[PATCH] nwfilter_driver: Make reload fail if racing with stateCleanup()

[Michal Privoznik]

When one thread is trying to reload NWFilter driver (by running
nwfilterStateReload()) but there's another thread that's
concurrently running nwfilterStateCleanup() a crash may occur.
This is despite nwfilterStateReload() checking for driver !=
NULL, because is done so without @driverMutex held. A typical
TOCTOU. Fortunately, the mutex is always initialized, so the
mutex can be acquired at all times and @driver can be checked
with the lock held.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2075837
Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
---
 src/nwfilter/nwfilter_driver.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/src/nwfilter/nwfilter_driver.c b/src/nwfilter/nwfilter_driver.c
index b66ba22737..d028efafbe 100644
--- a/src/nwfilter/nwfilter_driver.c
+++ b/src/nwfilter/nwfilter_driver.c
@@ -309,6 +309,8 @@ nwfilterStateInitialize(bool privileged,
 static int
 nwfilterStateReload(void)
 {
+    VIR_LOCK_GUARD lock = virLockGuardLock(&driverMutex);
+
     if (!driver)
         return -1;
 
@@ -319,15 +321,13 @@ nwfilterStateReload(void)
     /* shut down all threads -- they will be restarted if necessary */
     virNWFilterLearnThreadsTerminate(true);
 
-    VIR_WITH_MUTEX_LOCK_GUARD(&driverMutex) {
-        VIR_WITH_MUTEX_LOCK_GUARD(&driver->updateLock) {
-            virNWFilterObjListLoadAllConfigs(driver->nwfilters, driver->configDir);
-        }
-
-
-        virNWFilterBuildAll(driver, false);
+    VIR_WITH_MUTEX_LOCK_GUARD(&driver->updateLock) {
+        virNWFilterObjListLoadAllConfigs(driver->nwfilters, driver->configDir);
     }
 
+
+    virNWFilterBuildAll(driver, false);
+
     return 0;
 }
 
-- 
2.35.1