[Qemu-devel] [PATCH v2] vhost: Fix use-after-free in vhost_log_put()

[Jia-Shiun Li]

In commit 9e0bc24f dev->log_size was reset to zero too early before
syncing vhost log. It causes syncing to be skipped.

Use local variable to keep its value before resetting.

Signed-off-by: Jia-Shiun Li <address@hidden>
---

v1 -> v2:
 * Use local variable to keep value of dev->log_size.

---
 hw/virtio/vhost.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 6eddb09..c1c5714 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -371,6 +371,7 @@ static struct vhost_log *vhost_log_get(uint64_t size, bool 
share)
 static void vhost_log_put(struct vhost_dev *dev, bool sync)
 {
     struct vhost_log *log = dev->log;
+    uint64_t log_size = dev->log_size;
 
     if (!log) {
         return;
@@ -381,8 +382,8 @@ static void vhost_log_put(struct vhost_dev *dev, bool sync)
     --log->refcnt;
     if (log->refcnt == 0) {
         /* Sync only the range covered by the old log */
-        if (dev->log_size && sync) {
-            vhost_log_sync_range(dev, 0, dev->log_size * VHOST_LOG_CHUNK - 1);
+        if (log_size && sync) {
+            vhost_log_sync_range(dev, 0, log_size * VHOST_LOG_CHUNK - 1);
         }
 
         if (vhost_log == log) {
-- 
2.7.4