smb3: Send netname context during negotiate protocol

See MS-SMB2 2.2.3.1.4

Allows hostname to be used by load balancers
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/smb2pdu.c

@@ -495,6 +495,21 @@ build_encrypt_ctxt(struct smb2_encryption_neg_context *pneg_ctxt)
 	pneg_ctxt->Ciphers[1] = SMB2_ENCRYPTION_AES128_CCM;
 }
 
+static unsigned int
+build_netname_ctxt(struct smb2_netname_neg_context *pneg_ctxt, char *hostname)
+{
+	struct nls_table *cp = load_nls_default();
+
+	pneg_ctxt->ContextType = SMB2_NETNAME_NEGOTIATE_CONTEXT_ID;
+
+	/* copy up to max of first 100 bytes of server name to NetName field */
+	pneg_ctxt->DataLength = cpu_to_le16(2 +
+		(2 * cifs_strtoUTF16(pneg_ctxt->NetName, hostname, 100, cp)));
+	/* context size is DataLength + minimal smb2_neg_context */
+	return DIV_ROUND_UP(le16_to_cpu(pneg_ctxt->DataLength) +
+			sizeof(struct smb2_neg_context), 8) * 8;
+}
+
 static void
 build_posix_ctxt(struct smb2_posix_neg_context *pneg_ctxt)
 {
@@ -559,9 +574,15 @@ assemble_neg_contexts(struct smb2_negotiate_req *req,
 				8) * 8;
 		*total_len += ctxt_len;
 		pneg_ctxt += ctxt_len;
-		req->NegotiateContextCount = cpu_to_le16(4);
+		req->NegotiateContextCount = cpu_to_le16(5);
 	} else
-		req->NegotiateContextCount = cpu_to_le16(3);
+		req->NegotiateContextCount = cpu_to_le16(4);
+
+	ctxt_len = build_netname_ctxt((struct smb2_netname_neg_context *)pneg_ctxt,
+					server->hostname);
+	*total_len += ctxt_len;
+	pneg_ctxt += ctxt_len;
+
 	build_posix_ctxt((struct smb2_posix_neg_context *)pneg_ctxt);
 	*total_len += sizeof(struct smb2_posix_neg_context);
 }

fs/cifs/smb2pdu.h

@@ -317,6 +317,12 @@ struct smb2_compression_capabilities_context {
  * For smb2_netname_negotiate_context_id See MS-SMB2 2.2.3.1.4.
  * Its struct simply contains NetName, an array of Unicode characters
  */
+struct smb2_netname_neg_context {
+	__le16	ContextType; /* 0x100 */
+	__le16	DataLength;
+	__le32	Reserved;
+	__le16	NetName[0]; /* hostname of target converted to UCS-2 */
+} __packed;
 
 #define POSIX_CTXT_DATA_LEN	16
 struct smb2_posix_neg_context {