[libvirt] [PATCH] security: apparmor: make vhost-net access a static rule
So far we were detecting at guest start if any devices needed vhost net and only if that was true added a rule for /dev/vhost-net. It turns out that it is an absolutely valid case to start a guest without any vhost-net networking but later on wanting to hotplug such a device which then would be denied by apparmor. Unfortunately there also is no security labeling callback involved other than the one to /dev/net/tun. But on the other hand vhost-net is no more new and considered rather safe. Therefore drop the old detection and just add it as a static rule. Fixes: https://bugs.launchpad.net/ubuntu/+source/libvirt/+bug/1815910 Signed-off-by: Christian Ehrhardt <christian.ehrhardt@canonical.com> --- src/security/apparmor/libvirt-qemu | 1 + src/security/virt-aa-helper.c | 17 +---------------- 2 files changed, 2 insertions(+), 16 deletions(-) diff --git a/src/security/apparmor/libvirt-qemu b/src/security/apparmor/libvirt-qemu index eaa5167525..a71f34c175 100644 --- a/src/security/apparmor/libvirt-qemu +++ b/src/security/apparmor/libvirt-qemu @@ -21,6 +21,7 @@ signal (receive) peer=/usr/sbin/libvirtd, /dev/net/tun rw, + /dev/vhost-net rw, /dev/kvm rw, /dev/ptmx rw, /dev/kqemu rw, diff --git a/src/security/virt-aa-helper.c b/src/security/virt-aa-helper.c index 8e22e9978a..ebc4feac77 100644 --- a/src/security/virt-aa-helper.c +++ b/src/security/virt-aa-helper.c @@ -937,7 +937,7 @@ get_files(vahControl * ctl) size_t i; char *uuid; char uuidstr[VIR_UUID_STRING_BUFLEN]; - bool needsVfio = false, needsvhost = false; + bool needsVfio = false; /* verify uuid is same as what we were given on the command line */ virUUIDFormat(ctl->def->uuid, uuidstr); @@ -1248,21 +1248,6 @@ get_files(vahControl * ctl) } } - if (ctl->def->virtType == VIR_DOMAIN_VIRT_KVM) { - for (i = 0; i < ctl->def->nnets; i++) { - virDomainNetDefPtr net = ctl->def->nets[i]; - if (net && net->model) { - if (net->driver.virtio.name == VIR_DOMAIN_NET_BACKEND_TYPE_QEMU) - continue; - if (!virDomainNetIsVirtioModel(net)) - continue; - } - needsvhost = true; - } - } - if (needsvhost) - virBufferAddLit(&buf, " \"/dev/vhost-net\" rw,\n"); - if (needsVfio) { virBufferAddLit(&buf, " \"/dev/vfio/vfio\" rw,\n"); virBufferAddLit(&buf, " \"/dev/vfio/[0-9]*\" rw,\n"); -- 2.17.1
On Mon, 18 Feb 2019, Christian Ehrhardt wrote:
So far we were detecting at guest start if any devices needed vhost net and only if that was true added a rule for /dev/vhost-net.
It turns out that it is an absolutely valid case to start a guest without any vhost-net networking but later on wanting to hotplug such a device which then would be denied by apparmor.
Unfortunately there also is no security labeling callback involved other than the one to /dev/net/tun. But on the other hand vhost-net is no more new and considered rather safe. Therefore drop the old detection and just add it as a static rule.
Fixes: https://bugs.launchpad.net/ubuntu/+source/libvirt/+bug/1815910
Signed-off-by: Christian Ehrhardt <christian.ehrhardt@canonical.com> --- src/security/apparmor/libvirt-qemu | 1 + src/security/virt-aa-helper.c | 17 +---------------- 2 files changed, 2 insertions(+), 16 deletions(-)
diff --git a/src/security/apparmor/libvirt-qemu b/src/security/apparmor/libvirt-qemu index eaa5167525..a71f34c175 100644 --- a/src/security/apparmor/libvirt-qemu +++ b/src/security/apparmor/libvirt-qemu @@ -21,6 +21,7 @@ signal (receive) peer=/usr/sbin/libvirtd,
/dev/net/tun rw, + /dev/vhost-net rw, /dev/kvm rw, /dev/ptmx rw, /dev/kqemu rw, diff --git a/src/security/virt-aa-helper.c b/src/security/virt-aa-helper.c index 8e22e9978a..ebc4feac77 100644 --- a/src/security/virt-aa-helper.c +++ b/src/security/virt-aa-helper.c @@ -937,7 +937,7 @@ get_files(vahControl * ctl) size_t i; char *uuid; char uuidstr[VIR_UUID_STRING_BUFLEN]; - bool needsVfio = false, needsvhost = false; + bool needsVfio = false;
/* verify uuid is same as what we were given on the command line */ virUUIDFormat(ctl->def->uuid, uuidstr); @@ -1248,21 +1248,6 @@ get_files(vahControl * ctl) } }
- if (ctl->def->virtType == VIR_DOMAIN_VIRT_KVM) { - for (i = 0; i < ctl->def->nnets; i++) { - virDomainNetDefPtr net = ctl->def->nets[i]; - if (net && net->model) { - if (net->driver.virtio.name == VIR_DOMAIN_NET_BACKEND_TYPE_QEMU) - continue; - if (!virDomainNetIsVirtioModel(net)) - continue; - } - needsvhost = true; - } - } - if (needsvhost) - virBufferAddLit(&buf, " \"/dev/vhost-net\" rw,\n"); - if (needsVfio) { virBufferAddLit(&buf, " \"/dev/vfio/vfio\" rw,\n"); virBufferAddLit(&buf, " \"/dev/vfio/[0-9]*\" rw,\n");
A few things I noticed: - if I launch a vm with a virtio net device, then I can detach/attach as much as I want - if I launch a vm with one virtio net device, then detach it, /dev/vhost-net is not removed from the profile. - if launch a vm with one virtio net device, then I detach it and I shutdown the vm with no attached network devices, on the next vm start, the device is present and the profile still has the access. IIRC, this is by design - if I remove the net device from the vm definition then libvirtd updates profile to not allow the access. When I start the vm I cannot attach a virtio net device because the access is denied (this bug) - /dev/vhost-net is root:root 600 and vms typically run as non-root (libvirt-qemu:kvm here) and therefore a qemu process would not be able to open the device on its own. The only reason why qemu can is because libvirt passes an fd to it, and it is when qemu writes to it that the access is denied To me, it seems the real bug is that hotplug attach/detach is not updating the profile accordingly (attach adds it if it isn't there and detach removes it if no more net devices are present). Ideally, this would be the fix for this bug (we certainly support other hotplug/hotunplug events, like disks). Considering that the device expands the attack surface to this part of the kernel and because the root:root 600 permissions show that non-root is not meant to access the device, this is most correct. That said, libvirt itself is providing protection here because it is mediating the access to /dev/vhost-net for the VMs since the VMs can't open the device themselves and they must rely on libvirt to pass in the fd. Because of this, adding the access to the profile is not providing additional protections beyond DAC *for this common use case and configuration*. Conditionally adding the access would provide benefit when 'user = "root"' is set in qemu.conf or the device itself has different permissions that allow the access (eg, 660 root:kvm). I maintain a preference for updating the profile on hotplug events. I'm willing to concede that adding the access for now until the correct solution is implemented would be acceptable, but I'd better like to understand how common it is to start a VM with no network devices and then hotplug one. -- Jamie Strandboge | http://www.canonical.com
On Fri, Mar 1, 2019 at 5:56 PM Jamie Strandboge <jamie@canonical.com> wrote:
On Mon, 18 Feb 2019, Christian Ehrhardt wrote:
So far we were detecting at guest start if any devices needed vhost net and only if that was true added a rule for /dev/vhost-net.
It turns out that it is an absolutely valid case to start a guest without any vhost-net networking but later on wanting to hotplug such a device which then would be denied by apparmor.
Unfortunately there also is no security labeling callback involved other than the one to /dev/net/tun. But on the other hand vhost-net is no more new and considered rather safe. Therefore drop the old detection and just add it as a static rule.
Fixes: https://bugs.launchpad.net/ubuntu/+source/libvirt/+bug/1815910
Signed-off-by: Christian Ehrhardt <christian.ehrhardt@canonical.com> --- src/security/apparmor/libvirt-qemu | 1 + src/security/virt-aa-helper.c | 17 +---------------- 2 files changed, 2 insertions(+), 16 deletions(-)
diff --git a/src/security/apparmor/libvirt-qemu b/src/security/apparmor/libvirt-qemu index eaa5167525..a71f34c175 100644 --- a/src/security/apparmor/libvirt-qemu +++ b/src/security/apparmor/libvirt-qemu @@ -21,6 +21,7 @@ signal (receive) peer=/usr/sbin/libvirtd,
/dev/net/tun rw, + /dev/vhost-net rw, /dev/kvm rw, /dev/ptmx rw, /dev/kqemu rw, diff --git a/src/security/virt-aa-helper.c b/src/security/virt-aa-helper.c index 8e22e9978a..ebc4feac77 100644 --- a/src/security/virt-aa-helper.c +++ b/src/security/virt-aa-helper.c @@ -937,7 +937,7 @@ get_files(vahControl * ctl) size_t i; char *uuid; char uuidstr[VIR_UUID_STRING_BUFLEN]; - bool needsVfio = false, needsvhost = false; + bool needsVfio = false;
/* verify uuid is same as what we were given on the command line */ virUUIDFormat(ctl->def->uuid, uuidstr); @@ -1248,21 +1248,6 @@ get_files(vahControl * ctl) } }
- if (ctl->def->virtType == VIR_DOMAIN_VIRT_KVM) { - for (i = 0; i < ctl->def->nnets; i++) { - virDomainNetDefPtr net = ctl->def->nets[i]; - if (net && net->model) { - if (net->driver.virtio.name == VIR_DOMAIN_NET_BACKEND_TYPE_QEMU) - continue; - if (!virDomainNetIsVirtioModel(net)) - continue; - } - needsvhost = true; - } - } - if (needsvhost) - virBufferAddLit(&buf, " \"/dev/vhost-net\" rw,\n"); - if (needsVfio) { virBufferAddLit(&buf, " \"/dev/vfio/vfio\" rw,\n"); virBufferAddLit(&buf, " \"/dev/vfio/[0-9]*\" rw,\n");
A few things I noticed:
- if I launch a vm with a virtio net device, then I can detach/attach as much as I want - if I launch a vm with one virtio net device, then detach it, /dev/vhost-net is not removed from the profile. - if launch a vm with one virtio net device, then I detach it and I shutdown the vm with no attached network devices, on the next vm start, the device is present and the profile still has the access. IIRC, this is by design - if I remove the net device from the vm definition then libvirtd updates profile to not allow the access. When I start the vm I cannot attach a virtio net device because the access is denied (this bug) - /dev/vhost-net is root:root 600 and vms typically run as non-root (libvirt-qemu:kvm here) and therefore a qemu process would not be able to open the device on its own. The only reason why qemu can is because libvirt passes an fd to it, and it is when qemu writes to it that the access is denied
To me, it seems the real bug is that hotplug attach/detach is not updating the profile accordingly (attach adds it if it isn't there and detach removes it if no more net devices are present). Ideally, this would be the fix for this bug (we certainly support other hotplug/hotunplug events, like disks).
Yes ideally it would, but I that would be a major change how hotplug in general is handled by virt-aa-helper and I haven't had something like that around easily. I think we even talked about that quite a while a go when we also talked about the inability to get more insight into e.g. pools from the POV of virt-aa-helper. It is on my "long term find no time for it list" :-/
Considering that the device expands the attack surface to this part of the kernel and because the root:root 600 permissions show that non-root is not meant to access the device, this is most correct.
That said, libvirt itself is providing protection here because it is mediating the access to /dev/vhost-net for the VMs since the VMs can't open the device themselves and they must rely on libvirt to pass in the fd. Because of this, adding the access to the profile is not providing additional protections beyond DAC *for this common use case and configuration*. Conditionally adding the access would provide benefit when 'user = "root"' is set in qemu.conf or the device itself has different permissions that allow the access (eg, 660 root:kvm).
I maintain a preference for updating the profile on hotplug events. I'm willing to concede that adding the access for now until the correct solution is implemented would be acceptable, but I'd better like to understand how common it is to start a VM with no network devices and then hotplug one.
I agree that if the use case is unreasonable we might declare this as "work-as-intended" and the few people affected would then be supposed to add a local override opting-in to open /dev/vhost up to all guests. I'll ping on the bug for affected people to explain why/how they hit the case, that might shed some light on it to allow us making the decision if it is reasonable enough to concede the static rule as an interim solution until one day it would be detected correctly on every hotplug (and unplug) event.
On Mon, Mar 4, 2019 at 11:42 AM Christian Ehrhardt <christian.ehrhardt@canonical.com> wrote:
On Fri, Mar 1, 2019 at 5:56 PM Jamie Strandboge <jamie@canonical.com> wrote:
On Mon, 18 Feb 2019, Christian Ehrhardt wrote:
So far we were detecting at guest start if any devices needed vhost net and only if that was true added a rule for /dev/vhost-net.
It turns out that it is an absolutely valid case to start a guest without any vhost-net networking but later on wanting to hotplug such a device which then would be denied by apparmor.
Unfortunately there also is no security labeling callback involved other than the one to /dev/net/tun. But on the other hand vhost-net is no more new and considered rather safe. Therefore drop the old detection and just add it as a static rule.
Fixes: https://bugs.launchpad.net/ubuntu/+source/libvirt/+bug/1815910
Signed-off-by: Christian Ehrhardt <christian.ehrhardt@canonical.com> --- src/security/apparmor/libvirt-qemu | 1 + src/security/virt-aa-helper.c | 17 +---------------- 2 files changed, 2 insertions(+), 16 deletions(-)
diff --git a/src/security/apparmor/libvirt-qemu b/src/security/apparmor/libvirt-qemu index eaa5167525..a71f34c175 100644 --- a/src/security/apparmor/libvirt-qemu +++ b/src/security/apparmor/libvirt-qemu @@ -21,6 +21,7 @@ signal (receive) peer=/usr/sbin/libvirtd,
/dev/net/tun rw, + /dev/vhost-net rw, /dev/kvm rw, /dev/ptmx rw, /dev/kqemu rw, diff --git a/src/security/virt-aa-helper.c b/src/security/virt-aa-helper.c index 8e22e9978a..ebc4feac77 100644 --- a/src/security/virt-aa-helper.c +++ b/src/security/virt-aa-helper.c @@ -937,7 +937,7 @@ get_files(vahControl * ctl) size_t i; char *uuid; char uuidstr[VIR_UUID_STRING_BUFLEN]; - bool needsVfio = false, needsvhost = false; + bool needsVfio = false;
/* verify uuid is same as what we were given on the command line */ virUUIDFormat(ctl->def->uuid, uuidstr); @@ -1248,21 +1248,6 @@ get_files(vahControl * ctl) } }
- if (ctl->def->virtType == VIR_DOMAIN_VIRT_KVM) { - for (i = 0; i < ctl->def->nnets; i++) { - virDomainNetDefPtr net = ctl->def->nets[i]; - if (net && net->model) { - if (net->driver.virtio.name == VIR_DOMAIN_NET_BACKEND_TYPE_QEMU) - continue; - if (!virDomainNetIsVirtioModel(net)) - continue; - } - needsvhost = true; - } - } - if (needsvhost) - virBufferAddLit(&buf, " \"/dev/vhost-net\" rw,\n"); - if (needsVfio) { virBufferAddLit(&buf, " \"/dev/vfio/vfio\" rw,\n"); virBufferAddLit(&buf, " \"/dev/vfio/[0-9]*\" rw,\n");
A few things I noticed:
- if I launch a vm with a virtio net device, then I can detach/attach as much as I want - if I launch a vm with one virtio net device, then detach it, /dev/vhost-net is not removed from the profile. - if launch a vm with one virtio net device, then I detach it and I shutdown the vm with no attached network devices, on the next vm start, the device is present and the profile still has the access. IIRC, this is by design - if I remove the net device from the vm definition then libvirtd updates profile to not allow the access. When I start the vm I cannot attach a virtio net device because the access is denied (this bug) - /dev/vhost-net is root:root 600 and vms typically run as non-root (libvirt-qemu:kvm here) and therefore a qemu process would not be able to open the device on its own. The only reason why qemu can is because libvirt passes an fd to it, and it is when qemu writes to it that the access is denied
To me, it seems the real bug is that hotplug attach/detach is not updating the profile accordingly (attach adds it if it isn't there and detach removes it if no more net devices are present). Ideally, this would be the fix for this bug (we certainly support other hotplug/hotunplug events, like disks).
Yes ideally it would, but I that would be a major change how hotplug in general is handled by virt-aa-helper and I haven't had something like that around easily. I think we even talked about that quite a while a go when we also talked about the inability to get more insight into e.g. pools from the POV of virt-aa-helper. It is on my "long term find no time for it list" :-/
Considering that the device expands the attack surface to this part of the kernel and because the root:root 600 permissions show that non-root is not meant to access the device, this is most correct.
That said, libvirt itself is providing protection here because it is mediating the access to /dev/vhost-net for the VMs since the VMs can't open the device themselves and they must rely on libvirt to pass in the fd. Because of this, adding the access to the profile is not providing additional protections beyond DAC *for this common use case and configuration*. Conditionally adding the access would provide benefit when 'user = "root"' is set in qemu.conf or the device itself has different permissions that allow the access (eg, 660 root:kvm).
I maintain a preference for updating the profile on hotplug events. I'm willing to concede that adding the access for now until the correct solution is implemented would be acceptable, but I'd better like to understand how common it is to start a VM with no network devices and then hotplug one.
I agree that if the use case is unreasonable we might declare this as "work-as-intended" and the few people affected would then be supposed to add a local override opting-in to open /dev/vhost up to all guests. I'll ping on the bug for affected people to explain why/how they hit the case, that might shed some light on it to allow us making the decision if it is reasonable enough to concede the static rule as an interim solution until one day it would be detected correctly on every hotplug (and unplug) event.
Hi, there was no further comment here so far. On the bug the following is what I got: (Note that it was reported to be triggered by Openstack usage) James Page: This is not the default otherwise no ones cloud would actually work right now. Instances are created with a network interface in paused state - at which point the interface plugging in neutron is executed; once that's completed the instance transitions to running and boots. That's the default behaviour with neutron/ml2/ovs driver. Are you using a different neutron driver? Daniel Pawlik (bug reporter): I also use neutron ml2 ovs driver. I understand that in default nova policy, only administrator can spawn instance without any interface, but if someone else can "tune" the policy, he/she will have a problem. No other feedback was added so far. I personally tend to err on the side of caution and in this case would say an admin that wants to allow this can set up /dev/vhost-net as a local apparmor override. @Libvirt maintainers and @Jamie for apparmor guidance. Is in your opinion that enough of a common case that we'd add the the path as static rule in general? @JamesPage - you are likely the most experienced Openstack expert of us, what would be your opinion on the above? -- Christian Ehrhardt Software Engineer, Ubuntu Server Canonical Ltd
On Wed, Mar 20, 2019 at 8:45 AM Christian Ehrhardt <christian.ehrhardt@canonical.com> wrote:
On Mon, Mar 4, 2019 at 11:42 AM Christian Ehrhardt <christian.ehrhardt@canonical.com> wrote:
On Fri, Mar 1, 2019 at 5:56 PM Jamie Strandboge <jamie@canonical.com> wrote:
On Mon, 18 Feb 2019, Christian Ehrhardt wrote:
So far we were detecting at guest start if any devices needed vhost net and only if that was true added a rule for /dev/vhost-net.
It turns out that it is an absolutely valid case to start a guest without any vhost-net networking but later on wanting to hotplug such a device which then would be denied by apparmor.
Unfortunately there also is no security labeling callback involved other than the one to /dev/net/tun. But on the other hand vhost-net is no more new and considered rather safe. Therefore drop the old detection and just add it as a static rule.
Fixes: https://bugs.launchpad.net/ubuntu/+source/libvirt/+bug/1815910
Signed-off-by: Christian Ehrhardt <christian.ehrhardt@canonical.com> --- src/security/apparmor/libvirt-qemu | 1 + src/security/virt-aa-helper.c | 17 +---------------- 2 files changed, 2 insertions(+), 16 deletions(-)
diff --git a/src/security/apparmor/libvirt-qemu b/src/security/apparmor/libvirt-qemu index eaa5167525..a71f34c175 100644 --- a/src/security/apparmor/libvirt-qemu +++ b/src/security/apparmor/libvirt-qemu @@ -21,6 +21,7 @@ signal (receive) peer=/usr/sbin/libvirtd,
/dev/net/tun rw, + /dev/vhost-net rw, /dev/kvm rw, /dev/ptmx rw, /dev/kqemu rw, diff --git a/src/security/virt-aa-helper.c b/src/security/virt-aa-helper.c index 8e22e9978a..ebc4feac77 100644 --- a/src/security/virt-aa-helper.c +++ b/src/security/virt-aa-helper.c @@ -937,7 +937,7 @@ get_files(vahControl * ctl) size_t i; char *uuid; char uuidstr[VIR_UUID_STRING_BUFLEN]; - bool needsVfio = false, needsvhost = false; + bool needsVfio = false;
/* verify uuid is same as what we were given on the command line */ virUUIDFormat(ctl->def->uuid, uuidstr); @@ -1248,21 +1248,6 @@ get_files(vahControl * ctl) } }
- if (ctl->def->virtType == VIR_DOMAIN_VIRT_KVM) { - for (i = 0; i < ctl->def->nnets; i++) { - virDomainNetDefPtr net = ctl->def->nets[i]; - if (net && net->model) { - if (net->driver.virtio.name == VIR_DOMAIN_NET_BACKEND_TYPE_QEMU) - continue; - if (!virDomainNetIsVirtioModel(net)) - continue; - } - needsvhost = true; - } - } - if (needsvhost) - virBufferAddLit(&buf, " \"/dev/vhost-net\" rw,\n"); - if (needsVfio) { virBufferAddLit(&buf, " \"/dev/vfio/vfio\" rw,\n"); virBufferAddLit(&buf, " \"/dev/vfio/[0-9]*\" rw,\n");
A few things I noticed:
- if I launch a vm with a virtio net device, then I can detach/attach as much as I want - if I launch a vm with one virtio net device, then detach it, /dev/vhost-net is not removed from the profile. - if launch a vm with one virtio net device, then I detach it and I shutdown the vm with no attached network devices, on the next vm start, the device is present and the profile still has the access. IIRC, this is by design - if I remove the net device from the vm definition then libvirtd updates profile to not allow the access. When I start the vm I cannot attach a virtio net device because the access is denied (this bug) - /dev/vhost-net is root:root 600 and vms typically run as non-root (libvirt-qemu:kvm here) and therefore a qemu process would not be able to open the device on its own. The only reason why qemu can is because libvirt passes an fd to it, and it is when qemu writes to it that the access is denied
To me, it seems the real bug is that hotplug attach/detach is not updating the profile accordingly (attach adds it if it isn't there and detach removes it if no more net devices are present). Ideally, this would be the fix for this bug (we certainly support other hotplug/hotunplug events, like disks).
Yes ideally it would, but I that would be a major change how hotplug in general is handled by virt-aa-helper and I haven't had something like that around easily. I think we even talked about that quite a while a go when we also talked about the inability to get more insight into e.g. pools from the POV of virt-aa-helper. It is on my "long term find no time for it list" :-/
Considering that the device expands the attack surface to this part of the kernel and because the root:root 600 permissions show that non-root is not meant to access the device, this is most correct.
That said, libvirt itself is providing protection here because it is mediating the access to /dev/vhost-net for the VMs since the VMs can't open the device themselves and they must rely on libvirt to pass in the fd. Because of this, adding the access to the profile is not providing additional protections beyond DAC *for this common use case and configuration*. Conditionally adding the access would provide benefit when 'user = "root"' is set in qemu.conf or the device itself has different permissions that allow the access (eg, 660 root:kvm).
I maintain a preference for updating the profile on hotplug events. I'm willing to concede that adding the access for now until the correct solution is implemented would be acceptable, but I'd better like to understand how common it is to start a VM with no network devices and then hotplug one.
I agree that if the use case is unreasonable we might declare this as "work-as-intended" and the few people affected would then be supposed to add a local override opting-in to open /dev/vhost up to all guests. I'll ping on the bug for affected people to explain why/how they hit the case, that might shed some light on it to allow us making the decision if it is reasonable enough to concede the static rule as an interim solution until one day it would be detected correctly on every hotplug (and unplug) event.
Hi, there was no further comment here so far. On the bug the following is what I got: (Note that it was reported to be triggered by Openstack usage)
James Page: This is not the default otherwise no ones cloud would actually work right now. Instances are created with a network interface in paused state - at which point the interface plugging in neutron is executed; once that's completed the instance transitions to running and boots. That's the default behaviour with neutron/ml2/ovs driver. Are you using a different neutron driver?
Daniel Pawlik (bug reporter): I also use neutron ml2 ovs driver. I understand that in default nova policy, only administrator can spawn instance without any interface, but if someone else can "tune" the policy, he/she will have a problem.
No other feedback was added so far.
Today this was also added - quote here as FYI "The same behavior is reproduced in case when VM was created with network interface, interface detached, VM stopped (virsh destroy) and started again without network. This usecase does not need OpenStack admin privileges."
I personally tend to err on the side of caution and in this case would say an admin that wants to allow this can set up /dev/vhost-net as a local apparmor override.
@Libvirt maintainers and @Jamie for apparmor guidance. Is in your opinion that enough of a common case that we'd add the the path as static rule in general?
@JamesPage - you are likely the most experienced Openstack expert of us, what would be your opinion on the above?
-- Christian Ehrhardt Software Engineer, Ubuntu Server Canonical Ltd
-- Christian Ehrhardt Software Engineer, Ubuntu Server Canonical Ltd
On Wed, 20 Mar 2019, Christian Ehrhardt wrote:
On Wed, Mar 20, 2019 at 8:45 AM Christian Ehrhardt <christian.ehrhardt@canonical.com> wrote:
On Mon, Mar 4, 2019 at 11:42 AM Christian Ehrhardt <christian.ehrhardt@canonical.com> wrote:
On Fri, Mar 1, 2019 at 5:56 PM Jamie Strandboge <jamie@canonical.com> wrote:
On Mon, 18 Feb 2019, Christian Ehrhardt wrote:
So far we were detecting at guest start if any devices needed vhost net and only if that was true added a rule for /dev/vhost-net.
It turns out that it is an absolutely valid case to start a guest without any vhost-net networking but later on wanting to hotplug such a device which then would be denied by apparmor.
Unfortunately there also is no security labeling callback involved other than the one to /dev/net/tun. But on the other hand vhost-net is no more new and considered rather safe. Therefore drop the old detection and just add it as a static rule.
Fixes: https://bugs.launchpad.net/ubuntu/+source/libvirt/+bug/1815910
Signed-off-by: Christian Ehrhardt <christian.ehrhardt@canonical.com> --- src/security/apparmor/libvirt-qemu | 1 + src/security/virt-aa-helper.c | 17 +---------------- 2 files changed, 2 insertions(+), 16 deletions(-)
diff --git a/src/security/apparmor/libvirt-qemu b/src/security/apparmor/libvirt-qemu index eaa5167525..a71f34c175 100644 --- a/src/security/apparmor/libvirt-qemu +++ b/src/security/apparmor/libvirt-qemu @@ -21,6 +21,7 @@ signal (receive) peer=/usr/sbin/libvirtd,
/dev/net/tun rw, + /dev/vhost-net rw, /dev/kvm rw, /dev/ptmx rw, /dev/kqemu rw, diff --git a/src/security/virt-aa-helper.c b/src/security/virt-aa-helper.c index 8e22e9978a..ebc4feac77 100644 --- a/src/security/virt-aa-helper.c +++ b/src/security/virt-aa-helper.c @@ -937,7 +937,7 @@ get_files(vahControl * ctl) size_t i; char *uuid; char uuidstr[VIR_UUID_STRING_BUFLEN]; - bool needsVfio = false, needsvhost = false; + bool needsVfio = false;
/* verify uuid is same as what we were given on the command line */ virUUIDFormat(ctl->def->uuid, uuidstr); @@ -1248,21 +1248,6 @@ get_files(vahControl * ctl) } }
- if (ctl->def->virtType == VIR_DOMAIN_VIRT_KVM) { - for (i = 0; i < ctl->def->nnets; i++) { - virDomainNetDefPtr net = ctl->def->nets[i]; - if (net && net->model) { - if (net->driver.virtio.name == VIR_DOMAIN_NET_BACKEND_TYPE_QEMU) - continue; - if (!virDomainNetIsVirtioModel(net)) - continue; - } - needsvhost = true; - } - } - if (needsvhost) - virBufferAddLit(&buf, " \"/dev/vhost-net\" rw,\n"); - if (needsVfio) { virBufferAddLit(&buf, " \"/dev/vfio/vfio\" rw,\n"); virBufferAddLit(&buf, " \"/dev/vfio/[0-9]*\" rw,\n");
A few things I noticed:
- if I launch a vm with a virtio net device, then I can detach/attach as much as I want - if I launch a vm with one virtio net device, then detach it, /dev/vhost-net is not removed from the profile. - if launch a vm with one virtio net device, then I detach it and I shutdown the vm with no attached network devices, on the next vm start, the device is present and the profile still has the access. IIRC, this is by design - if I remove the net device from the vm definition then libvirtd updates profile to not allow the access. When I start the vm I cannot attach a virtio net device because the access is denied (this bug) - /dev/vhost-net is root:root 600 and vms typically run as non-root (libvirt-qemu:kvm here) and therefore a qemu process would not be able to open the device on its own. The only reason why qemu can is because libvirt passes an fd to it, and it is when qemu writes to it that the access is denied
To me, it seems the real bug is that hotplug attach/detach is not updating the profile accordingly (attach adds it if it isn't there and detach removes it if no more net devices are present). Ideally, this would be the fix for this bug (we certainly support other hotplug/hotunplug events, like disks).
Yes ideally it would, but I that would be a major change how hotplug in general is handled by virt-aa-helper and I haven't had something like that around easily. I think we even talked about that quite a while a go when we also talked about the inability to get more insight into e.g. pools from the POV of virt-aa-helper. It is on my "long term find no time for it list" :-/
Considering that the device expands the attack surface to this part of the kernel and because the root:root 600 permissions show that non-root is not meant to access the device, this is most correct.
That said, libvirt itself is providing protection here because it is mediating the access to /dev/vhost-net for the VMs since the VMs can't open the device themselves and they must rely on libvirt to pass in the fd. Because of this, adding the access to the profile is not providing additional protections beyond DAC *for this common use case and configuration*. Conditionally adding the access would provide benefit when 'user = "root"' is set in qemu.conf or the device itself has different permissions that allow the access (eg, 660 root:kvm).
I maintain a preference for updating the profile on hotplug events. I'm willing to concede that adding the access for now until the correct solution is implemented would be acceptable, but I'd better like to understand how common it is to start a VM with no network devices and then hotplug one.
I agree that if the use case is unreasonable we might declare this as "work-as-intended" and the few people affected would then be supposed to add a local override opting-in to open /dev/vhost up to all guests. I'll ping on the bug for affected people to explain why/how they hit the case, that might shed some light on it to allow us making the decision if it is reasonable enough to concede the static rule as an interim solution until one day it would be detected correctly on every hotplug (and unplug) event.
Hi, there was no further comment here so far. On the bug the following is what I got: (Note that it was reported to be triggered by Openstack usage)
James Page: This is not the default otherwise no ones cloud would actually work right now. Instances are created with a network interface in paused state - at which point the interface plugging in neutron is executed; once that's completed the instance transitions to running and boots. That's the default behaviour with neutron/ml2/ovs driver. Are you using a different neutron driver?
Daniel Pawlik (bug reporter): I also use neutron ml2 ovs driver. I understand that in default nova policy, only administrator can spawn instance without any interface, but if someone else can "tune" the policy, he/she will have a problem.
No other feedback was added so far.
Today this was also added - quote here as FYI "The same behavior is reproduced in case when VM was created with network interface, interface detached, VM stopped (virsh destroy) and started again without network. This usecase does not need OpenStack admin privileges."
I personally tend to err on the side of caution and in this case would say an admin that wants to allow this can set up /dev/vhost-net as a local apparmor override.
@Libvirt maintainers and @Jamie for apparmor guidance. Is in your opinion that enough of a common case that we'd add the the path as static rule in general?
@JamesPage - you are likely the most experienced Openstack expert of us, what would be your opinion on the above?
I maintain my preference as stated above for upstream libvirt since libvirt supports other configurations besides the default of running as non-root. Admins and distros are free to add the access as dictated by their requirements. I guess it would be conceivable to instead of addressing the real bug, checking if libvirt is configured to run VMs as non-root and if so, adding the access. This is really a band-aid on the problem and potentially confusing for users. I'd much rather see that effort go towards fixing the hotplug/unplug issue. -- Jamie Strandboge | http://www.canonical.com
participants (2)
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Christian Ehrhardt -
Jamie Strandboge