, true))
+                                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, true)) {
+
+                                        /* 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 (sd_bus_message_is_signal(m, NULL, NULL)) {
+                                /* If we forward a signal from dbus-1 to kdbus,
+                                 * we have no idea who the recipient is.
+                                 * Therefore, we cannot apply any dbus-1
+                                 * receiver policies that match on receiver
+                                 * credentials. We know sd-bus always sets
+                                 * KDBUS_MSG_SIGNAL, so the kernel applies
+                                 * receiver policies to the message. Therefore,
+                                 * skip policy checks in this case. */
+                                return 0;
+                        } else if (set_isempty(owned_names)) {
+                                if (policy_check_recv(policy, destination_uid, destination_gid, m->header->type, NULL, m->path, m->interface, m->member, true))
+                                        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, true))
+                                                return 0;
+                        }
+                }
+
+                /* Return an error back to the caller */
+                if (m->header->type == SD_BUS_MESSAGE_METHOD_CALL)
+                        return synthetic_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(Proxy *p, sd_bus_message *m) {
+        _cleanup_bus_message_unref_ sd_bus_message *n = NULL;
+        bool is_hello;
+        int r;
+
+        assert(p);
+        assert(m);
+
+        /* As reaction to hello we need to respond with two messages:
+         * the callback reply and the NameAcquired for the unique
+         * name, since hello is otherwise obsolete on kdbus. */
+
+        is_hello =
+                sd_bus_message_is_method_call(m, "org.freedesktop.DBus", "Hello") &&
+                streq_ptr(m->destination, "org.freedesktop.DBus");
+
+        if (!is_hello) {
+                if (p->got_hello)
+                        return 0;
+
+                return log_error_errno(-EIO, "First packet isn't hello (it's %s.%s), aborting.", m->interface, m->member);
+        }
+
+        if (p->got_hello)
+                return log_error_errno(-EIO, "Got duplicate hello, aborting.");
+
+        p->got_hello = true;
+
+        if (!p->dest_bus->is_kernel)
+                return 0;
+
+        r = sd_bus_message_new_method_return(m, &n);
+        if (r < 0)
+                return log_error_errno(r, "Failed to generate HELLO reply: %m");
+
+        r = sd_bus_message_append(n, "s", p->dest_bus->unique_name);
+        if (r < 0)
+                return log_error_errno(r, "Failed to append unique name to HELLO reply: %m");
+
+        r = bus_message_append_sender(n, "org.freedesktop.DBus");
+        if (r < 0)
+                return log_error_errno(r, "Failed to append sender to HELLO reply: %m");
+
+        r = bus_seal_synthetic_message(p->local_bus, n);
+        if (r < 0)
+                return log_error_errno(r, "Failed to seal HELLO reply: %m");
+
+        r = sd_bus_send(p->local_bus, n, NULL);
+        if (r < 0)
+                return log_error_errno(r, "Failed to send HELLO reply: %m");
+
+        n = sd_bus_message_unref(n);
+        r = sd_bus_message_new_signal(
+                        p->local_bus,
+                        &n,
+                        "/org/freedesktop/DBus",
+                        "org.freedesktop.DBus",
+                        "NameAcquired");
+        if (r < 0)
+                return log_error_errno(r, "Failed to allocate initial NameAcquired message: %m");
+
+        r = sd_bus_message_append(n, "s", p->dest_bus->unique_name);
+        if (r < 0)
+                return log_error_errno(r, "Failed to append unique name to NameAcquired message: %m");
+
+        r = bus_message_append_sender(n, "org.freedesktop.DBus");
+        if (r < 0)
+                return log_error_errno(r, "Failed to append sender to NameAcquired message: %m");
+
+        r = bus_seal_synthetic_message(p->local_bus, n);
+        if (r < 0)
+                return log_error_errno(r, "Failed to seal NameAcquired message: %m");
+
+        r = sd_bus_send(p->local_bus, n, NULL);
+        if (r < 0)
+                return log_error_errno(r, "Failed to send NameAcquired message: %m");
+
+        return 1;
+}
+
+static int patch_sender(sd_bus *a, sd_bus_message *m) {
+        char **well_known = NULL;
+        sd_bus_creds *c;
+        int r;
+
+        assert(a);
+        assert(m);
+
+        if (!a->is_kernel)
+                return 0;
+
+        /* We will change the sender of messages from the bus driver
+         * so that they originate from the bus driver. This is a
+         * speciality originating from dbus1, where the bus driver did
+         * not have a unique id, but only the well-known name. */
+
+        c = sd_bus_message_get_creds(m);
+        if (!c)
+                return 0;
+
+        r = sd_bus_creds_get_well_known_names(c, &well_known);
+        if (r < 0)
+                return r;
+
+        if (strv_contains(well_known, "org.freedesktop.DBus"))
+                m->sender = "org.freedesktop.DBus";
+
+        return 0;
+}
+
+static int proxy_process_dest_to_local(Proxy *p) {
+        _cleanup_bus_message_unref_ sd_bus_message *m = NULL;
+        int r;
+
+        assert(p);
+
+        r = sd_bus_process(p->dest_bus, &m);
+        if (r < 0) {
+                /* treat 'connection reset by peer' as clean exit condition */
+                if (r != -ECONNRESET)
+                        log_error_errno(r, "Failed to process destination bus: %m");
+                return r;
+        }
+
+        if (r == 0)
+                return 0;
+        if (!m)
+                return 1;
+
+        /* We officially got EOF, let's quit */
+        if (sd_bus_message_is_signal(m, "org.freedesktop.DBus.Local", "Disconnected"))
+                return -ECONNRESET;
+
+        r = synthesize_name_acquired(p->dest_bus, p->local_bus, m);
+        if (r < 0)
+                return log_error_errno(r, "Failed to synthesize message: %m");
+
+        patch_sender(p->dest_bus, m);
+
+        if (p->policy) {
+                r = process_policy(p->dest_bus, p->local_bus, m, p->policy, &p->local_creds, p->owned_names);
+                if (r < 0)
+                        return log_error_errno(r, "Failed to process policy: %m");
+                else if (r > 0)
+                        return 1;
+        }
+
+        r = sd_bus_send(p->local_bus, m, NULL);
+        if (r < 0) {
+                if (r == -EPERM && m->reply_cookie > 0) {
+                        /* If the peer tries to send a reply and it is rejected with EPERM
+                         * by the kernel, we ignore the error. This catches cases where the
+                         * original method-call didn't had EXPECT_REPLY set, but the proxy-peer
+                         * still sends a reply. This is allowed in dbus1, but not in kdbus. We
+                         * don't want to track reply-windows in the proxy, so we simply ignore
+                         * EPERM for all replies. The only downside is, that callers are no
+                         * longer notified if their replies are dropped. However, this is
+                         * equivalent to the caller's timeout to expire, so this should be
+                         * acceptable. Nobody sane sends replies without a matching method-call,
+                         * so nobody should care. */
+                        return 1;
+                } else {
+                        if (r != -ECONNRESET)
+                                log_error_errno(r, "Failed to send message to client: %m");
+                        return r;
+                }
+        }
+
+        return 1;
+}
+
+static int proxy_process_local_to_dest(Proxy *p) {
+        _cleanup_bus_message_unref_ sd_bus_message *m = NULL;
+        int r;
+
+        assert(p);
+
+        r = sd_bus_process(p->local_bus, &m);
+        if (r < 0) {
+                /* treat 'connection reset by peer' as clean exit condition */
+                if (r != -ECONNRESET)
+                        log_error_errno(r, "Failed to process local bus: %m");
+                return r;
+        }
+
+        if (r == 0)
+                return 0;
+        if (!m)
+                return 1;
+
+        /* We officially got EOF, let's quit */
+        if (sd_bus_message_is_signal(m, "org.freedesktop.DBus.Local", "Disconnected"))
+                return -ECONNRESET;
+
+        r = process_hello(p, m);
+        if (r < 0)
+                return log_error_errno(r, "Failed to process HELLO: %m");
+        else if (r > 0)
+                return 1;
+
+        r = bus_proxy_process_driver(p->dest_bus, p->local_bus, m, p->policy, &p->local_creds, p->owned_names);
+        if (r < 0)
+                return log_error_errno(r, "Failed to process driver calls: %m");
+        else if (r > 0)
+                return 1;
+
+        for (;;) {
+                if (p->policy) {
+                        r = process_policy(p->local_bus, p->dest_bus, m, p->policy, &p->local_creds, p->owned_names);
+                        if (r < 0)
+                                return log_error_errno(r, "Failed to process policy: %m");
+                        else if (r > 0)
+                                return 1;
+                }
+
+                r = sd_bus_send(p->dest_bus, m, NULL);
+                if (r < 0) {
+                        if (r == -EREMCHG) {
+                                /* The name database changed since the policy check, hence let's check again */
+                                continue;
+                        } else if (r == -EPERM && m->reply_cookie > 0) {
+                                /* see above why EPERM is ignored for replies */
+                                return 1;
+                        } else {
+                                if (r != -ECONNRESET)
+                                        log_error_errno(r, "Failed to send message to bus: %m");
+                                return r;
+                        }
+                }
+
+                break;
+        }
+
+        return 1;
+}
+
+int proxy_run(Proxy *p) {
+        int r;
+
+        assert(p);
+
+        for (;;) {
+                bool busy = false;
+
+                if (p->got_hello) {
+                        /* Read messages from bus, to pass them on to our client */
+                        r = proxy_process_dest_to_local(p);
+                        if (r == -ECONNRESET)
+                                return 0;
+                        else if (r < 0)
+                                return r;
+                        else if (r > 0)
+                                busy = true;
+                }
+
+                /* Read messages from our client, to pass them on to the bus */
+                r = proxy_process_local_to_dest(p);
+                if (r == -ECONNRESET)
+                        return 0;
+                else if (r < 0)
+                        return r;
+                else if (r > 0)
+                        busy = true;
+
+                if (!busy) {
+                        r = proxy_wait(p);
+                        if (r < 0)
+                                return r;
+                }
+        }
+
+        return 0;
+}