Re: [Qemu-devel] [Qemu-block] [PATCH 1/2] qcow2: add overlap check for bitmap directory

[John Snow <jsnow@redhat.com>]

On 11/30/2017 11:47 AM, Vladimir Sementsov-Ogievskiy wrote:
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>  block/qcow2.h          |  7 +++++--
>  block/qcow2-refcount.c | 12 ++++++++++++
>  block/qcow2.c          |  6 ++++++
>  3 files changed, 23 insertions(+), 2 deletions(-)
> 
> diff --git a/block/qcow2.h b/block/qcow2.h
> index 6f0ff15dd0..8f226a3609 100644
> --- a/block/qcow2.h
> +++ b/block/qcow2.h
> @@ -98,6 +98,7 @@
>  #define QCOW2_OPT_OVERLAP_SNAPSHOT_TABLE "overlap-check.snapshot-table"
>  #define QCOW2_OPT_OVERLAP_INACTIVE_L1 "overlap-check.inactive-l1"
>  #define QCOW2_OPT_OVERLAP_INACTIVE_L2 "overlap-check.inactive-l2"
> +#define QCOW2_OPT_OVERLAP_BITMAP_DIRECTORY "overlap-check.bitmap-directory"
>  #define QCOW2_OPT_CACHE_SIZE "cache-size"
>  #define QCOW2_OPT_L2_CACHE_SIZE "l2-cache-size"
>  #define QCOW2_OPT_REFCOUNT_CACHE_SIZE "refcount-cache-size"
> @@ -406,8 +407,9 @@ typedef enum QCow2MetadataOverlap {
>      QCOW2_OL_SNAPSHOT_TABLE_BITNR = 5,
>      QCOW2_OL_INACTIVE_L1_BITNR    = 6,
>      QCOW2_OL_INACTIVE_L2_BITNR    = 7,
> +    QCOW2_OL_BITMAP_DIRECTORY_BITNR = 8,
>  
> -    QCOW2_OL_MAX_BITNR            = 8,
> +    QCOW2_OL_MAX_BITNR              = 9,
>  
>      QCOW2_OL_NONE           = 0,
>      QCOW2_OL_MAIN_HEADER    = (1 << QCOW2_OL_MAIN_HEADER_BITNR),
> @@ -420,12 +422,13 @@ typedef enum QCow2MetadataOverlap {
>      /* NOTE: Checking overlaps with inactive L2 tables will result in bdrv
>       * reads. */
>      QCOW2_OL_INACTIVE_L2    = (1 << QCOW2_OL_INACTIVE_L2_BITNR),
> +    QCOW2_OL_BITMAP_DIRECTORY = (1 << QCOW2_OL_BITMAP_DIRECTORY_BITNR),
>  } QCow2MetadataOverlap;
>  
>  /* Perform all overlap checks which can be done in constant time */
>  #define QCOW2_OL_CONSTANT \
>      (QCOW2_OL_MAIN_HEADER | QCOW2_OL_ACTIVE_L1 | QCOW2_OL_REFCOUNT_TABLE | \
> -     QCOW2_OL_SNAPSHOT_TABLE)
> +     QCOW2_OL_SNAPSHOT_TABLE | QCOW2_OL_BITMAP_DIRECTORY)
>  
>  /* Perform all overlap checks which don't require disk access */
>  #define QCOW2_OL_CACHED \
> diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
> index 3de1ab51ba..a7a2703f26 100644
> --- a/block/qcow2-refcount.c
> +++ b/block/qcow2-refcount.c
> @@ -2585,6 +2585,18 @@ int qcow2_check_metadata_overlap(BlockDriverState *bs, int ign, int64_t offset,
>          }
>      }
>  
> +    if ((chk & QCOW2_OL_BITMAP_DIRECTORY) &&
> +        (s->autoclear_features & QCOW2_AUTOCLEAR_BITMAPS))
> +    {
> +        /* update_ext_header_and_dir_in_place firstly drop autoclear flag,
> +         * so it will not fail */
> +        if (overlaps_with(s->bitmap_directory_offset,
> +                          s->bitmap_directory_size))
> +        {
> +            return QCOW2_OL_BITMAP_DIRECTORY;
> +        }
> +    }
> +

Isn't the purpose of this function to test if a given offset conflicts
with known regions of the file? I don't see you actually utilize the
'offset' parameter here, but maybe I don't understand what you're trying
to accomplish.

>      return 0;
>  }
>  
> diff --git a/block/qcow2.c b/block/qcow2.c
> index 1914a940e5..8278c0e124 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -655,6 +655,11 @@ static QemuOptsList qcow2_runtime_opts = {
>              .help = "Check for unintended writes into an inactive L2 table",
>          },
>          {
> +            .name = QCOW2_OPT_OVERLAP_BITMAP_DIRECTORY,
> +            .type = QEMU_OPT_BOOL,
> +            .help = "Check for unintended writes into the bitmap directory",
> +        },
> +        {
>              .name = QCOW2_OPT_CACHE_SIZE,
>              .type = QEMU_OPT_SIZE,
>              .help = "Maximum combined metadata (L2 tables and refcount blocks) "
> @@ -690,6 +695,7 @@ static const char *overlap_bool_option_names[QCOW2_OL_MAX_BITNR] = {
>      [QCOW2_OL_SNAPSHOT_TABLE_BITNR] = QCOW2_OPT_OVERLAP_SNAPSHOT_TABLE,
>      [QCOW2_OL_INACTIVE_L1_BITNR]    = QCOW2_OPT_OVERLAP_INACTIVE_L1,
>      [QCOW2_OL_INACTIVE_L2_BITNR]    = QCOW2_OPT_OVERLAP_INACTIVE_L2,
> +    [QCOW2_OL_BITMAP_DIRECTORY_BITNR] = QCOW2_OPT_OVERLAP_BITMAP_DIRECTORY,
>  };
>  
>  static void cache_clean_timer_cb(void *opaque)
>