[PATCH RESEND 2/3] vhost: fix a null pointer reference of vhost_log

["Longpeng(Mike)" <longpeng2@huawei.com>]

From: Longpeng <longpeng2@huawei.com>

vhost_log_alloc() may fails and returned pointer of log is null.
However there're two places derefernce the return pointer without
check.

Signed-off-by: Longpeng <longpeng2@huawei.com>
---
 hw/virtio/vhost.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 9edfadc..c7ad6e5 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -219,6 +219,10 @@ static struct vhost_log *vhost_log_get(uint64_t size, bool share)
 
     if (!log || log->size != size) {
         log = vhost_log_alloc(size, share);
+        if (!log) {
+            return NULL;
+        }
+
         if (share) {
             vhost_log_shm = log;
         } else {
@@ -270,10 +274,17 @@ static bool vhost_dev_log_is_shared(struct vhost_dev *dev)
 
 static inline void vhost_dev_log_resize(struct vhost_dev *dev, uint64_t size)
 {
-    struct vhost_log *log = vhost_log_get(size, vhost_dev_log_is_shared(dev));
-    uint64_t log_base = (uintptr_t)log->log;
+    struct vhost_log *log;
+    uint64_t log_base;
     int r;
 
+    log = vhost_log_get(size, vhost_dev_log_is_shared(dev));
+    if (!log) {
+        return;
+    }
+
+    log_base = (uintptr_t)log->log;
+
     /* inform backend of log switching, this must be done before
        releasing the current log, to ensure no logging is lost */
     r = dev->vhost_ops->vhost_set_log_base(dev, log_base, log);
@@ -1640,6 +1651,10 @@ int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice *vdev)
         hdev->log_size = vhost_get_log_size(hdev);
         hdev->log = vhost_log_get(hdev->log_size,
                                   vhost_dev_log_is_shared(hdev));
+        if (!hdev->log) {
+            goto fail_vq;
+        }
+
         log_base = (uintptr_t)hdev->log->log;
         r = hdev->vhost_ops->vhost_set_log_base(hdev,
                                                 hdev->log_size ? log_base : 0,
-- 
1.8.3.1