Re: [Qemu-devel] [PULL 50/85] qcow2: add .bdrv_remove_persistent_dirty_bitmap

[Peter Maydell]

On 11 July 2017 at 17:07, Max Reitz <address@hidden> wrote:
> From: Vladimir Sementsov-Ogievskiy <address@hidden>
>
> Realize .bdrv_remove_persistent_dirty_bitmap interface.
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
> Reviewed-by: Max Reitz <address@hidden>
> Reviewed-by: John Snow <address@hidden>
> Message-id: address@hidden
> Signed-off-by: Max Reitz <address@hidden>

> +void qcow2_remove_persistent_dirty_bitmap(BlockDriverState *bs,
> +                                          const char *name,
> +                                          Error **errp)
> +{
> +    int ret;
> +    BDRVQcow2State *s = bs->opaque;
> +    Qcow2Bitmap *bm;
> +    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. */
> +        return;
> +    }
> +
> +    bm_list = bitmap_list_load(bs, s->bitmap_directory_offset,
> +                               s->bitmap_directory_size, errp);
> +    if (bm_list == NULL) {
> +        return;
> +    }
> +
> +    bm = find_bitmap_by_name(bm_list, name);
> +    if (bm == NULL) {
> +        goto fail;
> +    }
> +
> +    QSIMPLEQ_REMOVE(bm_list, bm, Qcow2Bitmap, entry);
> +
> +    ret = update_ext_header_and_dir(bs, bm_list);
> +    if (ret < 0) {
> +        error_setg_errno(errp, -ret, "Failed to update bitmap extension");
> +        goto fail;
> +    }
> +
> +    free_bitmap_clusters(bs, &bm->table);
> +
> +fail:
> +    bitmap_free(bm);
> +    bitmap_list_free(bm_list);
> +}

Coverity points out that this can crash in the error-exit paths,
because bitmap_free() doesn't handle being passed a NULL pointer.
(CID 1377700).

Probably the best fix for this is to make bitmap_free() do
nothing when handed NULL.

thanks
-- PMM