Re: [Qemu-devel] [PATCH] 9pfs: deprecate handle backend

["Daniel P. Berrange" <berrange@redhat.com>]

On Mon, Dec 18, 2017 at 02:46:00PM +0100, Greg Kurz wrote:
> This backend raise some concerns:
> 
> - doesn't support symlinks
> - fails +100 tests in the PJD POSIX file system test suite [1]
> - requires the QEMU process to run with the CAP_DAC_READ_SEARCH
>   capability, which isn't recommended for security reasons
> 
> For all these reasons, the handle backend is now deprecated.
> 
> [1] https://www.tuxera.com/community/posix-test-suite/
> 
> Signed-off-by: Greg Kurz <groug@kaod.org>
> ---
> 
> Aneesh,
> 
> Even if I see the benefit of using file handles in a userspace file
> server, the handle backend still has flaws that make it hardly usable
> IMHO. Also I haven't received anything about it in years. All users
> and contributors seem to stick to the local backend.
> 
> My guess is that nobody uses the handle backend, and unless I'm missing
> something, it wouldn't hurt to drop it. My motivation is to reduce the
> number of lines that I don't really have time/motivation to maintain,
> and that could be subject to a CVE in the future.
> 
> Any thoughts ?
> ---
>  hw/9pfs/9p-handle.c |    2 ++
>  qemu-doc.texi       |    8 ++++++++
>  2 files changed, 10 insertions(+)
> 
> diff --git a/hw/9pfs/9p-handle.c b/hw/9pfs/9p-handle.c
> index 9875f1894cc5..1291a2db6782 100644
> --- a/hw/9pfs/9p-handle.c
> +++ b/hw/9pfs/9p-handle.c
> @@ -657,6 +657,8 @@ static int handle_parse_opts(QemuOpts *opts, struct FsDriverEntry *fse)
>      const char *sec_model = qemu_opt_get(opts, "security_model");
>      const char *path = qemu_opt_get(opts, "path");
>  
> +    warn_report("handle backend is deprecated");
> +
>      if (sec_model) {
>          error_report("Invalid argument security_model specified with handle fsdriver");
>          return -1;
> diff --git a/qemu-doc.texi b/qemu-doc.texi
> index f7317dfc66cd..bf44e2752cb2 100644
> --- a/qemu-doc.texi
> +++ b/qemu-doc.texi
> @@ -2509,6 +2509,14 @@ default channel subsystem image for guests that do not support multiple
>  channel subsystems, all devices can be put into the default channel
>  subsystem image.
>  
> +@subsection -fsdev handle (since 2.12.0)
> +
> +The ``handle'' fsdev backend does not support symlinks and causes the 9p
> +filesystem in the guest to fail a fair amount of tests from the PJD POSIX
> +filesystem test suite. Also it requires the CAP_DAC_READ_SEARCH capability,
> +which is not the recommended way to run QEMU. This backend should not be
> +used and it will be removed with no replacement.
> +

I would suggest a slight teak to the last sentance.

 "This backend should not be used and wil be removed. The 'local' backend
  is the recommended alternative"

Regardless of whether you include this wording change though:

  Reviewed-by: Daniel P. Berrange <berrange@redhat.com>


Regards,
Daniel
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