[SCTP]: Implement the receive and verification of AUTH chunk

This patch implements the receive path needed to process authenticated
chunks. Add ability to process the AUTH chunk and handle edge cases
for authenticated COOKIE-ECHO as well.

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

include/net/sctp/constants.h

···
 	SCTP_IERROR_NO_DATA,
 	SCTP_IERROR_BAD_STREAM,
 	SCTP_IERROR_BAD_PORTS,
-
+	SCTP_IERROR_AUTH_BAD_HMAC,
+	SCTP_IERROR_AUTH_BAD_KEYID,
+	SCTP_IERROR_PROTO_VIOLATION,
 } sctp_ierror_t;
 
 

include/net/sctp/sm.h

···
 sctp_state_fn_t sctp_sf_do_9_2_reshutack;
 sctp_state_fn_t sctp_sf_eat_fwd_tsn;
 sctp_state_fn_t sctp_sf_eat_fwd_tsn_fast;
+sctp_state_fn_t sctp_sf_eat_auth;
 
 /* Prototypes for primitive event state functions.  */
 sctp_state_fn_t sctp_sf_do_prm_asoc;

include/net/sctp/structs.h

···
 	 */
 	struct sctp_transport *transport;
 
+	/* SCTP-AUTH:  For the special case inbound processing of COOKIE-ECHO
+	 * we need save a pointer to the AUTH chunk, since the SCTP-AUTH
+	 * spec violates the principle premis that all chunks are processed
+	 * in order.
+	 */
+	struct sk_buff *auth_chunk;
+
 	__u8 rtt_in_progress;	/* Is this chunk used for RTT calculation? */
 	__u8 resent;		/* Has this chunk ever been retransmitted. */
 	__u8 has_tsn;		/* Does this chunk have a TSN yet? */
···
 void sctp_inq_free(struct sctp_inq *);
 void sctp_inq_push(struct sctp_inq *, struct sctp_chunk *packet);
 struct sctp_chunk *sctp_inq_pop(struct sctp_inq *);
+struct sctp_chunkhdr *sctp_inq_peek(struct sctp_inq *);
 void sctp_inq_set_th_handler(struct sctp_inq *, work_func_t);
 
 /* This is the structure we use to hold outbound chunks.  You push

net/sctp/associola.c

···
 		state = asoc->state;
 		subtype = SCTP_ST_CHUNK(chunk->chunk_hdr->type);
 
+		/* SCTP-AUTH, Section 6.3:
+		 *    The receiver has a list of chunk types which it expects
+		 *    to be received only after an AUTH-chunk.  This list has
+		 *    been sent to the peer during the association setup.  It
+		 *    MUST silently discard these chunks if they are not placed
+		 *    after an AUTH chunk in the packet.
+		 */
+		if (sctp_auth_recv_cid(subtype.chunk, asoc) && !chunk->auth)
+			continue;
+
 		/* Remember where the last DATA chunk came from so we
 		 * know where to send the SACK.
 		 */

net/sctp/endpointola.c

···
 	sctp_subtype_t subtype;
 	sctp_state_t state;
 	int error = 0;
+	int first_time = 1;	/* is this the first time through the looop */
 
 	if (ep->base.dead)
 		return;
···
 	while (NULL != (chunk = sctp_inq_pop(inqueue))) {
 		subtype = SCTP_ST_CHUNK(chunk->chunk_hdr->type);
 
+		/* If the first chunk in the packet is AUTH, do special
+		 * processing specified in Section 6.3 of SCTP-AUTH spec
+		 */
+		if (first_time && (subtype.chunk == SCTP_CID_AUTH)) {
+			struct sctp_chunkhdr *next_hdr;
+
+			next_hdr = sctp_inq_peek(inqueue);
+			if (!next_hdr)
+				goto normal;
+
+			/* If the next chunk is COOKIE-ECHO, skip the AUTH
+			 * chunk while saving a pointer to it so we can do
+			 * Authentication later (during cookie-echo
+			 * processing).
+			 */
+			if (next_hdr->type == SCTP_CID_COOKIE_ECHO) {
+				chunk->auth_chunk = skb_clone(chunk->skb,
+								GFP_ATOMIC);
+				chunk->auth = 1;
+				continue;
+			}
+		}
+normal:
 		/* We might have grown an association since last we
 		 * looked, so try again.
 		 *
···
 		}
 
 		state = asoc ? asoc->state : SCTP_STATE_CLOSED;
+		if (sctp_auth_recv_cid(subtype.chunk, asoc) && !chunk->auth)
+			continue;
 
 		/* Remember where the last DATA chunk came from so we
 		 * know where to send the SACK.
···
 		 */
 		if (!sctp_sk(sk)->ep)
 			break;
+
+		if (first_time)
+			first_time = 0;
 	}
 }

net/sctp/input.c

···
 
 	ch = (sctp_chunkhdr_t *) skb->data;
 
-	/* If this is INIT/INIT-ACK look inside the chunk too. */
-	switch (ch->type) {
-	case SCTP_CID_INIT:
-	case SCTP_CID_INIT_ACK:
-		break;
-	default:
-		return NULL;
-	}
-
 	/* The code below will attempt to walk the chunk and extract
 	 * parameter information.  Before we do that, we need to verify
 	 * that the chunk length doesn't cause overflow.  Otherwise, we'll
···
 	return NULL;
 }
 
+/* SCTP-AUTH, Section 6.3:
+*    If the receiver does not find a STCB for a packet containing an AUTH
+*    chunk as the first chunk and not a COOKIE-ECHO chunk as the second
+*    chunk, it MUST use the chunks after the AUTH chunk to look up an existing
+*    association.
+*
+* This means that any chunks that can help us identify the association need
+* to be looked at to find this assocation.
+*
+* TODO: The only chunk currently defined that can do that is ASCONF, but we
+* don't support that functionality yet.
+*/
+static struct sctp_association *__sctp_rcv_auth_lookup(struct sk_buff *skb,
+				      const union sctp_addr *paddr,
+				      const union sctp_addr *laddr,
+				      struct sctp_transport **transportp)
+{
+	/* XXX - walk through the chunks looking for something that can
+	 * help us find the association.  INIT, and INIT-ACK are not permitted.
+	 * That leaves ASCONF, but we don't support that yet.
+	 */
+	return NULL;
+}
+
+/*
+ * There are circumstances when we need to look inside the SCTP packet
+ * for information to help us find the association.   Examples
+ * include looking inside of INIT/INIT-ACK chunks or after the AUTH
+ * chunks.
+ */
+static struct sctp_association *__sctp_rcv_lookup_harder(struct sk_buff *skb,
+				      const union sctp_addr *paddr,
+				      const union sctp_addr *laddr,
+				      struct sctp_transport **transportp)
+{
+	sctp_chunkhdr_t *ch;
+
+	ch = (sctp_chunkhdr_t *) skb->data;
+
+	/* If this is INIT/INIT-ACK look inside the chunk too. */
+	switch (ch->type) {
+	case SCTP_CID_INIT:
+	case SCTP_CID_INIT_ACK:
+		return __sctp_rcv_init_lookup(skb, laddr, transportp);
+		break;
+
+	case SCTP_CID_AUTH:
+		return __sctp_rcv_auth_lookup(skb, paddr, laddr, transportp);
+		break;
+	}
+
+	return NULL;
+}
+
 /* Lookup an association for an inbound skb. */
 static struct sctp_association *__sctp_rcv_lookup(struct sk_buff *skb,
 				      const union sctp_addr *paddr,
···
 	 * parameters within the INIT or INIT-ACK.
 	 */
 	if (!asoc)
-		asoc = __sctp_rcv_init_lookup(skb, laddr, transportp);
+		asoc = __sctp_rcv_lookup_harder(skb, paddr, laddr, transportp);
 
 	return asoc;
 }

net/sctp/inqueue.c

···
 	q->immediate.func(&q->immediate);
 }
 
+/* Peek at the next chunk on the inqeue. */
+struct sctp_chunkhdr *sctp_inq_peek(struct sctp_inq *queue)
+{
+	struct sctp_chunk *chunk;
+	sctp_chunkhdr_t *ch = NULL;
+
+	chunk = queue->in_progress;
+	/* If there is no more chunks in this packet, say so */
+	if (chunk->singleton ||
+	    chunk->end_of_packet ||
+	    chunk->pdiscard)
+		    return NULL;
+
+	ch = (sctp_chunkhdr_t *)chunk->chunk_end;
+
+	return ch;
+}
+
+
 /* Extract a chunk from an SCTP inqueue.
  *
  * WARNING:  If you need to put the chunk on another queue, you need to

net/sctp/sm_statefuns.c

···
 				     void *arg,
 				     sctp_cmd_seq_t *commands);
 
+static sctp_ierror_t sctp_sf_authenticate(const struct sctp_endpoint *ep,
+				    const struct sctp_association *asoc,
+				    const sctp_subtype_t type,
+				    struct sctp_chunk *chunk);
+
 /* Small helper function that checks if the chunk length
  * is of the appropriate length.  The 'required_length' argument
  * is set to be the size of a specific chunk we are testing.
···
 			      (sctp_init_chunk_t *)chunk->chunk_hdr, chunk,
 			      &err_chunk)) {
 
-		SCTP_INC_STATS(SCTP_MIB_ABORTEDS);
-
 		/* This chunk contains fatal error. It is to be discarded.
 		 * Send an ABORT, with causes if there is any.
 		 */
···
 			sctp_sf_tabort_8_4_8(ep, asoc, type, arg, commands);
 			error = SCTP_ERROR_INV_PARAM;
 		}
+
+		/* SCTP-AUTH, Section 6.3:
+		 *    It should be noted that if the receiver wants to tear
+		 *    down an association in an authenticated way only, the
+		 *    handling of malformed packets should not result in
+		 *    tearing down the association.
+		 *
+		 * This means that if we only want to abort associations
+		 * in an authenticated way (i.e AUTH+ABORT), then we
+		 * can't destory this association just becuase the packet
+		 * was malformed.
+		 */
+		if (sctp_auth_recv_cid(SCTP_CID_ABORT, asoc))
+			return sctp_sf_pdiscard(ep, asoc, type, arg, commands);
+
+		SCTP_INC_STATS(SCTP_MIB_ABORTEDS);
 		return sctp_stop_t1_and_abort(commands, error, ECONNREFUSED,
 						asoc, chunk->transport);
 	}
···
 	error = sctp_auth_asoc_init_active_key(new_asoc, GFP_ATOMIC);
 	if (error)
 		goto nomem_init;
+
+	/* SCTP-AUTH:  auth_chunk pointer is only set when the cookie-echo
+	 * is supposed to be authenticated and we have to do delayed
+	 * authentication.  We've just recreated the association using
+	 * the information in the cookie and now it's much easier to
+	 * do the authentication.
+	 */
+	if (chunk->auth_chunk) {
+		struct sctp_chunk auth;
+		sctp_ierror_t ret;
+
+		/* set-up our fake chunk so that we can process it */
+		auth.skb = chunk->auth_chunk;
+		auth.asoc = chunk->asoc;
+		auth.sctp_hdr = chunk->sctp_hdr;
+		auth.chunk_hdr = (sctp_chunkhdr_t *)skb_push(chunk->auth_chunk,
+					    sizeof(sctp_chunkhdr_t));
+		skb_pull(chunk->auth_chunk, sizeof(sctp_chunkhdr_t));
+		auth.transport = chunk->transport;
+
+		ret = sctp_sf_authenticate(ep, new_asoc, type, &auth);
+
+		/* We can now safely free the auth_chunk clone */
+		kfree_skb(chunk->auth_chunk);
+
+		if (ret != SCTP_IERROR_NO_ERROR) {
+			sctp_association_free(new_asoc);
+			return sctp_sf_pdiscard(ep, asoc, type, arg, commands);
+		}
+	}
 
 	repl = sctp_make_cookie_ack(new_asoc, chunk);
 	if (!repl)
···
 }
 
 /*
+ * SCTP-AUTH Section 6.3 Receving authenticated chukns
+ *
+ *    The receiver MUST use the HMAC algorithm indicated in the HMAC
+ *    Identifier field.  If this algorithm was not specified by the
+ *    receiver in the HMAC-ALGO parameter in the INIT or INIT-ACK chunk
+ *    during association setup, the AUTH chunk and all chunks after it MUST
+ *    be discarded and an ERROR chunk SHOULD be sent with the error cause
+ *    defined in Section 4.1.
+ *
+ *    If an endpoint with no shared key receives a Shared Key Identifier
+ *    other than 0, it MUST silently discard all authenticated chunks.  If
+ *    the endpoint has at least one endpoint pair shared key for the peer,
+ *    it MUST use the key specified by the Shared Key Identifier if a
+ *    key has been configured for that Shared Key Identifier.  If no
+ *    endpoint pair shared key has been configured for that Shared Key
+ *    Identifier, all authenticated chunks MUST be silently discarded.
+ *
+ * Verification Tag:  8.5 Verification Tag [Normal verification]
+ *
+ * The return value is the disposition of the chunk.
+ */
+static sctp_ierror_t sctp_sf_authenticate(const struct sctp_endpoint *ep,
+				    const struct sctp_association *asoc,
+				    const sctp_subtype_t type,
+				    struct sctp_chunk *chunk)
+{
+	struct sctp_authhdr *auth_hdr;
+	struct sctp_hmac *hmac;
+	unsigned int sig_len;
+	__u16 key_id;
+	__u8 *save_digest;
+	__u8 *digest;
+
+	/* Pull in the auth header, so we can do some more verification */
+	auth_hdr = (struct sctp_authhdr *)chunk->skb->data;
+	chunk->subh.auth_hdr = auth_hdr;
+	skb_pull(chunk->skb, sizeof(struct sctp_authhdr));
+
+	/* Make sure that we suport the HMAC algorithm from the auth
+	 * chunk.
+	 */
+	if (!sctp_auth_asoc_verify_hmac_id(asoc, auth_hdr->hmac_id))
+		return SCTP_IERROR_AUTH_BAD_HMAC;
+
+	/* Make sure that the provided shared key identifier has been
+	 * configured
+	 */
+	key_id = ntohs(auth_hdr->shkey_id);
+	if (key_id != asoc->active_key_id && !sctp_auth_get_shkey(asoc, key_id))
+		return SCTP_IERROR_AUTH_BAD_KEYID;
+
+
+	/* Make sure that the length of the signature matches what
+	 * we expect.
+	 */
+	sig_len = ntohs(chunk->chunk_hdr->length) - sizeof(sctp_auth_chunk_t);
+	hmac = sctp_auth_get_hmac(ntohs(auth_hdr->hmac_id));
+	if (sig_len != hmac->hmac_len)
+		return SCTP_IERROR_PROTO_VIOLATION;
+
+	/* Now that we've done validation checks, we can compute and
+	 * verify the hmac.  The steps involved are:
+	 *  1. Save the digest from the chunk.
+	 *  2. Zero out the digest in the chunk.
+	 *  3. Compute the new digest
+	 *  4. Compare saved and new digests.
+	 */
+	digest = auth_hdr->hmac;
+	skb_pull(chunk->skb, sig_len);
+
+	save_digest = kmemdup(digest, sig_len, GFP_ATOMIC);
+	if (!save_digest)
+		goto nomem;
+
+	memset(digest, 0, sig_len);
+
+	sctp_auth_calculate_hmac(asoc, chunk->skb,
+				(struct sctp_auth_chunk *)chunk->chunk_hdr,
+				GFP_ATOMIC);
+
+	/* Discard the packet if the digests do not match */
+	if (memcmp(save_digest, digest, sig_len)) {
+		kfree(save_digest);
+		return SCTP_IERROR_BAD_SIG;
+	}
+
+	kfree(save_digest);
+	chunk->auth = 1;
+
+	return SCTP_IERROR_NO_ERROR;
+nomem:
+	return SCTP_IERROR_NOMEM;
+}
+
+sctp_disposition_t sctp_sf_eat_auth(const struct sctp_endpoint *ep,
+				    const struct sctp_association *asoc,
+				    const sctp_subtype_t type,
+				    void *arg,
+				    sctp_cmd_seq_t *commands)
+{
+	struct sctp_authhdr *auth_hdr;
+	struct sctp_chunk *chunk = arg;
+	struct sctp_chunk *err_chunk;
+	sctp_ierror_t error;
+
+	if (!sctp_vtag_verify(chunk, asoc)) {
+		sctp_add_cmd_sf(commands, SCTP_CMD_REPORT_BAD_TAG,
+				SCTP_NULL());
+		return sctp_sf_pdiscard(ep, asoc, type, arg, commands);
+	}
+
+	/* Make sure that the AUTH chunk has valid length.  */
+	if (!sctp_chunk_length_valid(chunk, sizeof(struct sctp_auth_chunk)))
+		return sctp_sf_violation_chunklen(ep, asoc, type, arg,
+						  commands);
+
+	auth_hdr = (struct sctp_authhdr *)chunk->skb->data;
+	error = sctp_sf_authenticate(ep, asoc, type, chunk);
+	switch (error) {
+		case SCTP_IERROR_AUTH_BAD_HMAC:
+			/* Generate the ERROR chunk and discard the rest
+			 * of the packet
+			 */
+			err_chunk = sctp_make_op_error(asoc, chunk,
+							SCTP_ERROR_UNSUP_HMAC,
+							&auth_hdr->hmac_id,
+							sizeof(__u16));
+			if (err_chunk) {
+				sctp_add_cmd_sf(commands, SCTP_CMD_REPLY,
+						SCTP_CHUNK(err_chunk));
+			}
+			/* Fall Through */
+		case SCTP_IERROR_AUTH_BAD_KEYID:
+		case SCTP_IERROR_BAD_SIG:
+			return sctp_sf_pdiscard(ep, asoc, type, arg, commands);
+			break;
+		case SCTP_IERROR_PROTO_VIOLATION:
+			return sctp_sf_violation_chunklen(ep, asoc, type, arg,
+							  commands);
+			break;
+		case SCTP_IERROR_NOMEM:
+			return SCTP_DISPOSITION_NOMEM;
+		default:
+			break;
+	}
+
+	return SCTP_DISPOSITION_CONSUME;
+}
+
+/*
  * Process an unknown chunk.
  *
  * Section: 3.2. Also, 2.1 in the implementor's guide.
···
 	if (!abort)
 		goto nomem;
 
+	/* SCTP-AUTH, Section 6.3:
+	 *    It should be noted that if the receiver wants to tear
+	 *    down an association in an authenticated way only, the
+	 *    handling of malformed packets should not result in
+	 *    tearing down the association.
+	 *
+	 * This means that if we only want to abort associations
+	 * in an authenticated way (i.e AUTH+ABORT), then we
+	 * can't destory this association just becuase the packet
+	 * was malformed.
+	 */
+	if (sctp_auth_recv_cid(SCTP_CID_ABORT, asoc))
+		goto discard;
+
 	if (asoc) {
 		sctp_add_cmd_sf(commands, SCTP_CMD_REPLY, SCTP_CHUNK(abort));
 		SCTP_INC_STATS(SCTP_MIB_OUTCTRLCHUNKS);
···
 		SCTP_INC_STATS(SCTP_MIB_OUTCTRLCHUNKS);
 	}
 
+discard:
 	sctp_sf_pdiscard(ep, asoc, SCTP_ST_CHUNK(0), arg, commands);
 
 	SCTP_INC_STATS(SCTP_MIB_ABORTEDS);

net/sctp/sm_statetable.c

···
 	TYPE_SCTP_FWD_TSN,
 }; /*state_fn_t prsctp_chunk_event_table[][] */
 
+#define TYPE_SCTP_AUTH { \
+	/* SCTP_STATE_EMPTY */ \
+	TYPE_SCTP_FUNC(sctp_sf_ootb), \
+	/* SCTP_STATE_CLOSED */ \
+	TYPE_SCTP_FUNC(sctp_sf_ootb), \
+	/* SCTP_STATE_COOKIE_WAIT */ \
+	TYPE_SCTP_FUNC(sctp_sf_discard_chunk), \
+	/* SCTP_STATE_COOKIE_ECHOED */ \
+	TYPE_SCTP_FUNC(sctp_sf_eat_auth), \
+	/* SCTP_STATE_ESTABLISHED */ \
+	TYPE_SCTP_FUNC(sctp_sf_eat_auth), \
+	/* SCTP_STATE_SHUTDOWN_PENDING */ \
+	TYPE_SCTP_FUNC(sctp_sf_eat_auth), \
+	/* SCTP_STATE_SHUTDOWN_SENT */ \
+	TYPE_SCTP_FUNC(sctp_sf_eat_auth), \
+	/* SCTP_STATE_SHUTDOWN_RECEIVED */ \
+	TYPE_SCTP_FUNC(sctp_sf_eat_auth), \
+	/* SCTP_STATE_SHUTDOWN_ACK_SENT */ \
+	TYPE_SCTP_FUNC(sctp_sf_eat_auth), \
+} /* TYPE_SCTP_AUTH */
+
+/* The primary index for this table is the chunk type.
+ * The secondary index for this table is the state.
+ */
+static const sctp_sm_table_entry_t auth_chunk_event_table[SCTP_NUM_AUTH_CHUNK_TYPES][SCTP_STATE_NUM_STATES] = {
+	TYPE_SCTP_AUTH,
+}; /*state_fn_t auth_chunk_event_table[][] */
+
 static const sctp_sm_table_entry_t
 chunk_event_table_unknown[SCTP_STATE_NUM_STATES] = {
 	/* SCTP_STATE_EMPTY */
···
 
 		if (cid == SCTP_CID_ASCONF_ACK)
 			return &addip_chunk_event_table[1][state];
+	}
+
+	if (sctp_auth_enable) {
+		if (cid == SCTP_CID_AUTH)
+			return &auth_chunk_event_table[0][state];
 	}
 
 	return &chunk_event_table_unknown[state];