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Re: [Qemu-block] [Qemu-devel] [PULL 5/8] commit: Fix use after free in c
From: |
Peter Maydell |
Subject: |
Re: [Qemu-block] [Qemu-devel] [PULL 5/8] commit: Fix use after free in completion |
Date: |
Tue, 13 Jun 2017 17:12:46 +0100 |
On 7 June 2017 at 18:50, Kevin Wolf <address@hidden> wrote:
> 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.
>
> Signed-off-by: Kevin Wolf <address@hidden>
> Reviewed-by: John Snow <address@hidden>
> ---
> block/commit.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/block/commit.c b/block/commit.c
> index a3028b2..af6fa68 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);
Hi -- coverity complains about this change, because bdrv_ref()
assumes that its argument is not NULL, but later on in commit_complete()
we have a check
"if (overlay_bs && ...)"
which assumes its argument might be NULL. (CID 1376205)
Which is correct?
thanks
-- PMM
- [Qemu-block] [PULL 0/8] Block layer patches, Kevin Wolf, 2017/06/07
- [Qemu-block] [PULL 1/8] block: Fix anonymous BBs in blk_root_inactivate(), Kevin Wolf, 2017/06/07
- [Qemu-block] [PULL 2/8] migration: Inactivate images after .save_live_complete_precopy(), Kevin Wolf, 2017/06/07
- [Qemu-block] [PULL 3/8] migration/block: Clean up BBs in block_save_complete(), Kevin Wolf, 2017/06/07
- [Qemu-block] [PULL 4/8] qemu-iotests: Block migration test, Kevin Wolf, 2017/06/07
- [Qemu-block] [PULL 5/8] commit: Fix use after free in completion, Kevin Wolf, 2017/06/07
- Re: [Qemu-block] [Qemu-devel] [PULL 5/8] commit: Fix use after free in completion,
Peter Maydell <=
- [Qemu-block] [PULL 7/8] block/qcow.c: Fix memory leak in qcow_create(), Kevin Wolf, 2017/06/07
- [Qemu-block] [PULL 6/8] qemu-iotests: Test automatic commit job cancel on hot unplug, Kevin Wolf, 2017/06/07
- [Qemu-block] [PULL 8/8] block: fix external snapshot abort permission error, Kevin Wolf, 2017/06/07
- Re: [Qemu-block] [Qemu-devel] [PULL 0/8] Block layer patches, Peter Maydell, 2017/06/12