On Tue, Oct 07, 2014 at 04:53:24PM +0200, Michal Privoznik wrote:
https://bugzilla.redhat.com/show_bug.cgi?id=1147057
The code for relabelling the TAP FD is there due to a race. When libvirt creates a /dev/tapN device it's labeled as 'system_u:object_r:device_t:s0' by default. Later, when udev/systemd reacts to this device, it's relabelled to the expected label 'system_u:object_r:tun_tap_device_t:s0'. Hence, we have a code that relabels the device, to cut the race down. For more info see ae368ebfcc4.
But the problem is, the relabel function is called on all TUN/TAP devices. Yes, on /dev/net/tun too. This is however a special kind of device - other processes uses it too. We shouldn't touch it's label then.
Ideally, there would an API in SELinux that would label just the passed FD and not the underlying path. That way, we wouldn't need to care as we would be not labeling /dev/net/tun but the FD passed to the domain. Unfortunately, there's no such API so we have to workaround until then.
Signed-off-by: Michal Privoznik <mprivozn@redhat.com> --- src/security/security_selinux.c | 21 ++++++++++++++++++++- 1 file changed, 20 insertions(+), 1 deletion(-)
diff --git a/src/security/security_selinux.c b/src/security/security_selinux.c index b7c1015..25e8320 100644 --- a/src/security/security_selinux.c +++ b/src/security/security_selinux.c @@ -2352,7 +2352,7 @@ virSecuritySELinuxSetTapFDLabel(virSecurityManagerPtr mgr, struct stat buf; security_context_t fcon = NULL; virSecurityLabelDefPtr secdef; - char *str = NULL; + char *str = NULL, *proc = NULL, *fd_path = NULL; int rc = -1;
secdef = virDomainDefGetSecurityLabelDef(def, SECURITY_SELINUX_NAME); @@ -2370,6 +2370,23 @@ virSecuritySELinuxSetTapFDLabel(virSecurityManagerPtr mgr, goto cleanup; }
+ /* Label /dev/tap.* devices only. Leave /dev/net/tun alone! */ + if (virAsprintf(&proc, "/proc/self/fd/%d", fd) == -1) + goto cleanup; + + if (virFileResolveLink(proc, &fd_path) < 0) { + virReportSystemError(errno, + _("Unable to resolve link: %s"), proc); + goto cleanup; + } + + if (!STRPREFIX(fd_path, "/dev/tap")) { + VIR_DEBUG("fd=%d points to %s not setting SELinux label", + fd, fd_path); + rc = 0; + goto cleanup; + } + if (getContext(mgr, "/dev/tap.*", buf.st_mode, &fcon) < 0) { virReportError(VIR_ERR_INTERNAL_ERROR, _("cannot lookup default selinux label for tap fd %d"), fd); @@ -2384,6 +2401,8 @@ virSecuritySELinuxSetTapFDLabel(virSecurityManagerPtr mgr,
cleanup: freecon(fcon); + VIR_FREE(fd_path); + VIR_FREE(proc); VIR_FREE(str); return rc; }
I applied this patch (without any of Eric's suggested changes) to libvirt on Rawhide to see if it would fix the relabelling problems that are stopping libguestfs networking from working. It does indeed appear to fix them. Hence you can add: Tested-by: Richard W.M. Jones <rjones@redhat.com> Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-top is 'top' for virtual machines. Tiny program with many powerful monitoring features, net stats, disk stats, logging, etc. http://people.redhat.com/~rjones/virt-top