CVE-2010-2526: Medium severity lvm2 vulnerability

During some routine code review last week, Alasdair Kergon spotted a security flaw in the clustered LVM daemon, clvmd. The report from him is as follows:

Clvmd, a privileged process, accepts, acts upon and responds to communications from unprivileged processes.

Background information ======================

clvmd belongs to the lvm2-cluster package and as such is normally used in shared storage clusters, where several machines are using the same disks in parallel. It is run on every machine in such a cluster. The daemon has to be enabled explictly after installing the package: it does not run by default (since RHEL4.5). Systems not running the daemon i.e. most LVM systems, not subscribed to RHN clustering channels, are not vulnerable.

Clvmd has three roles that require root privilege:

(1) Communicate with clvmd processes on other machines;

(2) Hold locks to ensure conflicting commands are not run in parallel;

(3) Make Logical Volumes available for use on the local machine by issuing the appropriate device-mapper ioctls to the kernel.

When a LVM command is issued in a cluster, an instruction is sent to the local clvmd to obtain the necessary locks and to activate or deactivate logical volumes. Any changes to the on-disk LVM metadata are performed by the original LVM process - not by clvmd itself - and then the instance of clvmd on each machine reads the updated metadata independently from disk.

The flaw ========

The problem was caused by an upstream commit made in April 2004. Prior to that, the communication between lvm and clvmd was through a socket in the filesystem, so it was protected by standard file-system security mechanisms. The commit in question changed it to use an abstract socket starting with a NUL byte (see 'man 7 unix') but no attempt was made to secure it by exchanging credentials. Consequently an unprivileged process can instruct clvmd to perform operations that were supposed to be available only to root.

Operations available to an attacker:

(1) Instruct clvmd to suspend the use of any Logical Volume visible to any machine in the cluster with immediate effect.

(2) Instruct clvmd to activate, deactivate or reload any Logical Volume visible to any machine in the cluster. (Deactivation will fail if the Logical Volume is in use.)

(3) Instruct clvmd to die.

(4) Instruct clvmd to restart (versions 2.02.64 and later).

(5) Instruct clvmd to obtain, release or report the state of locks held by the daemon.

(6) Enable/disable clvmd's debugging mode which controls the amount of detail it logs.

(7) Instruct clvmd to create a backup of a Volume Group's metadata on all the other nodes.

(8) Instruct clvmd to report the cluster name.

(9) Instruct clvmd to echo back the command it received.

(10) Instruct clvmd to refresh its internal caches.

Several of these involve performing privileged operations and could impact upon service availability on machines belonging to the cluster.

The fix ======= We are reverting to using a pathname for the socket and relying upon standard filesystem security.