Re: [Qemu-devel] [Qemu-block] [PATCH] block/nfs: add support for setting debug level

[Stefan Hajnoczi <stefanha@gmail.com>]

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On Tue, Jun 23, 2015 at 10:12:15AM +0200, Peter Lieven wrote:
> upcoming libnfs versions will support logging debug messages. Add
> support for it in qemu through an URL parameter.
> 
> Signed-off-by: Peter Lieven <pl@kamp.de>
> ---
>  block/nfs.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/block/nfs.c b/block/nfs.c
> index ca9e24e..f7388a3 100644
> --- a/block/nfs.c
> +++ b/block/nfs.c
> @@ -329,6 +329,10 @@ static int64_t nfs_client_open(NFSClient *client, const char *filename,
>          } else if (!strcmp(qp->p[i].name, "readahead")) {
>              nfs_set_readahead(client->context, val);
>  #endif
> +#ifdef LIBNFS_FEATURE_DEBUG
> +        } else if (!strcmp(qp->p[i].name, "debug")) {
> +            nfs_set_debug(client->context, val);
> +#endif
>          } else {
>              error_setg(errp, "Unknown NFS parameter name: %s",
>                         qp->p[i].name);

Untrusted users may be able to set these options since they are encoded
in the URI.  I'm imagining a hosting or cloud scenario like OpenStack.

A verbose debug level spams stderr and could consume a lot of disk
space.

(The uid and gid options are probably okay since the NFS server cannot
trust the uid/gid coming from QEMU anyway.)

I think we can merge this patch for QEMU 2.4 but I'd like to have a
discussion about the security risk of encoding libnfs options in the
URI.

CCed Eric Blake in case libvirt is affected.

Has anyone thought about this and what are the rules?

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