Re: [Qemu-block] [PATCH 1/5] block/qcow2-bitmap: Skip length check in some cases

[Vladimir Sementsov-Ogievskiy]

06.03.2019 2:43, John Snow wrote:
> If we were to allow resizes, the length check that happens when we load
> bitmap headers from disk when we read or store bitmaps would begin to
> fail:
> 
> Imagine the circumstance where we've resized bitmaps in memory, but they still
> have the old values on-disk. The lengths will no longer match bdrv_getlength,
> so we must allow this check to be skipped when flushing bitmaps to disk.
> 
> Limit this to when we are about to overwrite the headers: we will verify the
> outgoing headers, but we will skip verifying the known stale headers.
> 
> Signed-off-by: John Snow <address@hidden>
> ---
>   block/qcow2-bitmap.c | 34 +++++++++++++++++++++-------------
>   1 file changed, 21 insertions(+), 13 deletions(-)
> 
> diff --git a/block/qcow2-bitmap.c b/block/qcow2-bitmap.c
> index c3b210ede1..d02730004a 100644
> --- a/block/qcow2-bitmap.c
> +++ b/block/qcow2-bitmap.c
> @@ -435,7 +435,8 @@ static inline Qcow2BitmapDirEntry 
> *next_dir_entry(Qcow2BitmapDirEntry *entry)
>       return (Qcow2BitmapDirEntry *)((uint8_t *)entry + 
> dir_entry_size(entry));
>   }
>   
> -static int check_dir_entry(BlockDriverState *bs, Qcow2BitmapDirEntry *entry)
> +static int check_dir_entry(BlockDriverState *bs, Qcow2BitmapDirEntry *entry,
> +                           bool allow_resize)
>   {
>       BDRVQcow2State *s = bs->opaque;
>       uint64_t phys_bitmap_bytes;
> @@ -462,8 +463,14 @@ static int check_dir_entry(BlockDriverState *bs, 
> Qcow2BitmapDirEntry *entry)
>           return len;
>       }
>   
> -    fail = (phys_bitmap_bytes > BME_MAX_PHYS_SIZE) ||
> -           (len > ((phys_bitmap_bytes * 8) << entry->granularity_bits));
> +    if (phys_bitmap_bytes > BME_MAX_PHYS_SIZE) {
> +        return -EINVAL;
> +    }
> +
> +    if (!allow_resize &&
> +        (len > ((phys_bitmap_bytes * 8) << entry->granularity_bits))) {
> +        return -EINVAL;
> +    }
>   
>       return fail ? -EINVAL : 0;
>   }
> @@ -534,7 +541,8 @@ static uint32_t bitmap_list_count(Qcow2BitmapList 
> *bm_list)
>    * checks it and convert to bitmap list.
>    */
>   static Qcow2BitmapList *bitmap_list_load(BlockDriverState *bs, uint64_t 
> offset,
> -                                         uint64_t size, Error **errp)
> +                                         uint64_t size, bool allow_resize,
> +                                         Error **errp)
>   {
>       int ret;
>       BDRVQcow2State *s = bs->opaque;
> @@ -593,7 +601,7 @@ static Qcow2BitmapList *bitmap_list_load(BlockDriverState 
> *bs, uint64_t offset,
>               goto fail;
>           }
>   
> -        ret = check_dir_entry(bs, e);
> +        ret = check_dir_entry(bs, e, allow_resize);
>           if (ret < 0) {
>               error_setg(errp, "Bitmap '%.*s' doesn't satisfy the 
> constraints",
>                          e->name_size, dir_entry_name_field(e));
> @@ -654,7 +662,7 @@ int qcow2_check_bitmaps_refcounts(BlockDriverState *bs, 
> BdrvCheckResult *res,
>       }
>   
>       bm_list = bitmap_list_load(bs, s->bitmap_directory_offset,
> -                               s->bitmap_directory_size, NULL);
> +                               s->bitmap_directory_size, false, NULL);
>       if (bm_list == NULL) {
>           res->corruptions++;
>           return -EINVAL;
> @@ -755,7 +763,7 @@ static int bitmap_list_store(BlockDriverState *bs, 
> Qcow2BitmapList *bm_list,
>           e->extra_data_size = 0;
>           memcpy(e + 1, bm->name, e->name_size);
>   
> -        if (check_dir_entry(bs, e) < 0) {
> +        if (check_dir_entry(bs, e, false) < 0) {
>               ret = -EINVAL;
>               goto fail;
>           }
> @@ -957,7 +965,7 @@ bool qcow2_load_dirty_bitmaps(BlockDriverState *bs, Error 
> **errp)
>       }
>   
>       bm_list = bitmap_list_load(bs, s->bitmap_directory_offset,
> -                               s->bitmap_directory_size, errp);
> +                               s->bitmap_directory_size, false, errp);
>       if (bm_list == NULL) {
>           return false;
>       }
> @@ -1066,7 +1074,7 @@ Qcow2BitmapInfoList 
> *qcow2_get_bitmap_info_list(BlockDriverState *bs,
>       }
>   
>       bm_list = bitmap_list_load(bs, s->bitmap_directory_offset,
> -                               s->bitmap_directory_size, errp);
> +                               s->bitmap_directory_size, false, errp);
>       if (bm_list == NULL) {
>           return NULL;
>       }
> @@ -1111,7 +1119,7 @@ int qcow2_reopen_bitmaps_rw_hint(BlockDriverState *bs, 
> bool *header_updated,
>       }
>   
>       bm_list = bitmap_list_load(bs, s->bitmap_directory_offset,
> -                               s->bitmap_directory_size, errp);
> +                               s->bitmap_directory_size, false, errp);
>       if (bm_list == NULL) {
>           return -EINVAL;
>       }
> @@ -1359,7 +1367,7 @@ void 
> qcow2_remove_persistent_dirty_bitmap(BlockDriverState *bs,
>       }
>   
>       bm_list = bitmap_list_load(bs, s->bitmap_directory_offset,
> -                               s->bitmap_directory_size, errp);
> +                               s->bitmap_directory_size, false, errp);
>       if (bm_list == NULL) {
>           return;
>       }
> @@ -1412,7 +1420,7 @@ void 
> qcow2_store_persistent_dirty_bitmaps(BlockDriverState *bs, Error **errp)
>           bm_list = bitmap_list_new();
>       } else {

Worth comment here, that we assume that image may be resized?

>           bm_list = bitmap_list_load(bs, s->bitmap_directory_offset,
> -                                   s->bitmap_directory_size, errp);
> +                                   s->bitmap_directory_size, true, errp);
>           if (bm_list == NULL) {
>               return;
>           }
> @@ -1593,7 +1601,7 @@ bool qcow2_can_store_new_dirty_bitmap(BlockDriverState 
> *bs,
>       }
>   
>       bm_list = bitmap_list_load(bs, s->bitmap_directory_offset,
> -                               s->bitmap_directory_size, errp);
> +                               s->bitmap_directory_size, false, errp);
>       if (bm_list == NULL) {
>           goto fail;
>       }
> 

With Eric's suggestion:
Reviewed-by: Vladimir Sementsov-Ogievskiy <address@hidden>

-- 
Best regards,
Vladimir