nfsd4: fix oops on secinfo_no_name result encoding

The secinfo_no_name code oopses on encoding with

	BUG: unable to handle kernel NULL pointer dereference at 00000044
	IP: [<e2bd239a>] nfsd4_encode_secinfo+0x1c/0x1c1 [nfsd]

We should implement a nfsd4_encode_secinfo_no_name() instead using
nfsd4_encode_secinfo().

Signed-off-by: Mi Jinlong <mijinlong@cn.fujitsu.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4xdr.c

@@ -2845,11 +2845,10 @@ nfsd4_encode_rename(struct nfsd4_compoundres *resp, __be32 nfserr, struct nfsd4_
 }
 
 static __be32
-nfsd4_encode_secinfo(struct nfsd4_compoundres *resp, __be32 nfserr,
-		     struct nfsd4_secinfo *secinfo)
+nfsd4_do_encode_secinfo(struct nfsd4_compoundres *resp,
+			 __be32 nfserr,struct svc_export *exp)
 {
 	int i = 0;
-	struct svc_export *exp = secinfo->si_exp;
 	u32 nflavs;
 	struct exp_flavor_info *flavs;
 	struct exp_flavor_info def_flavs[2];
@@ -2911,6 +2910,20 @@ nfsd4_encode_secinfo(struct nfsd4_compoundres *resp, __be32 nfserr,
 	return nfserr;
 }
 
+static __be32
+nfsd4_encode_secinfo(struct nfsd4_compoundres *resp, __be32 nfserr,
+		     struct nfsd4_secinfo *secinfo)
+{
+	return nfsd4_do_encode_secinfo(resp, nfserr, secinfo->si_exp);
+}
+
+static __be32
+nfsd4_encode_secinfo_no_name(struct nfsd4_compoundres *resp, __be32 nfserr,
+		     struct nfsd4_secinfo_no_name *secinfo)
+{
+	return nfsd4_do_encode_secinfo(resp, nfserr, secinfo->sin_exp);
+}
+
 /*
  * The SETATTR encode routine is special -- it always encodes a bitmap,
  * regardless of the error status.
@@ -3173,7 +3186,7 @@ static nfsd4_enc nfsd4_enc_ops[] = {
 	[OP_LAYOUTCOMMIT]	= (nfsd4_enc)nfsd4_encode_noop,
 	[OP_LAYOUTGET]		= (nfsd4_enc)nfsd4_encode_noop,
 	[OP_LAYOUTRETURN]	= (nfsd4_enc)nfsd4_encode_noop,
-	[OP_SECINFO_NO_NAME]	= (nfsd4_enc)nfsd4_encode_secinfo,
+	[OP_SECINFO_NO_NAME]	= (nfsd4_enc)nfsd4_encode_secinfo_no_name,
 	[OP_SEQUENCE]		= (nfsd4_enc)nfsd4_encode_sequence,
 	[OP_SET_SSV]		= (nfsd4_enc)nfsd4_encode_noop,
 	[OP_TEST_STATEID]	= (nfsd4_enc)nfsd4_encode_noop,