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bus/containers: Require connecting uid to match caller of AddServer

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If we're strict now, we can relax this later (either with a named
parameter or always); but if we're lenient now, we'll be stuck with it
forever, so be strict.

Signed-off-by: Simon McVittie <smcv@collabora.com>
Reviewed-by: Philip Withnall <withnall@endlessm.com>
Bug: https://bugs.freedesktop.org/show_bug.cgi?id=101354
This commit is contained in:
Simon McVittie 2017-06-22 18:02:00 +01:00
parent db6ba2d799
commit 12eed8cd66
1 changed files with 43 additions and 0 deletions
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43
bus/containers.c
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@ -31,6 +31,8 @@
# error DBUS_ENABLE_CONTAINERS requires DBUS_UNIX
#endif
#include <sys/types.h>
#include "dbus/dbus-hash.h"
#include "dbus/dbus-message-internal.h"
#include "dbus/dbus-sysdeps-unix.h"
@ -52,6 +54,7 @@ typedef struct
BusContext *context;
BusContainers *containers;
DBusServer *server;
unsigned long uid;
} BusContainerInstance;
/*
@ -284,6 +287,22 @@ static const char * const auth_mechanisms[] =
NULL
};
/* Statically assert that we can store a uid in a void *, losslessly.
*
* In practice this is always true on Unix. For now we don't support this
* feature on systems where it isn't. */
_DBUS_STATIC_ASSERT (sizeof (uid_t) <= sizeof (uintptr_t));
/* True by definition. */
_DBUS_STATIC_ASSERT (sizeof (void *) == sizeof (uintptr_t));
static dbus_bool_t
allow_same_uid_only (DBusConnection *connection,
unsigned long uid,
void *data)
{
return (uid == (uintptr_t) data);
}
static void
new_connection_cb (DBusServer *server,
DBusConnection *new_connection,
@ -294,6 +313,23 @@ new_connection_cb (DBusServer *server,
/* If this fails it logs a warning, so we don't need to do that */
if (!bus_context_add_incoming_connection (instance->context, new_connection))
return;
/* We'd like to check the uid here, but we can't yet. Instead clear the
* BusContext's unix_user_function, which results in us getting the
* default behaviour: only the user that owns the bus can connect.
*
* TODO: For the system bus we might want a way to opt-in to allowing
* other uids, in which case we would refrain from overwriting the
* BusContext's unix_user_function; but that isn't part of the
* lowest-common-denominator implementation. */
dbus_connection_set_unix_user_function (new_connection,
allow_same_uid_only,
/* The static assertion above
* allow_same_uid_only ensures that
* this cast does not lose
* information */
(void *) (uintptr_t) instance->uid,
NULL);
}
static const char *
@ -432,6 +468,13 @@ bus_containers_handle_add_server (DBusConnection *connection,
if (instance == NULL)
goto fail;
if (!dbus_connection_get_unix_user (connection, &instance->uid))
{
dbus_set_error (error, DBUS_ERROR_FAILED,
"Unable to determine user ID of caller");
goto fail;
}
/* We already checked this in bus_driver_handle_message() */
_dbus_assert (dbus_message_has_signature (message, "ssa{sv}a{sv}"));