SUNRPC: Fix callback channel

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>

2 files changed, 12 insertions, 8 deletions

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;