[PATCH] nwfilter: fix crash when counting number of network filters

[Daniel P. Berrangé <berrange@xxxxxxxxxx>]

The virNWFilterObjListNumOfNWFilters method iterates over the
driver->nwfilters, accessing virNWFilterObj instances. As such
it needs to be protected against concurrent modification of
the driver->nwfilters object.

This API allows unprivileged users to connect, so users with
read-only access to libvirt can cause a denial of service
crash if they are able to race with a call of virNWFilterUndefine.
Since network filters are usually statically defined, this is
considered a low severity problem.

This is assigned CVE-2022-0897.

Reviewed-by: Eric Blake <eblake@xxxxxxxxxx>
Signed-off-by: Daniel P. Berrangé <berrange@xxxxxxxxxx>
---

Pushed as a pre-reviewed patch from the security list

 src/nwfilter/nwfilter_driver.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/nwfilter/nwfilter_driver.c b/src/nwfilter/nwfilter_driver.c
index 3ce8fce7f9..a493205c80 100644
--- a/src/nwfilter/nwfilter_driver.c
+++ b/src/nwfilter/nwfilter_driver.c
@@ -478,11 +478,15 @@ nwfilterLookupByName(virConnectPtr conn,
 static int
 nwfilterConnectNumOfNWFilters(virConnectPtr conn)
 {
+    int ret;
     if (virConnectNumOfNWFiltersEnsureACL(conn) < 0)
         return -1;
 
-    return virNWFilterObjListNumOfNWFilters(driver->nwfilters, conn,
-                                        virConnectNumOfNWFiltersCheckACL);
+    nwfilterDriverLock();
+    ret = virNWFilterObjListNumOfNWFilters(driver->nwfilters, conn,
+                                           virConnectNumOfNWFiltersCheckACL);
+    nwfilterDriverUnlock();
+    return ret;
 }
 
 
-- 
2.35.1