Re: [libvirt] [Qemu-devel] [RFC 0/5] block: File descriptor passing using -open-hook-fd

Thanks for sending this out Stefan. On 05/01/2012 10:31 AM, Stefan Hajnoczi wrote: > Libvirt can take advantage of SELinux to restrict the QEMU process and > prevent > it from opening files that it should not have access to. This improves > security because it prevents the attacker from escaping the QEMU > process if > they manage to gain control. > > NFS has been a pain point for SELinux because it does not support > labels (which > I believe are stored in extended attributes). In other words, it's not > possible to use SELinux goodness on QEMU when image files are located > on NFS. > Today we have to allow QEMU access to any file on the NFS export > rather than > restricting specifically to the image files that the guest requires. > > File descriptor passing is a solution to this problem and might also > come in > handy elsewhere. Libvirt or another external process chooses files > which QEMU > is allowed to access and provides just those file descriptors - QEMU > cannot > open the files itself. > > This series adds the -open-hook-fd command-line option. Whenever QEMU > needs to > open an image file it sends a request over the given UNIX domain > socket. The > response includes the file descriptor or an errno on failure. Please > see the > patches for details on the protocol. > > The -open-hook-fd approach allows QEMU to support file descriptor passing > without changing -drive. It also supports snapshot_blkdev and other > commands > that re-open image files. > > Anthony Liguori<aliguori(a)us.ibm.com> wrote most of these patches. I > added a > demo -open-hook-fd server and added some small fixes. Since Anthony is > traveling right now I'm sending the RFC for discussion. What I like about this approach is that it's useful outside the block layer and is conceptionally simple from a QEMU PoV. We simply delegate open() to libvirt and let libvirt enforce whatever rules it wants. This is not meant to be an alternative to blockdev, but even with blockdev, I think we still want to use a mechanism like this even with blockdev. Regards, Anthony Liguori

> > Anthony Liguori (3): > block: add open() wrapper that can be hooked by libvirt > block: add new command line parameter that and protocol description > block: plumb up open-hook-fd option > > Stefan Hajnoczi (2): > osdep: add qemu_recvmsg() wrapper > Example -open-hook-fd server > > block.c | 107 ++++++++++++++++++++++++++++++++++++++ > block.h | 2 + > block/raw-posix.c | 18 +++---- > block/raw-win32.c | 2 +- > block/vdi.c | 2 +- > block/vmdk.c | 6 +-- > block/vpc.c | 2 +- > block/vvfat.c | 4 +- > block_int.h | 12 +++++ > osdep.c | 46 +++++++++++++++++ > qemu-common.h | 2 + > qemu-options.hx | 42 +++++++++++++++ > test-fd-passing.c | 147 > +++++++++++++++++++++++++++++++++++++++++++++++++++++ > vl.c | 3 ++ > 14 files changed, 378 insertions(+), 17 deletions(-) > create mode 100644 test-fd-passing.c >