path: root/m4
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authorAlban Crequy <>2014-05-20 14:37:37 +0100
committerSimon McVittie <>2014-06-05 14:41:59 +0100
commit4815aba0d3695afe871e9002ba474ce36c5299b4 (patch)
tree26206eea7257ffb89848c52239345570b2f98a09 /m4
parent98a18eb9516aa1f8829fd66cd67aef0e3a7c3c52 (diff)
CVE-2014-3477: deliver activation errors correctly, fixing Denial of Servicedbus-1.4
How it should work: When a D-Bus message activates a service, LSMs (SELinux or AppArmor) check whether the message can be delivered after the service has been activated. The service is considered activated when its well-known name is requested with org.freedesktop.DBus.RequestName. When the message delivery is denied, the service stays activated but should not receive the activating message (the message which triggered the activation). dbus-daemon is supposed to drop the activating message and reply to the sender with a D-Bus error message. However, it does not work as expected: 1. The error message is delivered to the service instead of being delivered to the sender. As an example, the error message could be something like: An SELinux policy prevents this sender from sending this message to this recipient, [...] member="MaliciousMethod" If the sender and the service are malicious confederates and agree on a protocol to insert information in the member name, the sender can leak information to the service, even though the LSM attempted to block the communication between the sender and the service. 2. The error message is delivered as a reply to the RequestName call from service. It means the activated service will believe it cannot request the name and might exit. The sender could activate the service frequently and systemd will give up activating it. Thus the denial of service. The following changes fix the bug: - bus_activation_send_pending_auto_activation_messages() only returns an error in case of OOM. The prototype is changed to return TRUE, or FALSE on OOM (and its only caller sets the OOM error). - When a client is not allowed to talk to the service, a D-Bus error message is pre-allocated to be delivered to the client as part of the transaction. The error is not propagated to the caller so RequestName will not fail (except on OOM). [fixed a misleading comment -smcv] Bug: Reviewed-by: Simon McVittie <> Reviewed-by: Colin Walters <>
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