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

Quoting Jamie Strandboge <jamie(a)canonical.com&gt;: > On Tue, 2012-07-03 at 12:05 -0400, rmarwah(a)linux.vnet.ibm.com wrote: >> Quoting Jamie Strandboge <jamie(a)canonical.com&gt;: >> >> > On Fri, 2012-06-29 at 14:08 -0400, rmarwah(a)linux.vnet.ibm.com wrote: >> >> From: Richa Marwaha <rmarwah(a)linux.vnet.ibm.com&gt; >> >> >> >> 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(a)linux.vnet.ibm.com&gt; >> >> Signed-off-by: Corey Bryant&lt;coreyb(a)linux.vnet.ibm.com&gt; >> >> --- >> >> 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). >> >> Thanks a lot reviewing the apparmor patch. We cannot detemine from the >> domain XML whether /usr/libexec/qemu-bridge-helper will be used or not >> because we cannot determine whether we are running as privileged user >> or not. > Hmmm, that's too bad. > >> Is there a way we can specify the configured path to the >> binary in the current policy we have? > > Not in a convenient way, no. The policy is intended as example policy > anyway, and distributions are expected to modify this, so I don't think > this alone is a blocker. Right now the only way we can think of is that whenever in domain XML we see interface=bridge we set the policy for the qemu-bridge-helper even though we don't know if the qemu-bridge-helper is going to be used or not.