NFS: Use xdr_stream-based XDR encoder for MNT's dirpath argument

Check the length of the supplied dirpath, and see that it fits
properly in the RPC buffer.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/mount_clnt.c

@@ -20,6 +20,21 @@
 # define NFSDBG_FACILITY	NFSDBG_MOUNT
 #endif
 
+/*
+ * Defined by RFC 1094, section A.3; and RFC 1813, section 5.1.4
+ */
+#define MNTPATHLEN		(1024)
+
+/*
+ * XDR data type sizes
+ */
+#define encode_dirpath_sz	(1 + XDR_QUADLEN(MNTPATHLEN))
+
+/*
+ * XDR argument and result sizes
+ */
+#define MNT_enc_dirpath_sz	encode_dirpath_sz
+
 /*
  * Defined by RFC 1094, section A.5
  */
@@ -135,6 +150,31 @@ static int xdr_encode_dirpath(struct rpc_rqst *req, __be32 *p,
 	return 0;
 }
 
+static int encode_mntdirpath(struct xdr_stream *xdr, const char *pathname)
+{
+	const u32 pathname_len = strlen(pathname);
+	__be32 *p;
+
+	if (unlikely(pathname_len > MNTPATHLEN))
+		return -EIO;
+
+	p = xdr_reserve_space(xdr, sizeof(u32) + pathname_len);
+	if (unlikely(p == NULL))
+		return -EIO;
+	xdr_encode_opaque(p, pathname, pathname_len);
+
+	return 0;
+}
+
+static int mnt_enc_dirpath(struct rpc_rqst *req, __be32 *p,
+			   const char *dirpath)
+{
+	struct xdr_stream xdr;
+
+	xdr_init_encode(&xdr, &req->rq_snd_buf, p);
+	return encode_mntdirpath(&xdr, dirpath);
+}
+
 static int xdr_decode_fhstatus(struct rpc_rqst *req, __be32 *p,
 			       struct mnt_fhstatus *res)
 {
@@ -164,16 +204,15 @@ static int xdr_decode_fhstatus3(struct rpc_rqst *req, __be32 *p,
 	return 0;
 }
 
-#define MNT_dirpath_sz		(1 + 256)
 #define MNT_fhstatus_sz		(1 + 8)
 #define MNT_fhstatus3_sz	(1 + 16)
 
 static struct rpc_procinfo mnt_procedures[] = {
 	[MOUNTPROC_MNT] = {
 		.p_proc		= MOUNTPROC_MNT,
-		.p_encode	= (kxdrproc_t) xdr_encode_dirpath,
+		.p_encode	= (kxdrproc_t)mnt_enc_dirpath,
 		.p_decode	= (kxdrproc_t) xdr_decode_fhstatus,
-		.p_arglen	= MNT_dirpath_sz,
+		.p_arglen	= MNT_enc_dirpath_sz,
 		.p_replen	= MNT_fhstatus_sz,
 		.p_statidx	= MOUNTPROC_MNT,
 		.p_name		= "MOUNT",
@@ -183,9 +222,9 @@ static struct rpc_procinfo mnt_procedures[] = {
 static struct rpc_procinfo mnt3_procedures[] = {
 	[MOUNTPROC3_MNT] = {
 		.p_proc		= MOUNTPROC3_MNT,
-		.p_encode	= (kxdrproc_t) xdr_encode_dirpath,
+		.p_encode	= (kxdrproc_t)mnt_enc_dirpath,
 		.p_decode	= (kxdrproc_t) xdr_decode_fhstatus3,
-		.p_arglen	= MNT_dirpath_sz,
+		.p_arglen	= MNT_enc_dirpath_sz,
 		.p_replen	= MNT_fhstatus3_sz,
 		.p_statidx	= MOUNTPROC3_MNT,
 		.p_name		= "MOUNT",