We need to ensure top lock is acquired before nested lock. Otherwise deadlock
issues may arise. We have the stack security driver, which internally manages
other security drivers, we call them "top" and "nested".
We call virSecurityStackPreFork() to lock the top one, and it also locks
and then unlocks the nested drivers prior to fork. Then in qemuSecurityPostFork(),
it unlocks the top one, but not the nested ones. Thus, if one of the nested
drivers ("dac" or "selinux") is still locked, it will cause a deadlock.
We discovered this case: the nested list obtained through the qemuSecurityGetNested()
will be locked for subsequent use, such as in virQEMUDriverCreateCapabilities(),
where the nested list is locked using qemuSecurityGetDOI, but the top one is not locked beforehand.
The problem stack is as follows:
libvirtd thread1 libvirtd thread2 child libvirtd
| | |
| | |
virsh capabilities qemuProcessLanuch |
| | |
| lock top |
| | |
lock nested | |
| | |
| fork------------------->|(held nested lock)
| | |
| | |
unlock nested unlock top unlock top
|
|
qemuSecuritySetSocketLabel
|
|
lock nested (deadlock)
In this commit, we ensure that the top lock is acquired before the nested lock,
so during fork, it's not possible for another task to acquire the nested lock.
Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1303031
Signed-off-by: hongmianquan <hongmianquan@xxxxxxxxxxxxx>
---
src/libvirt_private.syms | 3 ++-
src/qemu/qemu_conf.c | 9 ++++++++-
src/qemu/qemu_driver.c | 16 +++++++++-------
src/qemu/qemu_security.h | 2 ++
src/security/security_manager.c | 22 ++++++++++++++++++++++
src/security/security_manager.h | 2 ++
6 files changed, 45 insertions(+), 9 deletions(-)
diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index bac4a8a366..39cdb90772 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -1806,7 +1806,8 @@ virSecurityManagerTransactionAbort;
virSecurityManagerTransactionCommit;
virSecurityManagerTransactionStart;
virSecurityManagerVerify;
-
+virSecurityManagerStackLock;
+virSecurityManagerStackUnlock;
# security/security_util.h
virSecurityXATTRNamespaceDefined;
diff --git a/src/qemu/qemu_conf.c b/src/qemu/qemu_conf.c
index 4050a82341..21f0739fd5 100644
--- a/src/qemu/qemu_conf.c
+++ b/src/qemu/qemu_conf.c
@@ -1380,6 +1380,9 @@ virCaps *virQEMUDriverCreateCapabilities(virQEMUDriver *driver)
return NULL;
}
+ /* Ensure top lock is acquired before nested locks */
+ qemuSecurityStackLock(driver->securityManager);
+
/* access sec drivers and create a sec model for each one */
if (!(sec_managers = qemuSecurityGetNested(driver->securityManager)))
return NULL;
@@ -1402,8 +1405,10 @@ virCaps *virQEMUDriverCreateCapabilities(virQEMUDriver *driver)
lbl = qemuSecurityGetBaseLabel(sec_managers[i], virtTypes[j]);
type = virDomainVirtTypeToString(virtTypes[j]);
if (lbl &&
- virCapabilitiesHostSecModelAddBaseLabel(sm, type, lbl) < 0)
+ virCapabilitiesHostSecModelAddBaseLabel(sm, type, lbl) < 0) {
+ qemuSecurityStackUnlock(driver->securityManager);
return NULL;
+ }
}
VIR_DEBUG("Initialized caps for security driver \"%s\" with "
@@ -1412,6 +1417,8 @@ virCaps *virQEMUDriverCreateCapabilities(virQEMUDriver *driver)
caps->host.numa = virCapabilitiesHostNUMANewHost();
caps->host.cpu = virQEMUDriverGetHostCPU(driver);
+
+ qemuSecurityStackUnlock(driver->securityManager);
return g_steal_pointer(&caps);
}
diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index fc1704f4fc..c980a0990f 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -560,7 +560,6 @@ qemuStateInitialize(bool privileged,
bool autostart = true;
size_t i;
const char *defsecmodel = NULL;
- g_autofree virSecurityManager **sec_managers = NULL;
g_autoptr(virIdentity) identity = virIdentityGetCurrent();
qemu_driver = g_new0(virQEMUDriver, 1);
@@ -835,11 +834,8 @@ qemuStateInitialize(bool privileged,
if (!qemu_driver->qemuCapsCache)
goto error;
- if (!(sec_managers = qemuSecurityGetNested(qemu_driver->securityManager)))
- goto error;
-
- if (sec_managers[0] != NULL)
- defsecmodel = qemuSecurityGetModel(sec_managers[0]);
+ if (qemu_driver->securityManager != NULL)
+ defsecmodel = qemuSecurityGetModel(qemu_driver->securityManager);
if (!(qemu_driver->xmlopt = virQEMUDriverCreateXMLConf(qemu_driver,
defsecmodel)))
@@ -5663,7 +5659,12 @@ static int qemuDomainGetSecurityLabelList(virDomainPtr dom,
ret = 0;
} else {
int len = 0;
- virSecurityManager ** mgrs = qemuSecurityGetNested(driver->securityManager);
+ virSecurityManager ** mgrs = NULL;
+
+ /* Ensure top lock is acquired before nested locks */
+ qemuSecurityStackLock(driver->securityManager);
+
+ mgrs = qemuSecurityGetNested(driver->securityManager);
if (!mgrs)
goto cleanup;
@@ -5688,6 +5689,7 @@ static int qemuDomainGetSecurityLabelList(virDomainPtr dom,
}
cleanup:
+ qemuSecurityStackUnlock(driver->securityManager);
virDomainObjEndAPI(&vm);
return ret;
}
diff --git a/src/qemu/qemu_security.h b/src/qemu/qemu_security.h
index 41da33debc..19fcb3c939 100644
--- a/src/qemu/qemu_security.h
+++ b/src/qemu/qemu_security.h
@@ -151,3 +151,5 @@ int qemuSecurityCommandRun(virQEMUDriver *driver,
#define qemuSecuritySetTapFDLabel virSecurityManagerSetTapFDLabel
#define qemuSecurityStackAddNested virSecurityManagerStackAddNested
#define qemuSecurityVerify virSecurityManagerVerify
+#define qemuSecurityStackLock virSecurityManagerStackLock
+#define qemuSecurityStackUnlock virSecurityManagerStackUnlock
\ No newline at end of file
diff --git a/src/security/security_manager.c b/src/security/security_manager.c
index 24f2f3d3dc..c49c4f708f 100644
--- a/src/security/security_manager.c
+++ b/src/security/security_manager.c
@@ -989,6 +989,28 @@ virSecurityManagerGetNested(virSecurityManager *mgr)
return list;
}
+/*
+ * Usually called before virSecurityManagerGetNested().
+ * We need to ensure locking the stack security manager before
+ * locking the nested security manager to maintain the correct
+ * synchronization state.
+ * It must be followed by a call virSecurityManagerStackUnlock().
+ */
+void
+virSecurityManagerStackLock(virSecurityManager *mgr)
+{
+ if (STREQ("stack", mgr->drv->name))
+ virObjectLock(mgr);
+}
+
+
+void
+virSecurityManagerStackUnlock(virSecurityManager *mgr)
+{
+ if (STREQ("stack", mgr->drv->name))
+ virObjectUnlock(mgr);
+}
+
/**
* virSecurityManagerDomainSetPathLabel:
diff --git a/src/security/security_manager.h b/src/security/security_manager.h
index a416af3215..bb6d22bc31 100644
--- a/src/security/security_manager.h
+++ b/src/security/security_manager.h
@@ -158,6 +158,8 @@ int virSecurityManagerSetTapFDLabel(virSecurityManager *mgr,
char *virSecurityManagerGetMountOptions(virSecurityManager *mgr,
virDomainDef *vm);
virSecurityManager ** virSecurityManagerGetNested(virSecurityManager *mgr);
+void virSecurityManagerStackLock(virSecurityManager *mgr);
+void virSecurityManagerStackUnlock(virSecurityManager *mgr);
typedef enum {
VIR_SECURITY_DOMAIN_IMAGE_LABEL_BACKING_CHAIN = 1 << 0,
--
2.11.0
