Fix SNMP Error response PDUs and properly encode them when using v3 auth/encryption.

Reported by:	harti@

1 files changed, 43 insertions, 4 deletions

diff --git a/contrib/bsnmp/lib/snmpagent.c b/contrib/bsnmp/lib/snmpagent.c
index 888d622..ee92420 100644
--- a/contrib/bsnmp/lib/snmpagent.c
+++ b/contrib/bsnmp/lib/snmpagent.c
@@ -166,7 +166,7 @@ find_subnode(const struct snmp_value *value)
 }
 
 static void
-snmp_pdu_create_response(struct snmp_pdu *pdu, struct snmp_pdu *resp)
+snmp_pdu_create_response(const struct snmp_pdu *pdu, struct snmp_pdu *resp)
 {
 	memset(resp, 0, sizeof(*resp));
 	strcpy(resp->community, pdu->community);
@@ -952,18 +952,57 @@ enum snmp_ret
 snmp_make_errresp(const struct snmp_pdu *pdu, struct asn_buf *pdu_b,
     struct asn_buf *resp_b)
 {
+	u_char type;
 	asn_len_t len;
 	struct snmp_pdu resp;
 	enum asn_err err;
 	enum snmp_code code;
 
-	memset(&resp, 0, sizeof(resp));
+	snmp_pdu_create_response(pdu, &resp);
+
 	if ((code = snmp_pdu_decode_header(pdu_b, &resp)) != SNMP_CODE_OK)
 		return (SNMP_RET_IGN);
 
-	if (pdu_b->asn_len < len)
+	if (pdu->version == SNMP_V3) {
+		if (resp.user.priv_proto != SNMP_PRIV_NOPRIV &&
+		   (asn_get_header(pdu_b, &type, &resp.scoped_len) != ASN_ERR_OK
+		   || type != ASN_TYPE_OCTETSTRING)) {
+			snmp_error("cannot decode encrypted pdu");
+			return (SNMP_RET_IGN);
+		}
+
+		if (asn_get_sequence(pdu_b, &len) != ASN_ERR_OK) {
+			snmp_error("cannot decode scoped pdu header");
+			return (SNMP_RET_IGN);
+		}
+
+		len = SNMP_ENGINE_ID_SIZ;
+		if (asn_get_octetstring(pdu_b, (u_char *)resp.context_engine,
+		    &len) != ASN_ERR_OK) {
+			snmp_error("cannot decode msg context engine");
+			return (SNMP_RET_IGN);
+		}
+		resp.context_engine_len = len;
+		len = SNMP_CONTEXT_NAME_SIZ;
+		if (asn_get_octetstring(pdu_b, (u_char *)resp.context_name,
+		    &len) != ASN_ERR_OK) {
+			snmp_error("cannot decode msg context name");
+			return (SNMP_RET_IGN);
+		}
+		resp.context_name[len] = '\0';
+	}
+
+
+	if (asn_get_header(pdu_b, &type, &len) != ASN_ERR_OK) {
+		snmp_error("cannot get pdu header");
 		return (SNMP_RET_IGN);
-	pdu_b->asn_len = len;
+	}
+
+	if ((type & ~ASN_TYPE_MASK) !=
+	    (ASN_TYPE_CONSTRUCTED | ASN_CLASS_CONTEXT)) {
+		snmp_error("bad pdu header tag");
+		return (SNMP_RET_IGN);
+	}
 
 	err = snmp_parse_pdus_hdr(pdu_b, &resp, &len);
 	if (ASN_ERR_STOPPED(err))