On 6/25/24 12:03, hongmianquan via Devel wrote:
> 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 <[email protected]>
> ---
> 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;
>
This needs to be ordered differently. I believe 'ninja test' complains
about ordering.
> # 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)
There's one early 'return' in between these two hunks. It'll also need
to call qemuSecurityStackUnlock().
> 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);
I believe this can be moved before virCapabilitiesHostNUMANewHost() line.
> 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);
I'd prefer this change to be a separate patch as it's semantically
different change.
>
> 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);
This label is jumped onto also from other places which did not call
qemuSecurityStackLock().
> virDomainObjEndAPI(&vm);
> return ret;
> }
Otherwise makes sense.
Michal
