Re: [PATCH net-next v12 17/22] ovpn: implement peer add/get/dump/delete via netlink

[Paolo Abeni <pabeni@redhat.com>]

On 12/2/24 16:07, Antonio Quartulli wrote:
> +/**
> + * ovpn_nl_peer_modify - modify the peer attributes according to the incoming msg
> + * @peer: the peer to modify
> + * @info: generic netlink info from the user request
> + * @attrs: the attributes from the user request
> + *
> + * Return: a negative error code in case of failure, 0 on success or 1 on
> + *	   success and the VPN IPs have been modified (requires rehashing in MP
> + *	   mode)
> + */
> +static int ovpn_nl_peer_modify(struct ovpn_peer *peer, struct genl_info *info,
> +			       struct nlattr **attrs)
> +{
> +	struct sockaddr_storage ss = {};
> +	u32 sockfd, interv, timeout;
> +	struct socket *sock = NULL;
> +	u8 *local_ip = NULL;
> +	bool rehash = false;
> +	int ret;
> +
> +	if (attrs[OVPN_A_PEER_SOCKET]) {
> +		if (peer->sock) {
> +			NL_SET_ERR_MSG_FMT_MOD(info->extack,
> +					       "peer socket can't be modified");
> +			return -EINVAL;
> +		}
> +
> +		/* lookup the fd in the kernel table and extract the socket
> +		 * object
> +		 */
> +		sockfd = nla_get_u32(attrs[OVPN_A_PEER_SOCKET]);
> +		/* sockfd_lookup() increases sock's refcounter */
> +		sock = sockfd_lookup(sockfd, &ret);
> +		if (!sock) {
> +			NL_SET_ERR_MSG_FMT_MOD(info->extack,
> +					       "cannot lookup peer socket (fd=%u): %d",
> +					       sockfd, ret);
> +			return -ENOTSOCK;
> +		}
> +
> +		/* Only when using UDP as transport protocol the remote endpoint
> +		 * can be configured so that ovpn knows where to send packets
> +		 * to.
> +		 *
> +		 * In case of TCP, the socket is connected to the peer and ovpn
> +		 * will just send bytes over it, without the need to specify a
> +		 * destination.
> +		 */
> +		if (sock->sk->sk_protocol != IPPROTO_UDP &&
> +		    (attrs[OVPN_A_PEER_REMOTE_IPV4] ||
> +		     attrs[OVPN_A_PEER_REMOTE_IPV6])) {
> +			NL_SET_ERR_MSG_FMT_MOD(info->extack,
> +					       "unexpected remote IP address for non UDP socket");
> +			sockfd_put(sock);
> +			return -EINVAL;
> +		}
> +
> +		peer->sock = ovpn_socket_new(sock, peer);
> +		if (IS_ERR(peer->sock)) {
> +			NL_SET_ERR_MSG_FMT_MOD(info->extack,
> +					       "cannot encapsulate socket: %ld",
> +					       PTR_ERR(peer->sock));
> +			sockfd_put(sock);
> +			peer->sock = NULL;

This looks race-prone. If any other CPU can do concurrent read access to
peer->sock it could observe an invalid pointer
Even if such race does not exist, it would be cleaner store
ovpn_socket_new() return value in a local variable and set peer->sock
only on successful creation.

/P