Re: [Qemu-devel] [PATCH 1/4] mirror: Do not dereference invalid pointers

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

12.09.2019 16:56, Max Reitz wrote:
> mirror_exit_common() may be called twice (if it is called from
> mirror_prepare() and fails, it will be called from mirror_abort()
> again).
> 
> In such a case, many of the pointers in the MirrorBlockJob object will
> already be freed.  This can be seen most reliably for s->target, which
> is set to NULL (and then dereferenced by blk_bs()).
> 
> Cc: qemu-stable@nongnu.org
> Fixes: 737efc1eda23b904fbe0e66b37715fb0e5c3e58b
> Signed-off-by: Max Reitz <mreitz@redhat.com>

Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

> ---
>   block/mirror.c | 13 +++++++++----
>   1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/block/mirror.c b/block/mirror.c
> index fe984efb90..706d80fced 100644
> --- a/block/mirror.c
> +++ b/block/mirror.c
> @@ -620,11 +620,11 @@ static int mirror_exit_common(Job *job)
>   {
>       MirrorBlockJob *s = container_of(job, MirrorBlockJob, common.job);
>       BlockJob *bjob = &s->common;
> -    MirrorBDSOpaque *bs_opaque = s->mirror_top_bs->opaque;
> +    MirrorBDSOpaque *bs_opaque;
>       AioContext *replace_aio_context = NULL;
> -    BlockDriverState *src = s->mirror_top_bs->backing->bs;
> -    BlockDriverState *target_bs = blk_bs(s->target);
> -    BlockDriverState *mirror_top_bs = s->mirror_top_bs;
> +    BlockDriverState *src;
> +    BlockDriverState *target_bs;
> +    BlockDriverState *mirror_top_bs;
>       Error *local_err = NULL;
>       bool abort = job->ret < 0;
>       int ret = 0;
> @@ -634,6 +634,11 @@ static int mirror_exit_common(Job *job)
>       }
>       s->prepared = true;
>   
> +    mirror_top_bs = s->mirror_top_bs;
> +    bs_opaque = mirror_top_bs->opaque;
> +    src = mirror_top_bs->backing->bs;
> +    target_bs = blk_bs(s->target);
> +
>       if (bdrv_chain_contains(src, target_bs)) {
>           bdrv_unfreeze_backing_chain(mirror_top_bs, target_bs);
>       }
> 


-- 
Best regards,
Vladimir