security: implement sctp_assoc_established hook in selinux

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.

Fixes: 72e89f50 ("security: Add support for SCTP security hooks")
Reported-by: NPrashanth Prahlad <pprahlad@redhat.com>
Reviewed-by: NRichard Haines <richard_c_haines@btinternet.com>
Tested-by: NRichard Haines <richard_c_haines@btinternet.com>
Signed-off-by: NXin Long <lucien.xin@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

security/selinux/hooks.c

@@ -5502,7 +5502,8 @@ 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);
@@ -5558,6 +5559,16 @@ 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;
@@ -7228,6 +7239,7 @@ 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),