When Linux's netback sees a malformed packet, it tries to disable the interface which serves the misbehaving frontend.
This involves taking a mutex, which might sleep. But in recent versions of Linux the guest transmit path is handled by NAPI in softirq context, where sleeping is not allowed. The end result is that the backend domain (often, Dom0) crashes with "scheduling while atomic".
Malicious guest administrators can cause denial of service. If driver domains are not in use, the impact is a host crash.
Red Hat would like to thank the Xen project for reporting this issue. Upstream acknowledges Török Edwin for discovering this bug.
This issue does not affect the versions of the kernel-xen package as shipped with Red Hat Enterprise Linux 5.
This issue does not affect versions of Linux kernel packages as shipped with Red Hat Enterprise Linux 6 and Red Hat Enterprise MRG 2 as they do not have support for Xen hypervisor.
Created kernel tracking bugs for this issue:
Affects: fedora-all [bug 1080086]
MITRE assigned CVE-2014-2580 to this issue:
Xen Security Advisory CVE-2014-2580 / XSA-90 version 2: