[Qemu-devel] [PATCH 0/3] file descriptor passing using getfd over QMP

[Corey Bryant <coreyb@linux.vnet.ibm.com>]

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.

This patch series adds the getfd QMP monitor command, which allows
an fd to be passed via SCM_RIGHTS, and returns the received file
descriptor.  Support is also added to the block layer to allow QEMU
to dup() the fd when the filename is of the /dev/fd/X format.  This
is useful if MAC policy prevents QEMU from open()ing specific types
of files.

This solution will enable libvirt to open() an image file and push
the file descriptor down to QEMU.  When QEMU needs to "open" a file,
it will first check if the filename is of the /dev/fd/X format and
dup(X) if so.  Otherwise it will continue and open() the file as it
has in the past.

This series reuses the file_open() function that Anthony Liguori
<aliguori@us.ibm.com> created in a recent fd passing prototype.  It
also reuses the test driver that Stefan Hajnoczi
<stefanha@linux.vnet.ibm.com> created for that prototype, but with
several modifications.

Corey Bryant (3):
  qmp/hmp: Add QMP getfd command that returns fd
  block: Add support to "open" /dev/fd/X filenames
  Sample server that opens image files for QEMU

 block.c           |   15 +++
 block/raw-posix.c |   20 ++--
 block/raw-win32.c |    4 +-
 block/vdi.c       |    5 +-
 block/vmdk.c      |   21 ++--
 block/vpc.c       |    2 +-
 block/vvfat.c     |   21 ++--
 block_int.h       |   13 +++
 hmp-commands.hx   |    2 +-
 monitor.c         |   37 +++++-
 qapi-schema.json  |   13 +++
 qmp-commands.hx   |    6 +-
 test-fd-passing.c |  321 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 13 files changed, 439 insertions(+), 41 deletions(-)
 create mode 100644 test-fd-passing.c

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1.7.10.2