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Re: [libvirt] [PATCH] api: require write permission for guest agent interaction



On Tue, Jan 21, 2014 at 10:47:07AM -0700, Eric Blake wrote:
> I noticed that we allow virDomainGetVcpusFlags even for read-only
> connections, but that with a flag, it can require guest agent
> interaction.  It is feasible that a malicious guest could
> intentionally abuse the replies it sends over the guest agent
> connection to possibly trigger a bug in libvirt's JSON parser,
> or withhold an answer so as to prevent the use of the agent
> in a later command such as a shutdown request.  Although we
> don't know of any such exploits now (and therefore don't mind
> posting this patch publicly without trying to get a CVE assigned),
> it is better to err on the side of caution and explicitly require
> full access to any domain where the API requires guest interaction
> to operate correctly.
> 
> I audited all commands that are marked as conditionally using a
> guest agent.  Note that at least virDomainFSTrim is documented
> as needing a guest agent, but that such use is unconditional
> depending on the hypervisor (so the existing domain:fs_trim ACL
> should be sufficient there, rather than also requirng domain:write).
> But when designing future APIs, such as the plans for obtaining
> a domain's IP addresses, we should copy the approach of this patch
> in making interaction with the guest be specified via a flag, and
> use that flag to also require stricter access checks.
> 
> * src/libvirt.c (virDomainGetVcpusFlags): Forbid guest interaction
> on read-only connection.
> (virDomainShutdownFlags, virDomainReboot): Improve docs on agent
> interaction.
> * src/remote/remote_protocol.x
> (REMOTE_PROC_DOMAIN_SNAPSHOT_CREATE_XML)
> (REMOTE_PROC_DOMAIN_SET_VCPUS_FLAGS)
> (REMOTE_PROC_DOMAIN_GET_VCPUS_FLAGS, REMOTE_PROC_DOMAIN_REBOOT)
> (REMOTE_PROC_DOMAIN_SHUTDOWN_FLAGS): Require domain:write for any
> conditional use of a guest agent.
> * src/xen/xen_driver.c: Fix clients.
> * src/libxl/libxl_driver.c: Likewise.
> * src/uml/uml_driver.c: Likewise.
> * src/qemu/qemu_driver.c: Likewise.
> * src/lxc/lxc_driver.c: Likewise.
> 
> Signed-off-by: Eric Blake <eblake redhat com>
> ---
>  src/libvirt.c                | 12 +++++++++---
>  src/libxl/libxl_driver.c     |  6 +++---
>  src/lxc/lxc_driver.c         |  4 ++--
>  src/qemu/qemu_driver.c       |  8 ++++----
>  src/remote/remote_protocol.x |  5 +++++
>  src/uml/uml_driver.c         |  2 +-
>  src/xen/xen_driver.c         |  6 +++---
>  7 files changed, 27 insertions(+), 16 deletions(-)

ACK

Daniel
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