nfs4: limit callback decoding to received bytes

A truncated cb_compound request will cause the client to decode null or
data from a previous callback for nfs4.1 backchannel case, or uninitialized
data for the nfs4.0 case. This is because the path through
svc_process_common() advances the request's iov_base and decrements iov_len
without adjusting the overall xdr_buf's len field.  That causes
xdr_init_decode() to set up the xdr_stream with an incorrect length in
nfs4_callback_compound().

Fixing this for the nfs4.1 backchannel case first requires setting the
correct iov_len and page_len based on the length of received data in the
same manner as the nfs4.0 case.

Then the request's xdr_buf length can be adjusted for both cases based upon
the remaining iov_len and page_len.

Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/net/sunrpc/backchannel_rqst.c b/net/sunrpc/backchannel_rqst.c
index 229956bf8457..95f82d8d4888 100644
--- a/net/sunrpc/backchannel_rqst.c
+++ b/net/sunrpc/backchannel_rqst.c
@@ -353,12 +353,20 @@ 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);