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Date: Tue, 1 Feb 2022 13:33:46 +0100 From: Mickaël Salaün <mic@...ikod.net> To: Willem de Bruijn <willemdebruijn.kernel@...il.com>, Konstantin Meskhidze <konstantin.meskhidze@...wei.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 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?
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