CIFS: Fix NULL pointer deref on SMB2_tcon() failure

If SendReceive2() fails rsp is set to NULL but is dereferenced in the
error handling code.

Cc: stable@vger.kernel.org
Signed-off-by: Aurelien Aptel <aaptel@suse.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
Signed-off-by: Steve French <smfrench@gmail.com>

fs/cifs/smb2pdu.c

@@ -1255,7 +1255,7 @@ SMB2_tcon(const unsigned int xid, struct cifs_ses *ses, const char *tree,
 	struct smb2_tree_connect_req *req;
 	struct smb2_tree_connect_rsp *rsp = NULL;
 	struct kvec iov[2];
-	struct kvec rsp_iov;
+	struct kvec rsp_iov = { NULL, 0 };
 	int rc = 0;
 	int resp_buftype;
 	int unc_path_len;
@@ -1372,7 +1372,7 @@ SMB2_tcon(const unsigned int xid, struct cifs_ses *ses, const char *tree,
 	return rc;
 
 tcon_error_exit:
-	if (rsp->hdr.sync_hdr.Status == STATUS_BAD_NETWORK_NAME) {
+	if (rsp && rsp->hdr.sync_hdr.Status == STATUS_BAD_NETWORK_NAME) {
 		cifs_dbg(VFS, "BAD_NETWORK_NAME: %s\n", tree);
 	}
 	goto tcon_exit;