NFS: Account for XDR pad of buf->pages

Certain NFS results (eg. READLINK) might expect a data payload that
is not an exact multiple of 4 bytes. In this case, XDR encoding
is required to pad that payload so its length on the wire is a
multiple of 4 bytes. The constants that define the maximum size of
each NFS result do not appear to account for this extra word.

In each case where the data payload is to be received into pages:

- 1 word is added to the size of the receive buffer allocated by
  call_allocate

- rpc_inline_rcv_pages subtracts 1 word from @hdrsize so that the
  extra buffer space falls into the rcv_buf's tail iovec

- If buf->pagelen is word-aligned, an XDR pad is not needed and
  is thus removed from the tail

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

2 files changed, 7 insertions, 1 deletions

diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index f780605fffe0..4ea38b029e2f 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -1177,7 +1177,11 @@ void rpc_prepare_reply_pages(struct rpc_rqst *req, struct page **pages,
 			     unsigned int base, unsigned int len,
 			     unsigned int hdrsize)
 {
-	hdrsize += RPC_REPHDRSIZE + req->rq_cred->cr_auth->au_rslack;
+	/* Subtract one to force an extra word of buffer space for the
+	 * payload's XDR pad to fall into the rcv_buf's tail iovec.
+	 */
+	hdrsize += RPC_REPHDRSIZE + req->rq_cred->cr_auth->au_rslack - 1;
+
 	xdr_inline_pages(&req->rq_rcv_buf, hdrsize << 2, pages, base, len);
 	trace_rpc_reply_pages(req);
 }
diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
index 7cca51560442..aa8177ddcbda 100644
--- a/net/sunrpc/xdr.c
+++ b/net/sunrpc/xdr.c
@@ -189,6 +189,8 @@ xdr_inline_pages(struct xdr_buf *xdr, unsigned int offset,
 
 	tail->iov_base = buf + offset;
 	tail->iov_len = buflen - offset;
+	if ((xdr->page_len & 3) == 0)
+		tail->iov_len -= sizeof(__be32);
 
 	xdr->buflen += len;
 }