Re: [Qemu-devel] [PATCH v2 4/4] 9pfs: local: metadata file for the VirtFS root

[Eric Blake <eblake@redhat.com>]

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On 05/23/2017 09:32 AM, Greg Kurz wrote:
> When using the mapped-file security, credentials are stored in a metadata
> directory located in the parent directory. This is okay for all paths with
> the notable exception of the root path, since we don't want and probably
> can't create a metadata directory above the virtfs directory on the host.
> 
> This patch introduces a dedicated metadata file, sitting in the virtfs root
> for this purpose. It relies on the fact that the "." name necessarily refers
> to the virtfs root.
> 
> As for the metadata directory, we don't want the client to see this file.
> The current code only cares for readdir() but there are many other places
> to fix actually. The filtering logic is hence put in a separate function.
> 
> @@ -478,7 +504,8 @@ static off_t local_telldir(FsContext *ctx, V9fsFidOpenState *fs)
>  
>  static bool local_is_mapped_file_metadata(FsContext *fs_ctx, const char *name)
>  {
> -    return !strcmp(name, VIRTFS_META_DIR);
> +    return
> +        !strcmp(name, VIRTFS_META_DIR) || !strcmp(name, VIRTFS_META_ROOT_FILE);

We have to block VIRTFS_META_DIR at any depth in the hierarchy, but
can/should we change the blocking of VIRTFS_META_ROOT_FILE to only
happen at the root directory, rather than at all directories?  On the
other hand, if you can simultaneously map /path/to/a for one mount
point, and /path/to/a/b for another, then the root file for B is visible
at a lower depth than the root file for A, and blocking the metafile
name everywhere means that the mount A can't influence the behavior on
the mount for B.

Not tested, but looks sane, so:
Reviewed-by: Eric Blake <eblake@redhat.com>

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


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