Re: [Qemu-devel] [PATCH v7 0/6] file descriptor passing using fd sets

[Stefan Hajnoczi]

On Wed, Aug 8, 2012 at 7:51 PM, Corey Bryant <address@hidden> wrote:
>
>
> On 08/08/2012 11:58 AM, Stefan Hajnoczi wrote:
>>
>> On Wed, Aug 8, 2012 at 3:54 PM, Corey Bryant <address@hidden>
>> wrote:
>>>
>>>
>>>
>>> On 08/08/2012 09:04 AM, Stefan Hajnoczi wrote:
>>>>
>>>>
>>>> On Tue, Aug 7, 2012 at 4:58 PM, Corey Bryant <address@hidden>
>>>> wrote:
>>>>>
>>>>>
>>>>> libvirt's sVirt security driver provides SELinux MAC isolation for
>>>>> Qemu guest processes and their corresponding image files.  In other
>>>>> words, sVirt uses SELinux to prevent a QEMU process from opening
>>>>> files that do not belong to it.
>>>>>
>>>>> sVirt provides this support by labeling guests and resources with
>>>>> security labels that are stored in file system extended attributes.
>>>>> Some file systems, such as NFS, do not support the extended
>>>>> attribute security namespace, and therefore cannot support sVirt
>>>>> isolation.
>>>>>
>>>>> A solution to this problem is to provide fd passing support, where
>>>>> libvirt opens files and passes file descriptors to QEMU.  This,
>>>>> along with SELinux policy to prevent QEMU from opening files, can
>>>>> provide image file isolation for NFS files stored on the same NFS
>>>>> mount.
>>>>>
>>>>> This patch series adds the add-fd, remove-fd, and query-fdsets
>>>>> QMP monitor commands, which allow file descriptors to be passed
>>>>> via SCM_RIGHTS, and assigned to specified fd sets.  This allows
>>>>> fd sets to be created per file with fds having, for example,
>>>>> different access rights.  When QEMU needs to reopen a file with
>>>>> different access rights, it can search for a matching fd in the
>>>>> fd set.  Fd sets also allow for easy tracking of fds per file,
>>>>> helping to prevent fd leaks.
>>>>>
>>>>> Support is also added to the block layer to allow QEMU to dup an
>>>>> fd from an fdset when the filename is of the /dev/fdset/nnn format,
>>>>> where nnn is the fd set ID.
>>>>>
>>>>> No new SELinux policy is required to prevent open of NFS files
>>>>> (files with type nfs_t).  The virt_use_nfs boolean type simply
>>>>> needs to be set to false, and open will be prevented (and dup will
>>>>> be allowed).  For example:
>>>>>
>>>>>       # setsebool virt_use_nfs 0
>>>>>       # getsebool virt_use_nfs
>>>>>       virt_use_nfs --> off
>>>>>
>>>>> Corey Bryant (6):
>>>>>     qemu-char: Add MSG_CMSG_CLOEXEC flag to recvmsg
>>>>>     qapi: Introduce add-fd, remove-fd, query-fdsets
>>>>>     monitor: Clean up fd sets on monitor disconnect
>>>>>     block: Convert open calls to qemu_open
>>>>>     block: Convert close calls to qemu_close
>>>>>     block: Enable qemu_open/close to work with fd sets
>>>>>
>>>>>    block/raw-posix.c |   42 ++++-----
>>>>>    block/raw-win32.c |    6 +-
>>>>>    block/vdi.c       |    5 +-
>>>>>    block/vmdk.c      |   25 +++--
>>>>>    block/vpc.c       |    4 +-
>>>>>    block/vvfat.c     |   16 ++--
>>>>>    cutils.c          |    5 +
>>>>>    monitor.c         |  273
>>>>> +++++++++++++++++++++++++++++++++++++++++++++++++++++
>>>>>    monitor.h         |    5 +
>>>>>    osdep.c           |  117 +++++++++++++++++++++++
>>>>>    qapi-schema.json  |  110 +++++++++++++++++++++
>>>>>    qemu-char.c       |   12 ++-
>>>>>    qemu-common.h     |    2 +
>>>>>    qemu-tool.c       |   20 ++++
>>>>>    qerror.c          |    4 +
>>>>>    qerror.h          |    3 +
>>>>>    qmp-commands.hx   |  131 +++++++++++++++++++++++++
>>>>>    savevm.c          |    4 +-
>>>>>    18 files changed, 730 insertions(+), 54 deletions(-)
>>>>
>>>>
>>>>
>>>> Are there tests for this feature?  Do you have test scripts used
>>>> during development?
>>>
>>>
>>>
>>> Yes I have some C code that I've been using for testing.  I can clean it
>>> up
>>> and provide it if you'd like.
>>
>>
>> That would be very useful.  tests/ has test cases.  For the block
>> layer tests/qemu-iotests/ is especially relevant, that's where a lot
>> of the test cases go.  If you look at test case 030 you'll see how a
>> Python script interacts with QMP to test image streaming -
>> unfortunately I think Python doesn't natively support SCM_RIGHTS.  But
>> a test script would be very useful so it can be used as a regression
>> test in the future.
>>
>
> Sure I'll take a look.  Hopefully a C test is ok if I can't use SCM_RIGHTS
> in Python.

Great, thanks.

Stefan