qemu: Do not access stale data in virDomainBlockStats

CVE-2013-6458
https://bugzilla.redhat.com/show_bug.cgi?id=1043069

When virDomainDetachDeviceFlags is called concurrently to
virDomainBlockStats: libvirtd may crash because qemuDomainBlockStats
finds a disk in vm->def before getting a job on a domain and uses the
disk pointer after getting the job. However, the domain in unlocked
while waiting on a job condition and thus data behind the disk pointer
may disappear. This happens when thread 1 runs
virDomainDetachDeviceFlags and enters monitor to actually remove the
disk. Then another thread starts running virDomainBlockStats, finds the
disk in vm->def, and while it's waiting on the job condition (owned by
the first thread), the first thread finishes the disk removal. When the
second thread gets the job, the memory pointed to be the disk pointer is
already gone.

That said, every API that is going to begin a job should do that before
fetching data from vm->def.

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index 004ec881af4a1b17c0d189b6b5ac1c43319a64ea..eff3ac46dd7de010b341e4a02d9f94b7c5b718c4 100644 (file)
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -9028,34 +9028,29 @@ qemuDomainBlockStats(virDomainPtr dom,
     if (virDomainBlockStatsEnsureACL(dom->conn, vm->def) < 0)
         goto cleanup;
 
+    if (qemuDomainObjBeginJob(driver, vm, QEMU_JOB_QUERY) < 0)
+        goto cleanup;
+
     if (!virDomainObjIsActive(vm)) {
         virReportError(VIR_ERR_OPERATION_INVALID,
                        "%s", _("domain is not running"));
-        goto cleanup;
+        goto endjob;
     }
 
     if ((idx = virDomainDiskIndexByName(vm->def, path, false)) < 0) {
         virReportError(VIR_ERR_INVALID_ARG,
                        _("invalid path: %s"), path);
-        goto cleanup;
+        goto endjob;
     }
     disk = vm->def->disks[idx];
 
     if (!disk->info.alias) {
         virReportError(VIR_ERR_INTERNAL_ERROR,
                        _("missing disk device alias name for %s"), disk->dst);
-        goto cleanup;
+        goto endjob;
     }
 
     priv = vm->privateData;
-    if (qemuDomainObjBeginJob(driver, vm, QEMU_JOB_QUERY) < 0)
-        goto cleanup;
-
-    if (!virDomainObjIsActive(vm)) {
-        virReportError(VIR_ERR_OPERATION_INVALID,
-                       "%s", _("domain is not running"));
-        goto endjob;
-    }
 
     qemuDomainObjEnterMonitor(driver, vm);
     ret = qemuMonitorGetBlockStatsInfo(priv->mon,