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

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Message-ID: <CAFqZXNs89yGcoXumNwavLRQpYutfnLY-SM2qrHbvpjJxVtiniw@mail.gmail.com>
Date:   Mon, 25 Oct 2021 10:17:06 +0200
From:   Ondrej Mosnacek <omosnace@...hat.com>
To:     Xin Long <lucien.xin@...il.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 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.

> +       asoc->secid = sksec->sid;
> +       asoc->peer_secid = sksec->peer_sid;
> +}
> +
>  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.