[RFC PATCH 1/2] landlock: TCP network hooks implementation

[Willem de Bruijn]

On Mon, Jan 24, 2022 at 3:02 AM Konstantin Meskhidze
<konstantin.meskhidze at huawei.com> wrote:
>
> Support of socket_bind() and socket_connect() hooks.
> Current prototype can restrict binding and connecting of TCP
> types of sockets. Its just basic idea how Landlock could support
> network confinement.
>
> Changes:
> 1. Access masks array refactored into 1D one and changed
> to 32 bits. Filesystem masks occupy 16 lower bits and network
> masks reside in 16 upper bits.
> 2. Refactor API functions in ruleset.c:
>     1. Add void *object argument.
>     2. Add u16 rule_type argument.
> 3. Use two rb_trees in ruleset structure:
>     1. root_inode - for filesystem objects
>     2. root_net_port - for network port objects
>
> Signed-off-by: Konstantin Meskhidze <konstantin.meskhidze at huawei.com>

> +static int hook_socket_connect(struct socket *sock, struct sockaddr *address, int addrlen)
> +{
> +       short socket_type;
> +       struct sockaddr_in *sockaddr;
> +       u16 port;
> +       const struct landlock_ruleset *const dom = landlock_get_current_domain();
> +
> +       /* Check if the hook is AF_INET* socket's action */
> +       if ((address->sa_family != AF_INET) && (address->sa_family != AF_INET6))
> +               return 0;

Should this be a check on the socket family (sock->ops->family)
instead of the address family?

It is valid to pass an address with AF_UNSPEC to a PF_INET(6) socket.
And there are legitimate reasons to want to deny this. Such as passing
a connection to a unprivileged process and disallow it from disconnect
and opening a different new connection.

> +
> +       socket_type = sock->type;
> +       /* Check if it's a TCP socket */
> +       if (socket_type != SOCK_STREAM)
> +               return 0;
> +
> +       if (!dom)
> +               return 0;
> +
> +       /* Get port value in host byte order */
> +       sockaddr = (struct sockaddr_in *)address;
> +       port = ntohs(sockaddr->sin_port);
> +
> +       return check_socket_access(dom, port, LANDLOCK_ACCESS_NET_CONNECT_TCP);
> +}