qemu: fix crash with shared disks

Commit f36a94f2 introduced a double free on all success paths
in qemuSharedDeviceEntryInsert.

Only call qemuSharedDeviceEntryFree on the error path and
set entry to NULL before jumping there if the entry already
is in the hash table.

https://bugzilla.redhat.com/show_bug.cgi?id=1142722

src/qemu/qemu_conf.c

@@ -1011,38 +1011,36 @@ qemuSharedDeviceEntryInsert(virQEMUDriverPtr driver,
                             const char *name)
 {
     qemuSharedDeviceEntry *entry = NULL;
-    int ret = -1;
 
     if ((entry = virHashLookup(driver->sharedDevices, key))) {
         /* Nothing to do if the shared scsi host device is already
          * recorded in the table.
          */
-        if (qemuSharedDeviceEntryDomainExists(entry, name, NULL)) {
-            ret = 0;
-            goto cleanup;
+        if (!qemuSharedDeviceEntryDomainExists(entry, name, NULL)) {
+            if (VIR_EXPAND_N(entry->domains, entry->ref, 1) < 0 ||
+                VIR_STRDUP(entry->domains[entry->ref - 1], name) < 0) {
+                /* entry is owned by the hash table here */
+                entry = NULL;
+                goto error;
+            }
         }
-
-        if (VIR_EXPAND_N(entry->domains, entry->ref, 1) < 0 ||
-            VIR_STRDUP(entry->domains[entry->ref - 1], name) < 0)
-            goto cleanup;
     } else {
         if (VIR_ALLOC(entry) < 0 ||
             VIR_ALLOC_N(entry->domains, 1) < 0 ||
             VIR_STRDUP(entry->domains[0], name) < 0)
-            goto cleanup;
+            goto error;
 
         entry->ref = 1;
 
         if (virHashAddEntry(driver->sharedDevices, key, entry))
-            goto cleanup;
+            goto error;
     }
 
-    ret = 0;
+    return 0;
 
- cleanup:
+ error:
     qemuSharedDeviceEntryFree(entry, NULL);
-
-    return ret;
+    return -1;
 }
 
 

src/qemu/qemu_conf.h

@@ -294,8 +294,7 @@ bool qemuSharedDeviceEntryDomainExists(qemuSharedDeviceEntryPtr entry,
 char *qemuGetSharedDeviceKey(const char *disk_path)
     ATTRIBUTE_NONNULL(1);
 
-void qemuSharedDeviceEntryFree(void *payload, const void *name)
-    ATTRIBUTE_NONNULL(1);
+void qemuSharedDeviceEntryFree(void *payload, const void *name);
 
 int qemuAddSharedDevice(virQEMUDriverPtr driver,
                         virDomainDeviceDefPtr dev,