netdev - Re: [PATCH net 4/4] security: implement sctp_assoc

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Date:   Mon, 25 Oct 2021 18:51:39 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     Ondrej Mosnacek <omosnace@...hat.com>
Cc:     network dev <netdev@...r.kernel.org>,
        SElinux list <selinux@...r.kernel.org>,
        Linux Security Module list 
        <linux-security-module@...r.kernel.org>,
        "linux-sctp @ vger . kernel . org" <linux-sctp@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        James Morris <jmorris@...ei.org>,
        Paul Moore <paul@...l-moore.com>,
        Richard Haines <richard_c_haines@...nternet.com>
Subject: Re: [PATCH net 4/4] security: implement sctp_assoc_established hook
 in selinux

On Mon, Oct 25, 2021 at 4:17 PM Ondrej Mosnacek <omosnace@...hat.com> wrote:
>
> On Fri, Oct 22, 2021 at 8:36 AM Xin Long <lucien.xin@...il.com> wrote:
> > Different from selinux_inet_conn_established(), it also gives the
> > secid to asoc->peer_secid in selinux_sctp_assoc_established(),
> > as one UDP-type socket may have more than one asocs.
> >
> > Note that peer_secid in asoc will save the peer secid for this
> > asoc connection, and peer_sid in sksec will just keep the peer
> > secid for the latest connection. So the right use should be do
> > peeloff for UDP-type socket if there will be multiple asocs in
> > one socket, so that the peeloff socket has the right label for
> > its asoc.
>
> Hm... this sounds like something we should also try to fix (if
> possible). In access control we can't trust userspace to do the right
> thing - receiving from multiple peers on one SOCK_SEQPACKET socket
> shouldn't cause checking against the wrong peer_sid. But that can be
> addressed separately. (And maybe it's even already accounted for
> somehow - I didn't yet look at the code closely.)
>
> >
> > Fixes: 72e89f50084c ("security: Add support for SCTP security hooks")
> > Reported-by: Prashanth Prahlad <pprahlad@...hat.com>
> > Signed-off-by: Xin Long <lucien.xin@...il.com>
> > ---
> >  security/selinux/hooks.c | 16 ++++++++++++++++
> >  1 file changed, 16 insertions(+)
> >
> > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> > index f025fc00421b..793fdcbc68bd 100644
> > --- a/security/selinux/hooks.c
> > +++ b/security/selinux/hooks.c
> > @@ -5525,6 +5525,21 @@ static void selinux_sctp_sk_clone(struct sctp_association *asoc, struct sock *sk
> >         selinux_netlbl_sctp_sk_clone(sk, newsk);
> >  }
> >
> > +static void selinux_sctp_assoc_established(struct sctp_association *asoc,
> > +                                          struct sk_buff *skb)
> > +{
> > +       struct sk_security_struct *sksec = asoc->base.sk->sk_security;
> > +       u16 family = asoc->base.sk->sk_family;
> > +
> > +       /* handle mapped IPv4 packets arriving via IPv6 sockets */
> > +       if (family == PF_INET6 && skb->protocol == htons(ETH_P_IP))
> > +               family = PF_INET;
> > +
> > +       selinux_skb_peerlbl_sid(skb, family, &sksec->peer_sid);
>
> You could replace the above with
> `selinux_inet_conn_established(asoc->base.sk, skb);` to reduce code
> duplication.
Hi Ondrej,

will do, thanks!

>
> > +       asoc->secid = sksec->sid;
> > +       asoc->peer_secid = sksec->peer_sid;
> > +}
> > +
Now I'm thinking: 'peer_sid' should be correct here.

BUT 'sid' is copied from its parent socket. Later when doing peel-off,
asoc->secid will be set back to the peel-off socket's sksec->sid.

Do you think this is okay? or should the peel-off socket have its own
sksec->sid, which might be different from the parent socket's?
(Note the socket's sid initially was set in selinux_socket_post_create())


> >  static int selinux_inet_conn_request(const struct sock *sk, struct sk_buff *skb,
> >                                      struct request_sock *req)
> >  {
> > @@ -7290,6 +7305,7 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
> >         LSM_HOOK_INIT(sctp_assoc_request, selinux_sctp_assoc_request),
> >         LSM_HOOK_INIT(sctp_sk_clone, selinux_sctp_sk_clone),
> >         LSM_HOOK_INIT(sctp_bind_connect, selinux_sctp_bind_connect),
> > +       LSM_HOOK_INIT(sctp_assoc_established, selinux_sctp_assoc_established),
> >         LSM_HOOK_INIT(inet_conn_request, selinux_inet_conn_request),
> >         LSM_HOOK_INIT(inet_csk_clone, selinux_inet_csk_clone),
> >         LSM_HOOK_INIT(inet_conn_established, selinux_inet_conn_established),
> > --
> > 2.27.0
> >
>
> --
> Ondrej Mosnacek
> Software Engineer, Linux Security - SELinux kernel
> Red Hat, Inc.
>