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

[Mickaël Salaün]

On 26/01/2022 15:15, Willem de Bruijn wrote:
> On Wed, Jan 26, 2022 at 3:06 AM Konstantin Meskhidze
> <konstantin.meskhidze at huawei.com> wrote:
>>
>>
>>
>> 1/25/2022 5:17 PM, Willem de Bruijn пишет:
>>> 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?
>>
>> Actually connect() function checks address family:
>>
>> int __inet_stream_connect(... ,struct sockaddr *uaddr ,...) {
>> ...
>>          if (uaddr) {
>>                  if (addr_len < sizeof(uaddr->sa_family))
>>                  return -EINVAL;
>>
>>                  if (uaddr->sa_family == AF_UNSPEC) {
>>                          err = sk->sk_prot->disconnect(sk, flags);
>>                          sock->state = err ? SS_DISCONNECTING :
>>                          SS_UNCONNECTED;
>>                  goto out;
>>                  }
>>          }
>>
>> ...
>> }
> 
> Right. My question is: is the intent of this feature to be limited to
> sockets of type AF_INET(6) or to addresses?

This feature should handle all "TCP" sockets/ports, IPv4 or IPv6 or 
unspecified, the same way. What do you suggest to not miss corner cases? 
What are the guarantees about socket types we can trust/rely on?


> 
> I would think the first. Then you also want to catch operations on
> such sockets that may pass a different address family. AF_UNSPEC is
> the known offender that will effect a state change on AF_INET(6)
> sockets.

Indeed, Landlock needs to handle this case to avoid bypasses. This must 
be part of the tests.


> 
>>>
>>> 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.
>>
>> As far as I know using AF_UNSPEC to unconnect takes effect on
>> UDP(DATAGRAM) sockets.
>> To unconnect a UDP socket, we call connect but set the family member of
>> the socket address structure (sin_family for IPv4 or sin6_family for
>> IPv6) to AF_UNSPEC. It is the process of calling connect on an already
>> connected UDP socket that causes the socket to become unconnected.
>>
>> This RFC patch just supports TCP connections. I need to check the logic
>> if AF_UNSPEC provided in connenct() function for TCP(STREAM) sockets.
>> Does it disconnect already established TCP connection?
>>
>> Thank you for noticing about this issue. Need to think through how
>> to manage it with Landlock network restrictions for both TCP and UDP
>> sockets.
> 
> AF_UNSPEC also disconnects TCP.
> 
>>>
>>>> +
>>>> +       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);
>>>> +}
>>> .