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Re: [libvirt] [Patch v2 3/3] apparmor: QEMU bridge helper policy updates



On Fri, 2012-06-29 at 14:08 -0400, rmarwah linux vnet ibm com wrote:
> From: Richa Marwaha <rmarwah linux vnet ibm com>
> 
> This patch provides AppArmor policy updates for the QEMU bridge helper.
> The QEMU bridge helper is a SUID executable exec'd by QEMU that drops
> capabilities to CAP_NET_ADMIN and adds a tap device to a network bridge.
> 
> Signed-off-by: Richa Marwaha <rmarwah linux vnet ibm com>
> Signed-off-by: Corey Bryant<coreyb linux vnet ibm com>
> ---
>  examples/apparmor/libvirt-qemu |   21 ++++++++++++++++++++-
>  1 files changed, 20 insertions(+), 1 deletions(-)
> 
> diff --git a/examples/apparmor/libvirt-qemu b/examples/apparmor/libvirt-qemu
> index 10cdd36..766a334 100644
> --- a/examples/apparmor/libvirt-qemu
> +++ b/examples/apparmor/libvirt-qemu
> @@ -1,4 +1,4 @@
> -# Last Modified: Mon Apr  5 15:11:27 2010
> +# Last Modified: Fri Mar 9 14:43:22 2012
>  
>    #include <abstractions/base>
>    #include <abstractions/consoles>
> @@ -108,3 +108,22 @@
>    /bin/dash rmix,
>    /bin/dd rmix,
>    /bin/cat rmix,
> +
> +  /usr/libexec/qemu-bridge-helper Cx,
> +  # child profile for bridge helper process
> +  profile /usr/libexec/qemu-bridge-helper {
> +   #include <abstractions/base>
> +
> +   capability setuid,
> +   capability setgid,
> +   capability setpcap,
> +   capability net_admin,
> +
> +   network inet stream,
> +
> +   /dev/net/tun rw,
> +   /etc/qemu/** r,
> +   owner @{PROC}/*/status r,
> +
> +   /usr/libexec/qemu-bridge-helper rmix,
> +  }

Looking at the child profile itself, this seems fine.

However, the Cx transition makes it so that all libvirt-managed qemu
processes are allowed to execute this setuid helper and I wonder if that
is too much? Ie, a guest running under libvirt's NAT wouldn't need
access to this helper at all. I wonder if it would be better to adjust
virt-aa-helper to add this transition and child profile instead (the
child profile could theoretically still be in apparmor/libvirt-qemu, but
this is a bit messy)? Can we determine from the domain XML the
circumstances when /usr/libexec/qemu-bridge-helper will be used? If so,
virt-aa-helper could add the access only then. As a side-benefit,
handling this in virt-aa-helper allows us at compile-time to adjust the
path to qemu-bridge-helper to use the configured path to the binary (ie,
some distros may not use /usr/libexec).

-- 
Jamie Strandboge             | http://www.canonical.com

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