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 (7):
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: Prevent detection of /dev/fdset/ as floppy
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 | 46 +++++----
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 | 294 +++++++++++++++++++++++++++++++++++++++++++++++++++++
monitor.h | 5 +
osdep.c | 117 +++++++++++++++++++++
qapi-schema.json | 98 ++++++++++++++++++
qemu-char.c | 12 ++-
qemu-common.h | 2 +
qemu-tool.c | 20 ++++
qmp-commands.hx | 117 +++++++++++++++++++++
savevm.c | 4 +-
16 files changed, 721 insertions(+), 55 deletions(-)