sctp: add a function to verify the sctp reconf chunk

This patch is to add a function sctp_verify_reconf to do some length
check and multi-params check for sctp stream reconf according to rfc6525
section 3.1.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sctp/sm.h

@@ -277,6 +277,9 @@ struct sctp_chunk *sctp_make_strreset_tsnresp(
 				struct sctp_association *asoc,
 				__u32 result, __u32 sn,
 				__u32 sender_tsn, __u32 receiver_tsn);
+bool sctp_verify_reconf(const struct sctp_association *asoc,
+			struct sctp_chunk *chunk,
+			struct sctp_paramhdr **errp);
 void sctp_chunk_assign_tsn(struct sctp_chunk *);
 void sctp_chunk_assign_ssn(struct sctp_chunk *);
 

net/sctp/sm_make_chunk.c

@@ -3801,3 +3801,62 @@ struct sctp_chunk *sctp_make_strreset_tsnresp(
 
 	return retval;
 }
+
+bool sctp_verify_reconf(const struct sctp_association *asoc,
+			struct sctp_chunk *chunk,
+			struct sctp_paramhdr **errp)
+{
+	struct sctp_reconf_chunk *hdr;
+	union sctp_params param;
+	__u16 last = 0, cnt = 0;
+
+	hdr = (struct sctp_reconf_chunk *)chunk->chunk_hdr;
+	sctp_walk_params(param, hdr, params) {
+		__u16 length = ntohs(param.p->length);
+
+		*errp = param.p;
+		if (cnt++ > 2)
+			return false;
+		switch (param.p->type) {
+		case SCTP_PARAM_RESET_OUT_REQUEST:
+			if (length < sizeof(struct sctp_strreset_outreq) ||
+			    (last && last != SCTP_PARAM_RESET_RESPONSE &&
+			     last != SCTP_PARAM_RESET_IN_REQUEST))
+				return false;
+			break;
+		case SCTP_PARAM_RESET_IN_REQUEST:
+			if (length < sizeof(struct sctp_strreset_inreq) ||
+			    (last && last != SCTP_PARAM_RESET_OUT_REQUEST))
+				return false;
+			break;
+		case SCTP_PARAM_RESET_RESPONSE:
+			if ((length != sizeof(struct sctp_strreset_resp) &&
+			     length != sizeof(struct sctp_strreset_resptsn)) ||
+			    (last && last != SCTP_PARAM_RESET_RESPONSE &&
+			     last != SCTP_PARAM_RESET_OUT_REQUEST))
+				return false;
+			break;
+		case SCTP_PARAM_RESET_TSN_REQUEST:
+			if (length !=
+			    sizeof(struct sctp_strreset_tsnreq) || last)
+				return false;
+			break;
+		case SCTP_PARAM_RESET_ADD_IN_STREAMS:
+			if (length != sizeof(struct sctp_strreset_addstrm) ||
+			    (last && last != SCTP_PARAM_RESET_ADD_OUT_STREAMS))
+				return false;
+			break;
+		case SCTP_PARAM_RESET_ADD_OUT_STREAMS:
+			if (length != sizeof(struct sctp_strreset_addstrm) ||
+			    (last && last != SCTP_PARAM_RESET_ADD_IN_STREAMS))
+				return false;
+			break;
+		default:
+			return false;
+		}
+
+		last = param.p->type;
+	}
+
+	return true;
+}