Re: [PATCH for-4.2?] block/qcow2-bitmap: fix crash bug in qcow2_co_remove_persistent_dirty_bitmap

[John Snow <jsnow@redhat.com>]

On 12/5/19 2:30 PM, Vladimir Sementsov-Ogievskiy wrote:
> Here is double bug:
> 
> First, return error but not set errp. This may lead to:
> qmp block-dirty-bitmap-remove may report success when actually failed
> 
> block-dirty-bitmap-remove used in a transaction will crash, as
> qmp_transaction will think that it returned success and will cal
> block_dirty_bitmap_remove_commit which will crash, as state->bitmap is
> NULL
> 
> Second (like in anecdote), this case is not an error at all. As it is
> documented in the comment above bdrv_co_remove_persistent_dirty_bitmap
> definition, absence of bitmap is not an error, and similar case handled
> at start of qcow2_co_remove_persistent_dirty_bitmap, it returns 0 when
> there is no bitmaps at all..
> 
> But when there are some bitmaps, but not the requested one, it return
> error with errp unset.
> 
> Fix that.
> 
> Fixes: b56a1e31759b750
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
> 
> Hi all!
> 
> Ohm, suddenly we faced this bug. It's a regression in 4.2. I'm very
> sorry for introducing it, and it sad that it's found so late..
> 
> Personally, I think that this one worth rc5, as it makes new bitmap
> interfaces unusable. But the decision is yours.
> 
> Last minute edit: hmm, actually, transaction action introduced in
> 4.2, so crash is not a regression, only broken block-dirty-bitmap-remove
> command is a regression... Maybe it's OK for stable.
> 

Might be hard to justify an RC5 for the sake of this patch.

If we need an RC5 for other reasons, I'd want to include this.

>  block/qcow2-bitmap.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/block/qcow2-bitmap.c b/block/qcow2-bitmap.c
> index 8abaf632fc..c6c8ebbe89 100644
> --- a/block/qcow2-bitmap.c
> +++ b/block/qcow2-bitmap.c
> @@ -1469,8 +1469,10 @@ int coroutine_fn qcow2_co_remove_persistent_dirty_bitmap(BlockDriverState *bs,
>      Qcow2BitmapList *bm_list;
>  
>      if (s->nb_bitmaps == 0) {
> -        /* Absence of the bitmap is not an error: see explanation above
> -         * bdrv_remove_persistent_dirty_bitmap() definition. */
> +        /*
> +         * Absence of the bitmap is not an error: see explanation above
> +         * bdrv_co_remove_persistent_dirty_bitmap() definition.
> +         */
>          return 0;
>      }
>  
> @@ -1485,7 +1487,8 @@ int coroutine_fn qcow2_co_remove_persistent_dirty_bitmap(BlockDriverState *bs,
>  
>      bm = find_bitmap_by_name(bm_list, name);
>      if (bm == NULL) {
> -        ret = -EINVAL;
> +        /* Absence of the bitmap is not an error, see above. */
> +        ret = 0;
>          goto out;
>      }
>  
>