Re: [PATCH v1] security_manager: Ensure top lock is acquired before nested locks

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(a)bytedance.com&gt; --- 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; }