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

["bfields@fieldses.org" <bfields@fieldses.org>]

On Sat, Dec 22, 2018 at 08:46:55PM +0300, Vasily Averin wrote:
> 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? 

Right, in the rdma case it's:

	void svc_rdma_prep_reply_hdr(struct svc_rqst *rqstp)
	{
	}

> 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? ?

Haven't looked carefully, but off the top of my head I can't see why
that wouldn't work.

I also tried some patches that replace that op by a flag bit (doesn't
address the original problem here, just seemed like a simplification):

	git://linux-nfs.org/~bfields/linux-topics.git

but I don't if that's compatible with what you've done.

--b.