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

From: Vasily Averin <vvs@virtuozzo.com>
To: "bfields@fieldses.org" <bfields@fieldses.org>,
	Trond Myklebust <trondmy@hammerspace.com>
Cc: "anna.schumaker@netapp.com" <anna.schumaker@netapp.com>,
	"khorenko@virtuozzo.com" <khorenko@virtuozzo.com>,
	"linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>,
	"eshatokhin@virtuozzo.com" <eshatokhin@virtuozzo.com>,
	"chuck.lever@oracle.com" <chuck.lever@oracle.com>,
	"jlayton@kernel.org" <jlayton@kernel.org>
Subject: Re: [PATCH 1/4] nfs: use-after-free in svc_process_common()
Date: Sat, 22 Dec 2018 20:46:55 +0300	[thread overview]
Message-ID: <9082b04a-8235-4b9d-39ae-1462fe350935@virtuozzo.com> (raw)
In-Reply-To: <20181221010007.GA10196@fieldses.org>

On 12/21/18 4:00 AM, bfields@fieldses.org wrote:
> On Tue, Dec 18, 2018 at 02:55:15PM +0000, Trond Myklebust wrote:
>> No. We don't care about xpt_flags for the back channel because there is
>> no "server transport". The actual transport is stored in the 'struct
>> rpc_rqst', and is the struct rpc_xprt corresponding to the client
>> socket or RDMA channel.
>>
>> IOW: All we really need in svc_process_common() is to be able to run
>> rqstp->rq_xprt->xpt_ops->xpo_prep_reply_hdr(), and that can be passed
>> either as a pointer to the struct svc_xprt_ops itself.
> 
> For what it's worth, I'd rather get rid of that op--it's an awfully
> roundabout way just to do "svc_putnl(resv, 0);" in the tcp case.

Do you mean that svc_create_xprt(serv, "tcp-bc", ...) was used ONLY to call 
svc_tcp_prep_reply_hdr() in svc_process_common() ?
And according call for rdma-bc does nothing useful at all? 

I've just tried to remove svc_create_xprt() from xs_tcp_bc_up() and just 
provide pointer to svc_tcp_prep_reply_hdr() in  svc_process_common() 
via per-netns sunrpc_net -- and seems it was enough, my testcase worked correctly.

Am I missed something probably?
Should we really remove svc_create_xprt( "tcp/rdma-bc"...) related stuff? ?