[libvirt] [PATCH 4/3] Control LXC capabilities
Daniel P. Berrange
berrange at redhat.com
Tue Jun 23 11:02:12 UTC 2009
This patch updates the LXC driver to make use of libcap-ng for managing
process capabilities. Previously Ryota Ozaki had provided code to remove
the CAP_BOOT capabilities inside the container, preventing host reboots.
In addition to that one, I believe we should be removing ability to
load kernel modules, change the system clock and changing audit/MAC.
So this patch also clears the following:
CAP_SYS_MODULE, /* No kernel module loading */
CAP_SYS_TIME, /* No changing the clock */
CAP_AUDIT_CONTROL, /* No messing with auditing */
CAP_AUDIT_WRITE, /* No messing with auditing */
CAP_MAC_ADMIN, /* No messing with LSM */
CAP_MAC_OVERRIDE, /* No messing with LSM */
We use libcap-ng's capng_updatev/apply functions to remove these from
the permitted, inheritable, effective and bounding sets. Then we use
capng_lock to set NOROOT and NOROOT_LOCKED in the process securebits
to prevent them ever being re-acquired.
The other thing I realized is that the 'libvirt_lxc' controller process
does not need to keep any capabilities at all once it has spawned the
container process, since all its doing is forwarding I/O between 2 open
file descripts. So I also clear all capabilities from that. We should
probably make it chuid/gid to a non-root user in future too.
lxc_container.c | 66 +++++++++++++++++++++++++++++++++++++------------------
lxc_controller.c | 28 +++++++++++++++++++++++
2 files changed, 73 insertions(+), 21 deletions(-)
Regards,
Daniel
diff -r 7e766489c4a2 src/lxc_container.c
--- a/src/lxc_container.c Tue Jun 23 11:13:45 2009 +0100
+++ b/src/lxc_container.c Tue Jun 23 11:54:10 2009 +0100
@@ -41,8 +41,9 @@
/* For MS_MOVE */
#include <linux/fs.h>
-#include <sys/prctl.h>
-#include <linux/capability.h>
+#if HAVE_CAPNG
+#include <cap-ng.h>
+#endif
#include "virterror_internal.h"
#include "logging.h"
@@ -642,27 +643,50 @@ static int lxcContainerSetupMounts(virDo
return lxcContainerSetupExtraMounts(vmDef);
}
-static int lxcContainerDropCapabilities(virDomainDefPtr vmDef ATTRIBUTE_UNUSED)
+
+/*
+ * This is running as the 'init' process insid the container.
+ * It removes some capabilities that could be dangerous to
+ * host system, since they are not currently "containerized"
+ */
+static int lxcContainerDropCapabilities(void)
{
-#ifdef PR_CAPBSET_DROP
- int i;
- const struct {
- int id;
- const char *name;
- } caps[] = {
-#define ID_STRING(name) name, #name
- { ID_STRING(CAP_SYS_BOOT) },
- };
+#if HAVE_CAPNG
+ int ret;
- for (i = 0 ; i < ARRAY_CARDINALITY(caps) ; i++) {
- if (prctl(PR_CAPBSET_DROP, caps[i].id, 0, 0, 0)) {
- lxcError(NULL, NULL, VIR_ERR_INTERNAL_ERROR,
- _("failed to drop %s"), caps[i].name);
- return -1;
- }
+ capng_get_caps_process();
+
+ if ((ret = capng_updatev(CAPNG_DROP,
+ CAPNG_EFFECTIVE | CAPNG_PERMITTED |
+ CAPNG_INHERITABLE | CAPNG_BOUNDING_SET,
+ CAP_SYS_BOOT, /* No use of reboot */
+ CAP_SYS_MODULE, /* No kernel module loading */
+ CAP_SYS_TIME, /* No changing the clock */
+ CAP_AUDIT_CONTROL, /* No messing with auditing */
+ CAP_AUDIT_WRITE, /* No messing with auditing */
+ CAP_MAC_ADMIN, /* No messing with LSM */
+ CAP_MAC_OVERRIDE, /* No messing with LSM */
+ -1 /* sentinal */)) < 0) {
+ lxcError(NULL, NULL, VIR_ERR_INTERNAL_ERROR,
+ _("failed to remove capabilities %d"), ret);
+ return -1;
}
-#else /* ! PR_CAPBSET_DROP */
- VIR_WARN0(_("failed to drop capabilities PR_CAPBSET_DROP undefined"));
+
+ if ((ret = capng_apply(CAPNG_SELECT_BOTH)) < 0) {
+ lxcError(NULL, NULL, VIR_ERR_INTERNAL_ERROR,
+ _("failed to apply capabilities: %d"), ret);
+ return -1;
+ }
+
+ /* Need to prevent them regaining any caps on exec */
+ if ((ret = capng_lock()) < 0) {
+ lxcError(NULL, NULL, VIR_ERR_INTERNAL_ERROR,
+ _("failed to lock capabilities: %d"), ret);
+ return -1;
+ }
+
+#else
+ VIR_WARN0(_("libcap-ng support not compiled in, unable to clear capabilities"));
#endif
return 0;
}
@@ -735,7 +759,7 @@ static int lxcContainerChild( void *data
return -1;
/* drop a set of root capabilities */
- if (lxcContainerDropCapabilities(vmDef) < 0)
+ if (lxcContainerDropCapabilities() < 0)
return -1;
/* this function will only return if an error occured */
diff -r 7e766489c4a2 src/lxc_controller.c
--- a/src/lxc_controller.c Tue Jun 23 11:13:45 2009 +0100
+++ b/src/lxc_controller.c Tue Jun 23 11:54:10 2009 +0100
@@ -35,6 +35,10 @@
#include <getopt.h>
#include <sys/mount.h>
+#if HAVE_CAPNG
+#include <cap-ng.h>
+#endif
+
#include "virterror_internal.h"
#include "logging.h"
#include "util.h"
@@ -210,6 +214,25 @@ cleanup:
return rc;
}
+
+static int lxcControllerClearCapabilities(void)
+{
+#if HAVE_CAPNG
+ int ret;
+
+ capng_clear(CAPNG_SELECT_BOTH);
+
+ if ((ret = capng_apply(CAPNG_SELECT_BOTH)) < 0) {
+ lxcError(NULL, NULL, VIR_ERR_INTERNAL_ERROR,
+ _("failed to apply capabilities: %d"), ret);
+ return -1;
+ }
+#else
+ VIR_WARN0(_("libcap-ng support not compiled in, unable to clear capabilities"));
+#endif
+ return 0;
+}
+
typedef struct _lxcTtyForwardFd_t {
int fd;
int active;
@@ -562,6 +585,11 @@ lxcControllerRun(virDomainDefPtr def,
if (lxcContainerSendContinue(control[0]) < 0)
goto cleanup;
+ /* Now the container is running, there's no need for us to keep
+ any elevated capabilities */
+ if (lxcControllerClearCapabilities() < 0)
+ goto cleanup;
+
rc = lxcControllerMain(monitor, client, appPty, containerPty);
cleanup:
--
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