Re: [PATCHv2 net 4/4] security: implement sctp_assoc_established hook in selinux

[Ondrej Mosnacek <omosnace@redhat.com>]

Hi Xin,

On Tue, Nov 2, 2021 at 1:03 PM Xin Long <lucien.xin@gmail.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.
>
> v1->v2:
>   - call selinux_inet_conn_established() to reduce some code
>     duplication in selinux_sctp_assoc_established(), as Ondrej
>     suggested.
>   - when doing peeloff, it calls sock_create() where it actually
>     gets secid for socket from socket_sockcreate_sid(). So reuse
>     SECSID_WILD to ensure the peeloff socket keeps using that
>     secid after calling selinux_sctp_sk_clone() for client side.

Interesting... I find strange that SCTP creates the peeloff socket
using sock_create() rather than allocating it directly via
sock_alloc() like the other callers of sctp_copy_sock() (which calls
security_sctp_sk_clone()) do. Wouldn't it make more sense to avoid the
sock_create() call and just rely on the security_sctp_sk_clone()
semantic to set up the labels? Would anything break if
sctp_do_peeloff() switched to plain sock_alloc()?

I'd rather we avoid this SECSID_WILD hack to support the weird
created-but-also-cloned socket hybrid and just make the peeloff socket
behave the same as an accept()-ed socket (i.e. no
security_socket_[post_]create() hook calls, just
security_sctp_sk_clone()).

>
> Fixes: 72e89f50084c ("security: Add support for SCTP security hooks")
> Reported-by: Prashanth Prahlad <pprahlad@redhat.com>
> Reviewed-by: Richard Haines <richard_c_haines@btinternet.com>
> Tested-by: Richard Haines <richard_c_haines@btinternet.com>

You made non-trivial changes since the last revision in this patch, so
you should have also dropped the Reviewed-by and Tested-by here. Now
David has merged the patches probably under the impression that they
have been reviewed/approved from the SELinux side, which isn't
completely true.

> Signed-off-by: Xin Long <lucien.xin@gmail.com>
> ---
>  security/selinux/hooks.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index a9977a2ae8ac..341cd5dccbf5 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -5519,7 +5519,8 @@ static void selinux_sctp_sk_clone(struct sctp_association *asoc, struct sock *sk
>         if (!selinux_policycap_extsockclass())
>                 return selinux_sk_clone_security(sk, newsk);
>
> -       newsksec->sid = asoc->secid;
> +       if (asoc->secid != SECSID_WILD)
> +               newsksec->sid = asoc->secid;
>         newsksec->peer_sid = asoc->peer_secid;
>         newsksec->sclass = sksec->sclass;
>         selinux_netlbl_sctp_sk_clone(sk, newsk);
> @@ -5575,6 +5576,16 @@ static void selinux_inet_conn_established(struct sock *sk, struct sk_buff *skb)
>         selinux_skb_peerlbl_sid(skb, family, &sksec->peer_sid);
>  }
>
> +static void selinux_sctp_assoc_established(struct sctp_association *asoc,
> +                                          struct sk_buff *skb)
> +{
> +       struct sk_security_struct *sksec = asoc->base.sk->sk_security;
> +
> +       selinux_inet_conn_established(asoc->base.sk, skb);
> +       asoc->peer_secid = sksec->peer_sid;
> +       asoc->secid = SECSID_WILD;
> +}
> +
>  static int selinux_secmark_relabel_packet(u32 sid)
>  {
>         const struct task_security_struct *__tsec;
> @@ -7290,6 +7301,7 @@ 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.