From b85da76baeebccdb35c12bbc16f82692c42a7372 Mon Sep 17 00:00:00 2001
From: Michal Privoznik <mprivozn@redhat.com>
Date: Thu, 7 Jan 2021 15:51:02 +0100
Subject: [PATCH 077/108] network: Introduce mutex for bridge name generation

When defining/creating a network the bridge name may be filled in
automatically by libvirt (if none provided in the input XML or
the one provided is a pattern, e.g. "virbr%d"). During the
bridge name generation process a candidate name is generated
which is then checked with the rest of already defined/running
networks for collisions.

Problem is, that there is no mutex guarding this critical section
and thus if two threads line up so that they both generate the
same candidate they won't find any collision and the same name is
then stored.

Resolves: https://gitlab.com/libvirt/libvirt/-/issues/78
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Laine Stump <laine@redhat.com>
(cherry picked from commit ea0cfa115307ecb9fe05dd1953ec7ddd8dd39d72)
---
 src/network/bridge_driver.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/src/network/bridge_driver.c b/src/network/bridge_driver.c
index 21d02dd304..ce61ff483a 100644
--- a/src/network/bridge_driver.c
+++ b/src/network/bridge_driver.c
@@ -74,6 +74,8 @@
 #define VIR_FROM_THIS VIR_FROM_NETWORK
 #define MAX_BRIDGE_ID 256
 
+static virMutex bridgeNameValidateMutex = VIR_MUTEX_INITIALIZER;
+
 /**
  * VIR_NETWORK_DHCP_LEASE_FILE_SIZE_MAX:
  *
@@ -3255,20 +3257,27 @@ static int
 networkBridgeNameValidate(virNetworkObjListPtr nets,
                           virNetworkDefPtr def)
 {
+    virMutexLock(&bridgeNameValidateMutex);
+
     if (def->bridge && !strstr(def->bridge, "%d")) {
         if (virNetworkObjBridgeInUse(nets, def->bridge, def->name)) {
             virReportError(VIR_ERR_INTERNAL_ERROR,
                            _("bridge name '%s' already in use."),
                            def->bridge);
-            return -1;
+            goto error;
         }
     } else {
         /* Allocate a bridge name */
         if (networkFindUnusedBridgeName(nets, def) < 0)
-            return -1;
+            goto error;
     }
 
+    virMutexUnlock(&bridgeNameValidateMutex);
     return 0;
+
+ error:
+    virMutexUnlock(&bridgeNameValidateMutex);
+    return -1;
 }
 
 
-- 
2.33.0

