The imagelabel SELinux label was only generated when relabeling was
enabled. This prohibited labeling of files created by libvirt that need
to be labeled even if relabeling is turned off.
The only codepath this change has direct impact on is labeling of FDs
passed to qemu which is always safe in current state.
I realized after the fact that it's probably better in the long run to
give this function a name that matches the name of the link used in
sysfs to hold the group (iommu_group).
I'm changing it now because I'm about to add several more functions
that deal with iommu groups.
I noticed several unusual spacings in for loops, and decided to
fix them up. See the next commit for the syntax check that found
all of these.
* examples/domsuspend/suspend.c (main): Fix spacing.
* python/libvirt-override.c: Likewise.
* src/conf/interface_conf.c: Likewise.
* src/security/virt-aa-helper.c: Likewise.
* src/util/virconf.c: Likewise.
* src/util/virhook.c: Likewise.
* src/util/virlog.c: Likewise.
* src/util/virsocketaddr.c: Likewise.
* src/util/virsysinfo.c: Likewise.
* src/util/viruuid.c: Likewise.
* src/vbox/vbox_tmpl.c: Likewise.
* src/xen/xen_hypervisor.c: Likewise.
* tools/virsh-domain-monitor.c (vshDomainStateToString): Drop
default case, to let compiler check us.
* tools/virsh-domain.c (vshDomainVcpuStateToString): Likewise.
Signed-off-by: Eric Blake <eblake@redhat.com>
To not introduce more redundant code, helpers are added for
both "selinux", "dac", and "apparmor" backends.
Signed-off-by: Han Cheng <hanc.fnst@cn.fujitsu.com>
Signed-off-by: Osier Yang <jyang@redhat>
v2.5 - v3:
* Splitted from 8/10 of v2.5
* Don't forget the other backends (DAC, and apparmor)
These all existed before virfile.c was created, and for some reason
weren't moved.
This is mostly straightfoward, although the syntax rule prohibiting
write() had to be changed to have an exception for virfile.c instead
of virutil.c.
This movement pointed out that there is a function called
virBuildPath(), and another almost identical function called
virFileBuildPath(). They really should be a single function, which
I'll take care of as soon as I figure out what the arglist should look
like.
The source code base needs to be adapted as well. Some files
include virutil.h just for the string related functions (here,
the include is substituted to match the new file), some include
virutil.h without any need (here, the include is removed), and
some require both.
If virPCIDeviceGetVFIOGroupDev() failed,
virSecurity*(Set|Restore)HostdevLabel() would fail to free a
virPCIDevice that had been allocated.
These leaks were all introduced (by me) very recently, in commit
f0bd70a.
This isn't strictly speaking a bugfix, but I realized I'd gotten a bit
too verbose when I chose the names for
VIR_DOMAIN_HOSTDEV_PCI_BACKEND_TYPE_*. This shortens them all a bit.
Legacy kvm style pci device assignment requires changes to the
labelling of several sysfs files for each device, but for vfio device
assignment, the only thing that needs to be relabelled/chowned is the
"group" device for the group that contains the device to be assigned.
There will soon be other items related to pci hostdevs that need to be
in the same part of the hostdevsubsys union as the pci address (which
is currently a single member called "pci". This patch replaces the
single member named pci with a struct named pci that contains a single
member named "addr".
Detected by a simple Shell script:
for i in $(git ls-files -- '*.[ch]'); do
awk 'BEGIN {
fail=0
}
/# *include.*\.h/{
match($0, /["<][^">]*[">]/)
arr[substr($0, RSTART+1, RLENGTH-2)]++
}
END {
for (key in arr) {
if (arr[key] > 1) {
fail=1
printf("%d %s\n", arr[key], key)
}
}
if (fail == 1)
exit 1
}' $i
if test $? != 0; then
echo "Duplicate header(s) in $i"
fi
done;
A later patch will add the syntax-check to avoid duplicate
headers.
This patch refactors various places to allow removing of the
defaultConsoleTargetType callback from the virCaps structure.
A new console character device target type is introduced -
VIR_DOMAIN_CHR_CONSOLE_TARGET_TYPE_NONE - to mark that no type was
specified in the XML. This type is at the end converted to the standard
VIR_DOMAIN_CHR_CONSOLE_TARGET_TYPE_SERIAL. Other types that are
different from this default have to be processed separately in the
device post parse callback.
This patch adds instrumentation that will allow hypervisor drivers to
fill and validate domain and device definitions after parsed by the XML
parser.
With this patch, after the XML is parsed, a callback to the driver is
issued requesting to fill and validate driver specific details of the
configuration. This allows to use sensible defaults and checks on a per
driver basis at the time the XML is parsed.
Two callback pointers are stored in the new virDomainXMLConf object:
* virDomainDeviceDefPostParseCallback (devicesPostParseCallback)
- called for a single device parsed and for every single device in a
domain config. A virDomainDeviceDefPtr is passed along with the
domain definition and virCaps.
* virDomainDefPostParseCallback, (domainPostParseCallback)
- A callback that is meant to process the domain config after it's
parsed. A virDomainDefPtr is passed along with virCaps.
Both types of callbacks support arbitrary opaque data passed for the
callback functions.
Errors may be reported in those callbacks resulting in a XML parsing
failure.
This patch is the result of running:
for i in $(git ls-files | grep -v html | grep -v \.po$ ); do
sed -i -e "s/virDomainXMLConf/virDomainXMLOption/g" -e "s/xmlconf/xmlopt/g" $i
done
and a few manual tweaks.
otherwise we crash later on if we don't find a match like:
#0 0xb72c2b4f in virSecurityManagerGenLabel (mgr=0xb8e42d20, vm=0xb8ef40c0) at security/security_manager.c:424
#1 0xb18811f3 in qemuProcessStart (conn=conn@entry=0xb8eed880, driver=driver@entry=0xb8e3b1e0, vm=vm@entry=0xb8ef58f0,
migrateFrom=migrateFrom@entry=0xb18f6088 "stdio", stdin_fd=18,
stdin_path=stdin_path@entry=0xb8ea7798 "/var/lib/jenkins/jobs/libvirt-tck-build/workspace/tck.img", snapshot=snapshot@entry=0x0,
vmop=vmop@entry=VIR_NETDEV_VPORT_PROFILE_OP_RESTORE, flags=flags@entry=2) at qemu/qemu_process.c:3364
#2 0xb18d6cb2 in qemuDomainSaveImageStartVM (conn=conn@entry=0xb8eed880, driver=driver@entry=0xb8e3b1e0, vm=0xb8ef58f0, fd=fd@entry=0xb6bf3f98,
header=header@entry=0xb6bf3fa0, path=path@entry=0xb8ea7798 "/var/lib/jenkins/jobs/libvirt-tck-build/workspace/tck.img",
start_paused=start_paused@entry=false) at qemu/qemu_driver.c:4843
#3 0xb18d7eeb in qemuDomainRestoreFlags (conn=conn@entry=0xb8eed880,
path=path@entry=0xb8ea7798 "/var/lib/jenkins/jobs/libvirt-tck-build/workspace/tck.img", dxml=dxml@entry=0x0, flags=flags@entry=0)
at qemu/qemu_driver.c:4962
#4 0xb18d8123 in qemuDomainRestore (conn=0xb8eed880, path=0xb8ea7798 "/var/lib/jenkins/jobs/libvirt-tck-build/workspace/tck.img")
at qemu/qemu_driver.c:4987
#5 0xb718d186 in virDomainRestore (conn=0xb8eed880, from=0xb8ea87d8 "/var/lib/jenkins/jobs/libvirt-tck-build/workspace/tck.img") at libvirt.c:2768
#6 0xb7736363 in remoteDispatchDomainRestore (args=<optimized out>, rerr=0xb6bf41f0, client=0xb8eedaf0, server=<optimized out>, msg=<optimized out>)
at remote_dispatch.h:4679
#7 remoteDispatchDomainRestoreHelper (server=0xb8e1a3e0, client=0xb8eedaf0, msg=0xb8ee72c8, rerr=0xb6bf41f0, args=0xb8ea8968, ret=0xb8ef5330)
at remote_dispatch.h:4661
#8 0xb720db01 in virNetServerProgramDispatchCall (msg=0xb8ee72c8, client=0xb8eedaf0, server=0xb8e1a3e0, prog=0xb8e216b0)
at rpc/virnetserverprogram.c:439
#9 virNetServerProgramDispatch (prog=0xb8e216b0, server=server@entry=0xb8e1a3e0, client=0xb8eedaf0, msg=0xb8ee72c8) at rpc/virnetserverprogram.c:305
#10 0xb7206e97 in virNetServerProcessMsg (msg=<optimized out>, prog=<optimized out>, client=<optimized out>, srv=0xb8e1a3e0) at rpc/virnetserver.c:162
#11 virNetServerHandleJob (jobOpaque=0xb8ea7720, opaque=0xb8e1a3e0) at rpc/virnetserver.c:183
#12 0xb70f9f78 in virThreadPoolWorker (opaque=opaque@entry=0xb8e1a540) at util/virthreadpool.c:144
#13 0xb70f94a5 in virThreadHelper (data=0xb8e0e558) at util/virthreadpthread.c:161
#14 0xb705d954 in start_thread (arg=0xb6bf4b70) at pthread_create.c:304
#15 0xb6fd595e in clone () at ../sysdeps/unix/sysv/linux/i386/clone.S:130
This unbreaks libvirt-tck's domain/100-transient-save-restore.t with
qemu:///session and selinux compiled in but disabled.
Introduced by 8d68cbeaa8
https://bugzilla.redhat.com/show_bug.cgi?id=947387
If a user configures a domain to use a seclabel of a specific type,
but the appropriate driver is not accessible, we should refuse to
start the domain. For instance, if user requires selinux, but it is
either non present in the system, or is just disabled, we should not
start the domain. Moreover, since we are touching only those labels we
have a security driver for, the other labels may confuse libvirt when
reconnecting to a domain on libvirtd restart. In our selinux example,
when starting up a domain, missing security label is okay, as we
auto-generate one. But later, when libvirt is re-connecting to a live
qemu instance, we parse a state XML, where security label is required
and it is an error if missing:
error : virSecurityLabelDefParseXML:3228 : XML error: security label
is missing
This results in a qemu process left behind without any libvirt control.
With my previous patches, we unconditionally appended a seclabel,
even if it wasn't generated but found in array of defined seclabels.
This resulted in double free later when doing virDomainDefFree
and iterating over the array of defined seclabels.
Moreover, there was another possibility of double free, if the
seclabel was generated in the last iteration of the process of
walking trough security managers array.
https://bugzilla.redhat.com/show_bug.cgi?id=923946
The <seclabel type='none'/> should be added iff there is no other
seclabel defined within a domain. This bug can be easily reproduced:
1) configure selinux seclabel for a domain
2) disable system's selinux and restart libvirtd
3) observe <seclabel type='none'/> being appended to a domain on its
startup
The virDomainDefGetSecurityLabelDef was modifying the domain XML.
It tried to find a seclabel corresponding to given sec driver. If the
label wasn't found, the function created one which is wrong. In fact
it's security manager which should modify this part of domain XML.
Normally libvirtd should run with a SELinux label
system_u:system_r:virtd_t:s0-s0:c0.c1023
If a user manually runs libvirtd though, it is sometimes
possible to get into a situation where it is running
system_u:system_r:init_t:s0
The SELinux security driver isn't expecting this and can't
parse the security label since it lacks the ':c0.c1023' part
causing it to complain
internal error Cannot parse sensitivity level in s0
This updates the parser to cope with this, so if no category
is present, libvirtd will hardcode the equivalent of c0.c1023.
Now this won't work if SELinux is in Enforcing mode, but that's
not an issue, because the user can only get into this problem
if in Permissive mode. This means they can now start VMs in
Permissive mode without hitting that parsing error
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Pull the code which parses the current process MCS range
out of virSecuritySELinuxMCSFind and into a new method
virSecuritySELinuxMCSGetProcessRange.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
The body of the loop in virSecuritySELinuxMCSFind would
directly 'return NULL' on OOM, instead of jumping to the
cleanup label. This caused a leak of several local vars.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
The virCaps structure gathered a ton of irrelevant data over time that.
The original reason is that it was propagated to the XML parser
functions.
This patch aims to create a new data structure virDomainXMLConf that
will contain immutable data that are used by the XML parser. This will
allow two things we need:
1) Get rid of the stuff from virCaps
2) Allow us to add callbacks to check and add driver specific stuff
after domain XML is parsed.
This first attempt removes pointers to private data allocation functions
to this new structure and update all callers and function that require
them.
Rename AppArmorSetImageFDLabel to AppArmorSetFDLabel which could
be used as a common function for *ALL* fd relabelling in Linux.
In apparmor profile for specific vm with uuid cdbebdfa-1d6d-65c3-be0f-fd74b978a773
Path: /etc/apparmor.d/libvirt/libvirt-cdbebdfa-1d6d-65c3-be0f-fd74b978a773.files
The last line is for the tapfd relabelling.
# DO NOT EDIT THIS FILE DIRECTLY. IT IS MANAGED BY LIBVIRT.
"/var/log/libvirt/**/rhel6qcow2.log" w,
"/var/lib/libvirt/**/rhel6qcow2.monitor" rw,
"/var/run/libvirt/**/rhel6qcow2.pid" rwk,
"/run/libvirt/**/rhel6qcow2.pid" rwk,
"/var/run/libvirt/**/*.tunnelmigrate.dest.rhel6qcow2" rw,
"/run/libvirt/**/*.tunnelmigrate.dest.rhel6qcow2" rw,
"/var/lib/libvirt/images/rhel6u3qcow2.img" rw,
"/dev/tap45" rw,
With the apparmor security driver enabled, qemu instances fail
to start
# grep ^security_driver /etc/libvirt/qemu.conf
security_driver = "apparmor"
# virsh start test-kvm
error: Failed to start domain test-kvm
error: internal error security label already defined for VM
The model field of virSecurityLabelDef object is always populated
by virDomainDefGetSecurityLabelDef(), so remove the check for a
NULL model when verifying if a label is already defined for the
instance.
Checking for a NULL model and populating it later in
AppArmorGenSecurityLabel() has been left in the code to be
consistent with virSecuritySELinuxGenSecurityLabel().
Coverity found the DACGenLabel was checking for mgr == NULL after a
possible dereference; however, in order to get into the function the
virSecurityManagerGenLabel would have already dereferenced sec_managers[i]
so the check was unnecessary. Same check is made in SELinuxGenSecurityLabel.
The existing virSecurityManagerSetProcessLabel() API is designed so
that it must be called after forking the child process, but before
exec'ing the child. Due to the way the virCommand API works, that
means it needs to be put in a "hook" function that virCommand is told
to call out to at that time.
Setting the child process label is a basic enough need when executing
any process that virCommand should have a method of doing that. But
virCommand must be told what label to set, and only the security
driver knows the answer to that question.
The new virSecurityManagerSet*Child*ProcessLabel() API is the way to
transfer the knowledge about what label to set from the security
driver to the virCommand object. It is given a virCommandPtr, and each
security driver calls the appropriate virCommand* API to tell
virCommand what to do between fork and exec.
1) in the case of the DAC security driver, it calls
virCommandSetUID/GID() to set a uid and gid that must be set for the
child process.
2) for the SELinux security driver, it calls
virCommandSetSELinuxLabel() to save a copy of the char* that will be
sent to setexeccon_raw() *after forking the child process*.
3) for the AppArmor security drivers, it calls
virCommandSetAppArmorProfile() to save a copy of the char* that will
be sent to aa_change_profile() *after forking the child process*.
With this new API in place, we will be able to remove
virSecurityManagerSetProcessLabel() from any virCommand pre-exec
hooks.
(Unfortunately, the LXC driver uses clone() rather than virCommand, so
it can't take advantage of this new security driver API, meaning that
we need to keep around the older virSecurityManagerSetProcessLabel(),
at least for now.)
The hook scripts used by virCommand must be careful wrt
accessing any mutexes that may have been held by other
threads in the parent process. With the recent refactoring
there are 2 potential flaws lurking, which will become real
deadlock bugs once the global QEMU driver lock is removed.
Remove use of the QEMU driver lock from the hook function
by passing in the 'virQEMUDriverConfigPtr' instance directly.
Add functions to the virSecurityManager to be invoked before
and after fork, to ensure the mutex is held by the current
thread. This allows it to be safely used in the hook script
in the child process.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
On RHEL 5, I got:
security/security_selinux.c: In function 'getContext':
security/security_selinux.c:971: warning: unused parameter 'mgr' [-Wunused-parameter]
* src/security/security_selinux.c (getContext): Mark potentially
unused parameter.
The security manager drivers are not allowed to call back
out to top level security manager APIs, since that results
in recursive mutex acquisition and thus deadlock. Remove
calls to virSecurityManagerGetModel from SELinux / AppArmor
drivers
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Add locking to virSecurityManagerXXX APIs, so that use of the
security drivers is internally serialized. This avoids the need
to rely on the global driver locks to achieve serialization
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
To enable locking to be introduced to the security manager
objects later, turn virSecurityManager into a virObjectLockable
class
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
To enable virCapabilities instances to be reference counted,
turn it into a virObject. All cases of virCapabilitiesFree
turn into virObjectUnref
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Commit id a994ef2d1 changed the mechanism to store/update the default
security label from using disk->seclabels[0] to allocating one on the
fly. That change allocated the label, but never saved it. This patch
will save the label. The new virDomainDiskDefAddSecurityLabelDef() is
a copy of the virDomainDefAddSecurityLabelDef().
When changing to virArch, the virt-aa-helper.c file was not
completely changed. The vahControl struct was left with a
char *arch field, instead of virArch arch field.
Convert the host capabilities and domain config structs to
use the virArch datatype. Update the parsers and all drivers
to take account of datatype change
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Prepare to support different types of hostdevs by refactoring
the current SELinux security driver code
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
When LXC labels USB devices during hotplug, it is running in
host context, so it needs to pass in a vroot path to the
container root.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
The virSecurityManager{Set,Restore}AllLabel methods are invoked
at domain startup/shutdown to relabel resources associated with
a domain. This works fine with QEMU, but with LXC they are in
fact both currently no-ops since LXC does not support disks,
hostdevs, or kernel/initrd files. Worse, when LXC gains support
for disks/hostdevs, they will do the wrong thing, since they
run in host context, not container context. Thus this patch
turns then into a formal no-op when used with LXC. The LXC
controller will call out to specific security manager labelling
APIs as required during startup.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
The current SELinux policy only works for KVM guests, since
TCG requires the 'execmem' privilege. There is a 'virt_use_execmem'
boolean to turn this on globally, but that is unpleasant for users.
This changes libvirt to automatically use a new 'svirt_tcg_t'
context for TCG based guests. This obsoletes the previous
boolean tunable and makes things 'just work(tm)'
Since we can't assume we run with new enough policy, I also
make us log a warning message (once only) if we find the policy
lacks support. In this case we fallback to the normal label and
expect users to set the boolean tunable
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
When using vnc gaphics over a unix socket, virt-aa-helper needs to provide
access for the qemu domain to access the sockfile.
Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
When a qemu domain is backed by huge pages, apparmor needs to grant the domain
rw access to files under the hugetlbfs mount point. Add a hook, called in
qemu_process.c, which ends up adding the read-write access through
virt-aa-helper. Qemu will be creating a randomly named file under the
mountpoint and unlinking it as soon as it has mmap()d it, therefore we
cannot predict the full pathname, but for the same reason it is generally
safe to provide access to $path/**.
Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
The impls of virSecurityManagerGetMountOptions had no way to
return errors, since the code was treating 'NULL' as a success
value. This is somewhat pointless, since the calling code did
not want NULL in the first place and has to translate it into
the empty string "". So change the code so that the impls can
return "" directly, allowing use of NULL for error reporting
once again
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
For S390, the default console target type cannot be of type 'serial'.
It is necessary to at least interpret the 'arch' attribute
value of the os/type element to produce the correct default type.
Therefore we need to extend the signature of defaultConsoleTargetType
to account for architecture. As a consequence all the drivers
supporting this capability function must be updated.
Despite the amount of changed files, the only change in behavior is
that for S390 the default console target type will be 'virtio'.
N.B.: A more future-proof approach could be to to use hypervisor
specific capabilities to determine the best possible console type.
For instance one could add an opaque private data pointer to the
virCaps structure (in case of QEMU to hold capsCache) which could
then be passed to the defaultConsoleTargetType callback to determine
the console target type.
Seems to be however a bit overengineered for the use case...
Signed-off-by: Viktor Mihajlovski <mihajlov@linux.vnet.ibm.com>
The libvirt coding standard is to use 'function(...args...)'
instead of 'function (...args...)'. A non-trivial number of
places did not follow this rule and are fixed in this patch.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
When restoring selinux labels after a VM is stopped, any non-standard
path that doesn't have a default selinux label causes the process
to stop and exit early. This isn't really an error condition IMO.
Of course the selinux API could be erroring for some other reason
but hopefully that's rare enough to not need explicit handling.
Common example here is storing disk images in a non-standard location
like under /mnt.
Fixes a build failure on cygwin:
cc1: warnings being treated as errors
security/security_dac.c: In function 'virSecurityDACSetProcessLabel':
security/security_dac.c:862:5: error: format '%u' expects type 'unsigned int', but argument 7 has type 'uid_t' [-Wformat]
security/security_dac.c:862:5: error: format '%u' expects type 'unsigned int', but argument 8 has type 'gid_t' [-Wformat]
* src/security/security_dac.c (virSecurityDACSetProcessLabel)
(virSecurityDACGenLabel): Use proper casts.
We used to walk the backing file chain at least twice per disk,
once to set up cgroup device whitelisting, and once to set up
security labeling. Rather than walk the chain every iteration,
which possibly includes calls to fork() in order to open root-squashed
NFS files, we can exploit the cache of the previous patch.
* src/conf/domain_conf.h (virDomainDiskDefForeachPath): Alter
signature.
* src/conf/domain_conf.c (virDomainDiskDefForeachPath): Require caller
to supply backing chain via disk, if recursion is desired.
* src/security/security_dac.c
(virSecurityDACSetSecurityImageLabel): Adjust caller.
* src/security/security_selinux.c
(virSecuritySELinuxSetSecurityImageLabel): Likewise.
* src/security/virt-aa-helper.c (get_files): Likewise.
* src/qemu/qemu_cgroup.c (qemuSetupDiskCgroup)
(qemuTeardownDiskCgroup): Likewise.
(qemuSetupCgroup): Pre-populate chain.
BZ:https://bugzilla.redhat.com/show_bug.cgi?id=851981
When using macvtap, a character device gets first created by
kernel with name /dev/tapN, its selinux context is:
system_u:object_r:device_t:s0
Shortly, when udev gets notification when new file is created
in /dev, it will then jump in and relabel this file back to the
expected default context:
system_u:object_r:tun_tap_device_t:s0
There is a time gap happened.
Sometimes, it will have migration failed, AVC error message:
type=AVC msg=audit(1349858424.233:42507): avc: denied { read write } for
pid=19926 comm="qemu-kvm" path="/dev/tap33" dev=devtmpfs ino=131524
scontext=unconfined_u:system_r:svirt_t:s0:c598,c908
tcontext=system_u:object_r:device_t:s0 tclass=chr_file
This patch will label the tapfd device before qemu process starts:
system_u:object_r:tun_tap_device_t:MCS(MCS from seclabel->label)
We are currently able to work only with non-translated SELinux
contexts, but we are using functions that work with translated
contexts throughout the code. This patch swaps all SELinux context
translation relative calls with their raw sisters to avoid parsing
problems.
The problems can be experienced with mcstrans for example. The
difference is that if you have translations enabled (yum install
mcstrans; service mcstrans start), fgetfilecon_raw() will get you
something like 'system_u:object_r:virt_image_t:s0', whereas
fgetfilecon() will return 'system_u:object_r:virt_image_t:SystemLow'
that we cannot parse.
I was trying to confirm that the _raw variants were here since the dawn of
time, but the only thing I see now is that it was imported together in
the upstream repo [1] from svn, so before 2008.
Thanks Laurent Bigonville for finding this out.
[1] http://oss.tresys.com/git/selinux.git
All USB device lookup functions emit an error when they cannot find the
requested device. With this patch, their caller can choose if a missing
device is an error or normal condition.
The functions virGetUserID and virGetGroupID are now able to parse
user/group names and IDs in a similar way to coreutils' chown. So, user
and group parsing in security_dac can be simplified.
The DAC driver is missing parsing of group and user names for DAC labels
and currently just parses uid and gid. This patch extends it to support
names, so the following security label definition is now valid:
<seclabel type='static' model='dac' relabel='yes'>
<label>qemu:qemu</label>
<imagelabel>qemu:qemu</imagelabel>
</seclabel>
When it tries to parse an owner or a group, it first tries to resolve it as
a name, if it fails or it's an invalid user/group name then it tries to
parse it as an UID or GID. A leading '+' can also be used for both owner and
group to force it to be parsed as IDs, so the following example is also
valid:
<seclabel type='static' model='dac' relabel='yes'>
<label>+101:+101</label>
<imagelabel>+101:+101</imagelabel>
</seclabel>
This ensures that UID 101 and GUI 101 will be used instead of an user or
group named "101".
This allows the user to control labelling of each character device
separately (the default is to inherit from the VM).
Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
https://www.gnu.org/licenses/gpl-howto.html recommends that
the 'If not, see <url>.' phrase be a separate sentence.
* tests/securityselinuxhelper.c: Remove doubled line.
* tests/securityselinuxtest.c: Likewise.
* globally: s/; If/. If/
The DAC security driver silently ignored errors when parsing the DAC
label and used default values instead.
With a domain containing the following label definition:
<seclabel type='static' model='dac' relabel='yes'>
<label>sdfklsdjlfjklsdjkl</label>
</seclabel>
the domain would start normaly but the disk images would be still owned
by root and no error was displayed.
This patch changes the behavior if the parsing of the label fails (note
that a not present label is not a failure and in this case the default
label should be used) the error isn't masked but is raised that causes
the domain start to fail with a descriptive error message:
virsh # start tr
error: Failed to start domain tr
error: internal error invalid argument: failed to parse DAC seclabel
'sdfklsdjlfjklsdjkl' for domain 'tr'
I also changed the error code to "invalid argument" from "internal
error" and tweaked the various error messages to contain correct and
useful information.
If no 'security_driver' config option was set, then the code
just loaded the 'dac' security driver. This is a regression
on previous behaviour, where we would probe for a possible
security driver. ie default to SELinux if available.
This changes things so that it 'security_driver' is not set,
we once again do probing. For simplicity we also always
create the stack driver, even if there is only one driver
active.
The desired semantics are:
- security_driver not set
-> probe for selinux/apparmour/nop
-> auto-add DAC driver
- security_driver set to a string
-> add that one driver
-> auto-add DAC driver
- security_driver set to a list
-> add all drivers in list
-> auto-add DAC driver
It is not allowed, or possible to specify 'dac' in the
security_driver config param, since that is always
enabled.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
This reverts commit 9f9b7b85c9.
The DAC security driver needs special handling and extra parameters and
can't just be added to regular security drivers.
When starting a machine the DAC security driver tries to set the UID and
GID of the newly spawned process. This worked as desired if the desired
label was set. When the label was missing a logical bug in
virSecurityDACGenLabel() caused that uninitialised values were used as
uid and gid for the new process.
With this patch, default values (from qemu driver configuration)
are used if the label is not found.
Currently, if users set 'security_driver="dac"' in qemu.conf libvirtd
fails to initialize as DAC driver is not found because it is missing
in our security drivers array.
The DAC security driver uses the virStrToLong_ui function to
parse the uid/gid out of the seclabel string. This works on
Linux where 'uid_t' is an unsigned int, but on Mingw32 it is
just an 'int'. This causes compiler warnings about signed/
unsigned int pointer mis-match.
To avoid this, use explicit 'unsigned int ouruid' local
vars to pass into virStrToLong_ui, and then simply assign
to the 'uid_t' type after parsing
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Currently the dynamic label generation code will create labels
with a sensitivity of s0, and a category pair in the range
0-1023. This is fine when running a standard MCS policy because
libvirtd will run with a label
system_u:system_r:virtd_t:s0-s0:c0.c1023
With custom policies though, it is possible for libvirtd to have
a different sensitivity, or category range. For example
system_u:system_r:virtd_t:s2-s3:c512.c1023
In this case we must assign the VM a sensitivity matching the
current lower sensitivity value, and categories in the range
512-1023
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
The code to refactor sec label handling accidentally changed the
SELinux driver to use the 'domain_context' when generating the
image label instead of the 'file_context'
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
These changes make the security drivers able to find and handle the
correct security label information when more than one label is
available. They also update the DAC driver to be used as an usual
security driver.
Signed-off-by: Marcelo Cerri <mhcerri@linux.vnet.ibm.com>
This patch updates the structures that store information about each
domain and each hypervisor to support multiple security labels and
drivers. It also updates all the remaining code to use the new fields.
Signed-off-by: Marcelo Cerri <mhcerri@linux.vnet.ibm.com>
This is a fix for the object label generation. It uses a new flag for
virSecuritySELinuxGenNewContext that specifies whether the context is
for an object. If so the context role remains unchanged.
Without this fix it is not possible to start domains with image file or
block device backed storage when selinux is enabled.
Signed-off-by: Viktor Mihajlovski <mihajlov@linux.vnet.ibm.com>
The code for picking a MCS label is about to get significantly
more complicated, so it deserves to be in a standlone method,
instead of a switch/case body.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
When generating an SELinux context for a VM from the template
"system_u:system_r:svirt_t:s0", copy the role + user from the
current process instead of the template context. So if the
current process is
unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
then the VM context ends up as
unconfined_u:unconfined_r:svirt_t:s0:c386,c703
instead of
system_u:system_r:svirt_t:s0:c177,c424
Ideally the /etc/selinux/targeted/contexts/virtual_domain_context
file would have just shown the 'svirt_t' type, and not the full
context, but that can't be changed now for compatibility reasons.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
The virSecuritySELinuxGenNewContext method was not reporting any
errors, leaving it up to the caller to report a generic error.
In addition it could potentially trigger a strdup(NULL) in an
OOM scenario. Move all error reporting into the
virSecuritySELinuxGenNewContext method where accurate info
can be provided
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
There is currently no way to distinguish the case that a requested
security driver was disabled, from the case where no security driver
was available. Use VIR_ERR_CONFIG_UNSUPPORTED as the error when an
explicitly requested security driver was disabled
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
The security_manager.h header is not self-contained because it
uses the virDomainDefPtr without first including domain_conf.h
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
All callers used the same initialization seed (well, the new
viratomictest forgot to look at getpid()); so we might as well
make this value automatic. And while it may feel like we are
giving up functionality, I documented how to get it back in the
unlikely case that you actually need to debug with a fixed
pseudo-random sequence. I left that crippled by default, so
that a stray environment variable doesn't cause a lack of
randomness to become a security issue.
* src/util/virrandom.c (virRandomInitialize): Rename...
(virRandomOnceInit): ...and make static, with one-shot call.
Document how to do fixed-seed debugging.
* src/util/virrandom.h (virRandomInitialize): Drop prototype.
* src/libvirt_private.syms (virrandom.h): Don't export it.
* src/libvirt.c (virInitialize): Adjust caller.
* src/lxc/lxc_controller.c (main): Likewise.
* src/security/virt-aa-helper.c (main): Likewise.
* src/util/iohelper.c (main): Likewise.
* tests/seclabeltest.c (main): Likewise.
* tests/testutils.c (virtTestMain): Likewise.
* tests/viratomictest.c (mymain): Likewise.
If a domain is explicitly configured with <seclabel type="none"/> we
correctly ensure that no labeling will be done by setting
norelabel=true. However, if no seclabel element is present in domain XML
and hypervisor is configured not to confine domains by default, we only
set type to "none" without turning off relabeling. Thus if such a domain
is being started, security driver wants to relabel resources with
default label, which doesn't make any sense.
Moreover, with SELinux security driver, the generated image label lacks
"s0" sensitivity, which causes setfilecon() fail with EINVAL in
enforcing mode.
This is a follow up patch of commit f9ce7dad6, it modifies all
the files which declare the copyright like "See COPYING.LIB for
the License of this software" to use the detailed/consistent one.
And deserts the outdated comments like:
* libvirt-qemu.h:
* Summary: qemu specific interfaces
* Description: Provides the interfaces of the libvirt library to handle
* qemu specific methods
*
* Copy: Copyright (C) 2010, 2012 Red Hat, Inc.
Uses the more compact style like:
* libvirt-qemu.h: Interfaces specific for QEMU/KVM driver
*
* Copyright (C) 2010, 2012 Red Hat, Inc.
Per the FSF address could be changed from time to time, and GNU
recommends the following now: (http://www.gnu.org/licenses/gpl-howto.html)
You should have received a copy of the GNU General Public License
along with Foobar. If not, see <http://www.gnu.org/licenses/>.
This patch removes the explicit FSF address, and uses above instead
(of course, with inserting 'Lesser' before 'General').
Except a bunch of files for security driver, all others are changed
automatically, the copyright for securify files are not complete,
that's why to do it manually:
src/security/security_selinux.h
src/security/security_driver.h
src/security/security_selinux.c
src/security/security_apparmor.h
src/security/security_apparmor.c
src/security/security_driver.c
Instead of using an O(n) efficiency linked list for storing
MCS labels, use a hash table. Instead of having the list
be global, put it in the SELinux driver private data struct
to ensure uniqueness across different instances of the driver.
This also ensures thread safety when multiple hypervisor
drivers are used in the same libvirtd process
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
When adding MCS labels, OOM was not being handled correctly.
In addition when reserving an existing label, no check was
made to see if it was already reserved
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
The function names in the SELinux driver all start with
SELinux or 'mcs' as a prefix. Sanitize this so that they
all use 'virSecuritySELinux' as the prefix
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Update the security drivers to use virReportError instead of
the virSecurityReportError custom macro
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Remove a number of pointless checks against PATH_MAX and
add a syntax-check rule to prevent its use in future
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Most versions of libselinux do not contain the function
selinux_lxc_contexts_path() that the security driver
recently started using for LXC. We must add a conditional
check for it in configure and then disable the LXC security
driver for builds where libselinux lacks this function.
* configure.ac: Check for selinux_lxc_contexts_path
* src/security/security_selinux.c: Disable LXC security
if selinux_lxc_contexts_path() is missing
Some security drivers require special options to be passed to
the mount system call. Add a security driver API for handling
this data.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
The SELinux policy for LXC uses a different configuration file
than the traditional svirt one. Thus we need to load
/etc/selinux/targeted/contexts/lxc_contexts which contains
something like this:
process = "system_u:system_r:svirt_lxc_net_t:s0"
file = "system_u:object_r:svirt_lxc_file_t:s0"
content = "system_u:object_r:virt_var_lib_t:s0"
cleverly designed to be parsable by virConfPtr
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Currently the SELinux driver stores its state in a set of global
variables. This switches it to use a private data struct instead.
This will enable different instances to have their own data.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
The AppArmour driver does not currently have support for LXC
so ensure that when probing, it claims to be disabled
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
To allow the security drivers to apply different configuration
information per hypervisor, pass the virtualization driver name
into the security manager constructor.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
The code is splattered with a mix of
sizeof foo
sizeof (foo)
sizeof(foo)
Standardize on sizeof(foo) and add a syntax check rule to
enforce it
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Return statements with parameter enclosed in parentheses were modified
and parentheses were removed. The whole change was scripted, here is how:
List of files was obtained using this command:
git grep -l -e '\<return\s*([^()]*\(([^()]*)[^()]*\)*)\s*;' | \
grep -e '\.[ch]$' -e '\.py$'
Found files were modified with this command:
sed -i -e \
's_^\(.*\<return\)\s*(\(\([^()]*([^()]*)[^()]*\)*\))\s*\(;.*$\)_\1 \2\4_' \
-e 's_^\(.*\<return\)\s*(\([^()]*\))\s*\(;.*$\)_\1 \2\3_'
Then checked for nonsense.
The whole command looks like this:
git grep -l -e '\<return\s*([^()]*\(([^()]*)[^()]*\)*)\s*;' | \
grep -e '\.[ch]$' -e '\.py$' | xargs sed -i -e \
's_^\(.*\<return\)\s*(\(\([^()]*([^()]*)[^()]*\)*\))\s*\(;.*$\)_\1 \2\4_' \
-e 's_^\(.*\<return\)\s*(\([^()]*\))\s*\(;.*$\)_\1 \2\3_'
No thanks to 64-bit windows, with 64-bit pid_t, we have to avoid
constructs like 'int pid'. Our API in libvirt-qemu cannot be
changed without breaking ABI; but then again, libvirt-qemu can
only be used on systems that support UNIX sockets, which rules
out Windows (even if qemu could be compiled there) - so for all
points on the call chain that interact with this API decision,
we require a different variable name to make it clear that we
audited the use for safety.
Adding a syntax-check rule only solves half the battle; anywhere
that uses printf on a pid_t still needs to be converted, but that
will be a separate patch.
* cfg.mk (sc_correct_id_types): New syntax check.
* src/libvirt-qemu.c (virDomainQemuAttach): Document why we didn't
use pid_t for pid, and validate for overflow.
* include/libvirt/libvirt-qemu.h (virDomainQemuAttach): Tweak name
for syntax check.
* src/vmware/vmware_conf.c (vmwareExtractPid): Likewise.
* src/driver.h (virDrvDomainQemuAttach): Likewise.
* tools/virsh.c (cmdQemuAttach): Likewise.
* src/remote/qemu_protocol.x (qemu_domain_attach_args): Likewise.
* src/qemu_protocol-structs (qemu_domain_attach_args): Likewise.
* src/util/cgroup.c (virCgroupPidCode, virCgroupKillInternal):
Likewise.
* src/qemu/qemu_command.c(qemuParseProcFileStrings): Likewise.
(qemuParseCommandLinePid): Use pid_t for pid.
* daemon/libvirtd.c (daemonForkIntoBackground): Likewise.
* src/conf/domain_conf.h (_virDomainObj): Likewise.
* src/probes.d (rpc_socket_new): Likewise.
* src/qemu/qemu_command.h (qemuParseCommandLinePid): Likewise.
* src/qemu/qemu_driver.c (qemudGetProcessInfo, qemuDomainAttach):
Likewise.
* src/qemu/qemu_process.c (qemuProcessAttach): Likewise.
* src/qemu/qemu_process.h (qemuProcessAttach): Likewise.
* src/uml/uml_driver.c (umlGetProcessInfo): Likewise.
* src/util/virnetdev.h (virNetDevSetNamespace): Likewise.
* src/util/virnetdev.c (virNetDevSetNamespace): Likewise.
* tests/testutils.c (virtTestCaptureProgramOutput): Likewise.
* src/conf/storage_conf.h (_virStoragePerms): Use mode_t, uid_t,
and gid_t rather than int.
* src/security/security_dac.c (virSecurityDACSetOwnership): Likewise.
* src/conf/storage_conf.c (virStorageDefParsePerms): Avoid
compiler warning.
In case the caller specifies that confined guests are required but the
security driver turns out to be 'none', we should return an error since
this driver clearly cannot meet that requirement. As a result of this
error, libvirtd fails to start when the host admin explicitly sets
confined guests are required but there is no security driver available.
Since security driver 'none' cannot create confined guests, we override
default confined setting so that hypervisor drivers do not thing they
should create confined guests.
This eliminates the warning message reported in:
https://bugzilla.redhat.com/show_bug.cgi?id=624447
It was caused by a failure to open an image file that is not
accessible by root (the uid libvirtd is running as) because it's on a
root-squash NFS share, owned by a different user, with permissions of
660 (or maybe 600).
The solution is to use virFileOpenAs() rather than open(). The
codepath that generates the error is during qemuSetupDiskCGroup(), but
the actual open() is in a lower-level generic function called from
many places (virDomainDiskDefForeachPath), so some other pieces of the
code were touched just to add dummy (or possibly useful) uid and gid
arguments.
Eliminating this warning message has the nice side effect that the
requested operation may even succeed (which in this case isn't
necessary, but shouldn't hurt anything either).
Curently security labels can be of type 'dynamic' or 'static'.
If no security label is given, then 'dynamic' is assumed. The
current code takes advantage of this default, and avoids even
saving <seclabel> elements with type='dynamic' to disk. This
means if you temporarily change security driver, the guests
can all still start.
With the introduction of sVirt to LXC though, there needs to be
a new default of 'none' to allow unconfined LXC containers.
This patch introduces two new security label types
- default: the host configuration decides whether to run the
guest with type 'none' or 'dynamic' at guest start
- none: the guest will run unconfined by security policy
The 'none' label type will obviously be undesirable for some
deployments, so a new qemu.conf option allows a host admin to
mandate confined guests. It is also possible to turn off default
confinement
security_default_confined = 1|0 (default == 1)
security_require_confined = 1|0 (default == 0)
* src/conf/domain_conf.c, src/conf/domain_conf.h: Add new
seclabel types
* src/security/security_manager.c, src/security/security_manager.h:
Set default sec label types
* src/security/security_selinux.c: Handle 'none' seclabel type
* src/qemu/qemu.conf, src/qemu/qemu_conf.c, src/qemu/qemu_conf.h,
src/qemu/libvirtd_qemu.aug: New security config options
* src/qemu/qemu_driver.c: Tell security driver about default
config
The old virRandom() API was not generating good random numbers.
Replace it with a new API virRandomBits which instead of being
told the upper limit, gets told the number of bits of randomness
required.
* src/util/virrandom.c, src/util/virrandom.h: Add virRandomBits,
and move virRandomInitialize
* src/util/util.h, src/util/util.c: Delete virRandom and
virRandomInitialize
* src/libvirt.c, src/security/security_selinux.c,
src/test/test_driver.c, src/util/iohelper.c: Update for
changes from virRandom to virRandomBits
* src/storage/storage_backend_iscsi.c: Remove bogus call
to virRandomInitialize & convert to virRandomBits
When sVirt is integrated with the LXC driver, it will be neccessary
to invoke the security driver APIs using only a virDomainDefPtr
since the lxc_container.c code has no virDomainObjPtr available.
Aside from two functions which want obj->pid, every bit of the
security driver code only touches obj->def. So we don't need to
pass a virDomainObjPtr into the security drivers, a virDomainDefPtr
is sufficient. Two functions also gain a 'pid_t pid' argument.
* src/qemu/qemu_driver.c, src/qemu/qemu_hotplug.c,
src/qemu/qemu_migration.c, src/qemu/qemu_process.c,
src/security/security_apparmor.c,
src/security/security_dac.c,
src/security/security_driver.h,
src/security/security_manager.c,
src/security/security_manager.h,
src/security/security_nop.c,
src/security/security_selinux.c,
src/security/security_stack.c: Change all security APIs to use a
virDomainDefPtr instead of virDomainObjPtr
This wires up the XML changes in the previous patch to let SELinux
labeling honor user overrides, as well as affecting the live XML
configuration in one case where the user didn't specify anything
in the offline XML.
I noticed that the logs contained messages like this:
2011-12-05 23:32:40.382+0000: 26569: warning : SELinuxRestoreSecurityFileLabel:533 : cannot lookup default selinux label for /nfs/libvirt/images/dom.img
for all my domain images living on NFS. But if we would just remember
that on domain creation that we were unable to set a SELinux label (due to
NFSv3 lacking labels, or NFSv4 not being configured to expose attributes),
then we could avoid wasting the time trying to clear the label on
domain shutdown. This in turn is one less point of NFS failure,
especially since there have been documented cases of virDomainDestroy
hanging during an attempted operation on a failed NFS connection.
* src/security/security_selinux.c (SELinuxSetFilecon): Move guts...
(SELinuxSetFileconHelper): ...to new function.
(SELinuxSetFileconOptional): New function.
(SELinuxSetSecurityFileLabel): Honor override label, and remember
if labeling failed.
(SELinuxRestoreSecurityImageLabelInt): Skip relabeling based on
override.
Network disks don't have paths to be resolved or files to be checked
for ownership. ee3efc41e6 checked this
for some image label functions, but was partially reverted in a
refactor. This finishes adding the check to each security driver's
set and restore label methods for images.
Signed-off-by: Josh Durgin <josh.durgin@dreamhost.com>
The pathname for the pipe for tunnelled migration is unresolvable. The
libvirt apparmor driver therefore refuses access, causing migration to
fail. If we can't resolve the path, the worst that can happen is that
we should have given permission to the file but didn't. Otherwise
(especially since this is a /proc/$$/fd/N file) the file is already open
and libvirt won't be refused access by apparmor anyway.
Also adjust virt-aa-helper to allow access to the
*.tunnelmigrate.dest.name files.
For more information, see https://launchpad.net/bugs/869553.
Signed-off-by: Serge Hallyn <serge.hallyn@canonical.com>
Every instance of virCapsPtr must have the defaultConsoleTargetType
field set.
* src/security/virt-aa-helper.c: Add defaultConsoleTargetType to
virCapsPtr
While Xen only has a single paravirt console, UML, and
QEMU both support multiple paravirt consoles. The LXC
driver can also be trivially made to support multiple
consoles. This patch extends the XML to allow multiple
<console> elements in the XML. It also makes the UML
and QEMU drivers support this config.
* src/conf/domain_conf.c, src/conf/domain_conf.h: Allow
multiple <console> devices
* src/lxc/lxc_driver.c, src/xen/xen_driver.c,
src/xenxs/xen_sxpr.c, src/xenxs/xen_xm.c: Update for
internal API changes
* src/security/security_selinux.c, src/security/virt-aa-helper.c:
Only label consoles that aren't a copy of the serial device
* src/qemu/qemu_command.c, src/qemu/qemu_driver.c,
src/qemu/qemu_process.c, src/uml/uml_conf.c,
src/uml/uml_driver.c: Support multiple console devices
* tests/qemuxml2xmltest.c, tests/qemuxml2argvtest.c: Extra
tests for multiple virtio consoles. Set QEMU_CAPS_CHARDEV
for all console /channel tests
* tests/qemuxml2argvdata/qemuxml2argv-channel-virtio-auto.args,
tests/qemuxml2argvdata/qemuxml2argv-channel-virtio.args
tests/qemuxml2argvdata/qemuxml2argv-console-virtio.args: Update
for correct chardev syntax
* tests/qemuxml2argvdata/qemuxml2argv-console-virtio-many.args,
tests/qemuxml2argvdata/qemuxml2argv-console-virtio-many.xml: New
test file
This patch fixes the regression with using named pipes for qemu serial
devices noted in:
https://bugzilla.redhat.com/show_bug.cgi?id=740478
The problem was that, while new code in libvirt looks for a single
bidirectional fifo of the name given in the config, then relabels that
and continues without looking for / relabelling the two unidirectional
fifos named ${name}.in and ${name}.out, qemu looks in the opposite
order. So if the user had naively created all three fifos, libvirt
would relabel the bidirectional fifo to allow qemu access, but qemu
would attempt to use the two unidirectional fifos and fail (because it
didn't have proper permissions/rights).
This patch changes the order that libvirt looks for the fifos to match
what qemu does - first it looks for the dual fifos, then it looks for
the single bidirectional fifo. If it finds the dual unidirectional
fifos first, it labels/chowns them and ignores any possible
bidirectional fifo.
(Note commit d37c6a3a (which first appeared in libvirt-0.9.2) added
the code that checked for a bidirectional fifo. Prior to that commit,
bidirectional fifos for serial devices didn't work because libvirt
always required the ${name}.(in|out) fifos to exist, and qemu would
always prefer those.
