Re: [Qemu-devel] [PATCH v3 04/18] qcow: require image size to be > 1 for new images

[Eric Blake <eblake@redhat.com>]

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On 01/26/2017 04:18 AM, Daniel P. Berrange wrote:
> The qcow driver refuses to open images which are less than
> 2 bytes in size, but will happily create such images. Add
> a check in the create path to avoid this discrepancy.

I agree that we have the 2-byte limit:

static int qcow_open(BlockDriverState *bs, QDict *options, int flags,
...
    if (header.size <= 1) {
        error_setg(errp, "Image size is too small (must be at least 2
bytes)");
        ret = -EINVAL;
        goto fail;
    }

But why 2 bytes? That's a weird limit from history.  Oh well, no one
should be creating many new qcow images when we have qcow2, so I see no
problem with your patch as-is.

> 
> Reviewed-by: Max Reitz <mreitz@redhat.com>
> Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
> ---
>  block/qcow.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 

> +++ b/block/qcow.c
> @@ -799,6 +799,12 @@ static int qcow_create(const char *filename, QemuOpts *opts, Error **errp)
>      /* Read out options */
>      total_size = ROUND_UP(qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0),
>                            BDRV_SECTOR_SIZE);
> +    if (total_size <= 1) {

It will never be 1 because of the ROUND_UP (it will either be 0 or a
sector size), but your code is defensive to match the open check.

Reviewed-by: Eric Blake <eblake@redhat.com>

> +        error_setg(errp, "Image size is too small, cannot be zero length");
> +        ret = -EINVAL;
> +        goto cleanup;
> +    }
> +
>      backing_file = qemu_opt_get_del(opts, BLOCK_OPT_BACKING_FILE);
>      if (qemu_opt_get_bool_del(opts, BLOCK_OPT_ENCRYPT, false)) {
>          flags |= BLOCK_FLAG_ENCRYPT;
> 

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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