Merge branch 'sctp-enhancements-for-the-verification-tag'

Xin Long says:

====================
sctp: enhancements for the verification tag

This patchset is to address CVE-2021-3772:

  A flaw was found in the Linux SCTP stack. A blind attacker may be able to
  kill an existing SCTP association through invalid chunks if the attacker
  knows the IP-addresses and port numbers being used and the attacker can
  send packets with spoofed IP addresses.

This is caused by the missing VTAG verification for the received chunks
and the incorrect vtag for the ABORT used to reply to these invalid
chunks.

This patchset is to go over all processing functions for the received
chunks and do:

1. Make sure sctp_vtag_verify() is called firstly to verify the vtag from
   the received chunk and discard this chunk if it fails. With some
   exceptions:

   a. sctp_sf_do_5_1B_init()/5_2_2_dupinit()/9_2_reshutack(), processing
      INIT chunk, as sctphdr vtag is always 0 in INIT chunk.

   b. sctp_sf_do_5_2_4_dupcook(), processing dupicate COOKIE_ECHO chunk,
      as the vtag verification will be done by sctp_tietags_compare() and
      then it takes right actions according to the return.

   c. sctp_sf_shut_8_4_5(), processing SHUTDOWN_ACK chunk for cookie_wait
      and cookie_echoed state, as RFC demand sending a SHUTDOWN_COMPLETE
      even if the vtag verification failed.

   d. sctp_sf_ootb(), called in many types of chunks for closed state or
      no asoc, as the same reason to c.

2. Always use the vtag from the received INIT chunk to make the response
   ABORT in sctp_ootb_pkt_new().

3. Fix the order for some checks and add some missing checks for the
   received chunk.

This patch series has been tested with SCTP TAHI testing to make sure no
regression caused on protocol conformance.
====================

Link: https://lore.kernel.org/r/cover.1634730082.git.lucien.xin@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/sctp/sm_statefuns.c

@@ -156,6 +156,12 @@ static enum sctp_disposition __sctp_sf_do_9_1_abort(
 					void *arg,
 					struct sctp_cmd_seq *commands);
 
+static enum sctp_disposition
+__sctp_sf_do_9_2_reshutack(struct net *net, const struct sctp_endpoint *ep,
+			   const struct sctp_association *asoc,
+			   const union sctp_subtype type, void *arg,
+			   struct sctp_cmd_seq *commands);
+
 /* 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.
@@ -337,6 +343,14 @@ enum sctp_disposition sctp_sf_do_5_1B_init(struct net *net,
 	if (!chunk->singleton)
 		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
 
+	/* Make sure that the INIT chunk has a valid length.
+	 * Normally, this would cause an ABORT with a Protocol Violation
+	 * error, but since we don't have an association, we'll
+	 * just discard the packet.
+	 */
+	if (!sctp_chunk_length_valid(chunk, sizeof(struct sctp_init_chunk)))
+		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
+
 	/* If the packet is an OOTB packet which is temporarily on the
 	 * control endpoint, respond with an ABORT.
 	 */
@@ -351,14 +365,6 @@ enum sctp_disposition sctp_sf_do_5_1B_init(struct net *net,
 	if (chunk->sctp_hdr->vtag != 0)
 		return sctp_sf_tabort_8_4_8(net, ep, asoc, type, arg, commands);
 
-	/* Make sure that the INIT chunk has a valid length.
-	 * Normally, this would cause an ABORT with a Protocol Violation
-	 * error, but since we don't have an association, we'll
-	 * just discard the packet.
-	 */
-	if (!sctp_chunk_length_valid(chunk, sizeof(struct sctp_init_chunk)))
-		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
-
 	/* If the INIT is coming toward a closing socket, we'll send back
 	 * and ABORT.  Essentially, this catches the race of INIT being
 	 * backloged to the socket at the same time as the user issues close().
@@ -704,6 +710,9 @@ enum sctp_disposition sctp_sf_do_5_1D_ce(struct net *net,
 	struct sock *sk;
 	int error = 0;
 
+	if (asoc && !sctp_vtag_verify(chunk, asoc))
+		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
+
 	/* If the packet is an OOTB packet which is temporarily on the
 	 * control endpoint, respond with an ABORT.
 	 */
@@ -718,7 +727,8 @@ enum sctp_disposition sctp_sf_do_5_1D_ce(struct net *net,
 	 * in sctp_unpack_cookie().
 	 */
 	if (!sctp_chunk_length_valid(chunk, sizeof(struct sctp_chunkhdr)))
-		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
+		return sctp_sf_violation_chunklen(net, ep, asoc, type, arg,
+						  commands);
 
 	/* If the endpoint is not listening or if the number of associations
 	 * on the TCP-style socket exceed the max backlog, respond with an
@@ -1524,20 +1534,16 @@ static enum sctp_disposition sctp_sf_do_unexpected_init(
 	if (!chunk->singleton)
 		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
 
+	/* Make sure that the INIT chunk has a valid length. */
+	if (!sctp_chunk_length_valid(chunk, sizeof(struct sctp_init_chunk)))
+		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
+
 	/* 3.1 A packet containing an INIT chunk MUST have a zero Verification
 	 * Tag.
 	 */
 	if (chunk->sctp_hdr->vtag != 0)
 		return sctp_sf_tabort_8_4_8(net, ep, asoc, type, arg, commands);
 
-	/* Make sure that the INIT chunk has a valid length.
-	 * In this case, we generate a protocol violation since we have
-	 * an association established.
-	 */
-	if (!sctp_chunk_length_valid(chunk, sizeof(struct sctp_init_chunk)))
-		return sctp_sf_violation_chunklen(net, ep, asoc, type, arg,
-						  commands);
-
 	if (SCTP_INPUT_CB(chunk->skb)->encap_port != chunk->transport->encap_port)
 		return sctp_sf_new_encap_port(net, ep, asoc, type, arg, commands);
 
@@ -1882,7 +1888,7 @@ static enum sctp_disposition sctp_sf_do_dupcook_a(
 	 * its peer.
 	*/
 	if (sctp_state(asoc, SHUTDOWN_ACK_SENT)) {
-		disposition = sctp_sf_do_9_2_reshutack(net, ep, asoc,
+		disposition = __sctp_sf_do_9_2_reshutack(net, ep, asoc,
 							 SCTP_ST_CHUNK(chunk->chunk_hdr->type),
 							 chunk, commands);
 		if (SCTP_DISPOSITION_NOMEM == disposition)
@@ -2202,9 +2208,11 @@ enum sctp_disposition sctp_sf_do_5_2_4_dupcook(
 	 * enough for the chunk header.  Cookie length verification is
 	 * done later.
 	 */
-	if (!sctp_chunk_length_valid(chunk, sizeof(struct sctp_chunkhdr)))
-		return sctp_sf_violation_chunklen(net, ep, asoc, type, arg,
-						  commands);
+	if (!sctp_chunk_length_valid(chunk, sizeof(struct sctp_chunkhdr))) {
+		if (!sctp_vtag_verify(chunk, asoc))
+			asoc = NULL;
+		return sctp_sf_violation_chunklen(net, ep, asoc, type, arg, commands);
+	}
 
 	/* "Decode" the chunk.  We have no optional parameters so we
 	 * are in good shape.
@@ -2341,7 +2349,7 @@ enum sctp_disposition sctp_sf_shutdown_pending_abort(
 	 */
 	if (SCTP_ADDR_DEL ==
 		    sctp_bind_addr_state(&asoc->base.bind_addr, &chunk->dest))
-		return sctp_sf_discard_chunk(net, ep, asoc, type, arg, commands);
+		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
 
 	if (!sctp_err_chunk_valid(chunk))
 		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
@@ -2387,7 +2395,7 @@ enum sctp_disposition sctp_sf_shutdown_sent_abort(
 	 */
 	if (SCTP_ADDR_DEL ==
 		    sctp_bind_addr_state(&asoc->base.bind_addr, &chunk->dest))
-		return sctp_sf_discard_chunk(net, ep, asoc, type, arg, commands);
+		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
 
 	if (!sctp_err_chunk_valid(chunk))
 		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
@@ -2657,7 +2665,7 @@ enum sctp_disposition sctp_sf_do_9_1_abort(
 	 */
 	if (SCTP_ADDR_DEL ==
 		    sctp_bind_addr_state(&asoc->base.bind_addr, &chunk->dest))
-		return sctp_sf_discard_chunk(net, ep, asoc, type, arg, commands);
+		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
 
 	if (!sctp_err_chunk_valid(chunk))
 		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
@@ -2970,12 +2978,10 @@ enum sctp_disposition sctp_sf_do_9_2_shut_ctsn(
  * that belong to this association, it should discard the INIT chunk and
  * retransmit the SHUTDOWN ACK chunk.
  */
-enum sctp_disposition sctp_sf_do_9_2_reshutack(
-					struct net *net,
-					const struct sctp_endpoint *ep,
+static enum sctp_disposition
+__sctp_sf_do_9_2_reshutack(struct net *net, const struct sctp_endpoint *ep,
 			   const struct sctp_association *asoc,
-					const union sctp_subtype type,
-					void *arg,
+			   const union sctp_subtype type, void *arg,
 			   struct sctp_cmd_seq *commands)
 {
 	struct sctp_chunk *chunk = arg;
@@ -3010,6 +3016,26 @@ enum sctp_disposition sctp_sf_do_9_2_reshutack(
 	return SCTP_DISPOSITION_NOMEM;
 }
 
+enum sctp_disposition
+sctp_sf_do_9_2_reshutack(struct net *net, const struct sctp_endpoint *ep,
+			 const struct sctp_association *asoc,
+			 const union sctp_subtype type, void *arg,
+			 struct sctp_cmd_seq *commands)
+{
+	struct sctp_chunk *chunk = arg;
+
+	if (!chunk->singleton)
+		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
+
+	if (!sctp_chunk_length_valid(chunk, sizeof(struct sctp_init_chunk)))
+		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
+
+	if (chunk->sctp_hdr->vtag != 0)
+		return sctp_sf_tabort_8_4_8(net, ep, asoc, type, arg, commands);
+
+	return __sctp_sf_do_9_2_reshutack(net, ep, asoc, type, arg, commands);
+}
+
 /*
  * sctp_sf_do_ecn_cwr
  *
@@ -3662,6 +3688,9 @@ enum sctp_disposition sctp_sf_ootb(struct net *net,
 
 	SCTP_INC_STATS(net, SCTP_MIB_OUTOFBLUES);
 
+	if (asoc && !sctp_vtag_verify(chunk, asoc))
+		asoc = NULL;
+
 	ch = (struct sctp_chunkhdr *)chunk->chunk_hdr;
 	do {
 		/* Report violation if the chunk is less then minimal */
@@ -3777,12 +3806,6 @@ static enum sctp_disposition sctp_sf_shut_8_4_5(
 
 	SCTP_INC_STATS(net, SCTP_MIB_OUTCTRLCHUNKS);
 
-	/* If the chunk length is invalid, we don't want to process
-	 * the reset of the packet.
-	 */
-	if (!sctp_chunk_length_valid(chunk, sizeof(struct sctp_chunkhdr)))
-		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
-
 	/* We need to discard the rest of the packet to prevent
 	 * potential boomming attacks from additional bundled chunks.
 	 * This is documented in SCTP Threats ID.
@@ -3810,6 +3833,9 @@ enum sctp_disposition sctp_sf_do_8_5_1_E_sa(struct net *net,
 {
 	struct sctp_chunk *chunk = arg;
 
+	if (!sctp_vtag_verify(chunk, asoc))
+		asoc = NULL;
+
 	/* Make sure that the SHUTDOWN_ACK chunk has a valid length. */
 	if (!sctp_chunk_length_valid(chunk, sizeof(struct sctp_chunkhdr)))
 		return sctp_sf_violation_chunklen(net, ep, asoc, type, arg,
@@ -3845,6 +3871,11 @@ enum sctp_disposition sctp_sf_do_asconf(struct net *net,
 		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
 	}
 
+	/* Make sure that the ASCONF ADDIP chunk has a valid length.  */
+	if (!sctp_chunk_length_valid(chunk, sizeof(struct sctp_addip_chunk)))
+		return sctp_sf_violation_chunklen(net, ep, asoc, type, arg,
+						  commands);
+
 	/* ADD-IP: Section 4.1.1
 	 * This chunk MUST be sent in an authenticated way by using
 	 * the mechanism defined in [I-D.ietf-tsvwg-sctp-auth]. If this chunk
@@ -3853,13 +3884,7 @@ enum sctp_disposition sctp_sf_do_asconf(struct net *net,
 	 */
 	if (!asoc->peer.asconf_capable ||
 	    (!net->sctp.addip_noauth && !chunk->auth))
-		return sctp_sf_discard_chunk(net, ep, asoc, type, arg,
-					     commands);
-
-	/* Make sure that the ASCONF ADDIP chunk has a valid length.  */
-	if (!sctp_chunk_length_valid(chunk, sizeof(struct sctp_addip_chunk)))
-		return sctp_sf_violation_chunklen(net, ep, asoc, type, arg,
-						  commands);
+		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
 
 	hdr = (struct sctp_addiphdr *)chunk->skb->data;
 	serial = ntohl(hdr->serial);
@@ -3988,6 +4013,12 @@ enum sctp_disposition sctp_sf_do_asconf_ack(struct net *net,
 		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
 	}
 
+	/* Make sure that the ADDIP chunk has a valid length.  */
+	if (!sctp_chunk_length_valid(asconf_ack,
+				     sizeof(struct sctp_addip_chunk)))
+		return sctp_sf_violation_chunklen(net, ep, asoc, type, arg,
+						  commands);
+
 	/* ADD-IP, Section 4.1.2:
 	 * This chunk MUST be sent in an authenticated way by using
 	 * the mechanism defined in [I-D.ietf-tsvwg-sctp-auth]. If this chunk
@@ -3996,14 +4027,7 @@ enum sctp_disposition sctp_sf_do_asconf_ack(struct net *net,
 	 */
 	if (!asoc->peer.asconf_capable ||
 	    (!net->sctp.addip_noauth && !asconf_ack->auth))
-		return sctp_sf_discard_chunk(net, ep, asoc, type, arg,
-					     commands);
-
-	/* Make sure that the ADDIP chunk has a valid length.  */
-	if (!sctp_chunk_length_valid(asconf_ack,
-				     sizeof(struct sctp_addip_chunk)))
-		return sctp_sf_violation_chunklen(net, ep, asoc, type, arg,
-						  commands);
+		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
 
 	addip_hdr = (struct sctp_addiphdr *)asconf_ack->skb->data;
 	rcvd_serial = ntohl(addip_hdr->serial);
@@ -4575,6 +4599,9 @@ enum sctp_disposition sctp_sf_discard_chunk(struct net *net,
 {
 	struct sctp_chunk *chunk = arg;
 
+	if (asoc && !sctp_vtag_verify(chunk, asoc))
+		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
+
 	/* Make sure that the chunk has a valid length.
 	 * Since we don't know the chunk type, we use a general
 	 * chunkhdr structure to make a comparison.
@@ -4642,6 +4669,9 @@ enum sctp_disposition sctp_sf_violation(struct net *net,
 {
 	struct sctp_chunk *chunk = arg;
 
+	if (!sctp_vtag_verify(chunk, asoc))
+		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
+
 	/* Make sure that the chunk has a valid length. */
 	if (!sctp_chunk_length_valid(chunk, sizeof(struct sctp_chunkhdr)))
 		return sctp_sf_violation_chunklen(net, ep, asoc, type, arg,
@@ -6348,6 +6378,7 @@ static struct sctp_packet *sctp_ootb_pkt_new(
 		 * yet.
 		 */
 		switch (chunk->chunk_hdr->type) {
+		case SCTP_CID_INIT:
 		case SCTP_CID_INIT_ACK:
 		{
 			struct sctp_initack_chunk *initack;