[SCTP]: Correctly handle unexpected INIT-ACK chunk.

Consider the chunk as Out-of-the-Blue if we don't have
an endpoint. Otherwise discard it as before.

Signed-off-by: Vlad Yasevich <[e-mail]>
Signed-off-by: Sridhar Samudrala <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/sctp/sm.h

···
 sctp_state_fn_t sctp_sf_discard_chunk;
 sctp_state_fn_t sctp_sf_do_5_2_1_siminit;
 sctp_state_fn_t sctp_sf_do_5_2_2_dupinit;
+sctp_state_fn_t sctp_sf_do_5_2_3_initack;
 sctp_state_fn_t sctp_sf_do_5_2_4_dupcook;
 sctp_state_fn_t sctp_sf_unk_chunk;
 sctp_state_fn_t sctp_sf_do_8_5_1_E_sa;

net/sctp/sm_statefuns.c

···
 }
 
 
+/*
+ * Unexpected INIT-ACK handler.
+ *
+ * Section 5.2.3
+ * If an INIT ACK received by an endpoint in any state other than the
+ * COOKIE-WAIT state, the endpoint should discard the INIT ACK chunk.
+ * An unexpected INIT ACK usually indicates the processing of an old or
+ * duplicated INIT chunk.
+*/
+sctp_disposition_t sctp_sf_do_5_2_3_initack(const struct sctp_endpoint *ep,
+					    const struct sctp_association *asoc,
+					    const sctp_subtype_t type,
+					    void *arg, sctp_cmd_seq_t *commands)
+{
+	/* Per the above section, we'll discard the chunk if we have an
+	 * endpoint.  If this is an OOTB INIT-ACK, treat it as such.
+	 */
+        if (ep == sctp_sk((sctp_get_ctl_sock()))->ep)
+		return sctp_sf_ootb(ep, asoc, type, arg, commands);
+	else
+		return sctp_sf_discard_chunk(ep, asoc, type, arg, commands);
+}
 
 /* Unexpected COOKIE-ECHO handler for peer restart (Table 2, action 'A')
  *

net/sctp/sm_statetable.c

···
 	/* SCTP_STATE_EMPTY */ \
 	TYPE_SCTP_FUNC(sctp_sf_ootb), \
 	/* SCTP_STATE_CLOSED */ \
-	TYPE_SCTP_FUNC(sctp_sf_discard_chunk), \
+	TYPE_SCTP_FUNC(sctp_sf_do_5_2_3_initack), \
 	/* SCTP_STATE_COOKIE_WAIT */ \
 	TYPE_SCTP_FUNC(sctp_sf_do_5_1C_ack), \
 	/* SCTP_STATE_COOKIE_ECHOED */ \