The PCI backend driver in Xen, when running on an x86 system and using Linux 3.1.x through 4.3.x as the driver domain, allows local guest administrators to generate a continuous stream of WARN messages and cause a denial of service (disk consumption) by leveraging a system with access to a passed-through MSI or MSI-X capable physical PCI device and XEN_PCI_OP_enable_msi operations, aka "Linux pciback missing sanity checks."

Affected: Ubuntu:14.04:LTS: linux

Felix Wilhelm discovered a race condition in the Xen paravirtualized drivers which can cause double fetch vulnerabilities. An attacker in the paravirtualized guest could exploit this flaw to cause a denial of service (crash the host) or potentially execute arbitrary code on the host. (CVE-2015-8550)

Konrad Rzeszutek Wilk discovered the Xen PCI backend driver does not perform consistency checks on the device's state. An attacker could exploit this flaw to cause a denial of service (NULL dereference) on the host. (CVE-2015-8551)

Konrad Rzeszutek Wilk discovered the Xen PCI backend driver does not perform consistency checks on the device's state. An attacker could exploit this flaw to cause a denial of service by flooding the logging system with WARN() messages causing the initial domain to exhaust disk space. (CVE-2015-8552)

Jann Horn discovered a ptrace issue with user namespaces in the Linux kernel. The namespace owner could potentially exploit this flaw by ptracing a root owned process entering the user namespace to elevate its privileges and potentially gain access outside of the namespace. (http://bugs.launchpad.net/bugs/1527374, CVE-2015-8709)