net/handshake: Fix handshake_dup() ref counting

If get_unused_fd_flags() fails, we ended up calling fput(sock->file)
twice.

Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Suggested-by: Paolo Abeni <pabeni@redhat.com>
Fixes: 3b3009e ("net/handshake: Create a NETLINK service for handling handshake requests")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: chucklever

net/handshake/netlink.c

@@ -139,15 +139,16 @@ int handshake_nl_accept_doit(struct sk_buff *skb, struct genl_info *info)
 		goto out_complete;
 	}
 	err = req->hr_proto->hp_accept(req, info, fd);
-	if (err)
+	if (err) {
+		fput(sock->file);
 		goto out_complete;
+	}
 
 	trace_handshake_cmd_accept(net, req, req->hr_sk, fd);
 	return 0;
 
 out_complete:
 	handshake_complete(req, -EIO, NULL);
-	fput(sock->file);
 out_status:
 	trace_handshake_cmd_accept_err(net, req, NULL, err);
 	return err;