OracleVM 3.1 : xen (OVMSA-2013-0057)
High Nessus Plugin ID 79513
SynopsisThe remote OracleVM host is missing one or more security updates.
DescriptionThe remote OracleVM system is missing necessary patches to address critical security updates :
- x86: fix page refcount handling in page table pin error path In the original patch 7 of the series addressing XSA-45 I mistakenly took the addition of the call to get_page_light in alloc_page_type to cover two decrements that would happen: One for the PGT_partial bit that is getting set along with the call, and the other for the page reference the caller hold (and would be dropping on its error path). But of course the additional page reference is tied to the PGT_partial bit, and hence any caller of a function that may leave
->arch.old_guest_table non-NULL for error cleanup purposes has to make sure a respective page reference gets retained. Similar issues were then also spotted elsewhere: In effect all callers of get_page_type_preemptible need to deal with errors in similar ways. To make sure error handling can work this way without leaking page references, a respective assertion gets added to that function. This is CVE-2013-1432 / XSA-58.
- libxl: Restrict permissions on PV console device xenstore nodes Matthew Daley has observed that the PV console protocol places sensitive host state into a guest writeable xenstore locations, this includes :
- The pty used to communicate between the console backend daemon and its client, allowing the guest administrator to read and write arbitrary host files.
- The output file, allowing the guest administrator to write arbitrary host files or to target arbitrary qemu chardevs which include sockets, udp, ptr, pipes etc (see
-chardev in qemu(1) for a more complete list).
- The maximum buffer size, allowing the guest administrator to consume more resources than the host administrator has configured.
- The backend to use (qemu vs xenconsoled), potentially allowing the guest administrator to confuse host software. So we arrange to make the sensitive keys in the xenstore frontend directory read only for the guest.
This is safe since the xenstore permissions model, unlike POSIX directory permissions, does not allow the guest to remove and recreate a node if it has write access to the containing directory. There are a few associated wrinkles :
- The primary PV console is 'special'. It's xenstore node is not under the usual /devices/ subtree and it does not use the customary xenstore state machine protocol.
Unfortunately its directory is used for other things, including the vnc-port node, which we do not want the guest to be able to write to. Rather than trying to track down all the possible secondary uses of this directory just make it r/o to the guest. All newly created subdirectories inherit these permissions and so are now safe by default.
- The other serial consoles do use the customary xenstore state machine and therefore need write access to at least the 'protocol' and 'state' nodes, however they may also want to use arbitrary 'feature-foo' nodes (although I'm not aware of any) and therefore we cannot simply lock down the entire frontend directory. Instead we add support to libxl__device_generic_add for frontend keys which are explicitly read only and use that to lock down the sensitive keys.
- Minios' console frontend wants to write the 'type' node, which it has no business doing since this is a host/toolstack level decision. This fails now that the node has become read only to the PV guest. Since the toolstack already writes this node just remove the attempt to set it. This is CVE-XXXX-XXX / XSA-57
Conflicts (4.2 backport): tools/libxl/libxl.c (no vtpm, free front_ro on error in libxl__device_console_add) Conflicts (4.1 backport):
extras/mini-os/console/xenbus.c tools/libxl/libxl.c tools/libxl/libxl_device.c tools/libxl/libxl_internal.h tools/libxl/libxl_pci.c tools/libxl/libxl_xshelp.c
- minios code was in xencons_ring.c
- many places need &gc not just gc
- libxl__xs_writev path is not const
- varios minor context fixups
SolutionUpdate the affected xen / xen-devel / xen-tools packages.