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From 8efdae75ddf035c8c04983820f8d8cf767cc17b1 Mon Sep 17 00:00:00 2001
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From: Jan Synacek <jsynacek@redhat.com>
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Date: Fri, 31 Jan 2020 11:34:45 +0100
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Subject: [PATCH] sd-bus: introduce API for re-enqueuing incoming messages
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When authorizing via PolicyKit we want to process incoming method calls
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twice: once to process and figure out that we need PK authentication,
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and a second time after we aquired PK authentication to actually execute
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the operation. With this new call sd_bus_enqueue_for_read() we have a
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way to put an incoming message back into the read queue for this
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purpose.
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This might have other uses too, for example debugging.
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Related: CVE-2020-1712
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---
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 src/libsystemd/libsystemd.sym  |  1 +
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 src/libsystemd/sd-bus/sd-bus.c | 24 ++++++++++++++++++++++++
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 src/systemd/sd-bus.h           |  1 +
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 3 files changed, 26 insertions(+)
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diff --git a/src/libsystemd/libsystemd.sym b/src/libsystemd/libsystemd.sym
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index 1eec17db50..e9972593a6 100644
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--- a/src/libsystemd/libsystemd.sym
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+++ b/src/libsystemd/libsystemd.sym
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@@ -569,4 +569,5 @@ global:
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         sd_event_source_get_inotify_mask;
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         sd_event_source_set_destroy_callback;
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         sd_event_source_get_destroy_callback;
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+        sd_bus_enqueue_for_read;
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 } LIBSYSTEMD_238;
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diff --git a/src/libsystemd/sd-bus/sd-bus.c b/src/libsystemd/sd-bus/sd-bus.c
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index e49d58137d..68ad6cbe89 100644
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--- a/src/libsystemd/sd-bus/sd-bus.c
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+++ b/src/libsystemd/sd-bus/sd-bus.c
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@@ -4120,3 +4120,27 @@ _public_ int sd_bus_get_n_queued_write(sd_bus *bus, uint64_t *ret) {
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         *ret = bus->wqueue_size;
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         return 0;
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 }
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+
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+_public_ int sd_bus_enqueue_for_read(sd_bus *bus, sd_bus_message *m) {
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+        int r;
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+
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+        assert_return(bus, -EINVAL);
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+        assert_return(bus = bus_resolve(bus), -ENOPKG);
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+        assert_return(m, -EINVAL);
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+        assert_return(m->sealed, -EINVAL);
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+        assert_return(!bus_pid_changed(bus), -ECHILD);
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+
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+        if (!BUS_IS_OPEN(bus->state))
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+                return -ENOTCONN;
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+
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+        /* Re-enqeue a message for reading. This is primarily useful for PolicyKit-style authentication,
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+         * where we want accept a message, then determine we need to interactively authenticate the user, and
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+         * when we have that process the message again. */
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+
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+        r = bus_rqueue_make_room(bus);
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+        if (r < 0)
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+                return r;
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+
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+        bus->rqueue[bus->rqueue_size++] = bus_message_ref_queued(m, bus);
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+        return 0;
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+}
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diff --git a/src/systemd/sd-bus.h b/src/systemd/sd-bus.h
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index 54c4b1ca83..9ba757b13d 100644
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--- a/src/systemd/sd-bus.h
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+++ b/src/systemd/sd-bus.h
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@@ -193,6 +193,7 @@ int sd_bus_process(sd_bus *bus, sd_bus_message **r);
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 int sd_bus_process_priority(sd_bus *bus, int64_t max_priority, sd_bus_message **r);
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 int sd_bus_wait(sd_bus *bus, uint64_t timeout_usec);
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 int sd_bus_flush(sd_bus *bus);
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+int sd_bus_enqueue_for_read(sd_bus *bus, sd_bus_message *m);
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 sd_bus_slot* sd_bus_get_current_slot(sd_bus *bus);
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 sd_bus_message* sd_bus_get_current_message(sd_bus *bus);