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Re: [libvirt] [Qemu-devel] [RFC PATCH 0/4] block: file descriptor passing using -filefd and getfd_file





On 05/22/2012 04:18 AM, Kevin Wolf wrote:
Am 21.05.2012 22:19, schrieb Corey Bryant:
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 -filefd command-line option and the
getfd_file monitor command.  This will enable libvirt to open a
file and push the corresponding filename and file descriptor to
QEMU.  When QEMU needs to "open" a file, it will first check if the
file descriptor was passed by either of these methods before
attempting to actually open the file.

I thought we decided to avoid making some file names magic, and instead
go for the obvious /dev/fd/42?

Kevin


I understand that open("/dev/fd/42") would be the same as dup(42), but I'm not sure that I'm entirely clear on how this would work. Could you give an example?

--
Regards,
Corey


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