[PATCH] qemu: Label vhostuser net device
Attaching a newly created vhostuser port to a VM fails due to an apparmor denial internal error: unable to execute QEMU command 'chardev-add': Failed to bind socket to /run/openvswitch/vhu838c4d29-c9: Permission denied In the case of a net device type VIR_DOMAIN_NET_TYPE_VHOSTUSER, the underlying chardev is not labeled in qemuDomainAttachNetDevice prior to calling qemuMonitorAttachCharDev. Label the chardev before calling qemuMonitorAttachCharDev, and restore the label when removing the net device. Signed-off-by: Jim Fehlig <jfehlig@suse.com> --- src/qemu/qemu_hotplug.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c index c00e8a7852..42e7997112 100644 --- a/src/qemu/qemu_hotplug.c +++ b/src/qemu/qemu_hotplug.c @@ -1467,6 +1467,11 @@ qemuDomainAttachNetDevice(virQEMUDriver *driver, } if (actualType == VIR_DOMAIN_NET_TYPE_VHOSTUSER) { + virDomainChrDef chr = { .source = net->data.vhostuser }; + + if (qemuSecuritySetChardevLabel(driver, vm, &chr) < 0) + goto cleanup; + if (qemuMonitorAttachCharDev(priv->mon, charDevAlias, net->data.vhostuser) < 0) { ignore_value(qemuDomainObjExitMonitor(driver, vm)); virDomainAuditNet(vm, NULL, net, "attach", false); @@ -4692,6 +4697,8 @@ qemuDomainRemoveNetDevice(virQEMUDriver *driver, } if (actualType == VIR_DOMAIN_NET_TYPE_VHOSTUSER) { + virDomainChrDef chr = { .source = net->data.vhostuser }; + /* vhostuser has a chardev too */ if (qemuMonitorDetachCharDev(priv->mon, charDevAlias) < 0) { /* well, this is a messy situation. Guest visible PCI device has @@ -4699,6 +4706,8 @@ qemuDomainRemoveNetDevice(virQEMUDriver *driver, * to just ignore the error and carry on. */ } + if (qemuSecurityRestoreChardevLabel(driver, vm, &chr) < 0) + VIR_WARN("Unable to restore security label on vhostuser char device"); } else if (actualType == VIR_DOMAIN_NET_TYPE_VDPA) { int vdpafdset = -1; g_autoptr(qemuMonitorFdsets) fdsets = NULL; -- 2.32.0
On 8/13/21 11:36 PM, Jim Fehlig wrote:
Attaching a newly created vhostuser port to a VM fails due to an apparmor denial
internal error: unable to execute QEMU command 'chardev-add': Failed to bind socket to /run/openvswitch/vhu838c4d29-c9: Permission denied
In the case of a net device type VIR_DOMAIN_NET_TYPE_VHOSTUSER, the underlying chardev is not labeled in qemuDomainAttachNetDevice prior to calling qemuMonitorAttachCharDev. Label the chardev before calling qemuMonitorAttachCharDev, and restore the label when removing the net device.
Signed-off-by: Jim Fehlig <jfehlig@suse.com> --- src/qemu/qemu_hotplug.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c index c00e8a7852..42e7997112 100644 --- a/src/qemu/qemu_hotplug.c +++ b/src/qemu/qemu_hotplug.c @@ -1467,6 +1467,11 @@ qemuDomainAttachNetDevice(virQEMUDriver *driver, }
if (actualType == VIR_DOMAIN_NET_TYPE_VHOSTUSER) { + virDomainChrDef chr = { .source = net->data.vhostuser }; + + if (qemuSecuritySetChardevLabel(driver, vm, &chr) < 0) + goto cleanup; + if (qemuMonitorAttachCharDev(priv->mon, charDevAlias, net->data.vhostuser) < 0) { ignore_value(qemuDomainObjExitMonitor(driver, vm)); virDomainAuditNet(vm, NULL, net, "attach", false); @@ -4692,6 +4697,8 @@ qemuDomainRemoveNetDevice(virQEMUDriver *driver, }
if (actualType == VIR_DOMAIN_NET_TYPE_VHOSTUSER) { + virDomainChrDef chr = { .source = net->data.vhostuser }; + /* vhostuser has a chardev too */ if (qemuMonitorDetachCharDev(priv->mon, charDevAlias) < 0) { /* well, this is a messy situation. Guest visible PCI device has @@ -4699,6 +4706,8 @@ qemuDomainRemoveNetDevice(virQEMUDriver *driver, * to just ignore the error and carry on. */ } + if (qemuSecurityRestoreChardevLabel(driver, vm, &chr) < 0) + VIR_WARN("Unable to restore security label on vhostuser char device"); } else if (actualType == VIR_DOMAIN_NET_TYPE_VDPA) { int vdpafdset = -1; g_autoptr(qemuMonitorFdsets) fdsets = NULL;
What an interesting bug. Previously we assumed that the UNIX socket is created with broad enough permissions so that QEMU can connect to it. I mean, when a VM is starting up nor DAC nor SELinux drivers care about VHOSTUSER. It's AppArmor driver that cares. And it makes sense. But, what's problematic here is that upon attach the socket perms will be changed (because both DAC and SELinux drivers implement domainSetSecurityChardevLabel callback). And since sockets can't have XATTRs libvirt won't remember its original labels and thus subsequent restore changes owner to root:root. So I think we should address this inconsistency in behavior. But I don't know how :-( Also, looking at the code itself - please move qemuSecurity* calls outside of the monitor code. I mean, qemuDomainAttachNetDevice() has a section that prepares interfaces before calling qemuDomainObjEnterMonitor(). That looks like a better place to call qemuSecuritySetChardevLabel(). Similarly, the restore in detach path should be done outside of monitor handling code. Oh, a side note - don't forget that hotplug can fail and thus the seclabel should be restored if it was set. If you want to look around for inspiration, we usually use teardownlabel variable for that. Michal
On 8/17/21 4:13 AM, Michal Prívozník wrote:
On 8/13/21 11:36 PM, Jim Fehlig wrote:
Attaching a newly created vhostuser port to a VM fails due to an apparmor denial
internal error: unable to execute QEMU command 'chardev-add': Failed to bind socket to /run/openvswitch/vhu838c4d29-c9: Permission denied
In the case of a net device type VIR_DOMAIN_NET_TYPE_VHOSTUSER, the underlying chardev is not labeled in qemuDomainAttachNetDevice prior to calling qemuMonitorAttachCharDev. Label the chardev before calling qemuMonitorAttachCharDev, and restore the label when removing the net device.
Signed-off-by: Jim Fehlig <jfehlig@suse.com> --- src/qemu/qemu_hotplug.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c index c00e8a7852..42e7997112 100644 --- a/src/qemu/qemu_hotplug.c +++ b/src/qemu/qemu_hotplug.c @@ -1467,6 +1467,11 @@ qemuDomainAttachNetDevice(virQEMUDriver *driver, }
if (actualType == VIR_DOMAIN_NET_TYPE_VHOSTUSER) { + virDomainChrDef chr = { .source = net->data.vhostuser }; + + if (qemuSecuritySetChardevLabel(driver, vm, &chr) < 0) + goto cleanup; + if (qemuMonitorAttachCharDev(priv->mon, charDevAlias, net->data.vhostuser) < 0) { ignore_value(qemuDomainObjExitMonitor(driver, vm)); virDomainAuditNet(vm, NULL, net, "attach", false); @@ -4692,6 +4697,8 @@ qemuDomainRemoveNetDevice(virQEMUDriver *driver, }
if (actualType == VIR_DOMAIN_NET_TYPE_VHOSTUSER) { + virDomainChrDef chr = { .source = net->data.vhostuser }; + /* vhostuser has a chardev too */ if (qemuMonitorDetachCharDev(priv->mon, charDevAlias) < 0) { /* well, this is a messy situation. Guest visible PCI device has @@ -4699,6 +4706,8 @@ qemuDomainRemoveNetDevice(virQEMUDriver *driver, * to just ignore the error and carry on. */ } + if (qemuSecurityRestoreChardevLabel(driver, vm, &chr) < 0) + VIR_WARN("Unable to restore security label on vhostuser char device"); } else if (actualType == VIR_DOMAIN_NET_TYPE_VDPA) { int vdpafdset = -1; g_autoptr(qemuMonitorFdsets) fdsets = NULL;
What an interesting bug. Previously we assumed that the UNIX socket is created with broad enough permissions so that QEMU can connect to it. I mean, when a VM is starting up nor DAC nor SELinux drivers care about VHOSTUSER. It's AppArmor driver that cares. And it makes sense. But, what's problematic here is that upon attach the socket perms will be changed (because both DAC and SELinux drivers implement domainSetSecurityChardevLabel callback). And since sockets can't have XATTRs libvirt won't remember its original labels and thus subsequent restore changes owner to root:root.
How are existing chardevs with socket backends handled? It seems they would suffer the same problem when restoring the labels. The DAC and selinux callbacks seem to avoid labeling for "server" sockets https://gitlab.com/libvirt/libvirt/-/blob/master/src/security/security_dac.c... https://gitlab.com/libvirt/libvirt/-/blob/master/src/security/security_selin...
So I think we should address this inconsistency in behavior. But I don't know how :-(
My first attempt at fixing this introduced domain{Set,Restore}SecurityNetdevLabel to the security driver, but it seemed like overkill after I discovered virDomainChrSourceDef embedded in the virDomainNetDef structure. I can revisit that approach if it sounds more promising.
Also, looking at the code itself - please move qemuSecurity* calls outside of the monitor code. I mean, qemuDomainAttachNetDevice() has a section that prepares interfaces before calling qemuDomainObjEnterMonitor(). That looks like a better place to call qemuSecuritySetChardevLabel(). Similarly, the restore in detach path should be done outside of monitor handling code.
Good point. I'll change it in V2.
Oh, a side note - don't forget that hotplug can fail and thus the seclabel should be restored if it was set. If you want to look around for inspiration, we usually use teardownlabel variable for that.
Thanks for catching that! I'll fix it in V2. Before working on V2 I'd like to resolve your first item. Is it safe to use qemuSecuritySetChardevLabel for a vhostuser net device? Is the underlying socket always in listen mode for these devices? At least when adding an openvswitch vhostuser port to a running VM, the underlying socket has 'server=true' 2021-04-22 15:29:40.261+0000: 643: debug : qemuMonitorJSONCheckError:401 : unable to execute QEMU command {"execute":"chardev-add","arguments":{"id":"charnet1","backend":{"type":"socket","data":{"addr":{"type":"unix","data":{"path":"/run/openvswitch/vhu2fca98d5-52"}},"wait":false,"server":true}}},"id":"libvirt-689"}: {"id":"libvirt-689","error":{"class":"GenericError","desc":"Failed to bind socket to /run/openvswitch/vhu2fca98d5-52: Permission denied"}} Regards, Jim
On 8/17/21 12:11 PM, Jim Fehlig wrote:
On 8/17/21 4:13 AM, Michal Prívozník wrote:
On 8/13/21 11:36 PM, Jim Fehlig wrote:
Attaching a newly created vhostuser port to a VM fails due to an apparmor denial
internal error: unable to execute QEMU command 'chardev-add': Failed to bind socket to /run/openvswitch/vhu838c4d29-c9: Permission denied
In the case of a net device type VIR_DOMAIN_NET_TYPE_VHOSTUSER, the underlying chardev is not labeled in qemuDomainAttachNetDevice prior to calling qemuMonitorAttachCharDev. Label the chardev before calling qemuMonitorAttachCharDev, and restore the label when removing the net device.
Signed-off-by: Jim Fehlig <jfehlig@suse.com> --- src/qemu/qemu_hotplug.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c index c00e8a7852..42e7997112 100644 --- a/src/qemu/qemu_hotplug.c +++ b/src/qemu/qemu_hotplug.c @@ -1467,6 +1467,11 @@ qemuDomainAttachNetDevice(virQEMUDriver *driver, } if (actualType == VIR_DOMAIN_NET_TYPE_VHOSTUSER) { + virDomainChrDef chr = { .source = net->data.vhostuser }; + + if (qemuSecuritySetChardevLabel(driver, vm, &chr) < 0) + goto cleanup; + if (qemuMonitorAttachCharDev(priv->mon, charDevAlias, net->data.vhostuser) < 0) { ignore_value(qemuDomainObjExitMonitor(driver, vm)); virDomainAuditNet(vm, NULL, net, "attach", false); @@ -4692,6 +4697,8 @@ qemuDomainRemoveNetDevice(virQEMUDriver *driver, } if (actualType == VIR_DOMAIN_NET_TYPE_VHOSTUSER) { + virDomainChrDef chr = { .source = net->data.vhostuser }; + /* vhostuser has a chardev too */ if (qemuMonitorDetachCharDev(priv->mon, charDevAlias) < 0) { /* well, this is a messy situation. Guest visible PCI device has @@ -4699,6 +4706,8 @@ qemuDomainRemoveNetDevice(virQEMUDriver *driver, * to just ignore the error and carry on. */ } + if (qemuSecurityRestoreChardevLabel(driver, vm, &chr) < 0) + VIR_WARN("Unable to restore security label on vhostuser char device"); } else if (actualType == VIR_DOMAIN_NET_TYPE_VDPA) { int vdpafdset = -1; g_autoptr(qemuMonitorFdsets) fdsets = NULL;
What an interesting bug. Previously we assumed that the UNIX socket is created with broad enough permissions so that QEMU can connect to it. I mean, when a VM is starting up nor DAC nor SELinux drivers care about VHOSTUSER. It's AppArmor driver that cares. And it makes sense. But, what's problematic here is that upon attach the socket perms will be changed (because both DAC and SELinux drivers implement domainSetSecurityChardevLabel callback). And since sockets can't have XATTRs libvirt won't remember its original labels and thus subsequent restore changes owner to root:root.
How are existing chardevs with socket backends handled? It seems they would suffer the same problem when restoring the labels. The DAC and selinux callbacks seem to avoid labeling for "server" sockets
https://gitlab.com/libvirt/libvirt/-/blob/master/src/security/security_dac.c... https://gitlab.com/libvirt/libvirt/-/blob/master/src/security/security_selin...
So I think we should address this inconsistency in behavior. But I don't know how :-(
My first attempt at fixing this introduced domain{Set,Restore}SecurityNetdevLabel to the security driver, but it seemed like overkill after I discovered virDomainChrSourceDef embedded in the virDomainNetDef structure. I can revisit that approach if it sounds more promising.
Also, looking at the code itself - please move qemuSecurity* calls outside of the monitor code. I mean, qemuDomainAttachNetDevice() has a section that prepares interfaces before calling qemuDomainObjEnterMonitor(). That looks like a better place to call qemuSecuritySetChardevLabel(). Similarly, the restore in detach path should be done outside of monitor handling code.
Good point. I'll change it in V2.
Oh, a side note - don't forget that hotplug can fail and thus the seclabel should be restored if it was set. If you want to look around for inspiration, we usually use teardownlabel variable for that.
Thanks for catching that! I'll fix it in V2.
Before working on V2 I'd like to resolve your first item. Is it safe to use qemuSecuritySetChardevLabel for a vhostuser net device? Is the underlying socket always in listen mode for these devices?
Answering my own question: No. A vhostuser interface can have a mode='client|server' setting on the <source> element describing the socket. Perhaps the big hammer of adding domain{Set,Restore}SecurityNetdevLabel APIs is what's needed for this small nail? Regards, Jim
At least when adding an openvswitch vhostuser port to a running VM, the underlying socket has 'server=true'
2021-04-22 15:29:40.261+0000: 643: debug : qemuMonitorJSONCheckError:401 : unable to execute QEMU command {"execute":"chardev-add","arguments":{"id":"charnet1","backend":{"type":"socket","data":{"addr":{"type":"unix","data":{"path":"/run/openvswitch/vhu2fca98d5-52"}},"wait":false,"server":true}}},"id":"libvirt-689"}: {"id":"libvirt-689","error":{"class":"GenericError","desc":"Failed to bind socket to /run/openvswitch/vhu2fca98d5-52: Permission denied"}}
Regards, Jim
On 8/18/21 12:31 AM, Jim Fehlig wrote:
On 8/17/21 12:11 PM, Jim Fehlig wrote:
On 8/17/21 4:13 AM, Michal Prívozník wrote:
On 8/13/21 11:36 PM, Jim Fehlig wrote:
Attaching a newly created vhostuser port to a VM fails due to an apparmor denial
internal error: unable to execute QEMU command 'chardev-add': Failed to bind socket to /run/openvswitch/vhu838c4d29-c9: Permission denied
In the case of a net device type VIR_DOMAIN_NET_TYPE_VHOSTUSER, the underlying chardev is not labeled in qemuDomainAttachNetDevice prior to calling qemuMonitorAttachCharDev. Label the chardev before calling qemuMonitorAttachCharDev, and restore the label when removing the net device.
Signed-off-by: Jim Fehlig <jfehlig@suse.com> --- src/qemu/qemu_hotplug.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c index c00e8a7852..42e7997112 100644 --- a/src/qemu/qemu_hotplug.c +++ b/src/qemu/qemu_hotplug.c @@ -1467,6 +1467,11 @@ qemuDomainAttachNetDevice(virQEMUDriver *driver, } if (actualType == VIR_DOMAIN_NET_TYPE_VHOSTUSER) { + virDomainChrDef chr = { .source = net->data.vhostuser }; + + if (qemuSecuritySetChardevLabel(driver, vm, &chr) < 0) + goto cleanup; + if (qemuMonitorAttachCharDev(priv->mon, charDevAlias, net->data.vhostuser) < 0) { ignore_value(qemuDomainObjExitMonitor(driver, vm)); virDomainAuditNet(vm, NULL, net, "attach", false); @@ -4692,6 +4697,8 @@ qemuDomainRemoveNetDevice(virQEMUDriver *driver, } if (actualType == VIR_DOMAIN_NET_TYPE_VHOSTUSER) { + virDomainChrDef chr = { .source = net->data.vhostuser }; + /* vhostuser has a chardev too */ if (qemuMonitorDetachCharDev(priv->mon, charDevAlias) < 0) { /* well, this is a messy situation. Guest visible PCI device has @@ -4699,6 +4706,8 @@ qemuDomainRemoveNetDevice(virQEMUDriver *driver, * to just ignore the error and carry on. */ } + if (qemuSecurityRestoreChardevLabel(driver, vm, &chr) < 0) + VIR_WARN("Unable to restore security label on vhostuser char device"); } else if (actualType == VIR_DOMAIN_NET_TYPE_VDPA) { int vdpafdset = -1; g_autoptr(qemuMonitorFdsets) fdsets = NULL;
What an interesting bug. Previously we assumed that the UNIX socket is created with broad enough permissions so that QEMU can connect to it. I mean, when a VM is starting up nor DAC nor SELinux drivers care about VHOSTUSER. It's AppArmor driver that cares. And it makes sense. But, what's problematic here is that upon attach the socket perms will be changed (because both DAC and SELinux drivers implement domainSetSecurityChardevLabel callback). And since sockets can't have XATTRs libvirt won't remember its original labels and thus subsequent restore changes owner to root:root.
How are existing chardevs with socket backends handled? It seems they would suffer the same problem when restoring the labels. The DAC and selinux callbacks seem to avoid labeling for "server" sockets
https://gitlab.com/libvirt/libvirt/-/blob/master/src/security/security_dac.c...
https://gitlab.com/libvirt/libvirt/-/blob/master/src/security/security_selin...
Yeah, you're right. But I view chardevs as runtime, fire and go things. I mean, you start a VM with a chardev, say an UNIX socket and its lifetime is identical to the VM lifetime. vhostuser on the other hand is handled by a third party daemon (typically OVS) and thus UNIX socket lifetime is different to VM lifetime. IOW, I worry that if we changed the UNIX socket label we might be preventing other VMs from connecting to it. And I don't even know if a single socket can be shared between two VMs. For instance, if OVS created an UNIX socket whether I can attach vhostuser interface to one domain and then to the other. Because if I could, then we should not change labels. Perhaps Laine can shed more light here. I do understand that apparmor needs to add an entry to the VM's profile, but I worry that DAC and SELinux might screw things up.
So I think we should address this inconsistency in behavior. But I don't know how :-(
My first attempt at fixing this introduced domain{Set,Restore}SecurityNetdevLabel to the security driver, but it seemed like overkill after I discovered virDomainChrSourceDef embedded in the virDomainNetDef structure. I can revisit that approach if it sounds more promising.
I think it does sound more promising given my assumption above is correct. This way we can have only AppArmor driver implement the callback leaving us with consistent behavior. Michal
On 8/18/21 4:21 AM, Michal Prívozník wrote:
On 8/18/21 12:31 AM, Jim Fehlig wrote:
On 8/17/21 12:11 PM, Jim Fehlig wrote:
On 8/17/21 4:13 AM, Michal Prívozník wrote:
On 8/13/21 11:36 PM, Jim Fehlig wrote:
Attaching a newly created vhostuser port to a VM fails due to an apparmor denial
internal error: unable to execute QEMU command 'chardev-add': Failed to bind socket to /run/openvswitch/vhu838c4d29-c9: Permission denied
In the case of a net device type VIR_DOMAIN_NET_TYPE_VHOSTUSER, the underlying chardev is not labeled in qemuDomainAttachNetDevice prior to calling qemuMonitorAttachCharDev. Label the chardev before calling qemuMonitorAttachCharDev, and restore the label when removing the net device.
Signed-off-by: Jim Fehlig <jfehlig@suse.com> --- src/qemu/qemu_hotplug.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c index c00e8a7852..42e7997112 100644 --- a/src/qemu/qemu_hotplug.c +++ b/src/qemu/qemu_hotplug.c @@ -1467,6 +1467,11 @@ qemuDomainAttachNetDevice(virQEMUDriver *driver, } if (actualType == VIR_DOMAIN_NET_TYPE_VHOSTUSER) { + virDomainChrDef chr = { .source = net->data.vhostuser }; + + if (qemuSecuritySetChardevLabel(driver, vm, &chr) < 0) + goto cleanup; + if (qemuMonitorAttachCharDev(priv->mon, charDevAlias, net->data.vhostuser) < 0) { ignore_value(qemuDomainObjExitMonitor(driver, vm)); virDomainAuditNet(vm, NULL, net, "attach", false); @@ -4692,6 +4697,8 @@ qemuDomainRemoveNetDevice(virQEMUDriver *driver, } if (actualType == VIR_DOMAIN_NET_TYPE_VHOSTUSER) { + virDomainChrDef chr = { .source = net->data.vhostuser }; + /* vhostuser has a chardev too */ if (qemuMonitorDetachCharDev(priv->mon, charDevAlias) < 0) { /* well, this is a messy situation. Guest visible PCI device has @@ -4699,6 +4706,8 @@ qemuDomainRemoveNetDevice(virQEMUDriver *driver, * to just ignore the error and carry on. */ } + if (qemuSecurityRestoreChardevLabel(driver, vm, &chr) < 0) + VIR_WARN("Unable to restore security label on vhostuser char device"); } else if (actualType == VIR_DOMAIN_NET_TYPE_VDPA) { int vdpafdset = -1; g_autoptr(qemuMonitorFdsets) fdsets = NULL;
What an interesting bug. Previously we assumed that the UNIX socket is created with broad enough permissions so that QEMU can connect to it. I mean, when a VM is starting up nor DAC nor SELinux drivers care about VHOSTUSER. It's AppArmor driver that cares. And it makes sense. But, what's problematic here is that upon attach the socket perms will be changed (because both DAC and SELinux drivers implement domainSetSecurityChardevLabel callback). And since sockets can't have XATTRs libvirt won't remember its original labels and thus subsequent restore changes owner to root:root.
How are existing chardevs with socket backends handled? It seems they would suffer the same problem when restoring the labels. The DAC and selinux callbacks seem to avoid labeling for "server" sockets
https://gitlab.com/libvirt/libvirt/-/blob/master/src/security/security_dac.c...
https://gitlab.com/libvirt/libvirt/-/blob/master/src/security/security_selin...
Yeah, you're right. But I view chardevs as runtime, fire and go things. I mean, you start a VM with a chardev, say an UNIX socket and its lifetime is identical to the VM lifetime. vhostuser on the other hand is handled by a third party daemon (typically OVS) and thus UNIX socket lifetime is different to VM lifetime. IOW, I worry that if we changed the UNIX socket label we might be preventing other VMs from connecting to it.
And I don't even know if a single socket can be shared between two VMs. For instance, if OVS created an UNIX socket whether I can attach vhostuser interface to one domain and then to the other. Because if I could, then we should not change labels.
Perhaps Laine can shed more light here.
Sorry, I really know nothing about this topic. Who would be the proper person at the next level down to ask? Michael, do you know?
I do understand that apparmor needs to add an entry to the VM's profile, but I worry that DAC and SELinux might screw things up.
So I think we should address this inconsistency in behavior. But I don't know how :-(
My first attempt at fixing this introduced domain{Set,Restore}SecurityNetdevLabel to the security driver, but it seemed like overkill after I discovered virDomainChrSourceDef embedded in the virDomainNetDef structure. I can revisit that approach if it sounds more promising.
I think it does sound more promising given my assumption above is correct. This way we can have only AppArmor driver implement the callback leaving us with consistent behavior.
Michal
On Wed, Aug 18, 2021 at 09:00:52AM -0400, Laine Stump wrote:
On 8/18/21 4:21 AM, Michal Prívozník wrote:
On 8/18/21 12:31 AM, Jim Fehlig wrote:
On 8/17/21 12:11 PM, Jim Fehlig wrote:
On 8/17/21 4:13 AM, Michal Prívozník wrote:
On 8/13/21 11:36 PM, Jim Fehlig wrote:
Attaching a newly created vhostuser port to a VM fails due to an apparmor denial
internal error: unable to execute QEMU command 'chardev-add': Failed to bind socket to /run/openvswitch/vhu838c4d29-c9: Permission denied
In the case of a net device type VIR_DOMAIN_NET_TYPE_VHOSTUSER, the underlying chardev is not labeled in qemuDomainAttachNetDevice prior to calling qemuMonitorAttachCharDev. Label the chardev before calling qemuMonitorAttachCharDev, and restore the label when removing the net device.
Signed-off-by: Jim Fehlig <jfehlig@suse.com> --- src/qemu/qemu_hotplug.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c index c00e8a7852..42e7997112 100644 --- a/src/qemu/qemu_hotplug.c +++ b/src/qemu/qemu_hotplug.c @@ -1467,6 +1467,11 @@ qemuDomainAttachNetDevice(virQEMUDriver *driver, } if (actualType == VIR_DOMAIN_NET_TYPE_VHOSTUSER) { + virDomainChrDef chr = { .source = net->data.vhostuser }; + + if (qemuSecuritySetChardevLabel(driver, vm, &chr) < 0) + goto cleanup; + if (qemuMonitorAttachCharDev(priv->mon, charDevAlias, net->data.vhostuser) < 0) { ignore_value(qemuDomainObjExitMonitor(driver, vm)); virDomainAuditNet(vm, NULL, net, "attach", false); @@ -4692,6 +4697,8 @@ qemuDomainRemoveNetDevice(virQEMUDriver *driver, } if (actualType == VIR_DOMAIN_NET_TYPE_VHOSTUSER) { + virDomainChrDef chr = { .source = net->data.vhostuser }; + /* vhostuser has a chardev too */ if (qemuMonitorDetachCharDev(priv->mon, charDevAlias) < 0) { /* well, this is a messy situation. Guest visible PCI device has @@ -4699,6 +4706,8 @@ qemuDomainRemoveNetDevice(virQEMUDriver *driver, * to just ignore the error and carry on. */ } + if (qemuSecurityRestoreChardevLabel(driver, vm, &chr) < 0) + VIR_WARN("Unable to restore security label on vhostuser char device"); } else if (actualType == VIR_DOMAIN_NET_TYPE_VDPA) { int vdpafdset = -1; g_autoptr(qemuMonitorFdsets) fdsets = NULL;
What an interesting bug. Previously we assumed that the UNIX socket is created with broad enough permissions so that QEMU can connect to it. I mean, when a VM is starting up nor DAC nor SELinux drivers care about VHOSTUSER. It's AppArmor driver that cares. And it makes sense. But, what's problematic here is that upon attach the socket perms will be changed (because both DAC and SELinux drivers implement domainSetSecurityChardevLabel callback). And since sockets can't have XATTRs libvirt won't remember its original labels and thus subsequent restore changes owner to root:root.
How are existing chardevs with socket backends handled? It seems they would suffer the same problem when restoring the labels. The DAC and selinux callbacks seem to avoid labeling for "server" sockets
https://gitlab.com/libvirt/libvirt/-/blob/master/src/security/security_dac.c...
https://gitlab.com/libvirt/libvirt/-/blob/master/src/security/security_selin...
Yeah, you're right. But I view chardevs as runtime, fire and go things. I mean, you start a VM with a chardev, say an UNIX socket and its lifetime is identical to the VM lifetime. vhostuser on the other hand is handled by a third party daemon (typically OVS) and thus UNIX socket lifetime is different to VM lifetime. IOW, I worry that if we changed the UNIX socket label we might be preventing other VMs from connecting to it.
And I don't even know if a single socket can be shared between two VMs. For instance, if OVS created an UNIX socket whether I can attach vhostuser interface to one domain and then to the other. Because if I could, then we should not change labels.
Perhaps Laine can shed more light here.
Sorry, I really know nothing about this topic. Who would be the proper person at the next level down to ask? Michael, do you know?
hmm... Maxime?
I do understand that apparmor needs to add an entry to the VM's profile, but I worry that DAC and SELinux might screw things up.
So I think we should address this inconsistency in behavior. But I don't know how :-(
My first attempt at fixing this introduced domain{Set,Restore}SecurityNetdevLabel to the security driver, but it seemed like overkill after I discovered virDomainChrSourceDef embedded in the virDomainNetDef structure. I can revisit that approach if it sounds more promising.
I think it does sound more promising given my assumption above is correct. This way we can have only AppArmor driver implement the callback leaving us with consistent behavior.
Michal
On 8/19/21 11:10 AM, Michael S. Tsirkin wrote:
On Wed, Aug 18, 2021 at 09:00:52AM -0400, Laine Stump wrote:
On 8/18/21 4:21 AM, Michal Prívozník wrote:
On 8/18/21 12:31 AM, Jim Fehlig wrote:
On 8/17/21 12:11 PM, Jim Fehlig wrote:
On 8/17/21 4:13 AM, Michal Prívozník wrote:
On 8/13/21 11:36 PM, Jim Fehlig wrote: > Attaching a newly created vhostuser port to a VM fails due to an > apparmor denial > > internal error: unable to execute QEMU command 'chardev-add': Failed > to bind socket to /run/openvswitch/vhu838c4d29-c9: Permission denied > > In the case of a net device type VIR_DOMAIN_NET_TYPE_VHOSTUSER, the > underlying chardev is not labeled in qemuDomainAttachNetDevice prior > to calling qemuMonitorAttachCharDev. Label the chardev before calling > qemuMonitorAttachCharDev, and restore the label when removing the > net device. > > Signed-off-by: Jim Fehlig <jfehlig@suse.com> > --- > src/qemu/qemu_hotplug.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c > index c00e8a7852..42e7997112 100644 > --- a/src/qemu/qemu_hotplug.c > +++ b/src/qemu/qemu_hotplug.c > @@ -1467,6 +1467,11 @@ qemuDomainAttachNetDevice(virQEMUDriver *driver, > } > if (actualType == VIR_DOMAIN_NET_TYPE_VHOSTUSER) { > + virDomainChrDef chr = { .source = net->data.vhostuser }; > + > + if (qemuSecuritySetChardevLabel(driver, vm, &chr) < 0) > + goto cleanup; > + > if (qemuMonitorAttachCharDev(priv->mon, charDevAlias, > net->data.vhostuser) < 0) { > ignore_value(qemuDomainObjExitMonitor(driver, vm)); > virDomainAuditNet(vm, NULL, net, "attach", false); > @@ -4692,6 +4697,8 @@ qemuDomainRemoveNetDevice(virQEMUDriver *driver, > } > if (actualType == VIR_DOMAIN_NET_TYPE_VHOSTUSER) { > + virDomainChrDef chr = { .source = net->data.vhostuser }; > + > /* vhostuser has a chardev too */ > if (qemuMonitorDetachCharDev(priv->mon, charDevAlias) < 0) { > /* well, this is a messy situation. Guest visible PCI > device has > @@ -4699,6 +4706,8 @@ qemuDomainRemoveNetDevice(virQEMUDriver *driver, > * to just ignore the error and carry on. > */ > } > + if (qemuSecurityRestoreChardevLabel(driver, vm, &chr) < 0) > + VIR_WARN("Unable to restore security label on vhostuser > char device"); > } else if (actualType == VIR_DOMAIN_NET_TYPE_VDPA) { > int vdpafdset = -1; > g_autoptr(qemuMonitorFdsets) fdsets = NULL; >
What an interesting bug. Previously we assumed that the UNIX socket is created with broad enough permissions so that QEMU can connect to it. I mean, when a VM is starting up nor DAC nor SELinux drivers care about VHOSTUSER. It's AppArmor driver that cares. And it makes sense. But, what's problematic here is that upon attach the socket perms will be changed (because both DAC and SELinux drivers implement domainSetSecurityChardevLabel callback). And since sockets can't have XATTRs libvirt won't remember its original labels and thus subsequent restore changes owner to root:root.
How are existing chardevs with socket backends handled? It seems they would suffer the same problem when restoring the labels. The DAC and selinux callbacks seem to avoid labeling for "server" sockets
https://gitlab.com/libvirt/libvirt/-/blob/master/src/security/security_dac.c...
https://gitlab.com/libvirt/libvirt/-/blob/master/src/security/security_selin...
Yeah, you're right. But I view chardevs as runtime, fire and go things. I mean, you start a VM with a chardev, say an UNIX socket and its lifetime is identical to the VM lifetime. vhostuser on the other hand is handled by a third party daemon (typically OVS) and thus UNIX socket lifetime is different to VM lifetime. IOW, I worry that if we changed the UNIX socket label we might be preventing other VMs from connecting to it.
And I don't even know if a single socket can be shared between two VMs. For instance, if OVS created an UNIX socket whether I can attach vhostuser interface to one domain and then to the other. Because if I could, then we should not change labels.
In theory, I think there is nothing that prevents a Vhost-user socket created by OVS to be used by one VM and later by another one. But in practice, the management layer likely request OVS a new socket on VM creation. I'd like to add that the mode where OVS is the Vhost-user socket server is deprecated in OVS (but not yet removed) [0]: " Open vSwitch provides two types of vHost User ports: vhost-user (dpdkvhostuser) vhost-user-client (dpdkvhostuserclient) vHost User uses a client-server model. The server creates/manages/destroys the vHost User sockets, and the client connects to the server. Depending on which port type you use, dpdkvhostuser or dpdkvhostuserclient, a different configuration of the client-server model is used. For vhost-user ports, Open vSwitch acts as the server and QEMU the client. This means if OVS dies, all VMs must be restarted. On the other hand, for vhost-user-client ports, OVS acts as the client and QEMU the server. This means OVS can die and be restarted without issue, and it is also possible to restart an instance itself. For this reason, vhost-user-client ports are the preferred type for all known use cases; the only limitation is that vhost-user client mode ports require QEMU version 2.7. Ports of type vhost-user are currently deprecated and will be removed in a future release. "
Perhaps Laine can shed more light here.
Sorry, I really know nothing about this topic. Who would be the proper person at the next level down to ask? Michael, do you know?
hmm... Maxime?
I do understand that apparmor needs to add an entry to the VM's profile, but I worry that DAC and SELinux might screw things up.
So I think we should address this inconsistency in behavior. But I don't know how :-(
My first attempt at fixing this introduced domain{Set,Restore}SecurityNetdevLabel to the security driver, but it seemed like overkill after I discovered virDomainChrSourceDef embedded in the virDomainNetDef structure. I can revisit that approach if it sounds more promising.
I think it does sound more promising given my assumption above is correct. This way we can have only AppArmor driver implement the callback leaving us with consistent behavior.
Michal
On 8/18/21 2:21 AM, Michal Prívozník wrote:
On 8/18/21 12:31 AM, Jim Fehlig wrote:
On 8/17/21 12:11 PM, Jim Fehlig wrote:
On 8/17/21 4:13 AM, Michal Prívozník wrote:
On 8/13/21 11:36 PM, Jim Fehlig wrote:
Attaching a newly created vhostuser port to a VM fails due to an apparmor denial
internal error: unable to execute QEMU command 'chardev-add': Failed to bind socket to /run/openvswitch/vhu838c4d29-c9: Permission denied
In the case of a net device type VIR_DOMAIN_NET_TYPE_VHOSTUSER, the underlying chardev is not labeled in qemuDomainAttachNetDevice prior to calling qemuMonitorAttachCharDev. Label the chardev before calling qemuMonitorAttachCharDev, and restore the label when removing the net device.
Signed-off-by: Jim Fehlig <jfehlig@suse.com> --- src/qemu/qemu_hotplug.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c index c00e8a7852..42e7997112 100644 --- a/src/qemu/qemu_hotplug.c +++ b/src/qemu/qemu_hotplug.c @@ -1467,6 +1467,11 @@ qemuDomainAttachNetDevice(virQEMUDriver *driver, } if (actualType == VIR_DOMAIN_NET_TYPE_VHOSTUSER) { + virDomainChrDef chr = { .source = net->data.vhostuser }; + + if (qemuSecuritySetChardevLabel(driver, vm, &chr) < 0) + goto cleanup; + if (qemuMonitorAttachCharDev(priv->mon, charDevAlias, net->data.vhostuser) < 0) { ignore_value(qemuDomainObjExitMonitor(driver, vm)); virDomainAuditNet(vm, NULL, net, "attach", false); @@ -4692,6 +4697,8 @@ qemuDomainRemoveNetDevice(virQEMUDriver *driver, } if (actualType == VIR_DOMAIN_NET_TYPE_VHOSTUSER) { + virDomainChrDef chr = { .source = net->data.vhostuser }; + /* vhostuser has a chardev too */ if (qemuMonitorDetachCharDev(priv->mon, charDevAlias) < 0) { /* well, this is a messy situation. Guest visible PCI device has @@ -4699,6 +4706,8 @@ qemuDomainRemoveNetDevice(virQEMUDriver *driver, * to just ignore the error and carry on. */ } + if (qemuSecurityRestoreChardevLabel(driver, vm, &chr) < 0) + VIR_WARN("Unable to restore security label on vhostuser char device"); } else if (actualType == VIR_DOMAIN_NET_TYPE_VDPA) { int vdpafdset = -1; g_autoptr(qemuMonitorFdsets) fdsets = NULL;
What an interesting bug. Previously we assumed that the UNIX socket is created with broad enough permissions so that QEMU can connect to it. I mean, when a VM is starting up nor DAC nor SELinux drivers care about VHOSTUSER. It's AppArmor driver that cares. And it makes sense. But, what's problematic here is that upon attach the socket perms will be changed (because both DAC and SELinux drivers implement domainSetSecurityChardevLabel callback). And since sockets can't have XATTRs libvirt won't remember its original labels and thus subsequent restore changes owner to root:root.
How are existing chardevs with socket backends handled? It seems they would suffer the same problem when restoring the labels. The DAC and selinux callbacks seem to avoid labeling for "server" sockets
https://gitlab.com/libvirt/libvirt/-/blob/master/src/security/security_dac.c...
https://gitlab.com/libvirt/libvirt/-/blob/master/src/security/security_selin...
Yeah, you're right. But I view chardevs as runtime, fire and go things. I mean, you start a VM with a chardev, say an UNIX socket and its lifetime is identical to the VM lifetime. vhostuser on the other hand is handled by a third party daemon (typically OVS) and thus UNIX socket lifetime is different to VM lifetime. IOW, I worry that if we changed the UNIX socket label we might be preventing other VMs from connecting to it.
Agreed, particularly when an openvSwitch port is 'vhost-user' type https://docs.openvswitch.org/en/latest/topics/dpdk/vhost-user/ where openvSwitch acts as the server and qemu is the client.
And I don't even know if a single socket can be shared between two VMs. For instance, if OVS created an UNIX socket whether I can attach vhostuser interface to one domain and then to the other. Because if I could, then we should not change labels.
According to the above doc each vhostuser device would have its own socket "Note that a separate and different chardev path needs to be specified for each vhost-user device."
Perhaps Laine can shed more light here.
I do understand that apparmor needs to add an entry to the VM's profile, but I worry that DAC and SELinux might screw things up.
So I think we should address this inconsistency in behavior. But I don't know how :-(
My first attempt at fixing this introduced domain{Set,Restore}SecurityNetdevLabel to the security driver, but it seemed like overkill after I discovered virDomainChrSourceDef embedded in the virDomainNetDef structure. I can revisit that approach if it sounds more promising.
I think it does sound more promising given my assumption above is correct. This way we can have only AppArmor driver implement the callback leaving us with consistent behavior.
Unfortunately I agree. The unfortunate part is the huge diff compared to this small patch :-). Jim
On 8/18/21 12:03 PM, Jim Fehlig wrote:
On 8/18/21 2:21 AM, Michal Prívozník wrote:
On 8/18/21 12:31 AM, Jim Fehlig wrote:
On 8/17/21 12:11 PM, Jim Fehlig wrote:
On 8/17/21 4:13 AM, Michal Prívozník wrote:
On 8/13/21 11:36 PM, Jim Fehlig wrote:
Attaching a newly created vhostuser port to a VM fails due to an apparmor denial
internal error: unable to execute QEMU command 'chardev-add': Failed to bind socket to /run/openvswitch/vhu838c4d29-c9: Permission denied
In the case of a net device type VIR_DOMAIN_NET_TYPE_VHOSTUSER, the underlying chardev is not labeled in qemuDomainAttachNetDevice prior to calling qemuMonitorAttachCharDev. Label the chardev before calling qemuMonitorAttachCharDev, and restore the label when removing the net device.
Signed-off-by: Jim Fehlig <jfehlig@suse.com> --- src/qemu/qemu_hotplug.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c index c00e8a7852..42e7997112 100644 --- a/src/qemu/qemu_hotplug.c +++ b/src/qemu/qemu_hotplug.c @@ -1467,6 +1467,11 @@ qemuDomainAttachNetDevice(virQEMUDriver *driver, } if (actualType == VIR_DOMAIN_NET_TYPE_VHOSTUSER) { + virDomainChrDef chr = { .source = net->data.vhostuser }; + + if (qemuSecuritySetChardevLabel(driver, vm, &chr) < 0) + goto cleanup; + if (qemuMonitorAttachCharDev(priv->mon, charDevAlias, net->data.vhostuser) < 0) { ignore_value(qemuDomainObjExitMonitor(driver, vm)); virDomainAuditNet(vm, NULL, net, "attach", false); @@ -4692,6 +4697,8 @@ qemuDomainRemoveNetDevice(virQEMUDriver *driver, } if (actualType == VIR_DOMAIN_NET_TYPE_VHOSTUSER) { + virDomainChrDef chr = { .source = net->data.vhostuser }; + /* vhostuser has a chardev too */ if (qemuMonitorDetachCharDev(priv->mon, charDevAlias) < 0) { /* well, this is a messy situation. Guest visible PCI device has @@ -4699,6 +4706,8 @@ qemuDomainRemoveNetDevice(virQEMUDriver *driver, * to just ignore the error and carry on. */ } + if (qemuSecurityRestoreChardevLabel(driver, vm, &chr) < 0) + VIR_WARN("Unable to restore security label on vhostuser char device"); } else if (actualType == VIR_DOMAIN_NET_TYPE_VDPA) { int vdpafdset = -1; g_autoptr(qemuMonitorFdsets) fdsets = NULL;
What an interesting bug. Previously we assumed that the UNIX socket is created with broad enough permissions so that QEMU can connect to it. I mean, when a VM is starting up nor DAC nor SELinux drivers care about VHOSTUSER. It's AppArmor driver that cares. And it makes sense. But, what's problematic here is that upon attach the socket perms will be changed (because both DAC and SELinux drivers implement domainSetSecurityChardevLabel callback). And since sockets can't have XATTRs libvirt won't remember its original labels and thus subsequent restore changes owner to root:root.
How are existing chardevs with socket backends handled? It seems they would suffer the same problem when restoring the labels. The DAC and selinux callbacks seem to avoid labeling for "server" sockets
https://gitlab.com/libvirt/libvirt/-/blob/master/src/security/security_dac.c...
https://gitlab.com/libvirt/libvirt/-/blob/master/src/security/security_selin...
Yeah, you're right. But I view chardevs as runtime, fire and go things. I mean, you start a VM with a chardev, say an UNIX socket and its lifetime is identical to the VM lifetime. vhostuser on the other hand is handled by a third party daemon (typically OVS) and thus UNIX socket lifetime is different to VM lifetime. IOW, I worry that if we changed the UNIX socket label we might be preventing other VMs from connecting to it.
Agreed, particularly when an openvSwitch port is 'vhost-user' type
https://docs.openvswitch.org/en/latest/topics/dpdk/vhost-user/
where openvSwitch acts as the server and qemu is the client.
And I don't even know if a single socket can be shared between two VMs. For instance, if OVS created an UNIX socket whether I can attach vhostuser interface to one domain and then to the other. Because if I could, then we should not change labels.
According to the above doc each vhostuser device would have its own socket
"Note that a separate and different chardev path needs to be specified for each vhost-user device."
Perhaps Laine can shed more light here.
I do understand that apparmor needs to add an entry to the VM's profile, but I worry that DAC and SELinux might screw things up.
So I think we should address this inconsistency in behavior. But I don't know how :-(
My first attempt at fixing this introduced domain{Set,Restore}SecurityNetdevLabel to the security driver, but it seemed like overkill after I discovered virDomainChrSourceDef embedded in the virDomainNetDef structure. I can revisit that approach if it sounds more promising.
I think it does sound more promising given my assumption above is correct. This way we can have only AppArmor driver implement the callback leaving us with consistent behavior.
Unfortunately I agree. The unfortunate part is the huge diff compared to this small patch :-).
Actual size seen here https://listman.redhat.com/archives/libvir-list/2021-August/msg00547.html Jim
participants (5)
-
Jim Fehlig -
Laine Stump -
Maxime Coquelin -
Michael S. Tsirkin -
Michal Prívozník