Re: [Qemu-devel] [PATCH 3/8] qcow2: Fix refcount blocks beyond image end

["Benoît Canet" <benoit.canet@irqsave.net>]

The Wednesday 13 Aug 2014 à 23:01:45 (+0200), Max Reitz wrote :
> If the qcow2 check function detects a refcount block located beyond the
> image end, grow the image appropriately. This cannot break anything and
> is the logical fix for such a case.
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  block/qcow2-refcount.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++----
>  1 file changed, 46 insertions(+), 4 deletions(-)
> 
> diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
> index d1da8d5..a1d93e5 100644
> --- a/block/qcow2-refcount.c
> +++ b/block/qcow2-refcount.c
> @@ -1504,7 +1504,8 @@ static int check_refblocks(BlockDriverState *bs, BdrvCheckResult *res,
>                             int64_t *nb_clusters)
>  {
>      BDRVQcowState *s = bs->opaque;
> -    int64_t i;
> +    int64_t i, size;
> +    int ret;
>  
>      for (i = 0; i < s->refcount_table_size; i++) {
>          uint64_t offset, cluster;
> @@ -1520,9 +1521,50 @@ static int check_refblocks(BlockDriverState *bs, BdrvCheckResult *res,
>          }
>  
>          if (cluster >= *nb_clusters) {
> -            fprintf(stderr, "ERROR refcount block %" PRId64
> -                    " is outside image\n", i);
> -            res->corruptions++;
> +            fprintf(stderr, "%s refcount block %" PRId64 " is outside image\n",
> +                    fix & BDRV_FIX_ERRORS ? "Repairing" : "ERROR", i);
> +
> +            if (fix & BDRV_FIX_ERRORS) {
> +                int64_t old_nb_clusters = *nb_clusters;
> +
> +                ret = bdrv_truncate(bs->file, offset + s->cluster_size);
> +                if (ret < 0) {
> +                    goto resize_fail;
> +                }
> +                size = bdrv_getlength(bs->file);
> +                if (size < 0) {
> +                    ret = size;
> +                    goto resize_fail;
> +                }
> +
> +                *nb_clusters = size_to_clusters(s, size);
> +                assert(*nb_clusters >= old_nb_clusters);
> +
> +                *refcount_table = g_try_realloc(*refcount_table,
> +                        *nb_clusters * sizeof(uint16_t));
> +                if (!*refcount_table) {
> +                    res->check_errors++;
> +                    return -ENOMEM;

So you really want to make sure the code is not trying anything more
by directly returning -ENOMEM and not doing goto resize_fail.

This makes sense though.

> +                }
> +
> +                memset(*refcount_table + old_nb_clusters, 0,
> +                       (*nb_clusters - old_nb_clusters) * sizeof(uint16_t));
> +
> +                if (cluster >= *nb_clusters) {
> +                    ret = -EINVAL;
> +                    goto resize_fail;
> +                }
> +
> +                res->corruptions_fixed++;
> +                continue;
> +
> +resize_fail:
> +                res->corruptions++;
> +                fprintf(stderr, "ERROR could not resize image: %s\n",
> +                        strerror(-ret));

Isn't a "return ret;" missing here ?
the code will fall in the continue statement without it.

> +            } else {
> +                res->corruptions++;
> +            }
>              continue;
>          }
>  
> -- 
> 2.0.3
> 
>