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

["J. Bruce Fields" <bfields@fieldses.org>]

On Mon, Dec 17, 2018 at 07:23:54PM +0300, Vasily Averin wrote:
> if node have NFSv41+ mounts inside several net namespaces
> it can lead to use-after-free in svc_process_common()
> 
> svc_process_common() 
>         /* Setup reply header */
>         rqstp->rq_xprt->xpt_ops->xpo_prep_reply_hdr(rqstp); <<< HERE
> 
> svc_process_common() can use already freed rqstp->rq_xprt,
> it was assigned in bc_svc_process() where it was taken from serv->sv_bc_xprt.
> 
> serv is global structure but sv_bc_xprt is assigned per-netnamespace,
> so if nfsv41+ shares are mounted in several containers together
> bc_svc_process() can use wrong backchannel or even access freed memory.
> 
> To find correct svc_xprt of client-related backchannel
> bc_svc_process() now calls new .bc_get_xprt callback
> that executes svc_find_xprt() with proper xprt name.

This stuff is confusing and I need to stare at it some more before I
understand, but it's weird that we'd need to search for the right xprt.

We know which connection the backchannel request came over, and there
should only be one backchannel using that connection, why can't we find
it by just chasing pointers the right way?

OK, I do need to look at it more.

--b.

> 
> Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
> ---
>  include/linux/sunrpc/xprt.h       |  1 +
>  net/sunrpc/svc.c                  | 22 ++++++++++++++++------
>  net/sunrpc/xprtrdma/backchannel.c |  5 +++++
>  net/sunrpc/xprtrdma/transport.c   |  1 +
>  net/sunrpc/xprtrdma/xprt_rdma.h   |  1 +
>  net/sunrpc/xprtsock.c             |  7 +++++++
>  6 files changed, 31 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/sunrpc/xprt.h b/include/linux/sunrpc/xprt.h
> index a4ab4f8d9140..031d2843a002 100644
> --- a/include/linux/sunrpc/xprt.h
> +++ b/include/linux/sunrpc/xprt.h
> @@ -158,6 +158,7 @@ struct rpc_xprt_ops {
>  	int		(*bc_setup)(struct rpc_xprt *xprt,
>  				    unsigned int min_reqs);
>  	int		(*bc_up)(struct svc_serv *serv, struct net *net);
> +	struct svc_xprt*(*bc_get_xprt)(struct svc_serv *serv, struct net *net);
>  	size_t		(*bc_maxpayload)(struct rpc_xprt *xprt);
>  	void		(*bc_free_rqst)(struct rpc_rqst *rqst);
>  	void		(*bc_destroy)(struct rpc_xprt *xprt,
> diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
> index d13e05f1a990..a7264fd1b3db 100644
> --- a/net/sunrpc/svc.c
> +++ b/net/sunrpc/svc.c
> @@ -1450,16 +1450,22 @@ int
>  bc_svc_process(struct svc_serv *serv, struct rpc_rqst *req,
>  	       struct svc_rqst *rqstp)
>  {
> +	struct net	*net = req->rq_xprt->xprt_net;
>  	struct kvec	*argv = &rqstp->rq_arg.head[0];
>  	struct kvec	*resv = &rqstp->rq_res.head[0];
>  	struct rpc_task *task;
> +	struct svc_xprt *s_xprt;
>  	int proc_error;
>  	int error;
>  
>  	dprintk("svc: %s(%p)\n", __func__, req);
>  
> +	s_xprt = req->rq_xprt->ops->bc_get_xprt(serv, net);
> +	if (!s_xprt)
> +		goto proc_error;
> +
>  	/* Build the svc_rqst used by the common processing routine */
> -	rqstp->rq_xprt = serv->sv_bc_xprt;
> +	rqstp->rq_xprt = s_xprt;
>  	rqstp->rq_xid = req->rq_xid;
>  	rqstp->rq_prot = req->rq_xprt->prot;
>  	rqstp->rq_server = serv;
> @@ -1494,13 +1500,11 @@ bc_svc_process(struct svc_serv *serv, struct rpc_rqst *req,
>  
>  	/* Parse and execute the bc call */
>  	proc_error = svc_process_common(rqstp, argv, resv);
> +	svc_xprt_put(rqstp->rq_xprt);
>  
>  	atomic_inc(&req->rq_xprt->bc_free_slots);
> -	if (!proc_error) {
> -		/* Processing error: drop the request */
> -		xprt_free_bc_request(req);
> -		return 0;
> -	}
> +	if (!proc_error)
> +		goto proc_error;
>  
>  	/* Finally, send the reply synchronously */
>  	memcpy(&req->rq_snd_buf, &rqstp->rq_res, sizeof(req->rq_snd_buf));
> @@ -1517,6 +1521,12 @@ bc_svc_process(struct svc_serv *serv, struct rpc_rqst *req,
>  out:
>  	dprintk("svc: %s(), error=%d\n", __func__, error);
>  	return error;
> +
> +proc_error:
> +	/* Processing error: drop the request */
> +	xprt_free_bc_request(req);
> +	error = -EINVAL;
> +	goto out;
>  }
>  EXPORT_SYMBOL_GPL(bc_svc_process);
>  #endif /* CONFIG_SUNRPC_BACKCHANNEL */
> diff --git a/net/sunrpc/xprtrdma/backchannel.c b/net/sunrpc/xprtrdma/backchannel.c
> index e5b367a3e517..3e06aeacda43 100644
> --- a/net/sunrpc/xprtrdma/backchannel.c
> +++ b/net/sunrpc/xprtrdma/backchannel.c
> @@ -133,6 +133,11 @@ int xprt_rdma_bc_up(struct svc_serv *serv, struct net *net)
>  	return 0;
>  }
>  
> +struct svc_xprt *xprt_rdma_bc_get_xprt(struct svc_serv *serv, struct net *net)
> +{
> +	return svc_find_xprt(serv, "rdma-bc", net, AF_UNSPEC, 0);
> +}
> +
>  /**
>   * xprt_rdma_bc_maxpayload - Return maximum backchannel message size
>   * @xprt: transport
> diff --git a/net/sunrpc/xprtrdma/transport.c b/net/sunrpc/xprtrdma/transport.c
> index ae2a83828953..41d67de93531 100644
> --- a/net/sunrpc/xprtrdma/transport.c
> +++ b/net/sunrpc/xprtrdma/transport.c
> @@ -828,6 +828,7 @@ static const struct rpc_xprt_ops xprt_rdma_procs = {
>  #if defined(CONFIG_SUNRPC_BACKCHANNEL)
>  	.bc_setup		= xprt_rdma_bc_setup,
>  	.bc_up			= xprt_rdma_bc_up,
> +	.bc_get_xprt		= xprt_rdma_bc_get_xprt,
>  	.bc_maxpayload		= xprt_rdma_bc_maxpayload,
>  	.bc_free_rqst		= xprt_rdma_bc_free_rqst,
>  	.bc_destroy		= xprt_rdma_bc_destroy,
> diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h
> index a13ccb643ce0..2726d71052a8 100644
> --- a/net/sunrpc/xprtrdma/xprt_rdma.h
> +++ b/net/sunrpc/xprtrdma/xprt_rdma.h
> @@ -662,6 +662,7 @@ void xprt_rdma_cleanup(void);
>  #if defined(CONFIG_SUNRPC_BACKCHANNEL)
>  int xprt_rdma_bc_setup(struct rpc_xprt *, unsigned int);
>  int xprt_rdma_bc_up(struct svc_serv *, struct net *);
> +struct svc_xprt *xprt_rdma_bc_get_xprt(struct svc_serv *serv, struct net *net);
>  size_t xprt_rdma_bc_maxpayload(struct rpc_xprt *);
>  int rpcrdma_bc_post_recv(struct rpcrdma_xprt *, unsigned int);
>  void rpcrdma_bc_receive_call(struct rpcrdma_xprt *, struct rpcrdma_rep *);
> diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
> index 8a5e823e0b33..16f9c7720465 100644
> --- a/net/sunrpc/xprtsock.c
> +++ b/net/sunrpc/xprtsock.c
> @@ -1411,6 +1411,12 @@ static int xs_tcp_bc_up(struct svc_serv *serv, struct net *net)
>  	return 0;
>  }
>  
> +static struct svc_xprt *xs_tcp_bc_get_xprt(struct svc_serv *serv,
> +					   struct net *net)
> +{
> +	return svc_find_xprt(serv, "tcp-bc", net, AF_UNSPEC, 0);
> +}
> +
>  static size_t xs_tcp_bc_maxpayload(struct rpc_xprt *xprt)
>  {
>  	return PAGE_SIZE;
> @@ -2668,6 +2674,7 @@ static const struct rpc_xprt_ops xs_tcp_ops = {
>  #ifdef CONFIG_SUNRPC_BACKCHANNEL
>  	.bc_setup		= xprt_setup_bc,
>  	.bc_up			= xs_tcp_bc_up,
> +	.bc_get_xprt		= xs_tcp_bc_get_xprt,
>  	.bc_maxpayload		= xs_tcp_bc_maxpayload,
>  	.bc_free_rqst		= xprt_free_bc_rqst,
>  	.bc_destroy		= xprt_destroy_bc,
> -- 
> 2.17.1