Date:   Mon, 7 Feb 2022 05:31:28 +0300
From:   Konstantin Meskhidze <konstantin.meskhidze@...wei.com>
To:     Mickaël Salaün <mic@...ikod.net>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>
CC:     <linux-security-module@...r.kernel.org>, <netdev@...r.kernel.org>,
        <netfilter@...r.kernel.org>, <yusongping@...wei.com>,
        <artem.kuzin@...wei.com>
Subject: Re: [RFC PATCH 1/2] landlock: TCP network hooks implementation



2/1/2022 3:33 PM, Mickaël Salaün пишет:
> 
> On 31/01/2022 18:14, Willem de Bruijn wrote:
>> On Fri, Jan 28, 2022 at 10:12 PM Konstantin Meskhidze
>> <konstantin.meskhidze@...wei.com> wrote:
>>>
>>>
>>>
>>> 1/26/2022 5:15 PM, Willem de Bruijn пишет:
>>>> On Wed, Jan 26, 2022 at 3:06 AM Konstantin Meskhidze
>>>> <konstantin.meskhidze@...wei.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@...wei.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@...wei.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?
>>>>
>>>> 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.
>>>
>>>    The intent is to restrict INET sockets to bind/connect to some ports.
>>>    You can apply some number of Landlock rules with port defenition:
>>>          1. Rule 1 allows to connect to sockets with port X.
>>>          2. Rule 2 forbids to connect to socket with port Y.
>>>          3. Rule 3 forbids to bind a socket to address with port Z.
>>>
>>>          and so on...
>>>>
>>>>>>
>>>>>> 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.
>>>
>>> So its possible to call connect() with AF_UNSPEC and make a socket
>>> unconnected. If you want to establish another connection to a socket
>>> with port Y, and if there is a landlock rule has applied to a process
>>> (or container) which restricts to connect to a socket with port Y, it
>>> will be banned.
>>> Thats the basic logic.
>>
>> Understood, and that works fine for connect. It would be good to also
>> ensure that a now-bound socket cannot call listen. Possibly for
>> follow-on work.
> 
> Are you thinking about a new access right for listen? What would be the 
> use case vs. the bind access right?
> .

  If bind() function has already been restricted so the following 
listen() function is automatically banned. I agree with Mickaёl about
the usecase here. Why do we need new-bound socket with restricted listening?

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