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

[Vasily Averin <vvs@virtuozzo.com>]

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.

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