SUNRPC: Add rpc_auth::au_ralign field

Currently rpc_inline_rcv_pages() uses au_rslack to estimate the
size of the upper layer reply header. This is fine for auth flavors
where au_verfsize == au_rslack.

However, some auth flavors have more going on. krb5i for example has
two more words after the verifier, and another blob following the
RPC message. The calculation involving au_rslack pushes the upper
layer reply header too far into the rcv_buf.

au_rslack is still valuable: it's the amount of buffer space needed
for the reply, and is used when allocating the reply buffer. We'll
keep that.

But, add a new field that can be used to properly estimate the
location of the upper layer header in each RPC reply, based on the
auth flavor in use.

Signed-off-by: Chuck Lever <[e-mail]>
Signed-off-by: Anna Schumaker <[e-mail]>

include/linux/sunrpc/auth.h

···
 struct rpc_authops;
 struct rpc_auth {
 	unsigned int		au_cslack;	/* call cred size estimate */
-				/* guess at number of u32's auth adds before
-				 * reply data; normally the verifier size: */
-	unsigned int		au_rslack;
+	unsigned int		au_rslack;	/* reply cred size estimate */
 	unsigned int		au_verfsize;	/* size of reply verifier */
+	unsigned int		au_ralign;	/* words before UL header */
 
-	unsigned int		au_flags;	/* various flags */
-	const struct rpc_authops *au_ops;		/* operations */
+	unsigned int		au_flags;
+	const struct rpc_authops *au_ops;
 	rpc_authflavor_t	au_flavor;	/* pseudoflavor (note may
 						 * differ from the flavor in
 						 * au_ops->au_flavor in gss

net/sunrpc/auth_gss/auth_gss.c

···
 	auth->au_cslack = GSS_CRED_SLACK >> 2;
 	auth->au_rslack = GSS_VERF_SLACK >> 2;
 	auth->au_verfsize = GSS_VERF_SLACK >> 2;
+	auth->au_ralign = GSS_VERF_SLACK >> 2;
 	auth->au_flags = 0;
 	auth->au_ops = &authgss_ops;
 	auth->au_flavor = flavor;
···
 static int
 gss_unwrap_resp_auth(struct rpc_cred *cred)
 {
-	cred->cr_auth->au_rslack = cred->cr_auth->au_verfsize;
+	struct rpc_auth *auth = cred->cr_auth;
+
+	auth->au_rslack = auth->au_verfsize;
+	auth->au_ralign = auth->au_verfsize;
 	return 0;
 }
 
···
 {
 	struct xdr_buf integ_buf, *rcv_buf = &rqstp->rq_rcv_buf;
 	u32 data_offset, mic_offset, integ_len, maj_stat;
+	struct rpc_auth *auth = cred->cr_auth;
 	struct xdr_netobj mic;
 	__be32 *p;
 
···
 	if (maj_stat != GSS_S_COMPLETE)
 		goto bad_mic;
 
-	cred->cr_auth->au_rslack = cred->cr_auth->au_verfsize + 2 +
-				   1 + XDR_QUADLEN(mic.len);
+	auth->au_rslack = auth->au_verfsize + 2 + 1 + XDR_QUADLEN(mic.len);
+	auth->au_ralign = auth->au_verfsize + 2;
 	return 0;
 unwrap_failed:
 	trace_rpcgss_unwrap_failed(task);
···
 {
 	struct xdr_buf *rcv_buf = &rqstp->rq_rcv_buf;
 	struct kvec *head = rqstp->rq_rcv_buf.head;
+	struct rpc_auth *auth = cred->cr_auth;
 	unsigned int savedlen = rcv_buf->len;
 	u32 offset, opaque_len, maj_stat;
 	__be32 *p;
···
 	 */
 	xdr_init_decode(xdr, rcv_buf, p, rqstp);
 
-	cred->cr_auth->au_rslack = cred->cr_auth->au_verfsize + 2 +
-				   XDR_QUADLEN(savedlen - rcv_buf->len);
+	auth->au_rslack = auth->au_verfsize + 2 +
+			  XDR_QUADLEN(savedlen - rcv_buf->len);
+	auth->au_ralign = auth->au_verfsize + 2 +
+			  XDR_QUADLEN(savedlen - rcv_buf->len);
 	return 0;
 unwrap_failed:
 	trace_rpcgss_unwrap_failed(task);

net/sunrpc/auth_null.c

···
 	.au_cslack	= NUL_CALLSLACK,
 	.au_rslack	= NUL_REPLYSLACK,
 	.au_verfsize	= NUL_REPLYSLACK,
+	.au_ralign	= NUL_REPLYSLACK,
 	.au_ops		= &authnull_ops,
 	.au_flavor	= RPC_AUTH_NULL,
 	.au_count	= REFCOUNT_INIT(1),

net/sunrpc/auth_unix.c

···
 
 	auth->au_verfsize = XDR_QUADLEN(size) + 2;
 	auth->au_rslack = XDR_QUADLEN(size) + 2;
+	auth->au_ralign = XDR_QUADLEN(size) + 2;
 	return 0;
 }
 

net/sunrpc/clnt.c

···
 	/* 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;
+	hdrsize += RPC_REPHDRSIZE + req->rq_cred->cr_auth->au_ralign - 1;
 
 	xdr_inline_pages(&req->rq_rcv_buf, hdrsize << 2, pages, base, len);
 	trace_rpc_reply_pages(req);