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

[Peter Lieven <pl@kamp.de>]

Am 26.10.2015 um 11:45 schrieb Stefan Hajnoczi:
> On Thu, Oct 22, 2015 at 08:37:19AM +0200, Peter Lieven wrote:
>> Am 22.09.2015 um 08:13 schrieb Peter Lieven:
>>> Am 25.06.2015 um 15:18 schrieb Stefan Hajnoczi:
>>>> 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?
>>> As I hadn't time to work further on the best way to add options for NFS (and other
>>> protocols), would it be feasible to allow passing debug as an URL parameter, but
>>> limit the maximum debug level to limit a possible security impact (flooding logs)?
>>>
>>> If a higher debug level is needed it can be set via device specific options as soon
>>> there is a common scheme for them.
>> Any objections?
> If you are sure that ERROR and WARN levels (or similar) don't flood the
> logs, then it sounds like a solution.

Thats not the case. I use debug level 2 for quite some time. Mainly to see NFS connection interruptions.

So I would be happy if we could allow for debug <= 2 from the cmdline.

Peter