[Qemu-devel] [PATCH V5 00/14] Proxy FS driver for VirtFS

[M. Mohan Kumar]

From: "M. Mohan Kumar" <address@hidden>

Pass-through security model in QEMU 9p server needs root privilege to do
few file operations (like chown, chmod to any mode/uid:gid).  There are two
issues in pass-through security model

1) TOCTTOU vulnerability: Following symbolic links in the server could
provide access to files beyond 9p export path.

2) Running QEMU with root privilege could be a security issue.

To overcome above issues, following approach is used: A new filesytem
type 'proxy' is introduced. Proxy FS uses chroot + socket combination
for securing the vulnerability known with following symbolic links.
Intention of adding a new filesystem type is to allow qemu to run
in non-root mode, but doing privileged operations using socket IO.

Proxy helper(a stand alone binary part of qemu) is invoked with
root privileges. Proxy helper chroots into 9p export path and creates
a socket pair or a named socket based on the command line parameter.
Qemu and proxy helper communicate using this socket. QEMU proxy fs
driver sends filesystem request to proxy helper and receives the
response from it.

Proxy helper is designed so that it can drop the root privilege but
retaining capbilities that are needed for doing filesystem operations
(like CAP_DAC_OVERRIDE, CAP_FOWNER etc)

Changes from previous version V4:
* Handle the case request message > PROXY_MAX_IO_SZ as fatal, instead of
  recovering.
* Changed size data type to unsigned for both ProxyHeader and V9fsString
* Added chdir("/") before doing chroot()
* Code changes due to changing ProxyHeader size type to unsigned

Changes from previous version V3:
* Lots of code change involving
    * Improve error handling in marshaling/unmarshaling code
* Return ENOBUFS when request/response size exceeds maximum buffer size

Changes from previous version V2:
* Added check to handle failures in marshaling/unmarshaling code. Also make
  sure that request/response will not exceed maximum buffer size (BUFF_SZ)
* Addressed Stefan's review comments

Changes from previous version:
*) Communication between qemu and helper process is similar to 9p way of packing
elements (pdu marshaling).

Aneesh Kumar K.V (1):
  hw/9pfs: Move opt validation to FsDriver callback

M. Mohan Kumar (13):
  hw/9pfs: Move pdu_marshal/unmarshal code to a seperate file
  hw/9pfs: Add validation to {un}marshal code
  hw/9pfs: Add new proxy filesystem driver
  hw/9pfs: File system helper process for qemu 9p proxy FS
  hw/9pfs: Open and create files
  hw/9pfs: Create other filesystem objects
  hw/9pfs: Add stat/readlink/statfs for proxy FS
  hw/9pfs: File ownership and others
  hw/9pfs: xattr interfaces in proxy filesystem driver
  hw/9pfs: Proxy getversion
  hw/9pfs: Documentation changes related to proxy fs
  hw/9pfs: man page for proxy helper
  hw/9pfs: Add support to use named socket for proxy FS

 Makefile                       |   15 +-
 Makefile.objs                  |    3 +-
 configure                      |   19 +
 fsdev/file-op-9p.h             |   17 +-
 fsdev/qemu-fsdev.c             |   45 +--
 fsdev/qemu-fsdev.h             |   11 +-
 fsdev/virtfs-proxy-helper.c    | 1113 ++++++++++++++++++++++++++++++++++++
 fsdev/virtfs-proxy-helper.texi |   63 +++
 fsdev/virtio-9p-marshal.c      |  360 ++++++++++++
 fsdev/virtio-9p-marshal.h      |   90 +++
 hw/9pfs/virtio-9p-device.c     |   13 +-
 hw/9pfs/virtio-9p-handle.c     |   20 +
 hw/9pfs/virtio-9p-local.c      |   34 ++
 hw/9pfs/virtio-9p-proxy.c      | 1210 ++++++++++++++++++++++++++++++++++++++++
 hw/9pfs/virtio-9p-proxy.h      |   95 ++++
 hw/9pfs/virtio-9p.c            |  756 ++++++++++++--------------
 hw/9pfs/virtio-9p.h            |   83 +---
 qemu-config.c                  |   13 +
 qemu-options.hx                |   32 +-
 vl.c                           |   18 +-
 20 files changed, 3448 insertions(+), 562 deletions(-)
 create mode 100644 fsdev/virtfs-proxy-helper.c
 create mode 100644 fsdev/virtfs-proxy-helper.texi
 create mode 100644 fsdev/virtio-9p-marshal.c
 create mode 100644 fsdev/virtio-9p-marshal.h
 create mode 100644 hw/9pfs/virtio-9p-proxy.c
 create mode 100644 hw/9pfs/virtio-9p-proxy.h

-- 
1.7.6