[Qemu-devel] [PATCH v2 12/17] mirror: Fix potential use-after-free in active commit

[Kevin Wolf <kwolf@redhat.com>]

When starting an active commit job, other callbacks can run before
mirror_start_job() calls bdrv_ref() where needed and cause the nodes to
go away. Add another pair of bdrv_ref/unref() around it to protect
against this case.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block/mirror.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/block/mirror.c b/block/mirror.c
index 56d9ef7474..c8657991cf 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -1697,7 +1697,14 @@ void commit_active_start(const char *job_id, BlockDriverState *bs,
 
     orig_base_flags = bdrv_get_flags(base);
 
+    /* bdrv_reopen() drains, which might make the BDSes go away before a
+     * reference is taken in mirror_start_job(). */
+    bdrv_ref(bs);
+    bdrv_ref(base);
+
     if (bdrv_reopen(base, bs->open_flags, errp)) {
+        bdrv_unref(bs);
+        bdrv_unref(base);
         return;
     }
 
@@ -1707,6 +1714,10 @@ void commit_active_start(const char *job_id, BlockDriverState *bs,
                      &commit_active_job_driver, false, base, auto_complete,
                      filter_node_name, false, MIRROR_COPY_MODE_BACKGROUND,
                      &local_err);
+
+    bdrv_unref(bs);
+    bdrv_unref(base);
+
     if (local_err) {
         error_propagate(errp, local_err);
         goto error_restore_flags;
-- 
2.13.6