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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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