[lwip-devel] [bug #48342] SNMP Traps not working correct

[Marco Veeneman]

URL:
  <http://savannah.nongnu.org/bugs/?48342>

                 Summary: SNMP Traps not working correct
                 Project: lwIP - A Lightweight TCP/IP stack
            Submitted by: mave
            Submitted on: Wed 29 Jun 2016 02:12:42 PM GMT
                Category: None
                Severity: 3 - Normal
              Item Group: Faulty Behaviour
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: 
            lwIP version: git head

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Details:

I found two issues regarding SNMP Traps.

1) When trying to receive some generic traps (coldstart(0),
authenticationfailure(4)) i noticed the traps are received by my PC, but not
in the trap server.
This had worked before the SNMP rewrite. Diving into the trap encoding
functions and comparing wireshark captures i found the issue: the variable
bindings field is missing in the trap message. Even if there are no varbinds
attached to the trap, this field should still be present. See patch:

diff --git a/src/apps/snmp/snmp_traps.c b/src/apps/snmp/snmp_traps.c
index 3da2dca..528a054 100644
--- a/src/apps/snmp/snmp_traps.c
+++ b/src/apps/snmp/snmp_traps.c
@@ -247,6 +247,9 @@ snmp_trap_header_sum(struct snmp_msg_trap *trap)

   tot_len = 0;

+  snmp_asn1_enc_length_cnt(0, &lenlen);
+  tot_len += 1 + lenlen;
+
   snmp_asn1_enc_u32t_cnt(trap->ts, &len);
   snmp_asn1_enc_length_cnt(len, &lenlen);
   tot_len += 1 + len + lenlen;
@@ -359,6 +362,9 @@ snmp_trap_header_enc(struct snmp_msg_trap *trap, struct
snmp_pbuf_stream *pbuf_s
   snmp_asn1_enc_s32t_cnt(trap->ts, &tlv.value_len);
   snmp_ans1_enc_tlv(pbuf_stream, &tlv);
   snmp_asn1_enc_s32t(pbuf_stream, tlv.value_len, trap->ts);
+
+  SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_SEQUENCE, 0, 0);
+  snmp_ans1_enc_tlv(pbuf_stream, &tlv);
 }

 #endif /* LWIP_SNMP */

2) Generic snmpv1 traps should be sent from .1.3.6.1.2.1.11
(iso.org.dod.internet.mgmt.mib-2.snmp).
Currently they are sent from the oid set to snmp_device_enterprise_oid because
NULL is passed to snmp_send_trap from snmp_send_trap_generic. See patch:

diff --git a/src/apps/snmp/snmp_traps.c b/src/apps/snmp/snmp_traps.c
index 3da2dca..52ec101 100644
--- a/src/apps/snmp/snmp_traps.c
+++ b/src/apps/snmp/snmp_traps.c
@@ -207,7 +207,8 @@ snmp_send_trap(const struct snmp_obj_id
*device_enterprise_oid, s32_t generic_tr
 err_t
 snmp_send_trap_generic(s32_t generic_trap)
 {
-  return snmp_send_trap(NULL, generic_trap, 0);
+  static const struct snmp_obj_id oid = { 7, { 1, 3, 6, 1, 2, 1, 11 } };
+  return snmp_send_trap(&oid, generic_trap, 0, NULL);
 }

 err_t




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