Re: [PATCH 1/4] nfs: use-after-free in svc_process_common()

[Vasily Averin <vvs@virtuozzo.com>]

Dear Trond,
Red Hat security believes the problem is quite important security issue:
https://access.redhat.com/security/cve/cve-2018-16884

Fix should be backported to affected distributions.

Could you please approve my first patch and push it to stable@ ?
From my PoV it is correctly fixes the problem, it breaks nothing and easy for backports,
lightly modified it can be even live-patched.

Other patches including switch to using empty rqst->rq_xprt can wait.

Thank you,
	Vasily Averin

On 12/19/18 2:25 PM, Vasily Averin wrote:
> On 12/18/18 11:43 PM, Trond Myklebust wrote:
>> On Tue, 2018-12-18 at 23:02 +0300, Vasily Averin wrote:
>>> On 12/18/18 5:55 PM, Trond Myklebust wrote:
>>>>>> It probably also requires us to store a pointer to struct net
>>>>>> in
>>>>>> the
>>>>>> struct svc_rqst so that nfs4_callback_compound() and
>>>>>> svcauth_gss_accept() can find it, but that should be OK since
>>>>>> the
>>>>>> transport already has that referenced.
>>>
>>> Ok, I can fix these functions and their sub-calls.
>>> However  rqst->rq_xprt is used in other functions that seems can be
>>> called inside svc_process_common() 
>>> - in trace_svc_process(rqstp, progp->pg_name);
>>> - in svc_reserve_auth(rqstp, ...) -> svc_reserve()
>>> - svc_authorise() -> svcauth_gss_release()
>>>
>>> It seems I should fix these places too, it isn't?
>>> could you please advise how to fix svc_reserve() ?
>>
>> We don't want svc_reserve() to run at all for the back channel, so I
>> guess that a test for rqstp->rq_xprt != NULL is appropriate there too.
>>
>> svcauth_gss_release() is just using rqstp->rq_xprt to find the net
>> namespace, so if you add a pointer rqstp->rq_net to fix
>> nfs4_callback_compound, then that will fix the gss case as well.
>>
>> For trace_svc_process(), maybe pull rqst->rq_xprt->xpt_remotebuf out of
>> the tracepoint definition in include/trace/events/sunrpc.h and make it
>> a tracepoint argument that is allowed to be NULL?
> 
> This one seems works, could you please check it before formal submit ?
>   NFSv4 callback-1644  [002] ....  4731.064372: svc_process: addr=(null) xid=0x0b0924e3 service=NFSv4 callback vers=1 proc=1
> 
> Frankly speaking I'm afraid that I missed something,
> rqstp->rq_xprt is widely used and nobody expect that it can be NULL.
> 
> And even I missed nothing --  it's quite tricky anyway.
> Future cahnges can add new calls or execute old non-empty-xprt-aware
> functions and trigger crash in some exotic configuration.
> 
> Thank you,
> 	Vasily Averin
>