Re: [Qemu-devel] [PATCH 1/2] qemu-img: Resolve relative backing paths in rebase

[Eric Blake <eblake@redhat.com>]

On 05/09/2018 10:49 AM, Max Reitz wrote:
> Currently, rebase interprets a relative path for the new backing image
> as follows:
> (1) Open the new backing image with the given relative path (thus relative to
>      qemu-img's working directory).
> (2) Write it directly into the overlay's backing path field (thus
>      relative to the overlay).
> 
> If the overlay is not in qemu-img's working directory, both will be
> different interpretations, which may either lead to an error somewhere
> (either rebase fails because it cannot open the new backing image, or
>   your overlay becomes unusable because its backing path does not point
>   to a file), or, even worse, it may result in your rebase being
> performed for a different backing file than what your overlay will point
> to after the rebase.
> 
> Fix this by interpreting the target backing path as relative to the
> overlay, like qemu-img does everywhere else.
> 
> Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1569835
> Cc: qemu-stable@nongnu.org
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---

> -            blk_new_backing = blk_new_open(out_baseimg, NULL,
> +            overlay_filename = bs->exact_filename[0] ? bs->exact_filename
> +                                                     : bs->filename;
> +            out_real_path = g_malloc(PATH_MAX);
> +
> +            bdrv_get_full_backing_filename_from_filename(overlay_filename,
> +                                                         out_baseimg,
> +                                                         out_real_path,
> +                                                         PATH_MAX,
> +                                                         &local_err);
> +            if (local_err) {
> +                error_reportf_err(local_err,
> +                                  "Could not resolve backing filename: ");
> +                ret = -1;
> +                goto out;

Leaks out_real_path.

> +            }
> +
> +            blk_new_backing = blk_new_open(out_real_path, NULL,
>                                              options, src_flags, &local_err);
> +            g_free(out_real_path);

Otherwise looks good.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org