From 43003baf954053a0857535220292294512c8ada2 Mon Sep 17 00:00:00 2001
From: Kevin Wolf <kwolf@redhat.com>
Date: Mon, 12 Jun 2017 13:03:41 +0200
Subject: [PATCH 05/13] commit: Fix use after free in completion

RH-Author: Kevin Wolf <kwolf@redhat.com>
Message-id: <1497272622-32221-2-git-send-email-kwolf@redhat.com>
Patchwork-id: 75583
O-Subject: [RHEL-7.4 qemu-kvm-rhev PATCH 1/2] commit: Fix use after free in completion
Bugzilla: 1452048
RH-Acked-by: Jeffrey Cody <jcody@redhat.com>
RH-Acked-by: Max Reitz <mreitz@redhat.com>
RH-Acked-by: John Snow <jsnow@redhat.com>

The final bdrv_set_backing_hd() could be working on already freed nodes
because the commit job drops its references (through BlockBackends) to
both overlay_bs and top already a bit earlier.

One way to trigger the bug is hot unplugging a disk for which
blockdev_mark_auto_del() cancels the block job.

Fix this by taking BDS-level references while we're still using the
nodes.

Cc: qemu-stable@nongnu.org
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
(cherry picked from commit 19ebd13ed45ad5d5f277f5914d55b83f13eb09eb)
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 block/commit.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/block/commit.c b/block/commit.c
index 76a0d98..3bae46e 100644
--- a/block/commit.c
+++ b/block/commit.c
@@ -89,6 +89,10 @@ static void commit_complete(BlockJob *job, void *opaque)
     int ret = data->ret;
     bool remove_commit_top_bs = false;
 
+    /* Make sure overlay_bs and top stay around until bdrv_set_backing_hd() */
+    bdrv_ref(top);
+    bdrv_ref(overlay_bs);
+
     /* Remove base node parent that still uses BLK_PERM_WRITE/RESIZE before
      * the normal backing chain can be restored. */
     blk_unref(s->base);
@@ -124,6 +128,9 @@ static void commit_complete(BlockJob *job, void *opaque)
     if (remove_commit_top_bs) {
         bdrv_set_backing_hd(overlay_bs, top, &error_abort);
     }
+
+    bdrv_unref(overlay_bs);
+    bdrv_unref(top);
 }
 
 static void coroutine_fn commit_run(void *opaque)
-- 
1.8.3.1