[PATCH] SUNRPC: Fix callback channel

[Trond Myklebust <trond.myklebust@primarydata.com>]

The NFSv4.1 callback channel is currently broken because the receive
message will keep shrinking because the backchannel receive buffer size
never gets reset.
The easiest solution to this problem is instead of changing the receive
buffer, to rather adjust the copied request.

Fixes: 38b7631fbe42 ("nfs4: limit callback decoding to received bytes")
Cc: Benjamin Coddington <bcodding@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
---
 fs/nfs/callback_xdr.c         |  7 ++-----
 net/sunrpc/backchannel_rqst.c |  8 --------
 net/sunrpc/svc.c              | 12 ++++++++++++
 3 files changed, 14 insertions(+), 13 deletions(-)

diff --git a/fs/nfs/callback_xdr.c b/fs/nfs/callback_xdr.c
index beac58b0e09c..646cdac73488 100644
--- a/fs/nfs/callback_xdr.c
+++ b/fs/nfs/callback_xdr.c
@@ -78,8 +78,7 @@ static __be32 *read_buf(struct xdr_stream *xdr, int nbytes)
 
 	p = xdr_inline_decode(xdr, nbytes);
 	if (unlikely(p == NULL))
-		printk(KERN_WARNING "NFS: NFSv4 callback reply buffer overflowed "
-							"or truncated request.\n");
+		printk(KERN_WARNING "NFS: NFSv4 callback reply buffer overflowed!\n");
 	return p;
 }
 
@@ -890,7 +889,6 @@ static __be32 nfs4_callback_compound(struct svc_rqst *rqstp, void *argp, void *r
 	struct cb_compound_hdr_arg hdr_arg = { 0 };
 	struct cb_compound_hdr_res hdr_res = { NULL };
 	struct xdr_stream xdr_in, xdr_out;
-	struct xdr_buf *rq_arg = &rqstp->rq_arg;
 	__be32 *p, status;
 	struct cb_process_state cps = {
 		.drc_status = 0,
@@ -902,8 +900,7 @@ static __be32 nfs4_callback_compound(struct svc_rqst *rqstp, void *argp, void *r
 
 	dprintk("%s: start\n", __func__);
 
-	rq_arg->len = rq_arg->head[0].iov_len + rq_arg->page_len;
-	xdr_init_decode(&xdr_in, rq_arg, rq_arg->head[0].iov_base);
+	xdr_init_decode(&xdr_in, &rqstp->rq_arg, rqstp->rq_arg.head[0].iov_base);
 
 	p = (__be32*)((char *)rqstp->rq_res.head[0].iov_base + rqstp->rq_res.head[0].iov_len);
 	xdr_init_encode(&xdr_out, &rqstp->rq_res, p);
diff --git a/net/sunrpc/backchannel_rqst.c b/net/sunrpc/backchannel_rqst.c
index 95f82d8d4888..229956bf8457 100644
--- a/net/sunrpc/backchannel_rqst.c
+++ b/net/sunrpc/backchannel_rqst.c
@@ -353,20 +353,12 @@ void xprt_complete_bc_request(struct rpc_rqst *req, uint32_t copied)
 {
 	struct rpc_xprt *xprt = req->rq_xprt;
 	struct svc_serv *bc_serv = xprt->bc_serv;
-	struct xdr_buf *rq_rcv_buf = &req->rq_rcv_buf;
 
 	spin_lock(&xprt->bc_pa_lock);
 	list_del(&req->rq_bc_pa_list);
 	xprt_dec_alloc_count(xprt, 1);
 	spin_unlock(&xprt->bc_pa_lock);
 
-	if (copied <= rq_rcv_buf->head[0].iov_len) {
-		rq_rcv_buf->head[0].iov_len = copied;
-		rq_rcv_buf->page_len = 0;
-	} else {
-		rq_rcv_buf->page_len = copied - rq_rcv_buf->head[0].iov_len;
-	}
-
 	req->rq_private_buf.len = copied;
 	set_bit(RPC_BC_PA_IN_USE, &req->rq_bc_pa_state);
 
diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index 7fccf9675df8..cc9852897395 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -1363,7 +1363,19 @@ bc_svc_process(struct svc_serv *serv, struct rpc_rqst *req,
 	memcpy(&rqstp->rq_addr, &req->rq_xprt->addr, rqstp->rq_addrlen);
 	memcpy(&rqstp->rq_arg, &req->rq_rcv_buf, sizeof(rqstp->rq_arg));
 	memcpy(&rqstp->rq_res, &req->rq_snd_buf, sizeof(rqstp->rq_res));
+
+	/* Adjust the argument buffer length */
 	rqstp->rq_arg.len = req->rq_private_buf.len;
+	if (rqstp->rq_arg.len <= rqstp->rq_arg.head[0].iov_len) {
+		rqstp->rq_arg.head[0].iov_len = rqstp->rq_arg.len;
+		rqstp->rq_arg.page_len = 0;
+	} else if (rqstp->rq_arg.len <= rqstp->rq_arg.head[0].iov_len +
+			rqstp->rq_arg.page_len)
+		rqstp->rq_arg.page_len = rqstp->rq_arg.len -
+			rqstp->rq_arg.head[0].iov_len;
+	else
+		rqstp->rq_arg.len = rqstp->rq_arg.head[0].iov_len +
+			rqstp->rq_arg.page_len;
 
 	/* reset result send buffer "put" position */
 	resv->iov_len = 0;
-- 
2.5.0